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    This Low Dropout Voltage (LDO) solar charge controller uses a simple differential amplifier and series P channel MOSFET linear regulator –their compatibility seems like a marriage made in heaven. Voltage output is adjustable. It is mainly intended for charging 12V lead-acid batteries.

    Solar Charge Controller Specifications

    • Solar panel rating: 50W (4A, 12V nominal) (open circuit voltage: 18 to 20V)
    • Output voltage range: 7 to 14V (adjustable) (not recommended for 6V applications)
    • Max power dissipation: 16W (includes power dissipation of D3)
    • Typical dropout voltage: 1.25V @ 4A
    • Maximum current: 4A (current limiting provided by solar panel characteristics)
    • Voltage regulation: 10mV (no load to full load)
    • Battery discharge: 1mA (Chinese controls discharge at typically 5mA)
    • LED indicators:
      • RED: Solar panel active
      • GREEN: Series regulator limiting current (fully charged or topping off)
    • Reverse battery protection: Control shuts down if battery is inadvertently connected reverse

    Schematic of 12V Solar Charge Controller Circuit

    12V LDO Solar Charge Control schematic

    Bill of Materials

    Dropout Voltage

    The input voltage exceeds the input voltage by 1.25V when charging at the maximum rate –the lower, the better. Low Dropout Voltage (LDO) is the catch phrase for anything under approximately 2V. This could potentially be reduced to below 1V by making D3 a schottky rectifier.

    Current Limiting

    Current limiting is provided by the solar panel –it is not a commonly understood fact that the solar panel tends to be a constant current device. For this reason, a solar panel can withstand a short circuit. Therefore, the control does not need current limiting.

    Float Charge of Lead-Acid Batteries

    This control charges the battery at a constant voltage and also maintains a charged battery (float charge). The float charge voltage specification is a little lower than the charge voltage, so to accommodate both voltages, a compromise is reached by simply reducing the voltage slightly –that is how ALL automotive systems operate. To obtain maximum charge in a 12V battery, set the control to 14 to 14.6V. Automotive systems further reduce voltage to 13 to 13.5V in order to accommodate high temperature operation as the battery is usually located in the hot engine compartment –battery has a negative thermal coefficient of voltage.

    Voltage Adjustment

    To set the voltage, disconnect the battery and connect a 1K dummy load resistor to the output. The resistor is necessary to shunt potential MOSFET leakage current as well as the green LED current.

    LDO Solar Charge Control Circuit Operation

    R4 and D1 form a 6V shunt zener voltage reference. Q1 & Q2 make up the classic differential amplifier that amplifies the difference between the reference voltage and the feedback voltage from the arm of potentiometer R6. The output is taken from the collector of Q1 and drives the gate of P Channel MOSFET Q3. Differential voltage gain is probably in the order of 100 to 200. For best performance, I selected Q1 & Q2 for matched hFE. As the feedback voltage increases at the arm of R6, Q2 turns on harder and steals some of the emitter current away from Q1. The collector current of Q1 follows the emitter current and drops less voltage across R1 thus reducing Vgs of Q3 and turning it off. C2 provides frequency compensation to prevent the amplifier from oscillating.

    Q3 is dormant unless the battery is connected reverse –should this happen, Q3 turns on and reduces the reference voltage input to zero thus turning Q1 & Q3 and preventing damaging battery current.

    D3 prevents the battery voltage from appearing across an inactive solar panel.

    Thermal Management

    This is a linear series regulator that dissipates significant power when the pass transistor is both conducting current and dropping voltage simultaneously –during maximum charge rate when the voltage drop is low, the heatsink runs warm –when the battery is fully charged and there is low charge current, the heatsink is cold –but when the battery starts to top off at maximum voltage, the heatsink runs very hot –such is the nature of a linear regulator. At 4A, Q3 drops 3.3V (assuming solar panel voltage is 18V)(the remaining 0.7V is the D3 voltage drop. P = 4A * 3.3V = 13.2W. The heatsink is rated at 3.9°C/W, so heatsink temperature rise = 13.2W * 3.9°C/W = 51.5°C. Adding the 25°C ambient temperature results in a heatsink temperature of 76.5°C. While this may seem very HOT to the touch, it is still cool to the transistor that is rated for a junction temperature of 175°C.

    For the Future

    A 6V version –while this control may be adjusted down to 7V for charging 6V batteries, the performance is marginal, but will function at reduced current. A 6V version is on the drawing board.


    Perf board –sorry, no circuit board artwork at the time of publication.

    12V LDO Solar Charge Control Photo

    ask a question

    344 Responses to "12V LDO Solar Charge Controller"

    1. Woops, typo– There are two Q3 transistors–the lower one should be Q4 and that is the one that does the reverse battery protection.

      Also, on the upper right where it indicates “6/12V,” should be “12V”

      • hello sir, is there any equivalent MOSFET of FQP27P06?? reply as soon as possible sir. thanking you…

      • Read way back in the comments where I listed a few devices.
        If you use DigiKey’s search engine,
        start with MOSFET
        then select FET
        then select MOS P Channel
        then select all the numerous TO-220 packages
        then narrow it down to the Rdson parameter in the range of 70mOhms to 150mOhms
        this produces a list of some 33 devices–some have the same part #s.
        A 40V device is all that is needed.

        Since the product life of MOSFET power transistors is short (due to continuously improving mfg techniques & price reductions), you may locate many obsolete devices on ebay.

      • Hennie says: on May 20, 2014 at 8:00 am

        Hi Jim.
        I’ve build your LDO 12 volt solar charge controller.I plan to try the SSS 6A 12 controller aswell as my panel is a 120w panel.
        Can I include the 4k7 resistor and the green LED over the FED of the SS 6A 12 controller to see when the system starts to trim off, same as on the LDO 12v controller.
        Thanks for your valuable information and inputs.


      • Dear Mr. Keith,

        Sorry for a silly question. I am new to electronics and just trying to understand. This regarding the diff. amplifier you have made in the circuit. Pl. confirm my understanding.
        1) Mosfet is normally closed. When -2v is applied to gate (as per datasheet), it will open and hence stop charging.
        2) Now -2v is (Vq2-Vq1)*R1/R2.
        Vq1 is ref voltage of 6.2v and as soon as Vq2 (feedback voltage) reaches 5.2v from 6.2v (1v diif) Vgs will reach -2v since R1/R2 is 20k/10k.

        Is this understanding correct?

      • andre lotz says: on November 23, 2014 at 8:29 pm

        Dear Jim,
        You must be getting zillions of mails.
        I am a pensioner who went onto Solar to have more food money!
        I designed a double 12 volt regulator using 5 amp relays.
        Then I increased power and used 15 Amp relays. Now I had to use 30 amp relkays and they give m,e trouble!
        After the bastteries are full, thery hunt click click!
        I wanted to switch to solid staste switching and repaired a very expensive unit using the 100 Amp IRF 1405 mosfets. The unit is rasted 30 amps.
        I looked at your 12V LDO Solar Charge Controller and it looks lovely. Since thge average small home uses 500 watts, and charges with 15 – 20 amps per 12v volt bank, how can I switch the mosfet on?
        I assume that reducing the voltage suppl;y will create a lot of heat & melt bvthe transistors. How \do they do it?
        By switch mode control?
        Could you look at a relatively simple contoller usin this technique?
        Thank you very much,

      • Jim Keith says: on November 26, 2014 at 4:29 am

        You are dealing with some serious power there. This LDO charge control is far too limited in power for your application. A relay based or SSS based control is recommended for this power level. Check out all the solar charge controls under the “SOLAR” tab. This is one that I recommend:

        The hunting (oscillation) could be caused by a number of issues:

        Batteries too small or sulphated so that they have a high internal resistance –as soon as the relay drops the voltage immediately drops due to the internal resistance.

        Control issues –the above link has independent threshold that can be set to avoid this problem.

        Good luck.

      • I hope I speak to Andre I also want to convert to solar. I assume you live in south Africa if so where? please send me your e-mail address. i have millions of questions. baie dankie.


      • could you give me another mosfet to replace fqp27p06 mosfet in the circuit.

      • sir,
        what changes I have to make to use 12V,5W solar panel instead of 12V,50W panel?
        Please help me as soon as possible, because I’m doing a course project on it…
        thanking you sir.

      • Piyal Weerawarne says: on December 28, 2015 at 3:11 pm

        Good circuit I use this and functioning well
        Thanks lot.

        Piyal Weerawarne (Sri Lanka)

      • razakhalid41gmail-com says: on April 21, 2016 at 11:26 am

        sir can this circuit work properly of 12V 20W solar panel to charge 12 37amhr battery…?? or not..?? if not than what is the configration i change..?? plz reply as soon as possible plz

      • This circuit should work well for your application, but it will take a long time to bring that many batteries to full charge with a 20W solar panel.

    2. thanks for sharing your design(s).
      Do you have a controller circuit diagram for 12v @ 5w solar panel charging sla 12v 6AH battery? thanks again!

    3. useful and very infoRmative.

    4. how about if the input is 20W 1A solar panel?what will be changed

      • Jim Keith says: on September 9, 2012 at 2:41 pm

        No changes required for your 20V solar panel. The typical open circuit voltage for solar panels intended for 12V applications runs about 18 to 20V. The additional voltage assures that it can charge a battery at 14.6V + 1.25V regulator dropout voltage. Any additional voltage is dropped by the regulator and xcess power ends up in the heatsink.

    5. I was wondering what materials were needed for this project, the bill of materials does not produce the supplies needed

    6. does this controller operate the system of lvd, lvr,hvd and pwm. Shambhu raj malla

      • This is simply a linear regulator (not PWM (pulse width modulation) and this is why it has a relatively low power rating. It automatically reduces charge current to a very low level when fully charged. It does not have LDV (low voltage disconnect) to protect the battery against over-discharge. Nor does it have MPPT (maximum power point tracking).

        Please educate me on what these other acronyms stand for: “LVD/LVR, HVD/HVR parameters,” as I have been unable to find any definitions. It seems to me that these are simply buzzwords that are ignorantly repeated to impress…

    7. I have 10w ,21v,0.643Amps solar pannels and battery 12vdc i want store power in battery from solar energy .soplease share charge controller circuit diagram withfull detail.

      • Jim Keith says: on October 2, 2012 at 2:54 pm

        This circuit schematic has all the info needed–connect solar panel to the left terminals and battery to the right terminals.

    8. plz help me here…
      why is transistor Q3 used???

    9. and one more thing…v know that op-apms like 741 are also differential amplifiers so y cant we use them in open loop configuration?

