Solar panel battery charger

The solar battery charger circuit is nothing but a dual comparator that connects the solar panel to the battery when the voltage at the latter terminal is low and disconnected if exceeding a certain threshold. Since it is only by measuring the battery voltage, it is especially intended for lead batteries, a electrolyte liquid or gelled, that adapt the best of this way.

The battery voltage separated by R3 before being fed to the two comparators in IC2, When it is below the threshold determined by the output of P2,  IC2B goes high which also causes the output of IC2C high. T1 saturation and relay RL1 on, allowing the solar panel to recharging the battery via theD3. When the battery voltage exceeds the threshold set by P1, When the battery voltage exceeds the threshold set by P1, the output ICA goes low as well as IC-C … and therefore causes the relay off, thus avoiding overloading when charging the battery. In order the threshold determined by the P1 and P2 are stable, they are supplied with an integrated regulator IC, closely separated from the voltage of the solar panel through D2 and C4.

Parts list :

R1,R5 :15k 1/4W 5%
R2, R6, R7 : 22 k 1/4W 5%
R3 : 220 k 1/4W 5%
R4 : 100 k 1/4W 5%
R8 : 4,7 k 1/4W 5%
R9 : 6,8 k 1/4W 5%
R10 : 680 ohm 1/4W 5%
C1: 0.22 uF mylar
C2, C7: Chemical 10uF/25V radial
C3, C5, C6 0.1 uF mylar
C4: 100 | iF/25V chemical axial
D1, D4: 1N914 or 1N4148
D2: 1N4004
D3: BY252, BY255, 1N5402
LED1: LED red
T1: 2N2222A
IC: 78L05 regulator 5 V/100 mA, T092 package)
IC2: LM339
Solar panel: TGM 500-12 [500 mA, TGM 750-12 (750 mA), TGM 1000-1012 [1 A] example (Selectronic)
RL1: miniature relay or equivalent FBR 244 FUJITSU 12V/2RT/1 A
Pi, P2: Vertical cermet trimmer 10 k for IC
S1: a switch circuit 3 positions
A support IC 14 pin