Extractor motor occasionally won't start?

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Deadeye

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Hello

My dust extractor normally works perfectly. However, every now and then it doesn't turn, and the motor just buzzes. If I unplug, remove the inlet and give the impeller a turn (which it does freely), it then starts fine.

It's not a life changing issue, but annoying to dismantle and reassemble perhaps 1 start in 10-20.

Any thoughts appreciated. New capacitor?

The motor is a standard 3HP induction; 240V

Thanks
 
Most likely.
Not a lot else to go wrong with an induction motor provided that the windings are electrically intact.

Capacitors are not expensive - so it's best to replace exactly like-for-like in terms of Voltage and Capacitance. Physical size and shape is not important provided that it can be accommodated in the recess.
 
Most likely.
Not a lot else to go wrong with an induction motor provided that the windings are electrically intact.

Capacitors are not expensive - so it's best to replace exactly like-for-like in terms of Voltage and Capacitance. Physical size and shape is not important provided that it can be accommodated in the recess.


Thanks. I'll dig it out!
 
If you are taking it out for inspection, it's a good idea to void any residual charge - short the wires out without touching when disconnected. Not always, but it may contain enough juice to make you swear.

Next, look at the casing carefully; sometimes 'cooked' capacitors may exude melted insulation - can be a bit greasy, so be careful of that, wash it off your hands - nasty chemicals!
There may also be a change in shape - bulging on the sides is a give-away.

The ratings will usually be on the can somewhere.
 
I would suggest a good check would be to get it to the buzzing error state and then flick the impeller with something (not your finger, or anything that could whip up into your flesh, eye, etc)

If it spins up fine then, it would point toward the cap being bad.

Or just gamble the £6 or whatever, and do the cap from the offset.
 
If its single phase then its probably a capacitor start induction motor. The capacitor creates a phase angle between the start and run windings to enable the motor to start moving in the preferred direction. Normally there's a centrifugal switch on the end of the motor under the cooling fan. The centrifugal switch takes the capacitor and start winding out when the motor reaches speed. A motor sitting buzzing is normally an indication of a problem with the start winding - either burnt out/ knackered capacitor or sticky switch. As your issue is intermittent I would have a look at the switch and see if its either caked in crud or the terminals damaged. If the capacitor has gone or the run winding has burnt out then the motor normally just sits there humming until you persude it to go in one direction or another manually as once it starts to rotate it can operate on the run winding alone without the capacitor or start winding.
 
Thanks everyone!

<sigh>
Getting at the angular switch and start winding is a bigger strip down than I'd hoped.
Guess I''ll change the cap and see...
 
Not many cheap motors these days have centrifugal switches they are normally what is called “pcap” or permanent capacitor motors where the capacitor remains in circuit at all times.
Almost certainly the fault is down to the capacitor.
I would probably do the spin test also, but don’t tell any HSE bods out there! 😈
 

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