CPU PSU and 14.4V drill

[Hank Fletcher]

I picked up a 14.4V cordless drill at the pawnshop the other day ($5, with battery!), but I'm having some trouble running it from my computer power supply that I've converted to use as a bench supply. To keep a continuous load on the PSU I'm using a 1157 automotive lamp on the 5V rail.

When I attach a large radial type motor to the 12V rail, I can attach, detach, and run it in both directions and it works just fine. It's been awhile, but I think I once tried to measure this motor as I stalled it, and I got up to 2A before my fingers got sore (never could stop it altogether!).

When I attach the drill, it will run but only if I squeeze the trigger before plugging in the PSU (tricking the PSU into thinking this is part of the normal load), but as soon as I release the trigger the PSU fails the same way as when one of the power rails are shorted. I know that some cordless drills have electric braking - is it something to do with that? Does anyone out there have any thoughts on what might be going on and how I can work around it? I'd like to be able to stop and start the drill, and change directions, eventually using an h-bridge. Thanks for reading!

 

[sam2]

I had the same trouble trying to power a three amp tube radio from my CPS.

Its puts out 9 amps at 12 volt, but shuts down when you hook up somthing that draws alot of current when its first turned on, even if the draw does not exceed the CPS's rated output.

I have had the same problem with nicad and Nimh battery chargers hooked up to the CPS.

The power supply is seeing it as a short and shuts down.

I have read that you can fix it by using capacitors on the output of the power supply , but I dont know what size, you will have to experiment.

sam

 

[Sceadwian]

The bigger the better. I'm sure there's a way to alter the short circuit detect as well so it doesn't trigger so easily but playing with that too much could end up with a lot of smoke coming from your supply or exploding capacitors.