Ric wrote:
Hello,

I would like to charge the 9.6v NiCd batteries of my Makita electric drill
direct from the 12vDC supply on board my boat. Can anybody point me to a
circuit design?

Using a 12v/240v inverter and the existing 240v charger is not an option as
the old charger is broken.



This page is a decent explanation of how to do it-observing battery C
rating:
http://www.web-ee.com/Schematics/Bat...er/charger.gif
You can replace that D6 by something like an ordinary green LED (cathode
to Q2 emitter) and a resistor from the D6 cathode-Q2 emitter junction to
ground for a 10ma bias -something like R=(13-2)/10=120 ohms. The Iout
equation is then Iout=(Vled+Vbe)/R1 or about 2.7/R1- not super-critical.
Replace the full-wave bridge with a single series diode for reverse
hook-up protection. The MOSFET is heatsinked for a maximum power
dissipation of (Vin,max-Vnicad,min) x Iout. Add a fast blow, agc type,
fuse in series with the output driving NiCad (+) with rating of 1.5 x Iout.