      • Jim Keith says: on October 2, 2012 at 2:50 pm

        The top Q3 is the series regulator that turns off as the battery reaches 14V (or whatever it is set at). The lower Q3 (should have been Q4) turns off the regulator to prevent fault current should the battery accidentally get connected reverse.

        Yes, this circuit can be made to operate with a 741 op amp. Open loop DC, but closed loop AC via an integrating capacitor as C2 does in the circuit provided.

      • pinanknagda says: on October 2, 2012 at 3:03 pm

        bt can v just use the diode and remove the bottom Q3 (i.e Q4)?

      • Jim Keith says: on October 2, 2012 at 5:06 pm

        Good thinking. May work OK, but you would have to test. The base to emitter junction will zener and under that condition I do not know what will happen to collector voltage. This is an out-of-spec condition for Q1. Also, the negative transition on the cathode of C2 may over-voltage the gate of the MOSFET and turn in on fully thus creating quite a slug of current. On second thought, perhaps not a good idea.

    10. Hello Dears,
      Please Suggest me a circuit, with 6V Solar panel, 6V SLA Battery, 1W High power LED.
      With Battery full and drop Indicator.
      Thank You.

    11. pqp27p06 30A 60V P-FET is very difficult to find, any equivalent substitute?

      • Jim Keith says: on November 2, 2012 at 11:15 am

        FQP27P06 is a popular device available from major distributors such as DigiKey, and Newark /Farnell –also listed on ebay, ships from Hongkong /China. Not all countries trade with China –check postal restrictions.

        Here are a few more suitable devices

        Check the specifications –look for P-Channel, TO-220 package, Rdson 40V, Vgs threshold >3V

    12. Hi Jim,

      Do you think this circuit would work with 24V panels and batteries?


    13. hello, can i have your ym or facebook ? i have some problems with my project
      why in my board , ampe in output is 0,01A ?? with the input is 0,8A, how can i charge my acquy 12v 7A????

      • Appears that you are measuring LED current and MOSFET is not turning on.

        Disconnect the lower Q3 to eliminate reverse polarity protection and see what happens.

        Then try grounding gate of MOSFET to turn fully on and see what happens.

        Probably wiring error.

        Your device substitution is OK.

    14. oh in my country doesn’t have FQP27P06
      and i use IRF4905 and i use 6a10

      • You can tie cathode of LED (D5) to common, provided that the previous connection to the anode of D3 is broken. You may wish to increase the value of R9 to reduce brightness.

        IRF4905 and 6A10 are satisfactory substitutions.

    15. when i use this
      the led d5 is off and out put is ~14v and 0.001A
      when i reverse 123 = 321 the led is on but the out put is ~ 0.7 v
      what should i do now ????
      sorry for my english ^^

      • Measure solar panel open circuit voltage and short circuit current –or power via lab power supply.

        I cannot see any errors. Recheck your circuit, making no assumptions. Bad assumptions become roadblocks to solutions.

    16. I have 4 x 12V batteries that I use with a 1000W power converter as a backup solution when there is a power failure. I charge them from a solar panel too, but mainly from a battery charger. Can you please tell me how can I make a circuit that switches the charging process to solar panel when it’s sun outside and switches back to the charger when it’s night or cloudy. Thanks!

      • This could be an interesting project. Are your batteries connected in parallel? Do you want the backup charge to turn on only after the batteries are discharged? this would minimize purchased power. Also one very practical circuit that is sorely needed here is an automatic battery disconnect that prevents over-discharge –the same could turn on the backup charger. Let me know your ideas on this…

      • Yes, my batteries are in parallel. It will be nice if the charger charges only if the batteries charging level is below a certain level and to switch to solar panels if is sunny.

    17. I have a new concept in mind for creating a low power battery voltage monitor because this must be connected across battery continuously. What are the specs on your charger? Note that the charger must be transformer isolated for safety.

    18. hi Jim…

      I want to know that the 2 capacitors which are used in the circuit are 0.1uF or 0.1pF and does this circuit prevent the discharge of battery during night thru solar panel ( though I am currently using a solar charge controller circuit to charge 12V battery but it has a significant voltage loss at night even though I have a diode connected to prevent reverse current flow).

    19. And Also I tested your circuit but I am getting only 3.5V across the battery terminals then I removed the lower Q3 transistor and grounded the gate of mosfet but still I was getting only 5V across battery terminals.
      The solar panel is generating 20V at the input terminals.
      Any help regarding this would be appreciated.

    20. The capacitors are 0.1uf.
      Most commercial solar charge regulators power the electronics from the battery and thus significantly discharges the battery at night and on cloudy days. This unit powers the regulator from the solar panel so the only discharge from the battery at night is the 1mA feedback signal.

    21. Thnx Jim,

      I checked the circuit and found it was a connection problem but now when I connect the battery and solar panel at their respective places the green LEDs glows instantly and as per your circuit the green LED must only glow when the battery is fully charged. I have connect a 12V battery to be charged and it is charged to 6V but still the green LED is glowing.
      I think there is a problem while setting the reference voltage which specifies when the battery is fully charged. So can you through light on how to do that voltage adjustment or Am I going wrong somewhere else.

    22. Disconnect battery and connect 1K dummy load. Then adjust the output voltage to 14V via the potentiometer. On my prototype, I can set the output voltage anywhere between 6.02V to 17.6V (with 18V input)–just tried it…

      Reconnect the battery. The green LED should not come on until the battery reaches 14V.

      • Hai sir my circuit is working fine. now i want to connect the 100watt panele, what changes i make in this curcuit.

      • The solar panel power may be increased to 100W by using a bigger heatsink in the order of 2°C/W. This requires an aluminum extrusion as the best circuit board heat sink runs at about 3.1°C/W –the existing heat sink runs at 3.9°C/W. Other thermal impedances include junction-to-case, and case to heat sink –since the heatsink to ambient is by far the greatest, this is what to concentrate on reducing.

        Another approach would be forced cooling –it takes only about 50LFM (linear feet/min) airflow to halve the thermal resistance. A small 12VDC fan (50mm) could be powered via a series regulator (LM7812) directly from the solar panel so that the fan runs only when the sun is shining.

      • Hi sir my name is JC an ECE student,we have a project about using a 100W solar panel to power up a water pump and our group was assign to build a charge controller circuit, i have tried your circuit and i use some replacements for 6A4 and FQP27P06 for simulation. Our project requires a thyristor or an SCR to be use in the circuit, where can I make some changes in your circuit? I need you help sir. Please reply…

    23. Ok sir,
      this circuit have over charging protection. ?

    24. Good Evening Jim (It’s Evening in Australia).
      I am a school teacher working with students in a subject Systems Engineering in a secondary school.
      The circuit seems to suit their needs (thanks for your design).
      We have one query with Q3 (FQP27P06), could you please identify the numbers 1, 2, 3 as to which is the Drain, Source and Gate.
      We are looking forward to your kind reply to this issue.
      Regards Spiroelec.

    25. it is dificult to find 2N3904 transistor in my country any substitution

    26. Good afternoon Jim,
      I have just a couple of questions for the “12V Solar Charge Controller”. I plan to use a Solar Panel with Max power 20w, Rated Voltage 12v, Short Cct Current 1.3 amp, Open Cct. Voltage 21.6v to charge a 12volt 7 amphour Sealed Lead Acid Battery.

      1/ With the instructions on Voltage Adjustment, what should be the wattage of the 1K Dummy Resistor.
      Voltage Adjustment: To set the voltage, disconnect the battery and connect a 1K dummy load resistor to the output.
      2/ It is my understanding Sealed Lead Acid Batteries (SLA) rely on a float charger that consists of a DC power supply with an output voltage which is reasonably well regulated, to a level corresponding to 2.25V per battery cell (i.e., 13.5V for a .12V. SLA).
      When a discharged SLA battery is connected to this type of charger, a moderately high charging current flows at first, but gradually reduces as the stored charge level rises. By the time full charge is reached the current has dropped to a low and steady level, just sufficient to maintain the battery at full charge.

      Does my understanding of charging SLA Batteries match what the “12V Solar Charge Controller” on how it operates and gradually reduces as the stored charge level rises. By the time full charge is reached the current has dropped to a low and steady level, just sufficient to maintain the battery at full charge?

      This control charges the battery at a constant voltage and also maintains a charged battery (float charge). The float charge voltage specification is a little lower than the charge voltage, so to accommodate both voltages, a compromise is reached by simply reducing the voltage slightly—that is how ALL automotive systems operate. To obtain maximum charge in a 12V battery, set the control to 14 to 14.6V.
      Do I just set the output voltage to 13.5V of the 12V Solar Charge Controller to charge the SLA Battery?

      Regards Spiroelec

      • 1. For the resistor, a 0.25W, 1K will do.
        2. Yes, you have the correct understanding of operation and this works fine with a sealed lead-acid battery–yes current tapers off after the float charge voltage is reached–simply set the voltage to 13.5V with the 1K dummy load, and then connect to the battery.

    27. Circuit Operation

      Hi Sr I just make the circuit but I have a dude, on the circuit operation it said The output is taken from the collector of Q2 and drives the gate of P Channel MOSFET Q3, is that ok? or isted of Q2 is Q1

    28. hello bro Jim, i just have one doubt. Plz clarify me.
      1. Can I use this controller with a 80W solar panel.?
      2. Can I use output from this controller directly with an Inverter without the use of a battery.?
      thnx :)

    29. 1. It will handle up to a 100W (8A) solar panel if:
      a. The heatsink is changed to a 2.5″ high version
      Digikey: FA-T220-64E-ND (3°C/W)
      b. The MOSFET is changed to STP80PF55
      Digikey: 497-2729-5-ND
      C. The series diode is changed to ON Semi 80SQ045
      Digikey: 80SQ045NGOS-ND

      Make sure the diode has adequate heat sinking–refer to my 6V LDO solar regulator to see how I did it there.

      2. No, this cannot power the inverter directly–the inverter requires the presence of a battery to provide high peak current and also absorb potential reactive current that flows back into the battery. Inverters tend to be finicky and do not like to start or restart under ‘starved’ conditions like when clouds obscure the sun.

