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Help wanted:  motor stuck when powered
Help wanted:  motor stuck when powered
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Old 14th May 2019, 11:39 AM   #1
banpuku is offline banpuku  United States
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Help wanted:  motor stuck when powered
Default Help wanted: motor stuck when powered

Hello. I am refurbishing a Gates CB500 turntable with Ashland synchronous hysteresis AC motor. The motor was running OK prior to disassembly to clean and inspect. I re-assembled the motor. Without power, the motor turns freely by hand, so there is no mechanical issue. When powered, the motor freezes (magnetically). When un-powered, the motor turns freely.

The smoothing and power capacitor have been checked and they are in good working order as they measure to infinity using my ohm meter. I get good resistance measurements across the motor terminals.

Thoughts?

Thanks in advance, Pat
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Old 14th May 2019, 12:07 PM   #2
Kay Pirinha is offline Kay Pirinha  Germany
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Were there any washers or spacers on the axis that you might have muddled up when reassembling the motor? Did you mount the stator in the right direction?
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Old 14th May 2019, 01:55 PM   #3
Mark Tillotson is offline Mark Tillotson
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One winding or the capacitor is open-circuit? You need to measure the capacitance of the
run cap, not just that its not a resistor. If one winding is out there is no rotating magnetic field.
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Old 14th May 2019, 04:57 PM   #4
Galu is offline Galu  Scotland
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Not sure what you mean by the smoothing and the power capacitor. A circuit diagram and/or photo would be helpful.

If a single capacitor (probably around 3μF) is associated with this motor, it will be in series with the start winding.

As Mark says, you should measure the value of start capacitor (if present) and compare with the value written on the capacitor. The capacitance has to be exactly as specified for the motor to run satisfactorily.

If no capacitor is in series with the motor then, as Kay says, check you have not assembled he stator upside down.
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Old 14th May 2019, 05:10 PM   #5
Galu is offline Galu  Scotland
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Wait a minute though - is this the same Ashland motor you posted about here?:

Vinyl Asylum
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File Type: jpg Ashland Motor.JPG (134.2 KB, 199 views)
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Old 14th May 2019, 09:18 PM   #6
banpuku is offline banpuku  United States
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Help wanted:  motor stuck when powered
Thanks for the responses so far.

Galu - this is a different motor than what you are showing in your picture from 2012.

All - please see attached diagram from the user manual. It shows 2 capacitors:

1. Motor start capacitor

2. Filter assembly which has a cap + resistor

I am very confident the motor stator is in the correct direction. Washers are OK as well.

Still no luck. I can hear a small buzz/vibration when AC is powered to the motor, but that is when the motor freezes magnetically. Once the AC is shut off, the motor spins freely. I double checked the wiring and stator/rotor direction to ensure all is correct.
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File Type: png motor wire diagram.png (318.8 KB, 189 views)
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Old 14th May 2019, 10:18 PM   #7
banpuku is offline banpuku  United States
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Help wanted:  motor stuck when powered
Further follow-up. I have checked the capacitors and they measure 2uF (motor start) and 1uF (smoothing filter). I have tried reversing polarity of the mains and the polarity wiring to/from the caps. Still, motor freezes when AC is applied. Without AC, spins freely. Help!
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Old 14th May 2019, 10:28 PM   #8
Galu is offline Galu  Scotland
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Quote:
Originally Posted by banpuku View Post
I measure 2uF (motor start)
Tricky one! Sounds like you're missing the rotating magnetic field in the stator. Is 2uF the value which is printed on the motor start capacitor?
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Old 14th May 2019, 10:49 PM   #9
Mark Tillotson is offline Mark Tillotson
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Firstly is a run capacitor, not a motor start capacitor. Motor start caps are switched out of circuit by a centrifugal switch once upto speed, hence the name.

The other cap is not a smoothing cap. Its for snubbing and/or power factor correction. A smoothing cap is used with DC.

Anyway something is suppressing the rotation of the magnetic field, I'm wondering if you've got the capacitor on the correct winding, or the winding phasing right? It would be good to see the mechanical arrangement of the poles and measure the winding inductances to see how its supposed to connect up.
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Old 14th May 2019, 11:05 PM   #10
The Peasant is offline The Peasant  Canada
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Another possibility is that the alignment of the motor bearings/bushings are slightly off-centre, allowing the motor to spin freely without power but causing the rotor to be pulled over against the sides when power is applied.

Take care,
Doug
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