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Discuss Help single phase motor problems in the Electrical Forum area at ElectriciansForums.net

Gary Didwell

EF Member
Hello I am hoping someone can help me please.
I am having problems with a motor on my home made 2 x 72" belt grinder
20160912_131251.jpg This is the motor
20160912_131242.jpg
I have it wired via a DOL motor starter.
Recently it stopped running under load, once I removed the grinding belt the motor would stutter and my main drive wheel would go in forward or reverse before deciding which way it wanted to go.
If I pushed main drive wheel it will run but no torque and if you put pressure on drive wheel you can here the centrifugal switch clicking as you can slow it with your hand.
I changed the start capacitor for a 60 uf which I believe is the same as the original one as I cant read it as its been sprayed over, but looking at plate it does say 60 uf .
I have had the back off and the centrifugal switch looks as if its working ok the 2 contacts are shut until motor speeds up the it opens and re shuts once it slows down.
So I am hoping someone would be so kind to tell me what is wrong with it as the motor has only had a couple of hours use as it was new or reconditioned when I had it so would be a shame to bin it.
Thanks in advance
 

darkwood

Super Moderator
Staff member
Super Moderator
Have you done any testing like voltage at the motor, could there be a loose connection possibly in the DOL which breaks down when loaded?
This could be a few issues but best narrow it down to the simple ones first.

It sounds like it gets up to speed and clicks over but loses it when any load added so suspect a breakdown in the voltage possible or run capacitor issues.
 

Gary Didwell

EF Member
Hi Darkwood
When I first had the motor I wired it direct to a 240v uk plug which I think may have caused this problem I thought I had blown the Starter cap so got a new one and also added a new dol starter switch after reading this is what was needed. have I blown the motor ?
 

darkwood

Super Moderator
Staff member
Super Moderator
I cannot see how you have done anything wrong here be it via a plug or a dol starter, the only problem you could have introduced is where you connected the 230v in the motor circuit, do you have a pic' of the connection terminals and any wiring diagram supplied as they can vary according to motor wiring layout.
PS - it looks like a reconditioned motor given the screws are painted and it peels of when removing them.
 

Gary Didwell

EF Member
At first it worked fine it did trip the breaker a few times in my workshop while I had it wired via a plug only.
Here is the wiring
20190103_175741.jpg
20190103_175751.jpg
 

darkwood

Super Moderator
Staff member
Super Moderator
Was it working prior to this stuttering? ... maybe a faulty inertial switch but the run capacitor maybe suss, I have plenty experience on 3ph motors but single phase are rare in my trade experience so cannot nail the symptoms to the issue like some may be able to do?

Edit - connections seem fine.
 
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Gary Didwell

EF Member
yes motor was fine at first like I said it did trip my workshop breaker a few times then as it was running I could hear a difference in sound so stopped it and when I turned it back on this problem was there so after reading up on it I thought I had blown the starter cap so bought a new Cap and the DOL switch but problem still the same.
 

darkwood

Super Moderator
Staff member
Super Moderator
if the starter cap had gone it tends to stall the motor so it doesn't run and athus burns out, the fact it runs up to speed then clicks over suggests the starter cap is fine. I would be looking at a loose connection crashing the voltage under load or the run Cap' that is if the inertial switch is working ok, it not too easy to nail it down without test results on the cap's, supply and motor.
 

Gary Didwell

EF Member
I will run some tests on the caps tomorrow will have to do some research on how to test the motor its self as not sure what I am looking for.
But thanks for your help I will report back tomorrow
 

Lucien Nunes

Mercury Arc Rectifier
Respected Member
This is a Capacitor Start & Run motor. The 16μF run cap is always in circuit with the Z winding. When the centrifugal switch is closed, the 60μF starting cap is connected in parallel making 72μF. If the 60μF start cap is bad, it will lack starting torque but once it gets up to speed, the run torque will be normal. If the 16μF run cap is bad, it will start fine but lack torque once the centrifugal switch has opened.

As per Darkwood it sounds like the run cap is bad. The best test is substitution, as caps sometimes break down under working conditions but test OK on resistance and capacitance tests. If you like, check you have continuity through both windings U1-U2 and Z1-Z2, and if convenient test the insulation from one winding to the other and both to the frame if you like (with the caps out of circuit!) but the run cap is the prime suspect. If left connected to the mains with a bad run cap, the windings may be damaged, but you would probably have noticed it overheating at that point so hopefully this hasn't happened.
 

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