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
result.
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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