On Mon, Feb 25, 2013 at 6:33 AM, veegee wrote: > Hi all, > > I have an old 18V battery powered drill which is missing its battery > pack. I'm pretty sure the motor is a DC brushed motor, judging by the > sparks and smell of ozone. I haven't opened it (or any other drill, for > that matter) up yet to determine the trigger-switch mechanism, but it > seems to be two-speed. > > Since battery packs are outrageously expensive, I'm thinking of using > two cheap 12V AGM lead-acid batteries in series to power this thing. > Very cheap, available anywhere, dead-simple maintenance, very high surge > current, decently sized. > > Question: is it okay to build a simple PWM motor controller and drive > this thing at 24V, with a reduced max duty cycle to prevent burning out > the motor? Since it's a simple DC brushless motor, I'm assuming that it > should be safe as long as the average power is kept below its max power > at 18V. > > Suggestions? I have had a Black & Decker drill which was running on a 7.2V NiCd battery pack. The batter pack died a long time back and the drill was there unused for a long time since. A year back, I figured it was fun trying to play with a PWM regulator and power the drill from the PWM controller for fun sake, no real use meant for= it though. A PWM regulator based off a 18F452 and later 18F4550 and an IRFP9240 switch-mode buck regulator was born. The drill worked quite okay with the regulator. One thing that I felt was the drill didn't have the same amount = of torque that it had with the same battery pack. It could've been that I have= a bad memory that the drill had a better torque with the battery pack. (Maybe it could've been just a feeling)... Regards, Manu --=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 .