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Make pointed us to this how-to over on Instructables today, and I remember this is something that’s been discussed from time here on Toolmonger.  Though converting AC to DC isn’t any big deal, the trick seems to be making sure that the transformer you’re using can handle the power draw — which is something this writeup seems to cover nicely.

I’m surprised that some of the major manufacturers don’t offer an AC “battery replacement” unit for their most popular battery-powered lines; there’s nothing worse than running out of juice at in inopportune time when a) you’ve got AC right there, and b) all you have with you are cordless tools.

Convert a Battery Drill to Wall Power [Instructables] [via]


8 Responses to How-To: Convert a Battery Drill to Wall Power

  1. nrChris says:

    Saw this on Make this morning. The comments on the Instructible lead me to believe that the WalWart won’t provide enough ampherage on startup. The prevailing wisdom seems to be that some hybrid battery / wall adapter would be the best solution. Seems like you can’t lose if you try it on a junk wireless drill–I know that my the battery on my cordless detail sander will probably crap out soon so I will get to try this out first hand.

  2. Lee Gibson says:

    OK, COOL. I remember a few posts about this topic on Toolmonger a couple months ago, and I’m still wanting to sit down at a work bench and electrocute myself making one of these work.

    Any suggestions on where I could read more about running DC motors on AC power?

    Yeah, I’m gonna die. : )

  3. You can run a cordless drill well enough from a high current DC supply – several amps, at least – that has current limiting so it won’t just pop a fuse when you exceed its limits.

    The current limiting will also serve as a torque limiter. If your cordless drill has its own torque-limit clutch and you set that loose enough, then you’ll be able to keep the draw low enough to run the drill from a standard plugpack, but the drill won’t be good for much.

    As soon as you run the torque up far enough that the motor can get close to stalling, it’ll look pretty much like a dead short and start blowing fuses in simple power supplies.

  4. Cybergibbons says:

    I bought a cheap 10.something volt drill a few years back, and the battery pack died after a couple of months of use. I just soldered a flying lead and some croc clips onto it, and now I use it connected to a car battery for work on, well, cars. It’s lasted a good few years like that, and the torque is certainly a fair bit more impressive than it used to be.

  5. Don Bradshaw says:


    Don’t hook the 120 V AC wall supply directly into a DC motor…this will be a disaster. Even if you stepped the voltage down in AC througha transformer and current limited it, the motor still won’t run right. You need that AC/DC conversion.

    Daniel is right – a higher current DC supply is what you need. Current limiting is critical.

  6. Perry Jones says:

    Cybergibbons’s car battery idea is a good one, but another high-current 12V DC source is a commodity computer power supply.

    For example, here is a $13 power supply that’s rated for 19 amps at 12V: http://www.newegg.com/Product/Product.asp?Item=N82E16817174026

  7. I got connectors from performance-pcs.com and built a harness that mates with a standard ATX power supply, bringing out all the 12v it can offer. That way, I get solid connections without having to chop off the ends, which means if I ever have to send it back under warranty… 😉

    PC power supplies, and switching supplies in general, need a certain minimum load when they’re turned on. In most cases, the switching element can’t go down to a truly 0 duty cycle, meaning if you don’t have that load, the output voltage can skyrocket. This should be listed in the specs for your particular supply, and you can easily provide the load with a power resistor or a car lightbulb or something.

  8. Chris says:

    Instead of big car batteries I use smaller lead-acid batteries. Two of them fit nicely on my toolbelt to power my 24V drill and I have 2 more charged up available.
    You can get 5.5 Ah 12V ones for $10.

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