The following scheme diagram is the battery charger circuit for 6V Gel Cell battery type only.
Components List:
| R1 = 22 ohm, 1W R2 = 270 ohm R3 = 220 ohm *R4 = 715 ohm, 1% *R5 = 3.57K, 1% *R6 = 1.40K, 1% *R7 = 1.47K, 1% |
C1 = 0.1uF, ceramic C2 = 0.1uF, ceramic D1 = 1N4001 T1 = TIP31A, B, C (or equivalent) U1 = NE555V (or equivalent) S1 = Toggle switch, ON-OFF |
* Resistors are carbon type, 1/4 watt, 5% tolerance, unless otherwise indicated.
Circuit explanation:
This circuit requires a regulated 10V-DC front end capable of supplying 2 Amps electric current, you should build this kind of power supply first. Begins the charge period at 240mA and at full charge switches automatically to a float condition (trickle charge) of 12mA. The capacitors should be the ceramic 50V (or greater) model.
Switching transistor T1 is an NPN, Si-Power Output/SW, with a TO-220 case and can be changed by using a appropriate substitute such as the NTE291, ECG291, etc. Timer/Oscillator U1 is a 8-pin NE555V and can be changed with a NTE955M or ECG955M. Resistors R4, R5, R6, and R7 are 1% metal film types. They may not be obtainable at your nearby Radio Shack/Tandy retailer and need to be ordered in. Try Electro-Sonic or Newark Electronics supply stores.
NOTE: This circuit is only designed for 6-volt, 1.2Ah Gel Cell type batteries!