      On the other hand, if the power requirements are low and the inverter is well-behaved, you may possibly get by with a large computer grade electrolytic capacitor–I have never actually done this…

    30. Hello Sir Jim,

      Any advice or idea on how to design a charge controller (with roughly the same specifications as this design) for TWO 12V batteries using PWM that is:

      1. Able to detect which battery is under charged or at full state.

      2. Able to perform switch-charging between the 2 batteries via a microcontroller.

      Also, since I am a newbie, I would be very grateful to you if you could teach, provide a link or anything related to designing a solar panel charge controller as such. I’ve just started doing my research and things can be pretty messy to start, without proper guidance :(


    31. This is an aggressive project–far too difficult for the newbie. Forget the dual battery requirement –that part will be relatively easy after everything else is done.

      First step is to make a pwm buck regulator for your system in which the duty cycle is manually controlled by a potentiometer. I do not know if there is anything like this on this web site.

      Second step is to turn this into a MPPT (maximum power point transfer) control by adding a microcontroller etc. The micro adjusts the duty cycle to obtain the optimum power transfer. By doing this, the charge rate is significantly increased beyond the solar panel current. This is a busy task for the micro and also a busy hardware & firmware development task.

      This is in contrast to this simple LDO control that is simply a series linear regulator that is 1:1 (panel current = charge current).

      • Absolutely right :(

        Say if I were to follow this design but for the purpose of charging two batteries now.

        Is it still possible to integrate the use of a microcontroller? Does integrating a microcontroller automatically elevates the stage of this series linear regulator to a PWM/3 stage charge controller?

        Am I making any sense? Or am I confusing myself now.

    32. I have a soler pannel with Battery of 30W.
      I want to operate two Fans 0f 7W each and two bulbs of 3W each.
      Total Load is 20W.
      but on just a fan and a bulb (10W) it shows over load.
      please send me a cicuit which operate the battery at full load.
      Please reply must….PLZ PLZ PLZ..

      • You probably need a larger solar panel. Measure its short circuit current to see what it puts out in full sunlight. Then measure the actual load current of each connected device, one at a time. If the battery is charged, it can deliver a high current.

        For temporary operation & evaluation, connect the solar panel directly across the battery using only a series diode. Parallel solar panels require a series diode each.

      • I connect the load directly to the battery.
        when battery is fully charged it shows the overload condition only at 10W load…

      • How do you determine overload condition?

      • battery shutdown…

      • Readers are encouraged to weigh in on this issue –correct me if I am wrong.

        If you are using a “protected” or “smart” lithium-ion battery, forget it. This type of battery is not suitable for experimentation –the slightest overload disturbance shuts it down thus forcing it into a long “recharge” period to reset the overload circuit.

    33. HI! Thanks for schematics!
      I made the circuit but it doesn’t work :( , so I have some questions:
      1) I don’t want reverse bat prot so I drop Q3, D2 , R8. Its ok?
      2) green led NEVER lights, and
      3) VOUT is float, no stops at 14v.
      some ideas?
      Thanks in advance!!!!. Daniel.

      • Yes, you may omit the reverse battery connection components.

        Check your wiring, and test into resistance load –if it will not work with resistive load, it will not regulate float charge voltage.

        Read this article:

    34. ok sir iwill try this thank you.

    35. sir i just made the circuit but it didn’t lit the green led when reaches 14.5 i adjust the trimmer but it doesn’t work i trouble shoot and everything is fine what should i do? i read n your comment to put the gate in negative and deactivate the reverse protection and nothings happen

    36. is it ok i used generic capacitor instead of x7r? .1uf 50v ordinary capacitor i used in the board

      • Any type capacitor is acceptable here.

        Sorry to hear that it is not working for you–for troubleshooting, refer to my response to amoarg69 above.

    37. thanks for reply sir, now i found the problem :),, i just replace the 2 capacitor , bec. i put an electrolytic cap its my fault. and i test it again and it works..

      what is the voltage when the battery will charge again when it is low?

      • As soon as the battery voltage drops below the float charge voltage, it will begin charging. Actually, it does not stop charging at the float charge voltage, but the current becomes extremely low.

    38. im using sla 12v 12ah and a 10w solar but soon i will add another 10w pv, is it ok for the battery to set 14.6 volt in full charge?

    39. sir have you ever design simple mppt circuit for the future? tnx

      • manoj Tyagi says: on April 21, 2014 at 8:47 am

        we required ac(220v Single phase)/Dc (12V) Solar charge controller . can you send Ckt Diagram .

    40. Can i replace 2N3904 from BC547 or MPS3904.

      • Any small NPN transistors with an hFE of 150 or greater will work for this application–note that the pin-out may vary so check the datasheet.

    41. Hi Jim,

      I would like you to help me out, please:

      I am working on a semester project, I am supposed to design a Combined control device for solar charged battery and automatic emergency light. I have been given these specifications:

      The developed device should monitor and control the charging of a lead acid battery from a photovoltaic panel and its discharging. The device should also control automatically and emergency light in case the ambient luminance falls below certain level.

      The minimum specifications are:

      1. A controller should charge automatically a 7Ah lead acid battery from a photovoltaic panel until fully charged. The battery should not get overcharged.

      2. There should be provision for automatic initiation of the charging mode when the emergency light is ‘on’ even if the battery is still not fully discharged.

      3. The photovoltaic panels should be protected against reverse currents from the battery or the load.

      4. There should be a linear, ten level battery output voltage monitor with a range between 10 and 15 volts.

      5. The device should operate from 220 V, AC power source.

      6. The primary circuit of the power transformer should be fuse protected.

      7. Yellow LED should indicate “charging” mode of the controller.

      8. Green LED should indicate “charged” mode of the controller.

      9. Red LED should indicate “low battery” state, when the voltage of the battery is below 10.5V.

      10. Green LED should indicate “power on” of the device.

      11. Power switch for the device.

      12. An emergency light controller should operate a relay driven emergency light for ambient luminance below 20 lux.

      13. The device should have 220V output for supplying an emergency light with Pmax=100W

    42. hai sir , i need solar charger control circuit diagram for 200watts 12v solar panel with 150 ah battery please send me the circuit diagram

    43. hai sir , i am received your mail but i need 12v with 20ammp charger control circuit diagram,200watt pannel with 150ah battery ok ok. if you have plz send to me

    44. emmanuel carrasco says: on August 16, 2013 at 10:16 am

      sir thank you for the circuit. i built and its working 100%. im so happy with the result. God bless!

    45. How to Replace N channel FET

    46. Hi Jim.

      The circuit works great. I cant find a pchannel mosfet as discussed. is there any reason that a Nchannel be used with the long tailed amp be reversed, as mostly N channels are readily available (lower on state resistance.) which is good for losses?


      • Substantial circuit changes are required to utilize N-Channel devices. No, it will not work in this circuit. However, this would make a good project for the future.

      • Hi Jim

        As the regulating device (the Mosfet) the arrow should be pointing in the opposite direction for a P-Channel device,

        3 = source, 1 = gate, 2 = drain

    47. Jim my brother, do you still remember I asked for your help?

    48. What if we can not find FQP27P06 transisitor or any other P channel MOSFET transistor to replace it??
      Is there any substitute for that??

    49. sir, i need a circuit for solar charge controller mppt, with dusk to dawn type,solar panel 150w, battery 60ah, dc load out 60w, please send me circuit

    50. Navjot Singh Sains says: on September 24, 2013 at 6:50 pm

      Hi Jim,

      Thanks for the wonderful post and sharing out your designs. These proved very helpful for me.

      Well that said, I have a situation – I’m just struck with this … I’m unable to vary the output voltage with the potentiometer. It just remains the same if I change the potentiometer’s value. I’ve cross-checked the circuit repeatedly and it turns out that although the voltage varies at the base of Q2, the output remains the same.

      Instead of FQP27P06, I’ve used P55NF06 and 2N3904, I’ve used BC547.

      Can you kindly help me out, please? Thanks in advance!


    51. Navjot Singh Sains says: on September 24, 2013 at 7:36 pm

      Gosh! I didn’t realize that i was using an N-Channel Mosfet. One more question, please – can i use one of the followings?


      Is it fine to use a 12Amp Power Mosfet? Because i’m not too sure about the availability of any of the Mosfets in the market.


    52. demonhunter8585 says: on October 1, 2013 at 6:23 pm

      hi jim,
      thxs alot for sharing the design which i have tried building it. There a few question which i would like to ask you.
      1. After connecting a load resistor to replaced the battery, i check the voltage across and finds that it depends on the amount of light shining on the solar panel, so i not sure how you are able adjust between 6-14 volts.
      2. Is there any issue if i use a electrolytic capacitor instead of a ceramic one?

      • When adjusting with a dummy load (e.g. 1K) and you find that the output voltage is affected by sunlight, it is my guess that it is not working properly –recheck your wiring and make no assumptions –read my troubleshooting tips:

        On the capacitor, 0.1uf is extremely small for an electrolytic type –use a ceramic or film type.

      • demonhunter8585 says: on October 4, 2013 at 12:48 pm

        Hi Jim,
        Thanks for the information. I replaced the electrolytic capacitor with a ceramic one and now i am able to vary the voltage of the load resistor from the potentiometer. And is the green led suppose to light up all the time? cause after connecting solar panel to the circuit, i can see the green led lighting up although it is not as bright as the red LED, any comment on this issue?


      • On the electrolytic capacitor issue, the polarity could have been reverse thus causing excessive leakage.

        When setting the voltage with a dummy load, the green LED should light –during normal operation, it extinguishes when the pass transistor is saturated (battery at low charge level). LEDs vary greatly in efficiency and brightness –this is to be expected. Lately, I have been purchasing only Ultra-bright LEDs and have been satisfied with the results.

      • demonhunter8585 says: on October 4, 2013 at 8:02 pm

        Thanks for the advice. Greatly appreciated for the time taken to reply and once again thanks for sharing your charge controller circuit.


    53. Hi Jim

      I am busy with a semester project and I need assistance. I am designing a charger controller with MPPT. This will charger from a 75W (12V, 6.25A) a 24V (approx 100Ah) battery. I am struggling with PIC (PIC16f88) programming. Can you assist with the code if possible.

      As an alternative design will your cirucit work for my kind for system should I fail with MPPT controller?


      • I am not into the PIC, but can offer a tip that will make your MPPT algorithm much simpler –simply slowly adjust the PWM duty cycle for maximum output current –no voltage measurements or power calculations necessary.

        Sounds like you need a boost regulator — 12V input to 24V battery. If so, this linear regulator will not work.

        Using a solar panel source (basically a current source), you will need a hefty energy storage input capacitor to source the inductor charging circuit. Because the output waveform is anything but pure DC, the current measurement must be integrated over a time period –to make this simple, drive a VCO with the current signal and use your PIC to simply count (integrate) pulses –no engineering units necessary –just tune for maximum count.

