Convert a Battery Drill to Wall Power





Introduction: Convert a Battery Drill to Wall Power

Turn an old battery powered drill into a wall power unit.

In the spirt of Instuctables, I'm adding some of the sugestions for improvement and why I didn't do things that way in the first place. Some I had considered, others i had not.

Q. Why not just put in new batteries?
A. Too expensive. The drill was $5 (with case, extra drill and 2 battery packs) and worked for a while. The wall wart was free at another garage sale. Brand new unit would be about $20 and be ready 'out of the box.' A new set of batteries and a charger for them would not be worth the time or money. If it was a good brand name on the other hand...
A. While trying to find out which cells in the battery were live and which were dead, I lost the parts. Thus, no battery shell to reload : )

Q Use a Zener transorb/5 f. capacitor/ect.
A Aint got one. Too expensive to go out and get some just to play with. I don't feel comfortable enough with electronics to risk the parts.

Q Use a more powerful transformer.
A Aint got one. That and i don't know how much I can pump threw the motor before it burns out. I may end up finding a bigger transformer, or trying it on AC current-but not untill I don't need this one any longer.

You may notice a theme here-this is a cheep fix with what I had on hand. Nothing fancy, not a lot of pre-planning to get in the way of getting something finished. Are there better ways to do this? Absolutely : )

Step 1: Research!

wall transformer for project power supply
Reuse "Wallwart" transformers
in a perminant way.

How to solder
Soldering to large metal objects
if you are lazy like me and decide to solder onto the large battery clips rather than fiddle with the wires inside the case. or, you can't find your soldering gun but can find your butane torch...

you could even use
Handy box from scratch paper
for screws.

and, yes, i screwed up the batteries before i had a chance to use
Revive Nicad Batteries by Zapping with a Welder
Hot Rodding a Power Drill Battery

Step 2: Gather Your Parts (and Tools)

First, look at the drill. On the side it will (hopefully) have a description of the battery pack. If it doesn't, look up what a replacement would be. In this case, an old craftsman drill used a 9.6 v, 1400 mAh battery pack. Then find an old, unused wall wart that might work-in this case, i found a 12 v, 1.2 A unit. I figure higher voltage will give a higher rpm, and the lower amperage means less power.

(1 A = 1000 mA)

What I used:

Craftsman Drill/Driver ($5 at a garage sale)
Wall wart (12 v, 1.2 A)
Soldering equipment
-butane torch
wire cutter (and stripper, if you want)

Step 3: Void Your Warrenty

Open up the drill.

It's useful to figure out which leads on the drill and power supply are which. If you don't, and the drill doesn't work, try switching leads around. It turns out that the speed control needs to be biased correctly. Who woulda thunk?

Step 4: Playing With Fire

Cut the end off the power supply. If I had the parts, I might have put a jack in the drill. Instead, it's perminent.

Strip and tin the ends of the wire. Sand, flux and tin the battery conecter. If you prefer, you could remove the battery clip and solder wire to wire instead.

Solder the power supply wires to the battery clips. Try and figure out why it doesn't work. Test power supply with multi-meter. Re-solder wires the other way...

Sorry, no picture of me soldering. It takes me two hands to solder and two more to hold the camera.

Step 5: Conclusions

Put it all back together.

It works!

Well, it works as a drill, which is what i needed. It only overpowers the first setting on the clutch, otherwise I can stop the motor with my hand.



    • Creative Misuse Contest

      Creative Misuse Contest
    • Water Contest

      Water Contest
    • Oil Contest

      Oil Contest

    81 Discussions

    The most critical step is to find the power-tool's maximum current draw in Amps (amperes).

    You do that by disassembling the drill, looking inside, and reading off of the motor's casing it's power characteristics.

    If you are lucky it will say exactly how many Amps the motor will draw under (full) load. If it does not list the Amps then it should probably say how much power it needs in Watts, at which point you use the "Power (Watts) = Current (Amps) x Voltage (Volts)" equation (or simply P = I x V) to solve for Current and find out how many Amps the motor will draw.

    Then you need to find a GOOD AC to DC power converter which will provide the proper Voltage AND Current (e.g. Amps) to the motor. Remember (!), the Amps figure is the MOST critical component. If you provide less Amps the motor will be underpowered eventually burning out the power converter, possibly itself as well. If this happens that will definitely create a fire hazard. Be cautious.

