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I recently replaced a motor run capacitor in an old AC Fan. The replacement capacitor was of wrong value having previously been 2uf I replaced it with 6.3, It worked for about 2 weeks but then it started to run very slowly (barely even spinning) and hum. My first instinct was to replace the capacitor again with the right value this time as the symptoms where of capacitor failure however after replacing the capacitor again the fan still shows the same symptoms. I suspect that the motor has gone bad due to the incorrect capacitor value, any ideas on how I can fix it? If possible I would like to repair the motor and not completely replace it as its an antique fan and I would like to keep the parts as stock as possible.

Thank you.

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    \$\begingroup\$ disconnect that motor now. Improper replacement filter or phase-shift capacitors can e.g. burn out brushes or lead to greatly increased thermal losses in windings, which can burn isolation and lead to fiery failure. \$\endgroup\$ Sep 22 '20 at 11:52
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    \$\begingroup\$ If it's valuable, take it to a motor re-winder for a repair quote. Excessive current in the start winding may have overheated it, degrading its insulation. \$\endgroup\$ Sep 22 '20 at 12:41
  • \$\begingroup\$ Thank you all for the help, The fan is over 50 years old to be more specific. I'll get its motor disconnected and taken to a repair shop as i'm not sure that ill be able to do it myself. Thanks again! \$\endgroup\$
    – Nvidia
    Sep 22 '20 at 13:57
  • \$\begingroup\$ @nvidia, make sure you vote and mark answers as answered instead of saying thanks \$\endgroup\$
    – Voltage Spike
    Sep 22 '20 at 18:12
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A motor-run capacitor that is three times the design value can cause the current in the auxiliary winding to exceed the design value, overheat the winding and cause the insulation to fail. Failed insulation can result in shorted turns and further increase in temperature. The failing winding and overheating might cause the motor to lose torque and run slower.

Increased operating temperature or age can cause the bearings to fail. Failing bearings can cause the motor to slow down.

It may be difficult to find replacement bearings. Special tools may be required to remove the old bearings and install new ones. Rewinding the motor will require carefully removing the old windings and counting the turns. You may need to remove both windings. You will need to determine the correct wire size and length of wire needed. You will need to obtain the additional materials needed to protect the windings at the edges of the iron core etc. Look for instructions and videos about motor re-winding.

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Improper replacement filter or phase-shift capacitors can e.g. burn out brushes or lead to greatly increased thermal losses in windings, which can burn isolation and lead to fiery failure.

If possible I would like to repair the motor and not completely replace it as its an antique fan and I would like to keep the parts as stock as possible.

How antique is "antique"?

Because, honestly, I don't trust old consumer-grade motors. It might be wise to replace the motor to preserve the rest.

The things you can service about the motor are bearings, and if it is brushed, you can replace the brushes.

Everything else will come down to removing the windings (which is prone to exposing you to dust of enamel that might contain unhealthy fire retardants) and winding it yourself, which is neither going to be good as new nor easy or quick.

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  • \$\begingroup\$ What kind of motor has both brushes and a phase-shift capacitor? How can an inappropriate value of filter capacitor lead to thermal losses in the windings? \$\endgroup\$ Sep 22 '20 at 12:34
  • \$\begingroup\$ @CharlesCowie I don't know what kind of capacitor and what kind of motor we have, so I'm only stating the general cases. Wrong phase shift leads to ohmic losses when counter-EMF in windings meets external current, no? \$\endgroup\$ Sep 22 '20 at 12:53
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    \$\begingroup\$ It would make more sense if you stated assumptions and related the problem descriptions to the assumed types of motors and capacitor uses. I took the term "run-capacitor" and the askers two prior questions about the same problem to mean that this is a single-phase PSC motor. \$\endgroup\$ Sep 22 '20 at 13:21
  • \$\begingroup\$ @CharlesCowie I didn't think that far - well, can't double-upvote your answer. It's better than mine. Tempted to delete mine... \$\endgroup\$ Sep 22 '20 at 13:48

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