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/diy/ - Do It Yourself

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610914 No.610914[DELETED]  [Reply] [Original]

I found a cheap 7 volt cordless drill in my neighbors trash, the battery pack is broken which is probably why they threw it out.

I have loads of mains adapters and found a 7 volt one, it's easy enough to connect the terminals to the wires.

My question is, how many amps will the adapter need to be so that it doesn't burn out when using the drill? The drill itself isn't labeled. The adapter I currently have is 7 volts at 1 amp

Alternatively, could a 7 volt drill be powered from a 12 volt car battery? I suspect it will work but probably burn out the drill after a while

Thanks for your help

>> No.610924

>>610914
It's 7.2V nominal. You'll need several amps.

>> No.610929

>>610924
I don't understand what that means

Several as in 3?

Sorry for being an idiot

>> No.610935
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610935

>>610929

more than one, you'll have to experiment, carefully

>> No.610987

>>610929
Closer to 10

Does the drill have a power rating?

Watts=Volts*Current

>> No.611027

>>610987
Okay thanks

Would a 12 volt car battery work?

>> No.611030

> doesn't burn out

You don't know and they love love to burn out the magnets

>> No.611039
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611039

>>610914
>in my neighbors trash

>> No.611040

>>611027
until the motor burns out

since you got it out of the trash you might as well try. If it works, get a proper battery.

>> No.611094

Believe it or not a 7.2v drill can require up to 30 amps if under heavy load. If its a Makita open the fucker up and see if theirs a label on the motor. They are easy to take apart and get back together Google it and you can get the amp draw rating on it. I had a similar idea myself some time back and I found that the motor needed huge amps under max load. The good news is that these motors are pretty forgiving about their input voltage. While I wouldn't run it at 12 volts it would probably be okay up to about 10.

If you run it off a shitty little 1 amp power supply you will fry that power supply in pretty short order.

Another option is to rebuild the battery. They use 1.2v "sub-c" ni-cd or nimh batteries that are commonly available. Generally ones rated at 1500mah are good but the higher the better. In this case you will need 6 batteries to fill that original battery case. It takes a little soldering but thats it

>> No.611268

>>610914
The drill will need ALL THE AMPS the more it comes closer to being stalled. It can go from 1/2 an amp to 90 amps just be slowing it down with your hand on the chuck. A typical power adapter won't hold up being used for a drill. They are also unregulated, meaning they will simply fry or blow a fuse if they have one.

You can actually make your own adapter pretty easily though with a few fairly cheap parts and salvaged parts. All you need is a heafty transformer (a rewound microwave oven transformer [MOT] is awesome for this stuff), a smoothing capacitor that can handle everything, a bridge rectifier that can handle the amps, and a fuse or breaker that will blow/flip before any of the parts overheat. Except for the MOT, which you need to salvage and rewind the secondary, everything is actually pretty cheap from mouser and/or digikey. Most of those bridge rectifiers are pretty hefty and have a metal plate on their top so you can attach a heatsink if you want or need. They are normally under a $1 too, but you may need the higher end ones that cost $12. You'd need to google your drill's datasheet to see what the stall amps are.