    54. hello. thanks
      I have 3w ,9v, solar pannel and battery 12vdc,7AH. I need controller circuit diagram to charge that.Is it possible?

      • Unfortunately, this circuit cannot do this function. What you need is a boost type regulator that is more complex than this circuit–requires an inductor.

    55. Thank you Jim.Would you please help me to find suitable circuit diagram. I searched and find one circuit in this link:
      but I think that is only voltage regulator and couldn’t control charge of battery.Do you think I need two circuit or one circuit do it?

      • This circuit will probably work OK for your requirements.

        This one also looks OK except that the output capacitor must be moved to the input –the solar panel has too high a source resistance to effectively charge the inductor, and the output has no need for filtering because the inductor discharge is absorbed by the battery.

        In both circuits, the PWM duty cycle must be manually adjusted for maximum output current (Maximum Power Point Transfer (MPPT)) under average conditions. Otherwise the regulator may drag the solar panel voltage so low that most of the power is dissipated in the internal resistance of the solar panel.

        However, electroschematics.com/6888/solar-battery-charger-circuit/ will not work.

    56. Hello Jim. I saw your other circuit in this link:
      Do you think this circuit can solve my case with any change?
      I will be highly appreciate if you help me to find suitable circuit to my propose.

    57. hello Jim. Thank you for your help. I will try to test http://www.eleccircuit.com/circuit-battery-voltage-regulator-by-mc34063/
      but I do not know how I could manually adjust it for maximum output current.I will be highly appreciate if you explain me about.

    58. Hello again Jim.I have a question.I think this circuit is only voltage regulator and couldn’t control charge of battery and I should use this circuit with other circuit for battery charge control. Is it correct?
      Thank you for your help.

    59. I have a 20W solar pannel and a 12V 7.2Ah battery. I want to make a sutiable charge controller for the battery. please send me circuit design and working principe.

    60. Hi Jim,
      one question regrading this 12 volt LDO charge controller. I know that this circuit protects against overcharging of the battery by dissapating though the p-channel mosfet. Does this circuit provide over-discharging also? And if it does, can tell me how does it work? Hope to hear from you soon.


    61. hi jim!
      12V LDO Solar Charge Controller really works great!

      Actually finding a higher capacity P Channel Mosfet is so hard to find,

      Is it possible to place 2 FQP27P06 to handle 200W (16A) Solar Panel?

      Thanks and regards,

    62. To boost it to 16A, I would parallel (4) FQP27P06 devices (each with its own series diode). It would also require (4) heatsinks. So you see that this is already near the feasible limit of a linear regulator. Consider going with a MPPT type design that uses buck switching topology that essentially eliminates the heatsink–I do not have one of these yet.

    63. Hi Jim,
      i am really much thankful with your explanation using (4) FQP27P06 devices in parallel having (1) series diode each.

      I these event i would assume – adding more FQP27P06 devices in parallel will make my 12V LDO Solar Charge Controller can handle more loads… please correct me…

      Thanks and regards,

      • Yes, more parallel sections = more current.
        However, a little forced air cooling will easily increase the current rating by 50%. Run the fan from the solar panel raw voltage via its own LM7812 voltage regulator so that it runs only when the sun is shining.

    64. Dear Sir, I want to ask if this circuit considered as fast charging circuit and if i use electrolytic capacitor would it affect the charge controller?

      • This is not a fast charger, and I am unsure how you plan to employ an electrolytic capacitor–need more info.

      • Can you suggest to method to improve this circuit to a Fast charging circuit? About the electrolytic capacitor, I have constructed your circuit by using that type of capacitor. Did I need to replaced the capacitor to ceramic X7R to prevent any malfunction during the charging operation?

        Thanks in advance

    65. Hi Jim,

      Thank you so much for the great advises… and of getting
      knowledge about your 12V LDO Solar Charge Controller.

      Merry Christmas and may God bless you always.

    66. Suranga (4S5SN) says: on December 5, 2013 at 4:03 pm

      dear sir ,
      Thank for your circuit .It is working very good.
      i am using IRF5210 & D3 sottkey diode from old
      computer power supply unit .

    67. upon charging multiple kinds of battery (small sized to big sized lead acid battery) with the same 12Volts, is it necessary to have a current regulator.?

      I am curious if they can withstand the same current value even they have different sizes..

    68. hi sir,

      upon charging multiple kinds of battery (small sized to big sized lead acid battery) with the same 12Volts, is it necessary to have a current regulator.?

      I am curious if they can withstand the same current value even they have different sizes..

    69. Dear Sir,

      As you stated above that for voltage adjustment, disconnect the battery and connect a 1K dummy load resistor to the output.But as I’ve shunted the output with the 1K resistor, the voltage cannot be varies. The voltage can only be varies as the output does not connected to any load.

      • Please recheck the circuit & components– make no assumptions because this is how experimenters (and professionals too) get stumped. You have an error somewhere. Good luck!

      • Good Day!

        Hi sir Jim, after the voltage adjustment, the dummy load resistor should be remove or remain in the circuit??? Thanks

    70. Jim, thank you so much for publishing your design. A couple of questions.

      Did you choose the 6v Zener over a 5.1 or 5.6v unit so as to provide some temperature compensation ? The 5v zen ers are usually used in power supplies as they have an almost zero drift with temperature. Other voltages do. Just wondering if you had considered that and it was deliberate.

      How much larger do you think it would be possible to upscale the design, parallel connecting FETs etc. I have a remote radio hut, with 3x 170w panels & 500Ah batteries. Yes a big investment. Every commercial charge controller tried has produced unacceptable RF noise. So I’m thinking of building a linear system instead. We can spare the power for the efficiency loss. Perhaps 3, one on each (11 A) panel. Any thoughts would be greatly appreciated.

      Cheers. Greg.

      • Greg Banks says: on December 27, 2013 at 10:08 pm

        Jim I see you have already answered a similar question regarding parallel connecting FETs. Apologies, I didn’t see that page initially for some reason.

      • I generally use 6.2V zeners due to their sharp knee and relatively good temperature coefficient–check out my temperature compensated solar charge controls on ebay:

        You can easily get 11A per transistor if you use a decent heatsink, but the largest PCB mounted heatsink (3.1°C/W natural convection) limits the current to 7A. If you use forced air cooling this could be extended to 11A. The fans could be set up to run only when the solar panels are putting out power.

        Note that if outputs are paralleled, they tend to act goofy because one will start limiting current before the others–it is not easy to get them to load share after they reach the set voltage–not really necessary either.

    71. Hello sir,
      as i read the schematic i have also one schematic but in my schematic using Q1 & Q2 use IC LM358. as i m not an electronics engg. i have its hobby so can you guide me. as i made one solar tracker which is fully operational. as i read all comments and reply there is two points you changed circuit schematics error, so now your schematics is error less as shown at top page.

      i use IRF4905 instead of FQP27p06.

    72. sir i search P600G rectifier i dont get it in INDIA so any compatible rectifier diode

    73. I already get mail, but I want to know the charge controller ckt for 12v 7.2 Ah battery from 20 WATT SOLAR PANNEL

    74. Sir i made this circuit now i want one circuit for deep discharge protection of battery with auto cutoff please suggest me.

    75. Sir
      i built this circuit and get some following observation & readings
      I connect 20 watt 12 volt solar panel with 7.2AH 12 volt battery.
      1:Red LED glow
      2:Green LED Off
      3: Voltage of panel 21 volt
      4: Current checked placing amp meter series in controller & panel shows 0.6 amp
      5: Voltage at battery output of controller is 7.89 volt and amp is 0.18 amp
      so my question are
      1: how can increase voltage & current @ battery.
      2: How to check the battery get charge
      3: When Green LED glow or on
      4: How can i connect more batteries of 7.2AH in parrallel.
      5: Circuit can protect the battery over charge.

    76. Two R5 on schematic and BOM
      Lets call the 18K R10

    77. Sir
      i built this circuit and get some following observation & readings
      I connect 20 watt 12 volt solar panel with 7.2AH 12 volt battery.
      1:Red LED glow
      2:Green LED Off
      3: Voltage of panel 21 volt
      4: Current checked placing amp meter series in controller & panel shows 0.6 amp
      5: Voltage at battery output of controller is 7.89 volt and amp is 0.18 amp
      so my question are
      1: how can increase voltage & current @ battery.
      2: How to check the battery get charge
      3: When Green LED glow or on
      4: How can i connect more batteries of 7.2AH in parrallel.
      5: Circuit can protect the battery over charge.

      • Sounds like your battery is fully discharged or damaged (dead).
        Try charging it across an automotive system for about 15min to see if it comes up to normal voltage range.

        Then connect solar panel directly across battery and make some more measurements–this will not harm the battery short term (1 or 2 days).

        When you know your battery and solar panel function normally, reconnect the charge regulator and make new measurements.

      • Actually i check the battery voltage it gives 12.50 volt but when i connect charger regulator it shows measurement that 7.08volt & ampere meter reading is 0.18amp

      • Something is grossly wrong–connect solar panel directly with isolation diode.

      • actually i want to know that, can we change the voltage at charger controller at battery connection? any preset movement”?

    78. Sir
      Now i check two days battery get charged 12.90 to 13.32 volt. Now i want to know that when green light is on & how this circuit protect over charged?

      • If you followed the instructions and set the voltage to 14V using a dummy load, it will not overcharge. It appears that your battery is significantly discharged and may require a few more days to get to 14V –at that point, the green LED will come on and it will continue to charge until the current drops to a very low level.

      • How can we upgrade it using 100watt solar panel ?

      • This can be increased to 100W (8A) by changing Q3 to a P80PF55, the heatsink to the 2.5″ version (3.1°C/W) and D3 to an 80SQ045N. Beyond this, parallel devices and large heatsinks are required –not really feasible for a linear regulator like this.

        The high current rating of the MOSFET is not required –it is rather the extremely low internal thermal resistance. As a result, the heatsink runs stinking hot, but the transistor junction temp is kept below the 175°C spec. Of course, the only time it runs hot is when the battery is beginning to top off at max voltage.

      • Thank you for the response :) god bless

      • can we use IRF4905 as a substitute for the Q3? and we will use the same D3, coz we already have the components. Thanks in advance :)

      • The IRF4905 should work OK, but the 6A4 will not work at 8A. Perhaps you can parallel two 6A4 diodes in close proximity to each other so that they will tend to load share.

