Need a little help with variable resistor

Thread Starter

tourmax

Joined Aug 10, 2022
3
I'm in a bit of a pickle. I use a Danfoss Cycletrol 150 to control a Baldor DC motor on a metal lathe.

I flicked the power on today and things just went wild. The motor immediately went to full speed and I could smell magic smoke. I immediately turned the power off which seemed to activate the dynamic brake in the unit and the lathe chuck spun off it's spindle, hammered the lathe ways and shot the chuck out at my face. Luckily, my reflexes are still pretty good and I caught the chuck before it did any more damage. To either me or anything else around me, but it was still a "come to jeebus" moment..

I opened up the controller and you could smell the burn at the variable resistor/potentiometer, which is the adjustable speed control. I took the controller apart and sure enough, something failed internally and it was burnt and melted inside.

My issue is I can buy a NOS replacement, but they're pretty pricey. I'm looking for an equivalent to install that won't require me to take out a second mortgage. So I'm looking for suggestions.

here is a pdf of the cycletrol manual with wiring diagrams. I'm a little confused about the speed control as I've seen it refered to as a variable resistor and a potentiometer. It's been a long while since I last did electronics, but I believe it is accurately called a potentiometer becuase it has three legs instead of the two I woudl epect on a variable resistor.

The part numbers aren't very revealing. The manual just gives a Danfoss part number and the Potentiometer itself is marked "am1151 5k".

It can't be as simple as selecting a 5k pot and of proper voltage and subbing it in, can it? This is a pretty beefy looking pot, I'm pretty sure it must be some sort of special construction. I've got lots of 5k pots lying around, but they all look fairly physically small compared to the original/burnt one.

Not sure why it burnt, nothing has changed from the last use. I'm still chasing down the wiring to confirm it's all good though and no hidden shorts to ground....
 

Thread Starter

tourmax

Joined Aug 10, 2022
3
I think I can answer my own question now.

The original pot is carbon film, so i will stick with that.

Single turn.

5k ohm.

Graham/danfoss indicates the pot on the closed case model comes with a 1w pot, so I'll need to stay higher than that.

Other than that, I'm going to order a handful and try them out.

Worst thing that can happen is I let the smoke out again.....
 
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