Motor problem

[RF Lighting]

I've got a problem with a 0.29kW motor powering an animal feed auger. It sometimes fails to start, and will not start at all when the supply is heavily loaded.

The problem is that this is on a remote farm on the end of a very long LV run, and when the milking parlour is running, the supply voltage at the head drops to below 200V.

The DNO know about this, and are working to upgrade the supply network. Hopefully by next summer the supply will have been fully replaced.

Normally I would have put the problem down to low volts, but I am told the supply has been like this for years, and the motor used to run fine until a couple of weeks ago. There is also an identical auger in the parlour which still starts and runs fine on the low volts.

I'm now beginning to think that the low volts is just a contributing factor to another issue. The only other thing I can think of is there is an 8μF on the motor which may have gone up the spout?

Any one got any other ideas?

 

[ericmark]

Starting single phase motors under load has always been a problem I would agree the capacitor is likely the problem but could also be mechanical. Even with three phase I have been caught out I had a crushing plant motor fail through over greasing the operator greased every day even when only worked for half an hour lucky for me a very clever engineer was on site and he told fitter to remove bearing and remove a hand full of grease.

So since always worked in the past I would also look at all bearings.

 

[casamena]

Starting single phase motors under load has always been a problem I would agree the capacitor is likely the problem but could also be mechanical. Even with three phase I have been caught out I had a crushing plant motor fail through over greasing the operator greased every day even when only worked for half an hour lucky for me a very clever engineer was on site and he told fitter to remove bearing and remove a hand full of grease.

So since always worked in the past I would also look at all bearings.

I agree check the capacitor first if you can. Don't think it would be the bearings, although if the end shield bearing housings have worn which is common then the bearings would be slipping and the rotor will not turn. easy way to solve this would be to take the end shields off and tap the bearing housing with a centre pop all the way around, this will prevent bearings slipping. also spread a little loctite bearing retainer onto the housings, but not if the end shield has a bumper washer usually on the back end (fan). . if your bearings end up collapsing it will probably burn out in which case i reckon it'll be cheaper to buy a new one than have it rewound.

 

[flyingsparks]

My money is on the capacitor. 9/10 this is the problem with single phase motors failing to start.

 

[Lectrician]

Swap cap with the identical one if you don't want to purchase a replacement before diagnosing...

 

[bernardgreen]

Some capacitor start motors have a centrifugal switch that takes the capacitor out of circuit when the motor has reached running speed. If the contacts of this switch are worn the capacitor may not be in circuit when starting.

 

[Belle427]

can help sometimes to try and turn the load by hand ie with a pair of stilsons or similar to see how tight it is, you can compare it to the other auger if possible.

 

[casamena]

can RF confirm it is cap start, may be induction start.

 

[ricicle]

Capacitor if it's SP. If TP then I would be looking at mechanical resistance.

 

[RF Lighting]

It's a SP motor. I'm going to try a new cap and see if that cures it.

The cap is connected across two of the winding posts, so no centrifugal switch to worry about.

 

[casamena]

Capacitor if it's SP. If TP then I would be looking at mechanical resistance.

why? seems to be a misconception that all single phase motors are run with a cap. There are some that are single phase without the need for a capacitor, that incorporate a centrifugal switch. the motor has 2 windings a start winding and a run winding. the C/S is in line with the start motor as soon as the motor gets up to speed the C/S opens.

 

[ricicle]

Capacitor if it's SP. If TP then I would be looking at mechanical resistance.

why? seems to be a misconception that all single phase motors are run with a cap. There are some that are single phase without the need for a capacitor, that incorporate a centrifugal switch. the motor has 2 windings a start winding and a run winding. the C/S is in line with the start motor as soon as the motor gets up to speed the C/S opens.

Because most causes of a non-starting SP motor are to do with a faulty capacitor in my experience and if you read the OP you will see it has a capacitor !

 

[casamena]

Capacitor if it's SP. If TP then I would be looking at mechanical resistance.

why? seems to be a misconception that all single phase motors are run with a cap. There are some that are single phase without the need for a capacitor, that incorporate a centrifugal switch. the motor has 2 windings a start winding and a run winding. the C/S is in line with the start winding as soon as the motor gets up to speed the C/S opens.

Because most causes of a non-starting SP motor are to do with a faulty capacitor in my experience and if you read the OP you will see it has a capacitor !

The first 2 posts clarified that it was most probably due too a worn out capacitor, assuming it incorporated a capacitor which the OP did not clarify until asked. my why? was to your reply of- if TP then i would be looking at mechanical resistance?
usually if your motor buzzs and vibrates a little this means the cap has worn, if you cant check the mF of your cap with a capacitance tester.

 

[RF Lighting]

That was an oversight in my first post. I wrote it had a 8μF on the motor, but missed the crucial word "capacitor"

 

[RF Lighting]

Congratulations to every one who said capacitor!

Went back today, this time armed with my capacitor tester. Tested the old cap, and it read only 2.4μF.

Fitted a new 8μF cap, and it's all back up and running properly. Farmer reckons the motor is also running faster now which is a bonus.

Farmer happy, cows happy, I'm happy