    79. Sir can i use this solar charger for a 15 W pannel

    80. hy
      i have a 10AH MPPT solar charge controllar and 200 watts solar panell it’s all ok i need another charge controllar hope so you understand sorry for bad english

      • 200W is too much power for this unit–in one of the comments, I show how to stretch it from 50W to 100W, but 200W is too difficult. A relay contactor type may be the best way for you to go–this is the common variety that is commercially available in this power range.

    81. Jim thanks for your reply. I just wanted an advice on my project, my project needs a solar charge controller which connects 12v 7ah battery and a load having a mobile charger, a LED module and a Dc fan i have counted the load and came to a decision on using a 12v 7ah battery. My solar pannel 15W, SO I JUST WANTED TO KNOW THAT IS THIS CHARGE CONTROLLER USABLE IN THIS PROJECT PLZ REPLY ASAP!!

    82. even more where should i connect the load in this solar charge controller.

    83. all the components that u are listed out are not available in the
      market..will any one help me in this aspect

    84. If I have a 40 watt/48 Volt solar panel will this circuit charge a 80AH dry cell solar battery? If not can you help me find a circuit that will? Thanks

      • It is a 12 Volt battery

      • Your solar panel voltage is too high for this circuit to handle. What you need is a relay based charger control that measures battery voltage and drops the relay when the voltage exceeds the set level (14V). I have been considering posting a circuit that does this –quite simple, but effective at preventing overcharging.

      • Thank you. I think I found one that will work. If you have a chance could you check out http://mdpub.com/555Controller/ and let me know if it would work. It has it so you can tune your min and max cutoffs and is relay based. Thanks for the quick answer.

      • Cool idea –why didn’t I think of that one. The circuit looks OK with upper and lower thresholds. With solar (unlike wind), there is no need to dump the solar panel when the battery voltage exceeds the upper threshold.

    85. I have 1 x 65 watt 12 volt solar panel that actually runs around 17 volts and around 1 – 2 amps

      However I want / need to increase the amps using capacitors, either 1 20 volt cap or 4 x 5 volt caps

      More info you may need I am using a 30 amp (max) charge controller PWM that isnt getting enough amps from the 1 panel to charge 12 volt dc battery (100 ah).
      by adding a 25 volt capacitor across the solar panel input on the pwm charge controller this will increase the amps ???

      Please note i cant buy another solar panel or buy a mppt charge controller as i cant afford that, so my capacitor idea if it is a good idea we all could use to gain more amps if this is not the case please let me know :)

      • Unfortunately, there is no way to increase the solar panel output current via the use of capacitors. This treads in the area of “above unity power” where the output power exceeds the input power –physics impossibility…

    86. i dont mean over unity or free energy i mean stored energy to act as a boost and make current seem more constant to enble better or longer charge time or more consistant as the main purpose of caps are to stabelize current flow, or even out spikes so its more consistant!

      • OK, I see what you are getting at –two energy storage devices: capacitor and battery. The only possible benefit that I can see is that the average battery charging current may be reduced since the regulator input has potentially continuous power.

        In solar systems, the maximum charging current rarely exceeds the battery charging current limitation –this is due to the current limiting nature of the solar panel. So in my thinking, simply use only the battery.

    87. please i am getting only 2.44v at the load when i connect the 1k Dummy resistor please what should i do…I have reconnected the circuit about 6 times

    88. maybe your adjusting the current but not the voltage

    89. hello sir ,
      My project details –
      I am using a bicycle to give mechanical input to alternator(TVS lucas) and a field supply of 12V d.c .

      SIR , my alternator output varies from 12-24V d.c ,40A(max) depending upon the my pedalling speed.

      After that i am using a voltage regulator circuit which gives me a output voltage of constant 12V d.c and then converting this 12V d.c to 12 A.C(60WATT) and then by use of the transformer my final output is 220V A.C.

      The problem i am facing is that my voltage regutor I.C(7812) and invertor circuit does not work on 40 APMS of high current.

      Kindly i request you to plz guide me how i can get a 12V constant D.C at very low current of 5A(max).

      • Add an intermediate 12V battery or large capacitor because inverters run poorly on a high impedance voltage source and may not start properly. While a voltage regulated output may appear to be low impedance, inverters have high transient input current–especially upon starting.

        This circuit will run at 6A (current rating of D3) if the heatsink size is increased.

    90. use a couple fuses of low amps like 5 amp fuse for use with 12 volt and then use a 0.5 amp fuse after that 5 amp fuse. thing is with amps is a device after the 0.5 amp fuse should pull the amps it requires and if more than an amp is drawn then your small fuse will defently blow to protect your device.

    91. Sir,
      I have 12 volt 7AH battery and i used it for lightning 1 watt LED at 25 feet distance from battery i inspect that LED power get low as i think distance so for that what can i do, So i get Full LED light with regular consumption & what is thickness & type of cable has to use?

      Another What if I used grid of LED for 21 ft X 24 ft area for lightning? Any circuit for this lightning? Please guide me for this practical project.

    92. thanks for circuit, and your valuable follow ups.
      I am in need of making a Solar Charger for Car Battery
      which is 35 Ah.

      Will this circuit work for such car Battery ?
      Can I buy These (http://goo.gl/NbaeV5) Solar Panel 12 Volts 10 Watts, will they be able to charge the car battery ?
      if yes, how long.
      usually my battery is near 12v, when parked due to ICE(in-car-entertainment) Usage, bad habit of using it in garage :-)

    93. Sir,

      Can I use this controller with 2 solar panels of 30W each one?

      Thanks and regards.

      • That should work OK provided that each panel has its own isolation diode –note that some panels already have diodes…

      • Sir,

        Thanks for your answer.

        I have an other question: do the load stop if the level of the battery is too low? If yes, what is the minimal voltage?

        Thanks and regards.

      • This circuit does not provide for low voltage turn-off. However, that would make a great project –will think about it.

    94. Dr.Venkataramu.B.S says: on May 5, 2014 at 9:17 pm

      Sir i have less knowledge in electronics. My doubt is if lightening strikes a solar panel does it burn the circuits connected with it or solar panels are immune/resistant for lightning? What is the effect of lightning on solar panel itself?Kindly clarify the doubt. Thank you. I liked your previous posts even-though i have not done any circuit boards…

      • Lightening is a wild card and a direct hit will take out everything regardless of protection measures. A close miss can also wipe out everything or nothing. In my commercial solar controls, I provide a TVS (transient voltage suppressor) diode to absorb static discharge coming in from the solar panel, but this is mainly for specsmanship –everyone else is doing it…

        Fortunately, solar panels are relatively low compared to radio transmitter towers that DO receive direct hits. For a large, expensive roof installation, I recommend static discharge rods to reduce the possibility of a direct hit. Interesting subject, but I am not expert here.

    95. Hello, I need to make a battery charger circuit for a 5W MAX , Optimum Power Voltage 17.2V, Optimum operation current 0.29AMPs, max 600V , Short circuit Current 0.32Amps and Short circuit voltage 21.6 V. Charging a Lead Acid battery im Guessing? Any suggestions or can I use this circuit :) ? Thanks

    96. Dear Sir,

      I want to replace my 20A solar charge controller by connecting it to both the battery (100V) and the panel (120W). Wiring was long done and is in order. I happen to be on a weekend and need to go back to my place of work and I cant find anybody with technical know-how. Am trying to follow some instructions on the manual provided but it is a bit confusing. Can you please sketch me a diagram on how to go about it.

      • I think that there is something amiss here –my guess is that the 120W solar panel runs at approx 10A, 18V for charging a 12V battery –there is no (easy) way it can function with your 100V battery.

    97. Hi Jim.
      Can I use the 4k7 resistor and green Led across the mosfed on your 12v 6A sss solar charger to see the charging progress.

    98. Hi Jim.
      It looks like Led D4 is mainly used to setup the charge voltage for the controller, what other indications can one see from Led D4. Thanks for your valuable inputs.

      • LED D4 simply indicates that the sun is shining and the solar panel is actively generating power –you can do the same by observing if the sun is casting a shadow. It is an unnecessary frill, but adds a little pizazz to the project.

    99. Sir,
      its nice to see your efforts in making the world greener.
      there’s a slight change in my requirement, I want to have a charger for my Home inverter Battery which is a
      12v 150Ah Battery, currently charged by inverter itself.
      Had 22 hour black out and I believe I should make 1st solar project to get home battery charged and later make one for Car Battery.

      I plan to Integrate Solar charger to it, And applying a Isolation Switch which will disconnect the battery from Inverter wires, making the charging current to come from solar panel after the controller. in case of power cut during that phase (Solar charging) I would need to disconnect solar charger wires and turn switch back to Inverter mode so it can be used to get 220V required in House.

      How Long will it take to charge a 150 Ah battery using this with a single 12v 10W Solar Panel ?
      Will the same circuit work with car battery too ?

    100. Hi.
      Since this circuit Gerry use full. Can I just buy this circuit since some part is not available here in my country.. And since I am new to the electronics I can’t build this circuit alone

    101. Fitting them can take anything from 30 minutes to a few hours, but the
      fact is, saving money is what fitting panels yourself is all about.

      People have suddenly got conscious through the many mediums available
      and are shifting to this eco friendly option. More
      and more people are starting to inquire about solar generation.

    102. Dear Mr.Jim,

      it is very interesting and great to see your hard work to reply queries.
      I would like to use this circuit for charge 12V-4Ah battery from 12V-6W solar panel. My load is 6W LED bulb. kindly suggest the optimized components list to meet our application.


      • To optimize for your application, the heatsink may be made much smaller–just about any TO-220 heat sink will work as the power will be well below your 6W solar panel rating.

        Q3 need not be changed because it is already very inexpensive, but the Fairchild FQP17P06 is marginally less expensive.

        D3 may be reduced to a 1A current rating (1N4003 etc.).

        Good luck!

    103. Requesting to arrange pcb artwork file in case ready.

    104. Mother seals sometimes leave their babies on the beach while they go
      hunt, but return a short while later. When a dolphin gives birth, another female dolphin is present through the entire birth
      process. ” The farmer took the baby eagle and placed it with his chickens.

    105. hi sir,
      I am designing solar charge controller of 12v 10 amp with lead acid battery .actually my design is through negative switching but i am getting problem of not controlling current kindly let me know how to control current by changing duty function if you provide your e mail id i will send you the circuit pls.and also i would like to know how to choose heat sink for power mosfet and power diode pls

      Thanks and regards

    106. Sir Jim, could you please tell me the registers you have used in your circuit. I’m a student and trying to create the same circuit for my project but I’m unable to figure out all the registers you have used in your circuit. Thanks in advance.

