Power Tool Battery Charger Repair


[Webby] inherited a cordless drill from his dad and when he finally got around to using it, found that the charger was dead in the water. He disassembled it and narrowed the issue down to the charger’s primary transformer, but didn’t know where to go from there. A friend suggested that the coil’s thermal fuse might have blown, and upon further investigation, [Webby] discovered that his friend was right.

He removed the dead fuse and soldered in a piece of wire just for testing – not surprisingly the charger sprang to life. He picked up a new thermal fuse to replace the old one, but he wasn’t quite satisfied with the fix just yet. If the fuse burned out once already, there’s little to stop it from happening again, so he decided that installing a small cooling fan would be a good idea. He mounted the fan on the outside of the case after cutting some vent holes, leeching power from the charger itself.

While simply adding a fan to the charger might not be everyone’s idea of a perfect solution, it has worked out quite well for [Webby] in the past, so if it isn’t broken…

[via HackedGadgets]

14 thoughts on “Power Tool Battery Charger Repair

  1. Educationg process. However, for safety reasons I would rather toss the thing. The fuse probably went of for a reason- may it just be poor design. But a fan is not going to remedy this reason. Would be cool if he had put in a small switching supply with super low standy consumption or so!

  2. My first thought was just add some kind of circuit breaker. When I ran my stage lighting company, all it took was having 8 lights off during the middle of a concert for the time it took me to swap the fuse to convince me to swap the fuses in all my dimmers with breakers.

  3. @noone: the point is, he kept it out of the landfill for a minimal cost, and upgraded it. And yeah, a PTC fuse might be a good idea.
    I just (yesterday, in fact) rebuilt a 10-cell battery pack for a tool set that also had a bad charger. I’m not going to rebuild the charger as it was, however; I have a smart charger (Li-ion, NiMH, NiCd) that I am using now. I will put the charger back together, but cut the leads going in and simply attach them to studs so I can use the smart charger.

  4. I am in the process of reviving a dead Bosch 30 minute charger. Mine came to me with a perfect brute hammer drill and two batteries. Main fuse vaporized, mains rectifiers and capacitors test OK. Mains raw b+ measures a short on continuity test and about 4 ohms on resistance check. Source of the short is the primary side chopper transistor (v5}, a stp6nk90z power MOSFET. Swapping the MOSFET out with one from a computer power supply has the charger working again on the bench and the usual suspects all stock this transistor for under 3 dollars. I ordered one from digikey.

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