Power Supply Adapter

This is the circuit diagram of 12V NiCAD battery charger. The battery charger charging rate is at 200mA/Hour. The battery charger circuit will continue to charge the battery at 75 mA until the battery is fully charged, then it reduces the current to a trickle rate. It will fully recharge a dead/unpowered battery in 4 hours and the battery can be left in the charger indefinitely. To set the shut off point, connect a 270 ohm / 2 Watt resistor across the charge terminals and adjust the potensiometer for 15.5V across the resistor.

The output voltage of this power supply circuit can be adjusted from 6 volt to 12 volt. The output voltage is regulated by Q1. Parts List: R1 = 470 ohm, 5% R2 = 1K, 5% P1 = 10K ohm Potentiometer C1 = 1000uF/25V T1 = 115[220]/8VAC transformer. Center Tap not needed. Q1 = 2N1613, NTE128, or substitute. (TO-39 case) On coolrib! BR1 = 40V, 4A. (Check max current of your mini-drill and add 2A) Notes: C1 filters the noise and spikes off the AC. If you find the circuit output too noisy add another electrolytic capacitor over the output terminals. Value can be between 10 and 100uF/25V. 10K-potentiometer used to adjust the output voltage. The transformer input voltage refer to your home power source. You may change the bridge diode with four rectifier diodes.