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Compressor Motor, Early Failure.

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I recently attended a local food takeaway. A walk in chiller had been causing tripping problems. As a last resort the owner had plugged the chiller's compressor straight into another 13 Amp socket on another circuit via an extension lead. An instant trip resulted. The compressor unit had been replaced just over a year ago.

An insulation resistance test by me revealed a near dead short L to E.

Inside the control box/motor housing I saw a label on the big motor capacitor (about 115 microFarads) that said 60 Hz MADE IN MEXICO. Could the  make or design be the cause of the premature failure. The new compressor unit only had cost the owner about £3k just over a year ago. What Voltage is used for single phase equipment in Mexico?

Z.

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    It is possible that the kit is really intended for 60Hz rather than 50, and the cap is 20% undersized,  but most well thought out designs for export should work on either.  The makers are best placed to advise.

    Barring a manufacturing error, motor overheating is the most likely cause of the insulation fault, perhaps due to protracted starting, or a use case that leaves the door open too frequently and so involves far more starts per hour than the makers ever  intended, or of course just under-design generally.

    However, unless the capacitor itself is faulty (did you verify the capacitance? ) it is not likely to be the culprit, but never say never. Unless the cap was not changed last time, and has always been undersized..

    In UK refrigeration pumps usually  the motor starts with two windings, one start winding delayed by a capacitor as a phase shifter, and the other wired direct to main. There is then  a centrifugal or timer mechanism that disconnects the capacitor and starter winding once it has begun to rotate. Larger systems have solenoid actuated  valves in the coolant loop that can reduce the back pressure on starting up. Much beyond that it gets simpler again, as 3 phases become the norm and the starter switching is no longer needed.

    Do note that in south America generally,  (Except Argentina and Bolivia - always some exceptions) even the 220V regions  like Brazil, the mains frequency is nominally 60Hz - it makes their transformers and motors noticeably look a bit light by European standards.

    Mike.

    Mike.

  • 0 in reply to mapj1

    No Mike I did not test the capacitor apart from reading the info on its label. I passed the buck to enable me to get to my next job. I have learned from bitter experience not to get too involved with things you can't repair or which are beyond your skills set.

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  • 0 in reply to mapj1

    No Mike I did not test the capacitor apart from reading the info on its label. I passed the buck to enable me to get to my next job. I have learned from bitter experience not to get too involved with things you can't repair or which are beyond your skills set.

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