[Amps] Magnetic shielding 2

[Will Matney]

Borislav,

19 kilogauss is too high for M-6 or Hipersil material for about 28 or 29 gauge. It's max is about 17 kg., and it's recommended to be ran at 15 kg. because after 15 kg., the magnetizing current raises sharply and doesn't gain that much for it. After about 18-19 kg, it goes into saturation where the permeability drops off sharply, you get a distorted waveform, and it starts to act like a short. Then it will finally burn out. Also, did you see the correction for the formula from using 4.44 and use 1.11? I messed up there when I was in a hurry and didn't proof read it. If your using the 1.11, it's correct.

I'm afraid there's no other fix but to rewind it to make it work correctly. Even potting it will still leave it saturating, plus running hot. Eventually under load, it will finally burn out. If this will be ran ICAS as most amateur amps really are, you can get by with using about 700 to 800 circular mils per ampere for sizing the wire. If you want CCS, then it needs to be ran over 1000. The problem with 1000 is you may not be able to fit all the wire on the core. If you have the availability of extra wire, I'd cut the whole coil off and start from scratch making a new bobbin too. For layer insulation use 7-10 mil paper, and between the different windings use 15-20 mil. Use about 40 mil for the bobbin. There's several places on ebay carrying fish and kraft paper pretty cheap. That's the only solution and the correct cure I know. Maybe others on here may know of something else to do with it.

Best,

Will


> 
> 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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