lead acid battery charger

Lead-Acid Battery Charger Circuit

This circuit delivers an initial voltage of 2.5V per cell to rapidly charge a car battery. The charging current decreases as the battery charges and when the current drops to 180 mA the charging circuit reduces the output voltage to 2.35 V per cell, leaving the battery in a fully charged state. This lower voltage prevents the battery from overcharching, which will shorten its life.

The LM301A compares the voltage drop across R1 with a 18 mV reference set by R2. The comparator’s output controls the voltage regulator, and produce the lower float voltage when the battery-charging current, passing through R1, drops bellow 180 mA.

Temperature compensation helps prevent overcharging, the LM334 temperature sensor should be placed near or on the battery. Because batteries need more compensation at lower temperatures, change R5 to 30Ω for a tc of -5mV/0C per cell il this circuit will be used at temperatures below – 200C.

The charger’s input voltage must be filtered dc that is at least 3V higher than the maximum required output voltage. Choose a regulator for the maximum current needed: LM371 for 2A, LM350 for 4A, LM338 for 8A. At 250C and with no load, adjust R7 for a Vout of 7.05V, and adjust R8 for a Vout of 14.1V.

Car battery charger circuit diagram

lead acid battery charger


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  • Andrew Maraguinot

    I built it,it doesn’t work??

  • Robert

    Buy at Freight Harbor Freight Tools a Battery Float Charger, Automatic on sale for $9.99. Open the regulator, replace the 56 ohm resistor marked as VR1, with a 100 Ohm trim pot via two tiny wires. Now you have Voltage regulator battery trickle
    From 12.5 V to 14.0 V. Float charging a battery is like dancing on a needle. At 11.4 v the car battery is discharged and at 12.9V is fully charged. Increasing the voltage above 2.26V per element or > 13.5V the battery start boiling. Tiny current as low as 20mA, for long period of time oxidize the positive elements. I set the regulator at 13.25V set on the car and forget. I have more than one car and while not in drive I trickle the battery to keep at 12.9 V without charging element.

  • Sudheer

    Thank you so much for sharing this circuit. I would like to do this mini project on next month. Are there any limitations for this circuit?

  • Leyroy

    Would it be possible to modify the above circuit to produce a 14.3v charge and 13.5v float to charge a gel cell battery? Any help appreciated. Thanks, Leyroy.

  • John

    Thanks for this interesting charger Admin. I was not able to find the link to “Read the rest” as mentioned above.

    Kind regards.

  • Max

    i want a fast charger, the one i have cannot quickly charge 200Ah battery as power supply in my country is not regular. can your circuit be modified to charge at 10 -15 A?

  • thulasiram

    i want know about the circuit of the charger,since iam an electrical engineer

  • henry

    i want to know if there are other circuit that can be used instead of the above circuit. Please kindly send me a copy to practice.THANKS

  • henry

    Isa there no subst for LM301 used in the schematic diagram

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