    107. I think you mean resistor values. I used 0.25W, 5% carbon film resistors, but 0.5W, 5%, 1% film or carbon composition resistors are also acceptable. Good luck!

    108. hi sir
      here ashok again

      i made this circuit but output voltage not adjust as variable rotate abd input & output voltage is same. I check voltage at adj point of IC voltage varies from 9 volt to 7.9 as VR is move. plz help me any guidance for chk circuit.

    109. sir i used IRF4905 and PCB art work means i made Pcb at home.

    110. hi sir, do you think my IRF9540N is in right pins??
      please help me.. tnx :)

      see image below:


    111. Thanks a lot Sir.. 😀

    112. please email me the pdf file of this schematic… needed badly for our research.. i need clear value of its components.. thanks a lot in advance! best regards aldrin.. :) GODBLESS

    113. sir, i have doubts in your circuit.. is this circuit really functional? i just want to know sir if it;s really functional.. because i really want to build this circuit.. thanks best regards aldrin GODbless :)

      • Jim Keith says: on August 7, 2014 at 5:10 am

        I built it and it works well. If you follow the thread back, you will see that numerous others have done this also. The schematic issues are not with the circuit, but with the reference designations.

    114. please what size of C1 C2 and most be 50v can we use 100v

      • Jim Keith says: on August 12, 2014 at 4:57 am

        Voltage rating of capacitors is generally non-critical –it is OK to use a higher rated voltage device.

    115. Very informative… Can you please guide me about charge controller of wind turbine?? i
      have 300watt Dc generator

    116. Hi sir my name is JC an ECE student,we have a project about using a 100W solar panel to power up a water pump and our group was assign to build a charge controller circuit, i have tried your circuit and i use some replacements for 6A4 and FQP27P06 for simulation. Our project requires a thyristor or an SCR to be use in the circuit, where can I make some changes in your circuit? I need you help sir. Please reply…

      • Thyristors are intended for AC applications. I can see no way of implementing one in this particular DC charge controller.

        One possibility is to use the old force commutated SCR technique for a switch based control. This is what they did before they had decent high voltage bipolars or IGBTs. This would be a different, more difficult means of implementing this circuit:

        How it works:
        SCR1 is triggered via a 10uS pulse turning it on. When on, C1 charges to the battery voltage in about 100mS via R1. At this point, the battery voltage is sampled–if it does not exceed the voltage set point, SCR1 remains on and the battery continues to charge–when the set point is exceeded, SCR2 is triggered with a 10uS pulse. This forces the left side of the capacitor below ground potential thus reverse biasing SCR1 and force commutating it–the reverse bias voltage period is approx 100uS that should be adequate for SCR1 to turn off (commutate). Note that the current through R1 may not exceed the holding current of SCR2, or it will not self-commutate due to low current. For the capacitor, I would use the type that is used in permanent split capacitor motors–commonly used in air conditioner air handler motors. SCR1 & 2 must be non-sensitive gate types.

        In line voltage inverters using this technique, all kind of nasty things happen with voltage spikes etc. This requires the addition of inductors and snubbers, but at 12V I think that all this may be ignored.

      • yilits28 says: on August 25, 2014 at 7:54 am

        Hi Sir thank you for helping, but we are only allowed to use discrete components that’s why i can’t use the circuit from your link. But for the 10A switch based solar charge controller, where can I connect it from your previous circuit? Can I have a complete circuit where the 12V solar charge controller is already switch based by an SCR?

      • yilits28 says: on August 25, 2014 at 8:29 am

        can i use an S2800A instead of an S2040L?

      • yilits28 says: on August 25, 2014 at 8:46 am

        sir,what software do you use for simulation of your circuits? I used multism but not all components are present and sometimes it is not accurate.

      • The S2800A is a good choice.

        I do not have a simulator, although I have used the buggy Multisim in the past. Instead, I use my cranial simulator to visualize circuit operation.

        Does Multisim do the 2N6027 programmable unijunction? I will use it as an oscillator /gate driver.

        Do you have pulse transformers available? The circuit is more simple if the SCRs are moved to the high side, but that requires gate isolation.

        Will work out a complete circuit using discretes –what is your timeframe?

      • Per your requirement for discrete components, does the TL431 programmable voltage reference qualify?

    117. Yes sir, both 2N6027 and TL431 are qualify and is available in Multism. I need the circuit before september ends.

    118. Sir? what’s the update about the circuit? i really need it for our project, the project will be donated to the unfortunate people that don’t have electricity in their community.

      • Jim Keith says: on August 27, 2014 at 3:56 pm

        I have the schematic roughed out–now to test and see if it works as expected. Will then submit as an electroschematics project by the end of the month. If you really wish to help the unfortunate, do not use this expensive, outmoded technology–I view it merely as an informative, mind-stretching tech school experiment.

      • yilits28 says: on August 27, 2014 at 6:24 pm

        okay sir, i’ll wait for the schematic circuit you made. Thank you a lot sir for helping us :)

      • Jim Keith says: on August 31, 2014 at 1:28 am

        @yilits28, post your email address and I will send advance copy of the SCR Based SSS Solar Control Schematic.

      • “carlo_aquino26@yahoo.com”

    119. Sir,can this circuit used to charge a lithium-ion battery??

      • Jim Keith says: on August 31, 2014 at 1:34 am

        I have had good results charging at 4.1V /cell. This circuit requires (3) in series for 12.3V. Do not float charge for an extended period of time because some lithium ion batteries tend to degrade under this condition.

      • sir, kindly update me when you already send the advance copy of the Schematic. thank you…

    120. “carlo_aquino26@yahoo.com”

    121. thank you sir, hope this works :)

    122. sir ,i’ll wait for the write ups and its block diagram thank you…

    123. I’ve got the write ups sir, thanks for the help… my classmates are asking if you have an available power inverter circuit that can be connected to the charge controller to power up a water pump, they are hoping that you can help them too.. .

      • Jim Keith says: on September 3, 2014 at 5:38 am

        No, I do not have an inverter circuit. I have one that I have not yet finished, but much work needs to be done. I recommend a commercially available unit.

        There are square wave inverters available on electroschematics, but I do not recommend any of them–too weak to start a motor and high harmonic content greatly increases motor losses thus reducing pump run time.

    124. Sir can I have the block diagram of the circuit? :)

    125. Dear Sir,

      I have five (5) solar module(panels).
      each of: 35 watt, open circuit voltage: 21V,
      short circuit current: 2.4Amp.
      My inverter battery is 12V,150AH.

      so, can I use this circuit as a charge controller for 12V,150AH battery?.
      how I connect panels.?
      its good if you help me regarding my question.thanks

    126. [quote]This control charges the battery at a constant voltage and also maintains a charged battery (float charge). The float charge voltage specification is a little lower than the charge voltage, so to accommodate both voltages, a compromise is reached by simply reducing the voltage slightly –that is how ALL automotive systems operate. To obtain maximum charge in a 12V battery, set the control to 14 to 14.6V. Automotive systems further reduce voltage to 13 to 13.5V in order to accommodate high temperature operation as the battery is usually located in the hot engine compartment –battery has a negative thermal coefficient of voltage.[/quote]
      I don’t agree with this . Charging an auto 12V lead acid battery on the floor it gasses at 13.6V. Don’t ever take lead acid above 13.6V . You will root them , simple as that . Hold them above 13.6 Volts and they sulphate up or block up the spongy lead and that’s the end of them

    127. Dear Jim Keith,
      I am a final year student. my project is to make charge controller for charging an electrical vehicle from solar panel connected with vehicle. our solar panel is 100w, open ckt voltage= 17.5v. short circuit current=5.72 A… we use this to charge a 12v lead acid battery. is there any need to change this circuit? please give some suggestion what should we do now & what parameter should notice carefully to make a charge controller….
      Sabuj Islam
      CUET, Bangladesh

      • Jim Keith says: on October 21, 2014 at 3:43 am

        Sounds like a good match. I recommend that you go with the 2.5″ heatsink to handle the additional power. Part of your evaluation should be a thermal resistance analysis of the MOSFET and heatsink.

    128. Muhammad Arslan says: on October 27, 2014 at 4:47 am

      hello dears..i am engineering final year student….i want to make hybrid charge controller for solar panel…can anybody help me..?

    129. hello sir, i am final year engineering student, can we use above circuit for charge 48 volt batttery bank by using 12 volt,150 watt solar panel?….please reply fast…..it’s urgent.
      thank you.

    130. hello sir,
      I am research scholar I doing project hybrid energy for solar and wind. so I used battery charge controller I have no idea for battery charging controller so plz reply fast

      • What is your question?
        Note that wind power chargers are different and more complex than solar chargers –I have not dabbled with that one yet.

    131. Dear Jim Keith
      I have, what might seem to be stupid question. I bought a van with solar panels. The wiring is a mess and I like to sort it out. There is one outlet on the solar regulator that says Load. I looked at a wiring diagram on the net. It says to connect it to a auxiliary or night light.
      It also says to use 4mm wire. I’m confused. One does not need a 4mm wire to run a light bulb. My question is, what load does it have to be connected to and does it require a fuse between the regulator and the load. I would appreciate if you could help me out with this one.


    132. Dear Jim,
      Thanks for your wonderful blog.
      I do have some sympathy with you.
      May I ask another question.
      I am a vinal year engeneering studint.
      We built a solar car for a project We will be driving the car for three days to do a mileage test. We will be two drivers. If each driver drinks 2 liter of water per day we will need 6 liters. Our container can only hold 5 liter.
      Can you please send me a circuit to compress 6 liters water into a 5 liter can.
      This is urgent as we have to leave in two days.

