A portable charger for NiCd batteries can be designed using this electronic scheme. This portable charger can be connected to vehicle battery.
When the circuit is connected to the vehicle battery, D2 lights up only if the battery to be charged was connected with correct polarity.
For the component values given in the scheme, during the load can be adjusted with potentiometer P1, between 26 and 33 minutes. Charging can be terminated at any time by pressing the reset button S2.
NiCd battery charging current is determined by the value of R, which can be calculated using the formula:
R = [12 - (0.7 + 1.3 x no. Of items) / Ic] where is the load current.
Resistance R must be able to dissipate power IC2R watts.