And if unsure about phasing always bring the voltage up slowly with a variac
while monitoring the secondary voltage. If the phasing is correct output
will show with a small value of input...Jim..
----- Original Message -----
From: "W2RU - Bud Hippisley" <W2RU@frontiernet.net>
Sent: Saturday, March 11, 2006 7:56 PM
Subject: Re: [Amps] Transformers in series
> Rex Lint wrote:
> > Be careful tho, the primaries and the secondaries BOTH have to be in
> > parallel... or else you're just running a short circuit!
> I'm not sure Rex said exactly what he meant to say.
> You can put primaries in series and secondaries in parallel, or vice
> versa, depending on what voltages in and out you're trying to accomplish
> with the transformers you have on hand. What you CAN'T do with
> paralleled secondaries is parallel them with their voltage waveforms OUT
> OF PHASE.
> Examples: I have two filament transformers, 6.3 VAC @ 1 Amp secondary ,
> 115 VAC primary. If my input line voltage is 115 VAC, I would parallel
> the primaries, and then I could either parallel the secondaries with
> correct phasing to get 6.3 VAC @ 2 Amps, or I could put the secondaries
> in series with correct phasing to get 12.6 VAC @ 1 Amp. Alternatively,
> if my supply line was 230 VAC, I'd put the primaries in series and then
> do either series or parallel secondaries, as before, depending on
> whether I needed 6.3 VAC @ 2 Amp or 12.6 VAC @ 1 Amp.
> The problem is the PHASING. It is a bigger problem for paralleled
> secondaries than for the series case. If I wire the two secondaries in
> series out of phase, the only problem I have is my net secondary output
> voltage will be zero or very close to zero. But with paralleled
> secondaries, I have two voltage sources of opposite polarity trying to
> feed each other; instead of seeing the rated load resistance, each
> transformer will see very nearly a short circuit and catastrophe will
> If you're lucky, the two transformers are identical and the leads coming
> out of them are identically placed so that you can reasonably assume
> which leads need to be tied together for proper in-phase operation. If
> they're not identical, I use a scope or a small amperage fast blow fuse
> in the primary to help me figure it out. I'm sure there are other,
> cleverer techniques out there.
> Bud, W2RU
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