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Solar charger for lead-acid batteries

This circuit is still under development, but works well as shown.

This circuit is intended for charging lead-acid batteries with a solar panel. The customary diode that prevents the battery from discharging through the solar panel has been replaced by a FET-comparator combination. The charger will stop charging once a pre-set voltage (temperature compensated) has been reached, and recommence charging when the voltage has dropped off sufficiently. The load is disconnected when the baterry voltage drops below 11V and reconnected when it gets back to 12.5V.

The circuit has the following features:

Note that the charging current is limited only by the solar panel used.

Here's the circuit:


 Note the funny place of grounding of the first 2 comparators. There's some weirdness here: this bit of the circuit gives me headaches. Two problems:

Help would be greatly appreciated!

Next attempt

This one works fine and uses about 0.5mA, but that might improve because I'm not done tweeking yet:

click for higher resolution

by Oscar den Uijl,

Emmanuel 2010-12-08 14:12:10
I have seen your circuit.
You said 13.8 volts maxinum battery is adjustable but didnt tell us which circuit element has to be changed or adjusted to change this value.
You also said nothing about the input voltage from the solar panel.
Lastly I will like to know if this circuit can be modified to charge a 24 volts battery because that is the challenge i currently have. and if it is possible (lets say max bat voltage of 27volts and charging current of 2A) what changes do i have make.
I will appreciate a modified circuit diagram reflecting these changes

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