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Re: [Amps] capacitor across mains input to transformer

Subject: Re: [Amps] capacitor across mains input to transformer
From: Manfred Mornhinweg <>
Date: Wed, 11 Oct 2017 00:12:36 +0000
List-post: <>

Can someone direct me to reading material on this?

Plug alert: My web site, of course... The articles on "transformers and coils", and "practical transformer winding":

 I've wound a HT transformer and it's got a decent hum to it

That hum typically comes from vibrating parts, specially the laminations, and particularly the section of the laminations that's inside the bobbin and thus somewhat hard to compress properly. Try compressing the pack a bit harder, and use wedges to compress the part inside the bobbin. If that doesn't kill the hum, you have to impregnate the transformer. Get some transformer varnish, loosen up the core, soak both the core and the winding assembly with as much varnish as you can get in, then tighten the bolts of the core, insert wedges if possible to compress the center leg, and let dry. Ideally heat it up to speed drying. You can use DC through the high voltage winding to heat it up. Roughly the nominal secondary current, or even a little more.

> and draws about 1A @230V input with no load.

That doesn't sound bad at all. That current is strongly phase-shifted relative to the voltage. So the actual power consumed while idling (core loss) is likely to be far lower than 230W. If it's a transformer for a legal-limit amp, then this amount of idling current looks plenty low enough.

Do you have a true power meter? If so, you can measure how much of the 230VA is real power, and there you have the core loss - because essentially all the real power taken up by a transformer when idling is core loss.


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