Replace Transformer for Cordless Drill Battery Charger
I have a cheapo 18v cordless drill from Menard's and the battery charger supply went bad. I determined that the primary winding of the transformer is open. The specs on the outside of the transformer shows 24vDC output. My question is, if I can find a replacement transformer, does it need to be higher than 24vAC output in order to produce the required voltage to recharge the 18v cordless drill battery? (I'm assuming U.S. AC line voltage input.)I remember the .707 RMS calculation from my electronics school daze, butI looked at the lessons here in AAC and it shows divding by .707 for a full wave bridge rectifier (my case) produces a highter voltage than the AC secondary transformer output. So I'm confused. I would think the average DC output would be lower due to loss in the sine wave output, and I would think you would mulpitly by .707.In any case, what size transformer do I need?
You'd need to subtract the Vf of the rectifier diodes as well; roughly 0.7v at their rated current for standard silicon diodes. If you are using a full wave bridge (4 diodes) then it's roughly 1.4v. If you're using a CT secondary and 2 diodes, then it's just the 0.7v loss.It would help a lot if you posted clear photos of your existing circuit board, top and bottom.It's hard to take good photos of boards. Best lighting is outside on an overcast day; if it's clear weather drape a white sheet over yourself and your subject to diffuse the light. Don't use a direct flash; the picture will be very harsh and contrasty.
I believe it was somewhere in the neighborhood of .5 A. It's a coleman drill from Menard's (home improvement store), but el cheapo. I dissected the top layer of teh transformer and there appears to be a 2K resistor that is open. A tech I talked to here at work said it was probably to act as a fuse. I checked the diodes, they are ok. I can believe the batteries might be toast. They are NiCd. Or maybe it was cheap. There's a surplus store here that sells just about every kind of transformer you'd ever need, and they are cheap, so worth a shot.
