Can't seem to find it at the moment, but seem to remember something
like the following gut speculation....
Two electrolytic caps of equal value connected like terminals in
series will act as an AC capacitor of one half the value, because:
Since one electrolytic cap by itself will conduct a dc voltage one
way, I think the combination would quickly develop a charge, as in
electrons check in (because both caps only conduct DC one way, an
ersatz diode) and they don't check out (because BOTH DON'T conduct the
other way).
Model it by placing a diode across a regular capacitor of the same
value (in parallel). Do the same for 2nd identical regular capacitor.
Now connect the two combo's with both diode anodes together. Electrons
check in but they can't check out.
This bias would match 1/2 the peak-to-peak voltage of the AC, and
quickly, as mostly in the first quarter cycle starting either
direction.
This would have the effect of "biasing" BOTH caps with a DC voltage to
the point where no DC current flowed, making it REALLY two caps in
series
This would also mean that BOTH caps have to be DC rated by at least
the AC peak to peak. No splitting of the voltage drop. In either
direction at peak you have the sum of the bias and the AC together
across one cap (AC p-p) and the AC minus the bias (zero) across the
other cap.
You should be able to measure this bias after you take the AC off for
a bit if the Caps aren't real leaky. If the positive terminals are
connected together, the bias will be positive relative the outside
terminals.
Will keep looking, or maybe this will stir someone's memory.
73, Guy.
----- Original Message -----
From: <n4kg@juno.com>
To: <TOWERTALK@contesting.com>
Sent: Monday, August 05, 2002 3:23 PM
Subject: Re: [Towertalk] Tailtwister won't turn.
> The recommended / described use of electrolytic capacitors
> for replacing an AC motor start capacitor is a SERIES connection
> so the effective capacitance is HALF (unless the reverse biased
> side acts as a short on each half cycle...then the effective
capacitance
> would be equal to the marked value...anybody know?).
>
> Tom N4KG
>
> On Mon, 5 Aug 2002 "Mike & Coreen Smith" <ve9aa@nbnet.nb.ca>
writes:
> > Yes, you can stick two electrolytics together like that.
> > Remember that the value will double if you parallel 2 identical
caps
> > together like that.
> >
> > GL
> >
> > Mike-VE9AA
> > ----- Original Message -----
> > From: "Dale L Martin" <kg5u@hal-pc.org>
> > To: <towertalk@contesting.com>
> > Sent: Monday, August 05, 2002 12:49 PM
> > Subject: RE: [Towertalk] Tailtwister won't turn.
> > >
> > >
> > > I heard/read/dreamed/made up somewhere that, in the absence of a
> > replacement
> > > motor starting capacitor, a TEMPORARY motor starting capacitor
> > substitution
> > > (for testing purposes only) can be made by putting two
> > electrolytic
> > > capacitors of about 250Ufd/100VDC back to back
(plus-neg-neg-plus?
> > > neg-plus-plus-neg?) to see if it is indeed the motor starting
> > capacitor that is the problem.
> > >
> > > Does that actually work?
> > >
> > > 73,
> > > dale, kg5u
> > >
>
>
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