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Old 23rd June 2009, 03:18 AM   #1
roadie is offline roadie  United States
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Default Transformer wiring

I'm going to build an ESP p3a. How do I wire the xformer in the power supply? I have 115V in (USA) and need the 25-0-25 out, 300VA.

Toroidal xformers I've seen in catalogs have provision for both series and parallel primary and secondary.

Should I wire both the primary and secondary as series? Please explain, if you would.

And which are recommended models?

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Old 23rd June 2009, 12:22 PM   #2
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Transformers with dual primaries usually have two 110 or 115 V windings. Connect them in parallel for use in the US.

Concerning the secondaries there are two types of transformers. A single center-tapped winding that would be designated 50V CT or 25-0-25 V, which does not give you any choices, because it has only one winding.
The other type has dual secondaries, designated 2x25 V. In that case you have two choices. The preferable is two use a rectifier per winding and connect the rectifier outputs together, + of one with - of the other and ground, while the secondaries have no direct connection to each other. The alternative is to connect the windings in series and treat the common connection like the center tap on a center-tapped transformer.
If you've always done it like that, then it's probably wrong. (Henry Ford)
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Old 23rd June 2009, 03:33 PM   #3
taj is offline taj  Canada
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And to further clarify, the toroids you find in catalogs that mention parallel and series on the secondaries, will be the 2x25V type (aka 25+25V). They are quite common.

If that's the kind you get (as opposed to the 50VCT center tapped type which are also common) then just wire the secondaries in series and use the connected (center) one as the 0V center tap. The outside 2 wires go the AC connections on the bridge rectifier.

There are plenty of diagrams in these forums. Try to search.

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