Paralleling electrolytic capacitors for testing purposes

Edward Greeley etgreeley at WORLDNET.ATT.NET
Thu May 17 01:27:26 EDT 2001

john w. king wrote:

> The transformer has a shorted filament winding or open filament winding and a previous owner replaced the filament winding with a separate filament transformer. The has an audible hum just like a solenoid, which I attribute to the shorted filament winding. otherwist, the transmitter cranks out a solid 110 watts of carrier.
Hello John,

I guess you mean that the original trans is the one doing the humming.
If that is the case, it definitely sounds unsanitary. If the hum is,
indeed, caused by a shorted winding and not by a harmless case of loose
laminations, the shorted winding will very likely cause the transformer
to fry itself eventually. A shorted winding can cause a tremendous
amount of heat buildup. A good clue is to leave the power on it for a
while, say a couple of hours, and see if it gets too hot to touch. If it
does, you can probably log it out. If in doubt, disconnect all the loads
on the transf and see if it still gets hot. If it does, kiss it off,
because a transformer which is "idling" will hardly exceed room temp.
The only salvation for a transf with a seriously shorted winding is
replacement, EXCEPT, if the bad winding is on the outside layer(s) you
could dismantle the trans and strip the bad winding off. In that case,
of course, the thing to do would be to replace the winding with NEW wire
of the same guage and same number of turns, and get rid of the "extra"
transf. Even if the bad winding is two or three windings deep in the
transf (excluding the HV winding, too much work!) that would be the
thing to do because filament windings don't have a whole lot of turns.
If your transf is potted or hermetically sealed, of course, disregard
the foregoing transmission!

As to paralleling the filter caps: if the existing caps are causing
ripple due to being dried out ("dry" electrolytics are not dry, you
know, they are "moist" when new), then paralleling them with new ones
should fix the ripple problem, if the parallel caps are within plus or
minus 30% or so of the original value(s). On the other hand, if the
original caps have very high leakage current, paralleling them with new
caps could quite likely NOT provide total elimination of the ripple. If
the original caps have such a high leakage current, they will get HOT,
so beware of exploding caps and the ungodly mess they make when they "go
off" (foil, blood, guts & feathers)! Been there, done that, several
times over the last 55 years. :-(


Ed Greeley
Mobile, AL

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