      • Consider high power explosives to compress the liquid to critical mass –this will work for a few uS, so get your engineering student friends to figure out how to quickly cap the can…

    133. Switching to Solar:
      Hi Toktokkie & other interested people.
      Yes, I live in Kruger Park in South Africa where sunshine is a punishment (42 degrees C in the shade on a mad day) and I started Solar because our corrupt govenment paid out all the profits of our our electricity system to themvelves as bonusses. We have the highest per capita ownership of Mercedes and Porches. Our Monthly fee went up from R300 per month to R2600 per month, with another 3 x 40 % increaes approved. That while Pensions went up from R840 to R1200 per month.
      I started with real cheap Chinese panels of 200 watts. I since added 400 Watts. I designed the original Charge controller and had to increase the capacity. I used relays, ok for low power, but when you start getting to 25 amperes at 12 or 24 volt, the relays melt up! My Rich neighbour brought me an expensive German charge controller (two month’s pension) for repair.
      This handles 24 volt at 30 amperes with ease., using two power mosfets. I wanted to get did of my relays and that is why I contacted Jim Keith. I can not see why the unit should cost so much, as the component count does not even come to R200 all together!
      I just built a new apartment, and it was designed from scratch with ZERO ESKOM in mind!
      One of the biggest problems in Solar housing is running the 12 volt lights of the 24 volt supply!
      I think I just solved that problem!
      I just do not know whether I should try I patent it?
      Andre from Amamzimtoti Bushcamp.
      If you promise not to sell it to the spam syndicates, here is my e-mail. graskop@global.co.za
      I send photos of the very first bank of cheap 10 watt panels, made very difficult to steal. (top priority in a country where the president has hundreds of wifes, children and concubines and had 160? outstanding criminal charges against him, and a 80% unemployment rate in the country areas!
      Also, the twin 12 volt charge regulator, with the new 30 amperes German relays sitting piggyback on top, as there was no room on the PC board.

    134. Here is the other photo. I have stripped this large bank and use then in my hothouse and guest bungalows.

    135. hi Dear’s

      please help

      how to charge laptop from Car Battery (schematic Diagram)

    136. Hi Sir Jim,

      Is this circuit suitable to 12V 72Ah battery? ( I have 4 12V 18Ah battery connected in parallel). Planning to build this project.

      Appreciate your advise Sir.


    137. I do not see its help because when I rise a quetion its not answered

    138. how can we modify this cct for charging 24v bty

    139. Hi there. Im thinking about using this design to charge a 12v 2.3ah battery that is powering my portable amp system. My question is. i assume i can use this circuit with a 12v/250-500ma solar panel? and is there any components that wouldnt be required (working with a smaller current)??

      thank you for your Help!!

    140. Hi Keith.
      What do you think of this Pic solar charge controller found on this link.

      • Without appearing to have the NIH (Not Invented Here) syndrome, let me first say that his circuitry appears to be good. I have essentially 3 objections: First, I disagree with his open circuit battery voltage measurement philosophy –this tends to fall apart when there is battery loaded –virtually all automotive charging systems ever made measure and regulate the voltage while charging. Second, the PIC runs full time and discharges the battery when the sun is not shining (most of the time) –while the PIC may be efficient and not consume much power, it remains significant –estimated minimum battery load is about 15mA –R8 soaks up about 6mA alone –this would fare poorly in the North country where solar panels may be covered with snow for weeks at a time. Third, there really should be a series diode present –this is not present in many solar panels and causes the solar panel itself to soak up undetermined current when the sun is not shining. Hope that this is helpful.

      • Also, this is a form of SSS (Solid State Switch) regulator. As such it can handle much higher current than the LDO circuit posted.

    141. Thanks a lot for the feedback Keith.

    142. I built this LDO circuit and it works well. Thank you for the information Mr. Keith.

    143. Rajeev Srivastava says: on March 21, 2015 at 6:54 pm

      suggest one good circuit to use 12-24V/20Amp DC charge controller for manufacturing in India.

    144. Hi Mr. Keith

      With reference to the last post. It remains a wonder for me that you are still prepared to respond to these threads.

      • Jim Keith says: on March 23, 2015 at 12:26 pm

        The primary contributors are attempting to make this a good site, and it is working. On the other hand, we are not into providing free engineering for manufacturers.

        Glad you had a good experience with this solar charge control.

      • Rajeev Srivastava says: on March 24, 2015 at 5:24 am

        We can pay for that. I have already designed 3 different circuits 10Amp, 20Amp and 20 Amp. with Microcontroller based.

        But I need one more of 20 Amp with out using microcontroller to compare.

      • Jim Keith says: on March 24, 2015 at 12:18 pm

        MPPT? That is the only feature that a microcontroller may be needed for –and it also can be done without a microcontroller. One big issue with 20A version is the inductor –both expensive and difficult to obtain and I am weak on magnetics.

    145. Dear Keith,
      Sorry to bother you.
      I have a problem which I think is shared by Millions or at least 100, thousands of modern people. So, this is not STRICTLY a personal request.
      I am now on pension and have to live as such. I graduated on Valves. Since our country’s electricity system fell apart, solar is taking over. Just imagine having to feed a hundred wives, children and concubines. Especially when you have to charter jumbos to fly them to Paris for shopping, and filling up 5 star hotels with them and the body guards. No money left to run the country.
      As you well know, the higher your DC supply volts, the less the current and higher the efficiency.
      BUT, with batteries still the weak en expensive link, 24 volt is the most popular installation for domestic use!

      I ran two desperate 12 V charge controllers for my two banks of batteries.
      but even so the “biggest single problem” in the business is Running your 12 volt lights of a 24 volt system!
      Even if you only run 50 watts of lighting, on one battery, you are going to run into a unbalanced situation when your two batteries are charged in series. For series charging one assumes that the batteries are identical in capacity and charge level.

      I designed an circuit right in the beginning with a series regulator, using a 2n3055 on a medium heat sink. Output 13 volt, protected with a Thyristor and fuse crow bar circuit.
      As the 1 watt leds turned into 3 and 5 watts, this started running HOT, and after 8 years I got a chance to test the crowbar!
      I think chopper circuitry is now a practical solution, and heat is lost energy!
      Maybe you can look into a simple chopper circuit, reducing 24 – 30 volt, to a steady 13 volt at 5 – 10 amperes?
      Or, a few quick scribbles for me to play or experiment with will also help.
      Something like s simple sketch of a suitable switching device, with an trigger signal of which the mark space ration can regulate the output will suffice. I am old but not too stupid!
      Being of Pre transistor and definitely pre IC age, a two transistor multivibrator, with maybe another one for switching the solid state device on & off would be easiest. BUT, I have built 555 oscillators in my young days. LOL,

      • Jim Keith says: on March 24, 2015 at 12:23 pm

        What you need is a switching buck regulator –such has a high efficiency, and 10A version is feasible.

        Do you use the crowbar to blow a fuse?

        Never realized that things were that bad in SA –we also have corruption, but the govt protects itself via the controlled media that brainwashes the sheeple…

    146. Hi, that was a quick reply?
      Yes, the Zener detects 14+ volts and triggers a thyristor which blows the 5 amp fuse!
      Thanks, Think I will find the topic on Google?
      At work now, will check tonight.

      The worldbank just degraded our ESKOM to trhe lowest level. Can never get credit again!
      They borrowed 2,000 billion to pay for two urgently needed power stations. They blew the money, (it is missing) and the power stations are not paid!
      Also just saw another R600 Millon dissapeared without trace.
      They can not afford to run the normal day to day running of the utility at the moment., let alone pay the new power stations!
      SA was voted the most romantic country in the world, as all suppers are eaten by candle light!
      Our President who could not write his own name had 146 criminal charges hanging over his head.
      He spent R260 Million on upgrades to his private home etc!

      Our government is refered to as the cANCer!


      • Jim Keith says: on March 24, 2015 at 3:35 pm

        OK, will soon post a buck regulator based upon the dated LM78S40 IC that is made by TI. There have to be new ones available, but I have experience with this one and it works and remains available. The current can be scaled up substantially.

    147. need circuit for 12v,7.5ah sla battery charger

    148. We are having some troubles finding the diodes (D1 and D2)
      from those part numbers with the correct combination of
      voltage and current (or power).

      We are ofcourse finding some other diodes with these
      specs, but we were wondering if there are any other important
      specs about the diodes? (max surge current, recovery time,…)

      thank you in advance

    149. D1 is a garden variety 6.2V zener of any power rating–does not have to be the 1N4735A.
      D2 is a garden variety signal diode or rectifier that is applied far below its current /voltage rating–any silicon rectifier with low leakage is OK–how about a 1N4005?

    150. Dear Jim,

      I’m trying to understand how the reverse battery protection works here. It would help me so much if you could explain what exactly happens when the battery is connected in reverse.

      I understand that D3 prevents the battery voltage from appearing across an inactive solar panel and that together with D2 it makes sure the (potentially dangerous) current can only flow in the arm of potentiometer R6. Do correct me if I’m wrong please. How does this activate Q3 and why does the reference voltage become 0 if this is the case?

      Thanks in advance!

    151. When the battery is connected reverse, the voltage at TB3 is negative in relation to common. This causes emitter current to flow out of Q4 that is connected as a common base transistor. This causes the collector of Q4 to short out the reference voltage to Q1.

      The voltage across the power MOSFET (Q3) increases in the same polarity because the battery and solar panel are connected in series aiding (abnormal) rather than series opposing (normal), but Q3 cannot turn on because its gate voltage is zero (actually -0.6V).

    152. Thanks sir, I have just finished building this project, I have done all the tests and I am happy, I got it 100%!!!

    153. Could you tell what the scale is of the potentiometer R6?
      Linear or logaritmic?

      • Jim Keith says: on May 6, 2015 at 3:47 pm

        R6 is a linear type of pot. However, the control voltage output adjustment vs angle of rotation is a reciprocal function.

    154. hi Jim ,
      can i test the circuit using D.C power supply and i ahve question regards the FQP27P06 MOS P-channel as it can be seen in your uploaded picture that the source leg indicate the arrow going in to the gate as the datasheet indicate the reverse indication,

      thank you

      • Jim Keith says: on May 6, 2015 at 11:02 pm

        It can be tested using a DC power supply provided that it has a variable current limit or fixed current limit that is approximately the same as the solar panel output current.

        On the MOSFET symbol, I always seem to get them backwards–the datasheet is OK, but schematic incorrect. It is a P-Channel device.

      • thank you so much Jim :)

    155. Dear Jim,

      When using the potentiometer to adjust the output voltage to 14V over a 1K dummy load resistor we can only get to a maxmimum of 11.6V. Can you think of any reason why this could be?

      Thanks in advance!

      • Jim Keith says: on May 7, 2015 at 6:33 pm

        What is the input voltage at this time? Normal solar panel output voltage with no load is about 18 to 20V. Try shorting out R7 to see what happens –this should increase the range of adjustment.

      • Jonas says: on May 7, 2015 at 7:01 pm

        We used a DC generator, and went up to 20V and the voltage kept on a steady 11.6V. By shorting out the R7 we did get higher voltages, when the input voltage was high enough, thanks. However we wanted to get a charging voltage over the battery using 12V as input, is this possible? If so, how can we do this?

        Thanks in advance!

