Hi.

I have a 3-phase wide-belt sander with two sanding heads. Each is controlled by a traditional DOL start-stop button arrangement. A week or so ago, both heads stopped working. When you push a green button, the contactor stutters on and off for as long as you hold it down, and then stops when you release the button.

Given this started happening concurrently for both motor circuits, it would seem like there's something awry in the control circuitry, but for the life of me I can't figure out what it would be. I didn't change anything and it just started happening one day. Everything looks like it's properly connected. I'm stumped.

Anyone have thoughts on what might "typically" cause something like this?

Video here:
https://www.youtube.com/shorts/82lKSdfwXi0

Thanks,
-Ben

 

Sounds like the contacter is breaking it's own supply, check the wiring to the contacter across it's coil.

 

The very first step will be to check connections because the symptom is a motion sensitive break in the portion of the circuit that engages the contactor coil. A loose screw in a ring terminal, for one possibility.
This could also be a poor connection in the power feed to the machine, or even in the busbar connection, in a large shop. As the power is three-phase, then it could even be a failed fuse in one of the phases.
If you have a circuit schematic drawing, the contactor coil circuit loop would be a fair place to start looking.
Also, as it is a 3-phase system, just a bit of resistance because of a poor connection in the power feed can cause a large voltage drop that will make a contactor stutter .
Worst case, it could be a frozen motor .
To check for that, switch off and lock out the main disconnect switch before reaching in and checking that things still turn as they should.
Sorry to be so very general in suggestions, but there are quite a few rather different possible causes. And anything recently moved or disturbed could have caused a problem.
I have repaired a few machines, also designed and built quite a few. I did have help with the building.

 

Thanks for this @MisterBill2! I'll start working through the list here.

The very first step will be to check connections because the symptom is a motion sensitive break in the portion of the circuit that engages the contactor coil. A loose screw in a ring terminal, for one possibility.
This could also be a poor connection in the power feed to the machine, or even in the busbar connection, in a large shop. As the power is three-phase, then it could even be a failed fuse in one of the phases.
If you have a circuit schematic drawing, the contactor coil circuit loop would be a fair place to start looking.
Also, as it is a 3-phase system, just a bit of resistance because of a poor connection in the power feed can cause a large voltage drop that will make a contactor stutter .
Worst case, it could be a frozen motor .
To check for that, switch off and lock out the main disconnect switch before reaching in and checking that things still turn as they should.
Sorry to be so very general in suggestions, but there are quite a few rather different possible causes. And anything recently moved or disturbed could have caused a problem.
I have repaired a few machines, also designed and built quite a few. I did have help with the building.