6V Gel Cell Battery Charger

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The following diagram is the battery charger schematic for 6V Gel Cell battery type.

6V Gel Cell Battery Charger circuit

Component Parts 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 = 0.1μF, ceramic
C2 = 0.1μF, ceramic
D1 = 1N4001
T1 = TIP31A, B, C (or equivalent)
U1 = NE555V (or equivalent)
S1 = Toggle switch, ON-OFF

* Resistors are carbon, 1/4 watt, 5% tolerance, unless otherwise indicated.

Circuit explanation:
This circuit requires a regulated 10V-DC front end capable of supplying 2 Amps. 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!