TU56/TC11 restoration - VARIAC question

vrs vrs at msn.com
Fri Mar 18 08:58:59 CST 2005

From: "Paul Koning" <pkoning at equallogic.com>
> >>>>> "William" == William Donzelli <aw288 at osfn.org> writes:
>  >> Are these capacitors electrolytics at all?  I thought that motor
>  >> capacitors were generally oil-filled, but not electrolytic.
>  William> Nearly all are oil, but every so often you see an
>  William> electrolytic version. The oil caps will likely be good long
>  William> after we are gone.
> There are motor start caps and motor run caps.  The former have much
> higher capacitance and are only connected for a few seconds during
> motor start.  So my understanding is that start caps are often
> electrolytic because you can get away with it, while run caps are not
> because they are subjected to AC full time.

What you are saying is consistent with what I see on most sites selling
these things.  There, "run" caps are generally oil, and "start" caps are
generally electrolytic.  The exception being the occasional "start/run" cap,
whatever that is.

The original caps in the TU56 are high capacitance, and clearly
electrolytic.  But they appear to be wired for continuous phase shifting
duty.  Hence some of the people on the list insisting that they are "run"
caps, and that the beefier, more expensive "run" cap should be used.

Finding a 100uf oil-filled "run" cap is not easy, and they tend to be
expensive (as Jay pointed out).

Unfortunately, I do not have any insight as to whether the relatively
inexpensive electrolytics can be used, or whether the expensive oil-filled
caps are needed.

The TU55 uses a 7uf oil capacitor in this role, which again argues for a
"run" capacitor, except the values are wildly different.  Is it possible
"start" caps were used in the TU56 to save $$, but are being derated somehow
so they can be used as "run" caps??


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