12V PSU, 18V drill motor

What'll happen if I connect a 12V PSU to a 18V, cordless drill? The PSU is from a desktop pc, and the drill just happens to be the cheapest new one I can find off the shelves where I live ($30CAN). Can I just connect the PSU lines to the battery contacts inside the drill handle (sorry, not the contacts on the battery, I mean the ones those connect to on the drill, so that the drill is running off the PSU instead of needing a battery)? Will the drill just run less than its othewise top speed/torque? Sorry if I'm coming off paranoid, I just feel guilty hacking a brand new drill even if it doesn't cost much. Sure wish I knew where I could find old junk where I live now! Anyhoo, chime in with your two cents. Thanks!
Hank.

Should be okay, would put a fuse inline just in case. Don't know the stall current of the motor, or the output of the PSU, or what kind of abuse you have planned for the drill... Guessing that if you wanted a corded drill, it would have been cheaper then a battery one.

The drill's no-load speed will be approximately 18/12 (i.e. 2/3) of the original. Under load, it depends on the maximum output of your power source. NiCd or NiMH have enormous peak current capability.

mneary said:

NiMH have enormous peak current capability.

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What do you mean by "enormous?" Do you have a ballpark figure? Mostly just curious.

I know people out there in robot land must have been hacking drills for ages, so I have a couple of questions:
1. Is it possible to remove the transmission, so that the revs at the chuck are the same as the motor?
2. Am I way off here? Even if a cheap cordless drill has a single speed rating of 0-800rpm, is that an indication of motor revs, or is there some gearing involved?
3. If there is gearing involved, is there anyway to hack the transmission to reduce backlash? In a related question, what's the cause of/reason for the backlash in a single speed drill, anyway?
4. Are there any links to hack cordless drills you'd like to share?
Thanks!

The maximum current depends on the construction and capacity of the NiMH cells used to create the battery pack.

Hank Fletcher said:

What do you mean by "enormous?" Do you have a ballpark figure? Mostly just curious.

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More than enough for the battery to destroy itself if shorted out!. C size cells would probably exceed 100A?.

C NiMH cells are normally just AA cells with a load of padding; Nicad C cells are real C cells though.

That's too bad, a C sized NiMH would have one hell of a capacity. Then again you can get more capacity just by paralleling smaller packs.

Hero999 said:

C NiMH cells are normally just AA cells with a load of padding; Nicad C cells are real C cells though.

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Only cheap C cells are (even NiCd), more expensive ones are real C sized - such as radio controlled car battery packs or cordless power tools.