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My cheapo 18V Black and Decker cordless drill recently died, and thinking I could maybe fix it, I took everything apart and then couldn't figure out how it was ever working in the first place! Here's a picture of the internals: Black and Decker 18V cordless drill internals

The wall wart is 3.6 VAC, 200 mA output, which runs straight to the terminals of the 18 VDC battery at the bottom of the picture (and I've taken the battery apart to make sure and there is no circuitry inside, just battery cells). This seems completely odd, and I can't figure out how the battery ever charged while it was working.

The only thing I can possibly figure is that the switch housing also contains boosting/rectifying in addition to the PWM etc... to run the motor at various speeds according to the depression level of the switch. There does appear to be a transistor attached to silver colored heat sink, and I'd imagine they could be implementing both the PWM and a switching power supply with that, but that seems ... advanced for a cheap B&D drill, or maybe not? It also seems strange that the boosting circuitry would be connected to the same leads as those coming off the VAC power supply.

Measuring with my multimeter, I get 4 VAC from the wall wart open circuit, and connected to everything I measured 1.7VAC at the battery terminals, and 1.8V DC. (but again, this system is broken in that the charger no longer seems to work.)

Can someone shed light on how they think this setup is supposed to work? (and bonus points if you can think of what broke?). Thanks!

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2 Answers 2

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By any chance... is there another B&D wallwart in your possession? I don't think that's the right one for that drill, if the drill's battery is indeed an 18V battery. The wallwart shown looks like it might be intended for a cordless screwdriver instead.

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  • \$\begingroup\$ Dang, you know what.. it DID come with a cordless screwdriver that I never used. I (or maybe one of the kids :) must have switched it at some point. Should I leave this question here then? Sorry for the noise. \$\endgroup\$
    – JKnight
    Aug 17, 2014 at 16:56
  • \$\begingroup\$ Maybe it wasn't broke, then, maybe the battery was just really drained? :( \$\endgroup\$
    – EM Fields
    Aug 17, 2014 at 17:05
  • \$\begingroup\$ Exactly. I think JK just used the wrong charger, and the battery/drill is perfectly fine. \$\endgroup\$ Aug 17, 2014 at 17:36
  • \$\begingroup\$ I agree with that conclusion. Looks like this will be my dumb internet moment of the week then. \$\endgroup\$
    – JKnight
    Aug 18, 2014 at 0:38
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You have the wrong charger.

I have an 18 volt B&D drill with an HPB18 battery pack. The charger that came with it is 21.75 volts, 210 mA.

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  • \$\begingroup\$ Thanks, I'll look for a replacement matching those specs then. \$\endgroup\$
    – JKnight
    Aug 18, 2014 at 0:38

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