    Ideally the supplied current should be at least 25% more than the motor's requirements, if I were you I'd go as high as 50% to be on the safe side.

    If you do the math, you will see that the Amperage required is too high for the power converter (transformer) you are using. Eventually, you will wear out the motor and ultimately (if used for harder/longer jobs) you will risk the power supply overheating, metling possibly cacthing fire.

    Remember DC does not travel well over long cable runs, especially if the Amp draw is high. You need a heavy duty AC to DC transformer capable of providing high Amps, with heavy gauge cables, which will make the transformer big, heavy, cumbersome to use and above all expensive.

    This is a nice attempt but it won't work in the long run. Plus you are exposing your self to some degree of danger. Battery operated power tools are getting more affordable by the day while becoming more powerful, efficient and safer with LiPo battery technology.

    I say, throw this old tool away (I mean dispose it responsibly) and get yourself a new one, altogether.

    3 replies

    Don't just read the techno-babble - if you aren't sending a check, an upgrade isn't going to happen. That's the basis for the article.

    "More affordable" doesn't mean a drop in price from $150 to 'only' $125. See above : )

    "More affordable" cannot also mean "causing a fire". That wall-wart is running way over its maximum limits, it IS overheating, and it WILL fail. How it will fail is up to debate, likely the transformer magnet wire insulation will melt, short itself out and pop an internal fuse (non-replaceable), but it may also simply catch fire. This type of project should not be attempted by those who do not know the risks involved. I urge you to edit your instructions to say something to that effect.

    Current limited. Did not run hot. Did not pop circuit breaker. If you read the article, it didn't pull enough current to keep me from stopping it with my hand.

    Think about it-if it had a dead short on the output side, how hot would the designer allow it to get?

    Right now my motto is if you deserve a Darwin award, you should get one and I'm not going to stop you or hold your beer (I don't like beer).

    Looks like the guys at have built an industrial unit that actually provides more power than a battery. Only the dewalt 20v is available now, but it looks like Milwaukee and Makita versions will be available soon. Can't wait to get my hands on one of these!

    i tried this and it didnt work for some reason!!! (i used 1000mah, dc AND ac...).... errg... (yes i had the right polarity.) lahh

    12 replies

    What, exactly, does the power supply say-and are you sure the power supply and drill worked to start with?

    I have a 12v drill:

    What do I need to change it to wall powered, whilst being able to use all torque settings without burning it out but using its full power?

    You can't, just dispose of it properly and buy a new one with lithium technology power pack.

    The motors in drills are power hungry. My dewalt just took out a 20A rectifier (The part that makes AC to DC). It's gonna take a high power power pack to work efficiently.

    9.6v dc (w ac switch), 1000mah. i used it in a 9.6v cordless drill (used aligator clips for contacts in the drill handle). and i no the power supply works, because i use it a lot for random things, lol, and also tested it with a multimeter. And for the drill, ya it works cause i took the battery out and tried it w dc (batterys are dc), then tried it with ac, did not work, so i put the battery back in and it works w battery still, but no addapter...... :-|....

    Mah would be milli-amp-hours, odd for a power supply but normal for a battery. I suppose there could be some kind of switch (mechanical or electrical-checking the status of the battery if it runs on Li-ion or something) on the drill. Other than that, I don't know without seeing it : ) Might be as simple as the clips not making good contact or as complicated as the electronics in the drill and power supply fighting it out over power requirements.

    So, except for being completely different, it's the same power supply? Which drill? And how do you know that the clips are making good contact?

    errrg.... no i showed you that because it is the same type of power source im using, just i dont know what thos are called, so i showed you a pic! lol.... :-(.... What drill, umm it is a offbrand no namer i think? but it works, and i no it makes good contact because i opened the drill up once to see the motor, and see how it works :-), but i put it all back together, and it works the same with batterys as it did b4 i opened it.. and the contacts are thick bars, witch nicely got cliped onto by my aligator clips :-D

    I think you mean you used a wall wort rated for 1,000mA.

    Power tools use a lot more than 1,000mA. Drills use around 3A (3,000mA.) Saws can easily pull 18-25A.


    I Convert a battery of Cordless drill to ATX power supply

    I have a full set of dewalt 18v, would this work?