Advertisement

Dual Power Supply Circuit

Here is a Dual power source for the Home Security system which has to be switched on continuously. It is a power saving circuit that uses a Solar panel for providing power during day time and a transformer power supply during night. It has a battery backup and the power to the security system is derived from the 12 Volt 4.5 Ah battery. So that even if the day light is not sufficient in clody days, the security system will work normally.

About the Solar Power source

During day time, the security system gets 12 volt power supply from the battery or the Solar Panel. If the amount of power from the solar panel is not sufficient, battery will compensate it. Typically a single solar cell generates 0.5 volt and around 50 mA current in bright light. A single solar cell is rated at 45 mW. So in the 12 volt solar panel, there will be 24 solar cells connected serially. It can give 1 Ampere current in day light. Typically a 15 W Solar panel gives 1 Ampere current in bright light. Here a 12 V 5W Solar panel is used in the circuit to give power to the security system and charging current to the battery. It gives around 300 mA current.

About the DC power source

Night charging is attained by the 12 volt DC obtained from a 0-12 volt 1 Amps step down transformer and the fullwave rectifier comprising D3 through D6. Capacitor C2 removes ripples from DC to give clean power to the security system and for the battery.Resistor R4 gives 80 mA current during night for Trickle charging the battery.At the same time, power to the security system will be available from the battery. The trickle charging provision save AC power and protect battery from over charging since the battery will get sufficient charge during day time.

Dual Power source Circuit diagram

Battery status indicator

This part of the circuit indicates the voltage level in the battery as well as the voltage from the solar panel.Zenerdiode ZD conducts only when the battery holds more than 11.6 volts. When ZD conducts Red LED illuminates.When the battery voltage goes below 11 volts ,LED turns off.If the LED is not lighting, it indicates that battery is not attaining full charge or the solar panel is not giving 12 volts.

LDR switch

This is used to switch on the DC power from the transformer power supply at night. LDR offers low resistance in day light so that it gives more current to the base of T1.It is a PNP transistor and it remains off during day time due high voltage in its base. T2 also remains off due the lack of base bias. During night,resistance of LDR decreases, and the base of T1 becomes negative. It then turns on. T2 also turns on and charging current is available from the emitter of T2. Resistor R4 reduces the charging current to 80 mA for trickle charging the battery. Adjust VR1 to set the sensitivity of LDR.

BD139 and BC557 Pin connections

Setting of the Dual Power source circuit

Assemble the circuit on a General purpose PCB and enclose in a suitable case. LDR should be mounted on the case to get sunlight.Solar panel should be placed in a place where bright sunlight is available.Before connecting the battery, fully charge it using a charger.

12 V 4.5 Ah Battery and 12 V 5W Solar panel

14 Comments

Join the conversation!

Error! Please fill all fields.
  • John

    Hi Jombeth, I’m replicating an exact circuit system as your but it will be operated under 6V condition. Do i have to replace any of the circuit component? It seem like I have to replace the existing ZN diode 10v 1w(1N 4740a) to a ZN 5.6v 1w (1N 4734a)?

    I’m using a 6v 7.5ah battery, 6v 420mAh solar panel, 6v DC input.

    Thanks : )

  • lurch68b

    Hello Jim, Is there a BOM for this schematic?

    • Jim Keith

      No –you must work up the BOM yourself and make substitutions as you go –that is the way most of these circuits are –when I provide a BOM for my stuff, it is generally only for the higher level devices

    • lurch68b

      ok, thanks.

  • Jim Keith

    The crossover is actually a connection–the dot indicating connection is quite small. The zener is a voltage threshold device that conducts only when the battery voltage exceeds approx 12.6V thus indicating a reasonably high charge level. Unfortunately, during a simultaneous AC power outage and lack of sunshine, it tends to discharge the battery–such is often the case with LED indicators in battery circuits.

    • naren

      hello sir, i want to charge a lead acid battery 12v 100ah with two source at the same time like one is the grid supply and another is solar power,i dont want to waste the solar power so when there is the sufficient power from solar to the battery i want to limit the grid supply and if there is some shortage in the solar supply, grid supply can do its work, and i am going to use 200w solar panel and 600VA inverter for this can u please help me regarding this i want to do this as my college project

  • Tosin

    sir what is function zener diode in the circuit, more so the connection between solar and transformer seem different. Perhaps, the solar line is connected to dc line to charge the battery. Please kindly explain more, thanks.

  • adelusi tosin

    Sir i have solar panel of 24 cell each rated 5v making 120v at time 124v, yet, it can’t power my ups. Sir what can i to make it effective even to charge 12v 85ah car battery.

    • Jim Keith

      It takes lots of solar to run a UPS–probably will not work directly.

      The best means is to configure your solar panels in a series/parallel array to charge your 12V battery–connect enough cells in series to generate about 18 to 20V open circuit in full sunlight–then parallel as many of these series sections as possible. This will provide the maximum charge rate. If you do not have a solar charge regulator, you must monitor battery voltage and disconnect at about 14.5V to prevent overcharging. Hope it works well for you.

  • adelusi tosin

    Thanks for the knowledge sharing, sir, what is the function of home securiy system in this circuit? What are those things to use as security? Moreso, sir, can this circuit power on 2000w equipment at once?
    Thanks.

  • sagar naugriya

    hello.sir i want to move a toy motor with the help of LDR .when the lignt focus on LDR motor will be work and when light not focus motor will not work. Plz help me…

  • jombeth

    You are right Sigma 6!!!

  • Sigma 6

    It looks like that your bridge rectifier is with the wrong polarity,

    best regards.

    • naren

      hello sir, i want to charge a lead acid battery 12v 100ah with two source at the same time like one is the grid supply and another is solar power,i dont want to waste the solar power so when there is the sufficient power from solar to the battery i want to limit the grid supply and if there is some shortage in the solar supply, grid supply can do its work, and i am going to use 200w solar panel and 600VA inverter for this can u please help me regarding this i want to do this as my college project

Looking for the latest from TI?