Resistors are carbon, 1/4 watt, 5% tolerance, unless otherwise indicated.
R1 = 22 ohm, 1W C1 = 0.1µF, ceramic
R2 = 270 ohm C2 = 0.1µF, ceramic
R3 = 220 ohm D1 = 1N4001
*R4 = 715 ohm, 1% Q1 = TIP31A, B, C (or equivalent)
*R5 = 3.57K, 1% U1 = NE555V (or equivalent)
*R6 = 1.40K, 1% S1 = Toggle switch, ON-OFF
*R7 = 1.47K, 1%
This circuit needs a regulated 10V-DC front end capable of supplying 2 Amps.
Starts the charge cycle at 240mA and at full charge switches automatically to a float condition (trickle charge) of
The capacitors are the ceramic 50V (or better) type. Switching transistor Q1 is a NPN, Si-Power Output/SW, with a
TO-220 case and can be replaced with a suitable substitute like the NTE291, ECG291, etc.
Timer/Oscillator U1 is a 8-pin NE555V and can be replaced with a NTE955M or ECG955M.
Resistors R4, R5, R6, and R7 are 1% metal film types. They may not be available at your local Radio Shack/Tandy
store and have to be ordered in. Try Electro-Sonic or Newark Electronics supply stores.
NOTE: For 6-volt, 1.2Ah Gel Cell type batteries only!
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Copyright © 2001 by Tony van Roon