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Car NiCad Charger

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
Car NiCad Charger circuit

Table 1

Part Description DigiKey # Notes
IC1 TDA2003, Au Amp   Pwr Amp,10A, lin, 5-pin
Q1 2N3055T, Transistor   NPN, Power
D1/D2 1N4002, Diode 1N4002DICT-ND Gen purp rect diodes
Led1 Red, 5mm   Light Emitting Diode
R1 390K, resistor 390KQBK-ND 5%, 1/4W, carbon
R2 2.2M, resistor 2.2MQBK-ND 5%, 1/4W, carbon
R3 2.2K, resistor 2.2KQBK-ND 5%, 1/4W, carbon
R4 10 Ohm, resistor 10QBK-ND 5%, 1/4W, carbon
C1 1µF, Capacitor   25V, electrolytic
C2 220µF, Capacitor 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.

Led1 is lights up whenever a NiCad pack is connected to the '+' and '-' output terminals.

Charge Rate Diagram

Cell Size

Amp/hr Rate

R4 Value



120 ohms/0.25 W



47 ohms/0.5W



12 ohms/0.5W



12 ohms/0.5W



3.3 ohms/2W

(High Capacity)


R4 value at 14hrrate

Pin Configuration

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