Slow induction motor

I have an old Clarke motor (1/5 HP, 0.15 KW, 240 v, 1.8 A, 1400 rpm,
type 5DB, single phase according to the rating plate,) that only runs at
400 rpm whether loaded or unloaded. I am looking for suggestions for why
it is slow, and how I can rectify the fault.
My inspection of the motor reveals that:
[1] It has no brushes so I guess it is an induction motor.
[2] It has a 8 microFarad external capacitor which suggests it is a run
capacitor not a start capacitor from what I have gleaned from the internet.
[3] The bearings are not binding or rough, and the spindle is free to turn.
[4] A cheap multimeter test of the disconnected capacitor gives a
gradually increasing resistance up to 20 ohms.
[5] A cheap multimeter test of the windings from the capacitor terminals
reads 58 ohms.
Any clues folks?
Reply to
Clifford Coggin
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I would take a look and see if there is a centrifugal switch that is stuck on. Richard
Reply to
Richard
Possibly a permanent split capacitor motor and those, as well as shaded pole motors, can be speed controlled to a degree by varying the voltage so maybe the motor is somehow getting supplied a reduced voltage.
Reply to
David Billington
Assuming DC tests your multimeter should show a resistance reading approaching infinity asymptotically. 20 ohms is a long way short of infinity !!!!
Andrew
Reply to
Andrew Mawson
That's the first thing I looked for, but there is no centrifugal switch.
Reply to
Clifford Coggin
If that is the case the motor is junk and I need a new one.
Reply to
Clifford Coggin
It may have gone to a higher reading if I had continued the test, but I stopped after 10 seconds or so because the increase was so gradual. Are you suggesting a faulty capacitor or a useless meter?
Reply to
Clifford Coggin
Either is a possibility - your meter is easily tested against a known resistance. What resistance range was it switched to.
Andrew
Reply to
Andrew Mawson
I was just wondering if you had checked the supply voltage at the motor terminals. It used to be that Machinemart sold single phase motors were all PSC motors so not a good start-up torque but good for some applications.
Reply to
David Billington
I am not an electrician and don't have any known resistances. The meter is auto ranging so I can't answer your second question.
I shall order a new capacitor in the hope that it will solve the problem. If it doesn't, the motor is destined for the bin as I don't intend to spend any more time on the job.
Thanks for your help Andrew.
Reply to
Clifford Coggin

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