Car NiCad Charger
Power circuits

Car NiCad Charger

By Tony van Roon

This circuit provides up to 20V output from a regular 13.2V automotive battery, to enable constant current charging of nicad battery packs up to 15 cells at 1.2V.

Car NiCad Charger circuit
Car NiCad Charger circuit

Table 1
Part Description Radio Shack # DigiKey # Notes
IC1 TDA2003, Au Amp n/a Pwr Amp,10A, lin, 5-pin
Q1 2N3055T, Transistor NPN, Power
D1/D2 1N4002, Diode 276-1102 1N4002DICT-ND Gen purp rect diodes
Led1 Red, 5mm 276-033 Light Emitting Diode
R1 390K, resistor 271- 390KQBK-ND 5%, 1/4W, carbon
R2 2.2M, resistor 271-8061 2.2MQBK-ND 5%, 1/4W, carbon
R3 2.2K, resistor 271-1325 2.2KQBK-ND 5%, 1/4W, carbon
R4 10 Ohm, resistor 271-1301 10QBK-ND 5%, 1/4W, carbon
C1 1F, Capacitor 25V, electrolytic
C2 220F, Capacitor 272-1029 P5699-ND 25V, electrolytic
S1 Switch, on-off SPST, sub-miniature
Fuse 750mA Slow Blow

IC1 is a Linear, Audio Power Amp (10W) and was orginally designed for car radios by Toshiba. Several replacement types can be used, like the ECG1288, NTE1288 and other substitutes will work fine.
In this circuit, with S1 set in the 'boost' position, IC1 is used to form a squarewave oscillator, and by coupling this square wave to the 13.2V battery supply via D1 and D2 to obtain over 20 vdc. If this is not needed, S1 is left open (normal).

Q1 acts as a current regulator to determine the charge rate of the battery pack. Q1 should be mounted on a sufficient coolrib. R4 is selected from the table below, or it can be adapted and switched with a rotary selector switch (watch current rating!).

R4 can easily be adjusted for any value to suit your needs other than listed here.

Charge Rate DiagramPin Configuration

5201 21 August 2007

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