Electrical – converted cordless drill to corded drill – only works once

drillswitch-mode-power-supply

I have read several articles about converting cordless drill into corded drill.

I have an old Craftsman 10.8V NiCd battery. It comes with 2 batteries. One is completely dead and the other is 90% dead. I opened the battery, it is basically a bunch of NiCd cells connected in series. No circuits whatsoever. I decided to do away with the cells and convert it to corded.

I found a Switching Power Supply that outputs 12V/12.5Amp. I thought 12V is close enough and proceed to convert. But when I put it together, it didn't work. When I first press the trigger, the drill works great. But as soon as I release the trigger, it stops working. I have to unplug the AC and plug it back in only to repeat the cycle.

I read several similar posts but none reporting the same issue. I figured maybe it is because of the safety feature of the Switching Power Supply but I can't see why it fails only when I stop the drill. It is hard to find a P/S that gives out high current. I wonder if there is an explanation to the behavior and if there is a simple way to fix it?

Best Answer

Possible causes are either the drill's electronics or the power supply's electronics.

The Drill:

  • You're supplying a fixed voltage and a fixed current limit and the drill measures the voltage, sees the voltages fall of the cliff due to the high current draw, assumes it's a low battery and turns the motor off to stop over discharging the cells
  • Your supply is too good from the PSU, so the current is high and the voltage is high, this confuses the drill and causes some safety lockout

The Supply:

  • The supply isn't used to getting so much noise back from the supplies, it's erroring out with all the back EMF from the motor
  • The current draw is too high, safety factors cut in, such as over current lock out etc (though this would probably happen as you turn the drill on and the motor tries to spin up)
Related Topic