Link: now.

Circuit monitors a battery being charged using a LM317T or LM338T TO 220 type voltage regulator:

A cheaper BC547 transistor can be substituted for the 2N2222 which cuts off charging voltage
When the battery voltage reaches a fully charged voltage set by P2, the Op Amp turns off the voltage
regulator. This circuit is similar to the tool charger circuit except that the op amp is driven by the battery as a solar panel cannot be counted on to supply a steady voltage. Normally voltages will go up and down with the brightness. The regulator should deliver the same current, but limit the voltage supplied to the battery to 14 volts.

Next...

Next..

Link - now

ARDUINO SOLAR CHARGE CONTROLLER (Version-1) - now

ARDUINO SOLAR CHARGE CONTROLLER ( Version 2.0) - now

ARDUINO MPPT SOLAR CHARGE CONTROLLER (Version-3.0) - now

link picture - now

СХЕМЫ ЗАРЯДНЫХ УСТРОЙСТВ (герметичных, не обслуживаемых) АККУМУЛЯТОРОВ - тут

Отключение аккумулятора при разрядке -  тут и тут

 

На 4-х ОУ в одном корпусе LM324 за 5 рублей народ творит чудеса компарации