Car NiCad Charger

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   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   1uF, Capacitor       25V, electrolytic
C2   220uF, Capacitor   272-1029   P5699-ND   25V, electrolytic
S1   Switch, on-off       SPST, sub-miniature
Fuse   750mA       Slow Blow

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 (18V total).

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 Pin Configuration

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