NiCad charger

Now that the price of small nicad cells is relatively low the cost of the necessary charger is dispro- portionally high. It is hardly possible to find a less expensive method of charging 4 penlight cells than the one described here. Furthermore, the circuit offers low dissipation and provides a constant current for the cells to be charged. The circuit uses two capacitors connected in parallel, instead of the usual transformer, to obtain suf- ficient current (a tenth of the batteries" capacity or 50 mA) from the mains supply. The voltage appearing at the "cool" end of the capacitors is then rectified by means of four diodes. The LED has been included to provide an indication that the circuit is actually charging. The resistors, R1 and R2, have been added as a measure of safety. This is because when the battery charger is switched off the capacitors may still be fully charged unless some form of discharge path is provided. Safety is quite an important aspect for this circuit, since ...