Capacitor(s) for a single phase 3HP compressor motor.

[Andrew TinsleyParticipant @andrewtinsley63637]

I have a 3 HP single phase motor, which came out of a Centec Mill. I replaced it with a 3 Phase motor. It has been taking up space and needs to go. But first, I need to put it into working order. It obviously never ran the mill!

There are no identifiers on the motor, except in the degutted, cast in connection box. There it has MEC 90 S cast into the body. Looking on the net, this appears to be a special, intended for driving a hefty air compressor. Looking at various images of MEC 90 motors, they are almost identical to the motor I have.

The connection plate is not there and just 4 wires come out from the motor. There is a pair of hefty black and Red wires which have a resistance of 2.3 Ohms, the other pair is blue and white, which are somewhat thinner wire, these have a resistance of 4.2 Ohm. I assume the red and black are the run winding and the blue and white are the start winding. I have not disassembled the motor, so not sure if there is a centrifugal switch, but I assume so.

What puzzles me is that the housing for the capacitor/s is huge in the photos on the net. Certainly big enough to house two hefty capacitors, side by side! This rings a faint bell regarding motors intended for large start currents such as an air compressor load. Needless to say there is no sign of the capacitor(s) or housing.

Anyone familiar with this type of motor? Are there one or two capacitors normally? If so what sort of value would they be and how would the second one be connected, if indeed there are two capacitors.

The motor appears to be unused and apart from the butchering by persons unknown, it seems well worth restoring to a usable condition. Especially as the new price is north of £280!

Thanks in advance,

Andrew.

[Andrew TinsleyParticipant @andrewtinsley63637]

Having failed to find any info on the net, I gave up, but decided to try again after I had posted the above.

Must have hit the correct combination of words, as information suddenly appeared. The run capacitor is around 50 microfarad and the start capacitor seems to be around 200 microfarad. Would this line up with any experience the forum members might have?

Not overly cheap to obtain a housing and capacitors, but probably worth doing if I can move it on at a small profit, to cover the labour costs!

Goodness knows what the butchered motor was doing in the Centec, it was never going to work in the state I found it.

Andrew.

[noel shelleyParticipant @noelshelley55608]

Hi Andrew, IF it is a cap start and cap run then the values could be right, they are inline for a 2.2Kw motor found on air commpressors. It’s value is unlikely to be as high as you think and incomplete even if running. Please Note the use of IF ! Why was it robbed of parts ? Are the windings cooked ? If you do not need the motor I would be wary of spending money on an unknown unit. Good luck.  Noel.

[Dave HalfordParticipant @davehalford22513]

The capacitor boxes are generic and sometimes also house an overload button reset

[Andrew TinsleyParticipant @andrewtinsley63637]

Hello Noel,

The Centec had not been commissioned and the old gentleman seems to have gone into a home and the house was being cleared. The motor looked new and I took one end plate off to check the state of the windings as you advised, they were pristine, so no burnt out coils! Why the capacitors and housing were missing is a mystery, maybe they fouled something or perhaps the previous owner was having some mental problems?

Looks like £10 or £15 should be sufficient for the required capacitors, so well worth a punt to see if it is a worker. As for the £280 price tag for a new motor, that seem somewhat OTT! If it can be shown to be a working proposition, then I would not expect a sale price of more than £50, or keep it in my motor stock. In its existing state, it is neither useful to man nor beast!

Andrew.

[Andrew TinsleyParticipant @andrewtinsley63637]

Hello again,

Purchased a 200 MFD start capacitor and a 50 MFD run capacitor. I held off the capacitor housing in case the motor was U/S.

Did a temporary hook up and the motor ran very smoothly. So thanks Noel, for confirming the capacitor values. Did a load test for 20 minutes before I shut down and all seemed well. I have just purchased a dual capacitor housing and an appropriate motor terminal block for the princely sum of £11.50 So total outlay was £27. Well worth the cost for a near new 3HP single phase motor.

Thanks for the advice.

Andrew.

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