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Re: [Amps] Magnetic shielding 2

Subject: Re: [Amps] Magnetic shielding 2
From: Borislav Trifonov <>
Date: Sun, 19 Jun 2005 18:49:54 -0700
List-post: <>
Thanks for the replies.

The steel looks like grain oriented silicon steel, which I thought would be around 15; with the formula Will provided, I'm calculating about 19... I checked the secondary waveform on my scope through a voltage divider and I have attached a sketch of the trace (no load except the divider, which was several MOhm). Pretty bad. I only added 15 extra turns to the primary, when I should have added 45. Worse, to fit more turns I'd have to rewind the primary with a smaller gauge (and that also is going to need 700 turns more on the secondary to recover lost voltage). Given that I used nail polish to put the laminations back together (got no shellac or epoxy), I'll have to soak the whole thing in solvent to take apart again.

It is definitely the leakage due to saturation that's causing the case hum. The hum increases as I lower the transformer into the chassis regardless of physical contact. Even if I bring a scredriver near the core, I can feel the 60 Hz in my hand.

Now, besides the noise issue, how is performance affected? My application feeds the output into a bridge rectifier, then a large CLCRC filter. Will I be getting significant power reductions when driving this load? Will the leakage amount change when connected to such a load?

If performance doesn't suffer too much, perhaps I could just reinforce the chassis and pot the transformer. I'm thinking that potting would make the pot vibrate instead of the chassis, and then if I fill it with epoxy, that should physically reinforce the pot from vibrating. Does that sound like a good solution? I guess I could find a bigger transformer, but I've not found anything large with 2 kV secondaries that is not very expensive. Not to mention that I'll have to get a bigger case, and throw out the $60 I spent on this one, and hours of drilling...
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