Solar charger for lead-acid batteries; first attempt.

This circuit (updated here) is intended for charging sealed lead-acid batteries with a solar panel in small and portable applications. The customary diode that prevents the battery from discharging through the solar panel has been replaced by a FET-comparator combination.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 battery 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:

I have since developed a better version, but I'm still curious about what goes wrong in this one.

This page was created by Oscar den Uijl,