Not Stag related, electric motor query

[Dave M]

I know this is a long shot and not at all Stag related but someone on here may be able help I hope.

Ive got a 240v Ac two speed pump motor that has blown one of its capacitors. Its blown to bits so I cant find any trace of the capacitor size.

Motor details are as follows :-

High Speed 1.5Kw 240v 8.4 amp 2050 Rpm

Low Speed 0.37Kw 240v 1.5 amp 1450 Rpm

One of the windings has a 36 micro farad capacitor fitted but as i say the other is blown to bits so no idea what the size is.

Looking at £400 for a new pump so worth trying a couple of new capacitors.

Dave

[marshman]

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Hi Dave,

Unfortunately it is not as easy as knowing the motor power, speed etc.The manufacturer usually specifies the correct value. I had one go on my compressor, like yours its value was unreadable. I went to a motor rewind specialist who "guestimated" a value from their experience. You probably need to do some more investigation to find if it was a Start or Run capacitor as well. Did it look to be physically similar in size to the 36mfd one? if so try another 36mfd. The motor will still work but won't be as efficient and may lack power. the problem with experimenting is the capacitors are not cheap. I found the best buys were on ebay - I paid 8 pounds inc postage - but was quoted upto 40 pounds at local electrical factors.

Can you work out which winding it was on? high or low speed?

Roger

[Dave M]

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Thanks for the info Roger, Ive had a look on ebay and one of the capacitor suppliers on there also supplies the motors that the pump has fitted so Im hoping they will be able to help.

Thanks again

Dave

[V Mad]

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Pump motors are low starting torque so usually have one capacitor permanently connected in series with a tertiary winding to get them started.

It depends which capacitor has gone. My guess is that one capacitor is to phase shift the current for one of the windings, the other may be a capacitor that is switched in seriesto reduce current, hence power and speed.

[Dave M]

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Chris

Thanks for the info, its a two speed pump that wont start on low speed, however it will start on high speed and then will run on low speed if its selected. Im hoping its the start capacitor on the low speed thats blown and a new cap will solve the problem as a new motor/pump is a bit expensive.

Dave

[V Mad]

imported post

OK. Start capacitor needs to be as small as possible, but still enough to start the pump; too high a value will cause excessive current/heat in start circuit;so try some low values