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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Help needed w/battery charger circuit
The problem is finding a battery charger for a cordless drill. I
inherited a Skil 12-volt drill and battery, but no charger. The only hope of finding one seems to be getting a used one, which I haven't been able to find. I opened my friend's charger and drew the circuit, which I've attached a link to. (PDF, and a big one, sorry; somehow a little bitty 35 KB JPG made the file bloat up over a megabyte.) Can someone comment on this? I've got all the values except for the one resistor in series with the LED, which I can probably figure out (or maybe just omit altogether, as it seems only to be an indicator lamp). What's the function of the capacitor? (I believe it's a non-polarized electrolytic in the original unit.) Would this work if I constructed it? The other problem is that the battery has 3 terminals instead of just 2. Two are marked "+" and "-", but there's an unmarked middle terminal. But the charger only had connections to the two terminals. What's the 3rd terminal for? (Picture of bottom in the PDF.) Oh, yeah, the PDF is he http://www.geocities.com/bonezphoto/...eryCharger.pdf -- Pierre, mon ami. Jetez encore un Scientologiste dans le baquet d'acide. - from a posting in alt.religion.scientology titled "France recommends dissolving Scientologists" |
#2
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Help needed w/battery charger circuit
In article ,
David Nebenzahl wrote: The problem is finding a battery charger for a cordless drill. I inherited a Skil 12-volt drill and battery, but no charger. The only hope of finding one seems to be getting a used one, which I haven't been able to find. Easy to make one. I'd go for a constant current 1/10th capacity charge rate. This will charge the battery overnight (approx 14 hours) and it will have a very long service life - much longer than a fast charged one. A constant current charger may be made with a suitable DC supply, and one power transistor with few extra components. I opened my friend's charger and drew the circuit, which I've attached a link to. (PDF, and a big one, sorry; somehow a little bitty 35 KB JPG made the file bloat up over a megabyte.) Site's not available at the moment so can't comment. Can someone comment on this? I've got all the values except for the one resistor in series with the LED, which I can probably figure out (or maybe just omit altogether, as it seems only to be an indicator lamp). An LED is current driven so needs the series resistor. You'll find tables for this resistor value from the voltage if you Google. Or it can be worked out by a formula. If you emit the resistor the LED will fail. What's the function of the capacitor? (I believe it's a non-polarized electrolytic in the original unit.) Would this work if I constructed it? The other problem is that the battery has 3 terminals instead of just 2. Two are marked "+" and "-", but there's an unmarked middle terminal. But the charger only had connections to the two terminals. What's the 3rd terminal for? (Picture of bottom in the PDF.) Some makers use the same battery with different chargers. The third terminal is usually a temperature sensor, and this connection is omitted with nasty or low output chargers. -- *Taxation WITH representation ain't much fun, either. Dave Plowman London SW To e-mail, change noise into sound. |
#3
Posted to sci.electronics.repair
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Help needed w/battery charger circuit
In article ,
Dave Plowman (News) wrote: I opened my friend's charger and drew the circuit, which I've attached a link to. (PDF, and a big one, sorry; somehow a little bitty 35 KB JPG made the file bloat up over a megabyte.) Site's not available at the moment so can't comment. Have seen it now. Avoid like the plague. It is not a suitable circuit for a decent battery life. And I'd call it dangerous - it would not pass modern testing in the UK. -- *It ain't the size, it's... er... no, it IS ..the size. Dave Plowman London SW To e-mail, change noise into sound. |
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