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I have a dewalt 18V cordless drill. I am wondering if it is feasible to build an adapter that can power the drill from a standard US wall socket?

A typical DeWalt drill needs 2.6 amps with no-load. I am assuming this jumps significantly higher under load. Most DeWalt motors have a stall current over 250 amps...

Any insight would be greatly appreciated!!

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I assume that it is, since corded drills exist...Is there a reason you don't want to use a corded drill? –  Kevin Vermeer Mar 31 '11 at 14:27
Batteries as quite expensive so if you are near an outlet and mobility isnt the issue then you might as well plug it in. Also lets you keep working while your batteries are charging. –  aaronfarr Mar 31 '11 at 14:39
Corded drills do exist so in theory you'd imagine it is possible! But how you could make it compatible with the specs on a cordless drill is beyond my knowledge :( –  aaronfarr Mar 31 '11 at 14:41
What is the rating of the battery? Should say some value of Ah or Ampere hours. –  Matthew Whited Mar 31 '11 at 14:50
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6 Answers 6

up vote 5 down vote accepted

It would be possible to build such and adapter. It would depend on the rating of your drills and how you want to plug in the power.

Either way a cordless drill has a DC motor so it will require a step down transformer and a full wave bridge rectifier. Probably also need a regulator and a few capacitors. You might be able to use the power transformer from a laptop or some other device. But the voltage must match the drill and the ampere requirement must be very similar (more you can fry the drill less you can fry the power supply.)

As for how you attach the power supply I would recommend building the interface out of an old battery pack so you don’t have to modify the drill. But it should be possible to add an auxiliary power jack to the drill as well.

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The current from the supply needs to be at least as high as the current the drill draws. You will not "fry the drill" by building a supply that can source more current. Loads determine current, not supplies. –  endolith Mar 31 '11 at 15:10
You can if the motor stalls and has no protection in the circuit. A battery has an internal resistance that would reduce the possible load on the device. A non-certified source couldn't promise the same. This could be like me attaching a LED with an internal 1k resistor up to a wall outlet and expecting it not to get damaged. –  Matthew Whited Mar 31 '11 at 15:16
@Matthew the LED would get killed by a 110V batter as easily. If the battery had any significant internal resistance it would cause serious problems in normal operation. They could put in some kind of overload protection but this not intended for use without human supervision. –  jpc Mar 31 '11 at 15:46
@jpc, that wasn't the point I was trying to make. I was making the point that you don't know what the ratings of all of the internal points are. If you build a supplemental powerfully without knowing what the circuit is you don't know for sure what the internal ratings are. If something is built on the cheap it may not have the ability to limit current on its own and lower specification parts in the drive may be overwhelmed. It could even be a burnt brush, overheated pot, blown fuse and many more things. –  Matthew Whited Mar 31 '11 at 15:57
Actually, in high draw applications, internal resistance of cells is a major limiting factor. –  Chris Stratton Aug 13 '11 at 16:31
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The answer is simple: Don't. If you did, odds are that you'd spend lots of money on high-current step-down transformers or other kind of power supply and run the risk of destroying your cordless drill. Corded drills, new from Home Depot, start at thirty dollars and will have as good or better performance than a $150 cordless. You'd be time and money ahead by just buying one-- and not have the headaches or risk of electrocution.

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Assuming cost is not an issue though. How might one go about doing this from scratch? –  aaronfarr Apr 26 '11 at 19:43
@aaronfarr The easy way would be to start with an AC/DC power supply that has the correct voltage and current. Then, take a battery pack, remove the batteries, and either fit the power supply in it or use the battery pack as a sort of bulky adapter. In that way the drill would remain unmodified and hopefully wouldn't kill the drill. I don't know if that meets your "from scratch" requirement, but that's how I'd do it. –  user3624 Apr 26 '11 at 23:26
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The aforementioned corded drills work from 110V which means 1/6 of the current. I think it is easier to get a 18V battery with very high discharge current rating than it is to make a cheap high current 18V supply.

If you want to do this then a toroidal power transformer + a bridge rectifier should work well. I don't think you will need to stabilize the voltage but a quick inspection of the internal circuity may prove me wrong.

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My corded drill works with 230v :) –  BG100 Mar 31 '11 at 15:45
@BG100 Mine too. In our case my point is even more valid. :P –  jpc Mar 31 '11 at 15:47
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It's possible but by no means straightforward. An irreversible change is shown here: http://www.instructables.com/id/Convert-a-battery-drill-to-wall-power/

I could have sworn that I saw plug adapters for cordless drills before but for the life of me I can't find them now. I suppose it would be difficult - batteries are high-current beast and fitting a power supply that could manage that sort of current into a manageable size on the drill might be difficult.

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Please don't just paste links to Instructables. Not all of us have subscriptions, and as such, it's a pain to work with (they're always urging you to 'Go pro!' so you can view the community-contributed content). I navigated the morasse, and that one is about a guy who hooked up a 12V, 1A wall-wart in place of his old battery by soldering two wires, and got crappy torque but a spinning drill as a result. –  Kevin Vermeer Mar 31 '11 at 17:42
@reemrevnivek We're all in the same boat with instructables. Is there an alternative? Can we make one? –  AngryEE Apr 1 '11 at 13:27
Yes, that's basically what we're doing with this Stack Exchange! If you described the process presented in the Instructable here, linking to it for attribution, we wouldn't have to follow the link. (In this case, it's (1) Determine polarity on the wall wart and on the drill motor (2) Solder the wires together (3) There is no step three). –  Kevin Vermeer Apr 1 '11 at 14:10
@rem I wouldn't call a stack exchange a good place to put writeups of projects. I would like a free and open version of instructables - something like Github + documentation. –  AngryEE Apr 1 '11 at 17:41
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I used a 19v dc power supply from a computer with 4amp rating. My drill would run in bursts unless I slowly pulled the trigger to full power. If I put any amount of resistance, like trying to release a drill bit from the chuck, the drill would stall out and give short bursts of life never with any significant torque.

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This not only possible, but additionally inexpensively and simply http://www.edaboard.com/thread212631.html

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