[Amps] Magnetic shielding 2
Borislav Trifonov
bdt at shaw.ca
Sun Jun 19 21:49:54 EDT 2005
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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