Hi Roy,
I wrote:
> Concerning:
>
> "Heat will happen, and maybe failure.
>
> It is not advisable to directly parallel two same-kind transformers,
> and parallelling two dissimilar transformers is a real bad thing. The
> effect, if there is any voltage difference, is like a shorted turn or
> turns.."
> I have personally built and used HV power supplies with paralleled
> transformer secondaries and experienced no problems of any type. Small
> voltage differences are 'equalized' by transformer losses. In any case,
> they can be easily tested and determined in advance before building.
>
> 73, Roy K6XK/0
A good HV transformer suitable for a cap input supply has a very
low ESR, typically less than one ohm per hundred volts. With
such a low resistance, it does not take much secondary voltage
error to produce significant heating when the transformers are
idling.
The question indicated the voltages "were different". I'm sure you
actually aren't recommending he parallel two dissimilar
transformers and let "transformer resistance" sort out the
differences!!!!
I certainly agree if you confirm voltages are matched, it isn't a
problem. But most people doing this are using old stuff they find
laying around, and have no idea if the transformers are from the
same production batches or not.
In general, it is a bad idea to directly parallel the transformers
when a few bucks worth of parts will make sure you don't have
needless dissipation in the transformers. With separate rectifiers,
transformer bucking is not an issue.
73, Tom W8JI
w8ji@contesting.com
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