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Toroidal transformers wiring configuration.

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davelectronic:
I have two toroidal transformers, both are 2 x 115 Volts primary windings. And 2 x 12 Volt secondary windings. I wanted to find out if I could put both primary windings on each transformers, and both secondary windings series to get 6 Volts output from both transformers under voltage input on the primary windings. Hope that makes sense. There 300 VA each transformers. I think the primary windings under voltage might sag under secondary load, dropping the output secondarys below 6 Volts. Thoughts on this appreciated.

Benta:
If the transformers are identical, there's no problem playing around with the windings.
But it's unclear what you want.
1: a 6-0-6 V output?
2: a single 6 V output?

There's zero problem in running the primaries at half voltage, in fact it's advantageous. Much lower core losses and less inrush current problems.
But  you'll have increased resistive losses due to thinner wires. All in all, derate the power to 270 VA per transformer, and you'll be OK.

But whatever you do, be damned certain about the polarity/phase of all windings.

I've attached the options:

davelectronic:
Thank you for the help, and the diagrams. Yes I wanted a single high current 6 Volts output from two 300 VA 12 Volt toroidal transformers. Yes I will play about with the windings. I know I can get 12 Volts or 24 Volts from the secondary windings. I just thought I could derate the twin primary windings so the output drops to half the rated voltage. But I know lowering the primary voltage might sag the secondary voltage to much. I think I have to try it and see.

Benta:

--- Quote from: davelectronic on June 21, 2024, 09:49:26 pm ---But I know lowering the primary voltage might sag the secondary voltage to much. I think I have to try it and see.

--- End quote ---

Why would it "sag" the outputs? Not running the core at full magnetization actually makes it a better transformer, but larger and heavier than it needs to be.

davelectronic:
I thought the secondary voltage might sag under load at the primary. As i would only be putting half the rated voltage into each primary side of the transformers. They would be wired in parallel, for the two primary windings, them put the single inputs primary in series with each other. So a parallel series input, and a series secondary output. As each transformer would be receiving 120 Volts AC.

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