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How can I make an AC adapter that will fit a standard 1/2" drive 18V DeWalt drill?

I am sick of buying batteries or having them not stay charged very long. How can I make an AC adapter that will fit a standard 1/2" drive 18V DeWalt drill. I want to drop 120 volt to the 18V (with lower amps?) and do it in a hollow battery house so it will take the place of a battery when I run low on charge. You would think a cordless drill company would offer something like this as an accessory. I bought a cordless drill for the convenience, but 9 times out of 10 I am still close to an outlet. If I don't get an answer here I will just go ahead and figure it out on my own. But I really don't want to have to re-invent this wheel if someone has already done this.

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You need a power supply that can supply AT LEAST 20 amps at 18V. Sawsalls, Circular Saws, and Hammer Drills can all hit 20 Amps if you stall them. I think drills will likely max out around 15 amps, but let's be safe.
It'd be nice if you knew how much current your drill draws when loaded, and since you're planning on splicing in a new power supply it is not a big deal to put an ammeter in series with it and find out.

Don't worry too much about that number: 18 volts. I mean when the battery is loaded by the actual voltage seen at the terminals of the battery will be somewhere between 18 and 0.

One compatible power supply you might already own is a car battery, if you own a car. Try this, either by way of a cigarette-lighter type plug, or whatever you've got available. Measure the current the drill uses when loaded, and see if the drill is turning as fast as you'd like it to turn.

Anyway the current requirement is important. Once you know this you can then make a guess at what other types of power supply might be suitable.

A laptop charger might be a good match. These typically supply 16 or 19 volts at a current of 2 to 3 amperes.

Also you might try a cheap lead-acid battery charger, plus a capacitor, to sort of smooth out the ripple. A picture of such an unregulated DC supply is attached. I use it to run my beer cooler. Looking closely at this picture, at the meter, you can see it is supplying about 2 amperes.
charger-power-supply.jpg

+1 on the voltage. A friend of mine converted a 9 volt drill to run on a small 12v SLA battery (like you would find as a back up battery in a domestic burglar alarm). The drill ran all day without a battery change when it would have normally required at least 3 recharges.
seandogue6 years ago
FIrst, buy an old battery pack off eBay.

Then modify it to accept the wiring from a 18V, 10A DC power supply, by carefully opening the battery pack enclosure, removing the cells, drilling a proper hole for a cable clamp into the bottom, installing said cable clamp and appropriate wiring (a utility replacement cable for a power drill would probably be perfect).

Dispose of the old cells in an environmentally friendly way.

Purchase a 10A, 18VDC power supply, connect the other end of the cable to its output, along with a circuit breaker or fuse of appropriate value, and drill away.

I myself would be far more inclined to spend the time purchasing a couple of extra battery packs for the portable.
Burf6 years ago