> I am planning to rewind 3 transformers and am looking for some
> information regarding core plate insulation. The goal here isn't to
> save $- I know I could pay to have them rewound, but rather to learn
> something by trying it myself.
Bravo Dave...way to go on that!
> I understand shellac was used for the insulation of individual
> plates in the past- is this still done? Information about this is
> hard to come by- I have been searching for months.
I would imagine so...don't know for sure, but either shellac
or varnish would be acceptable. The idea is to keep the
laminations separated to avoid eddy current losses.
I've rolled my own xfmrs before and use the shellac
because it dries quicker and is good insulation. Be sure to
use fresh shellac. Old stock may take a long time
to dry.
There was at least one article in QST, perhaps back in the 70's
that went into detail about winding xfmrs....maybe you found
it.
> If shellac is
> the way to go, what grade? I assume dewaxed (super-blonde) is best,
> but I am guessing. Can I get by with "blonde" (at 4.5% average wax
> content)? I cannot locate any information on the "cut" of shellac
> either.
Sounds like one is more purified than the other. Shellac is just
alcohol and the bodies of insects...Sourced in Asia I believe.
Try Wikipedia for "shellac"....I'll bet they have all kinds of info
on the stuff.
> It was suggested to me to just use AC-43 spray on each plate
> but, given the plates are all "used", I have to wonder if that will
> be create too much build-up between plates & hence a larger core en
> toto.
I think the idea is to just keep the plates close together without
them touching. One could clean the laminations off with a solvent
or maybe even tumble them for hours in an abrasive like
walnut shells, then apply a new coating. I'm pretty sure that
the laminations should be put together while they are still
wet. Letting it dry then will fuse the whole stack into a
solid unit free from "hum" caused by loose laminations.
> Another source suggested that, after stacking dry, the stack
> be "shifted" to allow wicking of varnish between plates. Without a
> coat of shellac as "insurance" that seems risky.
Wicking doesn't sounds like a good way to do it.
Have fun putting those I's and E's together! :)
73,
Charlie, N0TT
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