Here the another variable power supply which have adjustabled output voltage from 6-12 DC volt. Parts List: T1 = 115[220]/8 VAC transformer. Q1 = 2N1613, NTE128, or substitute. Use heatsink! BR1 = 40V, 4A. (Check max current of your mini-drill and add 2A) R1 = 470 ohm, 5% R2 = 1K, 5% P1 = potentiometer, 10K C1 = 1000uF, 25V 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. The output voltage is variable with the 10K-potentiometer. The transformer input voltage refer to your home power source.