> I have an old 18V battery powered drill

The 18V is nominal. I also have a drill which had the batteries
ruined by a rubbish charger

The pack had 15 NiCd =3D 18V

But, fully charged, (assuming the manufacturer had any sympathy
for the motor) the pack will be as high as 21V or 15 x 1.4V

So I made an SMPS with an MC34063 + external FET (for amps)
that puts out 20V from nominal 12V input, SLA or PSU. Works fine,
good speed maintenance and screwdriving torque, whilst V is being
below the maximum possibly designed for

I could have used 2 x 12V and PWM but the SMPS option seemed
easier with one battery and of course less cumbersome than two

By chance I saw a James May's Toy Stories episode at the w/e

http://en.wikipedia.org/wiki/James_May's_Toy_Stories#The_Great_Train_Race

in which the German team powered an 18V loco with 24V (no
PWM presumably), for extra fastiness. Which it had, right up to
the point where it died

Joe
--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.