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Faulty bandsaw switch?11/26
I've got an SCM 3 phase 220v 7.5hp bandsaw motor that will buzz when power button is depressed but won't start. This has happened many times since I bought it a couple years ago, usually the 2nd/3rd time it fires up so it's never been an issue. Contacted the service techs while it was still under warranty and they thought it was the switch, but wouldn't replace it since it still started up.
I've checked all the electrical connections at the switch and at the motor, cleaned the dust out of the switch box and the blade spins freely. It has an eaton motor protective circuit breaker style switch and the overload dial is set @23amps, machine draws 22amps.
One of my other machines had an over voltage message on the computer today, which rarely if ever happens, so I checked the volts at the bandsaw and got 233-237v between the legs which is normal.
Any thoughts or ways to isolate the guilty party?
I would recheck the electrical connections. If one leg has a bad connection that will happen. Go from one end to the other. Also check the resistance of the fuses.
You need to check the wiring all the way back to the source. You could have a loose connection in breaker panel.
I've checked each terminal several times at every contact point from the breaker through the switch to the motor and there doesn't seem to be any loose/faulty connections.
Today I noticed the 'over voltage' message on the other machine only gets displayed when I engage the bandsaw switch which is bizarre because I use these machines everyday and that's never happened before. All the machines in the shop are on their own circuits and fed from a sub panel off the phase converter.
Another clue...I just turned the blade a bit and the machine started up no problem. Now I'm wondering if there's a dead spot in the windings or some other motor problem.
Did you ever check the amperage of each leg before it is spinning?
Did you try to bypass the switch?
Did you manually engage the starter?
Turning the blade and having it start means one of the legs is not working. You can run a 3 phase motor on two legs but it won't start to rotate. A static phase converter is a capacitor that jolts the unused leg once at startup to get it spinning. I think you have a dead/intermittent leg. Check the running amperage of each leg also.
I got 20 amps on each leg. When I bypassed the switch it fired up so it looks like the switch needs to be replaced. I tried spinning the blade a few more times after I last posted and couldn't get it to start, so that may have been an aberration. Thanks Bill!
Glad it's fixed. Seems like you knew what was wrong when you started.
Initially I thought it was the switch, but I wasn't 100%. A few years ago I had a couple new machines from a manufacturer I'm not allowed to trash on this site and there was some electrical issue burning up motors none of their techs or engineers could figure out and some of the obvious fixes never worked. One machine was down for over a month before they finally replaced it. Long story short, ever since then I find myself overthinking the potential causes. Didn't want to throw away $100 on a switch if there was a bigger issue. Wasn't until trying some of your suggestions that it became clear the switch was shot. Annoying it wasn't replaced initially by the manufacturer but this is a drop in the bucket compared to the nightmare I dealt with a few years ago.