12v Solar Charge Controller v3

The battery on the far right is the one being charged. No current limiting resistors included in design, use what is appropriate for your panel and battery. Also left out are the voltage regulators for the supply voltage. The battery on the far left is one supply voltage, the one in the middle the other. Circuit initially charges at 14.4 (there is a diode in series with the supply to drop the voltage and stop the battery from sending current to the panel), once the battery reaches 14.4v the green charging led shuts off and the red comes on and the relay switches to the other regulated supply for a float charge at 13.6v. Once again use the appropriate current limiting resistor for your battery and supply. The circuit will not resume normal charging unless the battery drops to 13.2v. The voltages at which the system changes state can be adjusted via the 2 potentionmeters. You could easily modify this design for 6v batteries or greater. I'm completely untrained in electronics and this is probably the most complicated circuit I've designed myself from the bottom up so please forgive me if I've made any glaring mistakes.

published 10 years ago