Re: [CAD_CAM_EDM_DRO] OT: AC Motor capacitor question

beer@... wrote:

> A good friend with meager finances has in his possession a 5HP 220V
> single phase motor that he wishes to use on a compressor.
>
> The run cap is defective. It has lost one of the connections through
> corrosion and requires replacement. There are no markings on this cap
> any more and the manufacturer of the motor is unknown.
>
> The start cap appears to be 60 uf.
>
> 1. Can someone give me a guesstimate size for a run cap, should we be
> forced into buying SOMETHING and then hoping ?
>
> 2. Can a conventional RLC bridge accurately measure the value of this
> cap ? ( There is enough meat left to get a probe tip on, but that's
> all )

Yes, if the only problem is corrosion of the terminal, but the capacitor
is not internally shorted or open, then you would have no trouble
measuring it on an AC bridge. There is nothing special about a motor
run cap. Start caps are electrolytic, and may have such poor ESR that
a bridge may give unreliable readings without difficulty. But, the run
caps are generally oil-paper caps with good characteristics.

Jon