    156. this is a good blog.im much into solar and i have 1000 watts solar panels but am having problems finding the right charge controller which i believe will be around 70 amps,so pliz if anyone has a schematic, pcb layout for it may u pliz help me , i will be grateful

    157. this is my correct email address

    158. Hi. JIM
      Hope you are well.
      I want to know what charge controller can I use to charge a 12V 105AH deepcycle batery. That I can use with solar pannels. Also something like a batery pack to connect 8 12V Led lights.
      Kind Regards

    159. HI JIM ,
      am sorry i know my question is kind of funny, but can i use 20 w solar panel instead of 50 w is that possible or is there any other way to run the circuit with low power . thank you

      • Jim Keith says: on June 3, 2015 at 6:00 pm

        This is a frequent question. The 50W indicated is a maximum –it can always be applied at lower power.

    160. thank you Jim i really do appreciated

    161. Dear Sir

      I’m new in electronics and need help in designing the following.

      Design and build a circuit with two inputs and one output. The inputs will be used to connect to a photovoltaic (PV) solar panel and a wind turbine alternator, with built in rectifier and regulator, both designed for charging 12 V battery systems.
      • The PV panel output is 0-21 V DC depending on the amount of sunshine and the maximum power that it can deliver is 35 W.
      • The wind turbine alternator has a rectified and regulated 15V DC output and can deliver a maximum output power of 200 W.
      The output of the circuit will be connected to a 7 A/Hr lead-acid battery which is also connected to a load which will draw 4 A. The circuit’s output must not deliver more than 3,5A to the loaded battery.
      Each group starts with a’ fully charged battery and, since the battery load is greater than the supply, the battery will discharge. The objective is for the circuit to provide the maximum of 3.5A of current to the 12 V system for as long as possible. A timer will keep time from the start of the trial and will stop when the battery voltage has dropped to 11 V.

      Thank you

    162. Dear SirI’m new in electronics and need help in designing the following.Design and build a circuit with two inputs and one output. The inputs will be used to connect to a photovoltaic (PV) solar panel and a wind turbine alternator, with built in rectifier and regulator, both designed for charging 12 V battery systems.
      • The PV panel output is 0-21 V DC depending on the amount of sunshine and the maximum power that it can deliver is 35 W.
      • The wind turbine alternator has a rectified and regulated 15V DC output and can deliver a maximum output power of 200 W.
      The output of the circuit will be connected to a 7 A/Hr lead-acid battery which is also connected to a load which will draw 4 A. The circuit’s output must not deliver more than 3,5A to the loaded battery.
      Each group starts with a’ fully charged battery and, since the battery load is greater than the supply, the battery will discharge. The objective is for the circuit to provide the maximum of 3.5A of current to the 12 V system for as long as possible. A timer will keep time from the start of the trial and will stop when the battery voltage has dropped to 11 V. Help will be much appreciate and I’m doing my best to get this done.

      Thank you.

    163. Can I use this circuits with solar cells that open circuit voltage is 17.93 V.

      • Your open circuit voltage is acceptable –the circuit will probably work with open circuit voltages as low as about 17V, but this also depends upon the source resistance of the solar panel.

    164. Hello Sir,

      First of all let me thank you for the excellent circuit diagram of the LDO Solar charger controller you have posted in this forum..
      This will help a lot of electronics engineers like me and students and others in the field of electronics ,i usually go through all of your articles
      published in this forum you are really a gift to the readers of Electo Schematics forum.

      sir i am a retied engineer from a govt electronics company in india.
      i want a video camera/recorder to be operated for 24 hrs which works
      on 12v dc consuming 1.2 amps of current to be used with sealed lead acid
      my question is.
      1. what should be the solar panel rating .
      2. what should be the out put voltage of the solar panel.
      3. what should be the ah rating of the 12v sealed lead acid battery for 24 hrs
      back up for camera.
      4. since the camera supply is taken directly from the bat supply a voltage
      polarity protection diode is required from the bat + end.
      5. since camera operates directly fr battery a dc reg circuit with current
      limit may be required for the camera supply .
      6. as per my above requirement will your LDO solar charger circuit suits
      my requirement if so what are the changes i have to make in the circuit,

      Waiting for your valuable reply.

      Thank you

      V.Sambath kumar.

      • Jim Keith says: on October 6, 2015 at 4:08 pm

        @ Mr. V.Sambath kumar

        3. AH rating of the battery: 1.2A * 24hr = 28AH (Assuming a rainy day with no sunshine for charging)
        Minimum battery discharge level = 50%, so 28AH /.5 = 56AH

        1. Solar panel rating: Fully charge battery within 8hours
        = 56AH /8H = 7A
        7A * 14V = 98W (use 100W panel)

        2. Solar panel output voltage: 18 to 20V open circuit (nominal 12V during charging)

        4. Isolation diode is required to prevent the battery from discharging into the solar panel under dark conditions.

        5. Current limit not required as camera has a fixed load current, and solar panel is inherently current limited at 7A

        6. The above LDO controller will do the job except for current rating. Recommended changes are as follows:
        D3: 8 or 10A Schottky rectifier
        Heatsink: Thermal resistance = 2°C /W or better

    165. I built your LDO Solar Charge Controller. I’ve been trying to test it with a bench power supply. I installed the 1k resistor and disconnected the battery but when I power the controller my supply current limits at 3.8A, the output voltage of the supply drops to 8V to maintain the current, and there is no output voltage from the charge controller (didn’t expect there to be at 8V input). The heat sink and device heats up pretty quickly.

      Does this sound right for the scenario that I just outlined?

      I’ll connect it to a solar panel as soon as it arrives and test it the properly then. I was hoping to preset the output voltage before the panel arrives.

      • Jim Keith says: on October 4, 2015 at 1:44 pm

        You must have a gross wiring problem –check and recheck –make no assumptions that this or that is OK. The solar panel will not make any difference other than current limiting at a lower level. Make sure that the heatsink is not grounded.

      • Ah… that’s the problem. The heatsink is grounded. I soldered it to the bottom copper and the bottom copper is referenced to ground. Easy fix. Thank you

      • That did it. It works perfectly now.

    166. nice and very use ful says: on October 10, 2015 at 1:09 pm

      Hello sir,

      the circuit is very innovative and useful , i am electronics engineer we need some clarification and information from your side ,

      your giving only fully battery charged indication in the circuit i need low level battery indication also , so can you give the solution for this ?

      and one more thing is i need circuit for 5A and 10A solar charger circuit , is it possible in this circuit or we have to change the circuit to produce the 5 and 10 amp of current ,

      please reply me,i need this urgently


    167. hello sir,

      please share the 5a and 10A charger circuit diagrams

    168. V.Sambath kumar says: on October 14, 2015 at 6:08 am

      Mr Jim Keith,

      Hello Sir,
      Today only i have seen your reply to my questions, every
      thing is clear to me now ,now i should see whether the mosfet and the
      schottky diodes are available in the market,anyway thanks a lot for
      your feedback .

      Regards V.Sambath kumar.

    169. Thanks again for the design work. I made a prototype and tested it. Also thanks to your help earlier, I made a slight change and the board works flawlessly. I had some boards made from Osh Park. I built a thru hole version and a thru hole / SMD hybrid version. I’ve included a photo of the populated thru hole board and the unpopulated SMD hybrid board side by side. I could have reduced the board size even further but there was no point. The hybrid board is 2″ x 3″ ( almost 50mm x 75mm). The hybrid board cost about 1/2 of the cost of what the thru hole component board was. I’ve attached a photo of the two boards side by side.

      Am I correct to assume that the next step, 100W solar panel and / or higher voltage (24V or 48V), is a much more challenging design?

    170. I ended up using a BAV99 in place of the 1N4148 in my SMD version of your charge controller. It seems to work fine. I have some 1N148 SOT23 packages ordered so I can swap out the diode if necessary. Considering the service, the BAV99 seems to be ok to sub in but I wanted your opinion

      • Jim Keith says: on October 18, 2015 at 5:20 pm

        The BAV99 is a good selection –all of these small fast recovery diodes vary only in small details including package, reverse recovery time, voltage & current rating, etc.

    171. Sir
      ur circuit is somewhat difficult to understand for me.could u please tell me the better way to understand it.

    172. dear sir,
      i am sri lankan student.i like to make this charging circuit.but i have a question.
      this is my battery name plate.
      i have a 25W 17V sola panel. can i change my battery using this circuit?

    173. Chathura
      The controller will easily handle your panel as it is half of the output specified by the designer. Your panel will deliver in the region of 2 Amperes. You will be able to charge your battery with this charger as the battery specifies a charge voltage of between 14.1 and 14.4 volts in a solar application which is in the range of adjustment of this controller. This is however not the real question.

      The real question is how many ampere/hours you intend to drain from the battery between charging cycles and if your solar panel can deliver sufficient amps to replenish what you have used in the time available for charging during a charge cycle.

    174. Actually i want to charge only the battery.
      then i can used it.
      thank you.

    175. I did a little load test on your circuit. The photo that I added is the output graph (Voltage vs Current). I set the CBAIV up to increment .5A, hold for 15s, stop at 9A. There are two graphs. The red lines represents the first test. My bench power supply dropped out on over current at around 5A.

      I switched to an Astron 35A supply and that is what I used for the test data on the second graph (green trend). Unfortunately the CBA unit did not capture temperature data. The heat sink never got above 95°F (35°C) however at 8.5A D3 reached 160°F (71°C). The CBA dropped out at 8.5A so the test halted there.

    176. Can I use two of these in parallel with a 100W solar panel?

      Do you know of a good 24V output charge controller schematic?

    177. Hello !!!
      Why we use the MOSFET P but not N ??

    178. Jim
      What is mean in the schematic by D3, 6A4 I get Diode 3 is there a typo? is that any 6A diode? ot part of a part #?

    179. Sir keith, can i see your ready made controller,the zoom one sir please, i just need this for our thesis and sir? Which part is the switching part?

      • Jim Keith says: on January 25, 2016 at 6:39 pm

        Provide your email address and I will send full documentation of a similar unit that uses an LM358 op amp.

    180. I would dearly love to have the documentation as well please. Is there somewhere where I can provide my email address without publishing it in the open.

    181. gokotanocarlgmail-com says: on April 29, 2016 at 7:06 pm

      Good day sir. I am very interested with this circuit as our study is also related with charge controllers. I tried to simulate the circuit with multisim however, diode 6A4 is not available at multisim. What can you suggest as a replacement for 6A4 so that I can simulate this circuit with multisim? Thank you very much for your help.

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