Electric motor fault

[NormanV]

Hi, I have a scroll saw fitted with a 240v 85w motor. The motor runs
very slowly, it is not the machine binding. Any suggestions on what to
look for or how I can check it?
I have thought of simply replacing it but the only type of motor that I
can find is a sewing machine motor but they run at 6000rpm which is
a tad fast for a scroll saw. Also I want to do it as cheaply as possible.
Thanks, Norman

[John Rudd]

These simple motors have a start/run capacitor to get them going

Looks like the motor start capacitor is dying...Mend it with a new one...

Should have a small value of a couple of MicroFarads or so but make sure it is AC rated...

[NormanV]

Thanks for the quick reply, I did wonder about the capacitor. Is there any way to test it?
I have a digital multi meter.

[John Rudd]

Thanks for the quick reply, I did wonder about the capacitor. Is there any way to test it?
I have a digital multi meter.

Not really.......

Replacement is the best option..

[NormanV]

Thanks, I've ordered one.

[John Rudd]

Thanks, I've ordered one.

Norm, Let us know how you get on...

i.e if the advice offered helps you sort the problem...

I ask not for my own edification ( or self satisfaction), but for the benefit of others who might encounter a similar issue.

[NormanV]

Will do, but it might be a while as it is coming from Hong Kong.

[NormanV]

I've fitted the new capacitor. Same problem, the motor is running slowly. Could it be a loose connection somewher?

[NormanV]

I've just tried bypassing the switch to eliminate that but it had no effect. Strange thing when I first fitted the new capacitor, it ran fast but on switching it off and then on it was running slowly. It has been intermittant before.

[Bluechip]

Bypassing what switch ??
If this is one of the low power 'cap always in circuit' types, ie, no start switch in series with the cap. and start winding, then it seems likely that the run winding is shot.
Do we have any pics of the rating plate ??
What size capacitor?
What MAY be happening is the motor is trying to run on the start winding in series with the cap.
The reactance of a 20uF cap at 50Hz is some 160 Ohms, it ain't likely to whizz away with a miserable current through it .
Dave BC
 

[NormanV]

It was the on-off switch that I bypassed. It is  a no volt release switch so I wanted to eliminate that. The capacitor is 1.5uf and is always in circuit, there is no centrifugal switch. The motor does not have a rating plate. I checked the spec online and it is a 100w motor.
I am beginning to agree with you that the winding is gone. I will have to look out for another motor.
Norman

[Bluechip]

Norman
I would take it apart. Have a look inside. The windings will be solid copper, there is a joint where they are connected to the stranded wire to the connections. I have known these joints fail. No problem at all with the actual windings.
At least you can meter the windings for continuity.
Don't abandon hope 'til you sure no hope is left ...   
Best of luck .. 
Dave BC

[NormanV]

I took it apart, it looks as though it is the end of the road for this motor. The windings are burnt.
Where can I find a cheap 100w motor? I thought about a sewing machine motor but the one that I checked
was 6000rpm, but I suppose that I could use the speed control. It might be quite useful on a scroll saw.
Any other ideas?

[John Hill]

Norman, it looks like the connections are burned, not the coils themselves.  I suggest carefully cutting those 'cloth' sleeves off and looking at what is inside.  My guess is that you will find a poor connection which you will be able to repair.
John

[NormanV]

YABBADABBADOO!!!!!!
John, I followed your suggestion and found a broken wire. I rejoined it and reassembled
the motor and now it is runnung at normal speed and with plenty of power.
Thank you those who made suggestions, I would have given up sooner without your help.
Norman