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RE: NST insulations
My comments interspersed:
>Original Poster: "Christopher Boden" <chrisboden-at-hotmail-dot-com>
>
>Having never de- or Re potted an NST I have a few questions :).
>
>I have 3 15/60 Jeffersons (the baby-blue painted ones) filled with the
>standard Black Tar. They are all dead from Tesla Duty, most with one side
>toast.
>
>1. Is a hot-plate suitable for cooking them? Other ideas? The oven is NOT
an
>option :)
I also resurrected a blue Jefferson 15/60. I used a covered Weber charcoal
BBQ,
and placed the NST in a disposable aluminum roasting pan to catch the tar.
When most of the liquid tar had been poured out, you'll have to cut the
primary connections
to free the assembly from the case. The secondary connections were so tiny
that they just
broke without any help from me. Get a pair of disposable heavy work gloves
to handle the hot,
free core assembly, and have a waiting pail of paint thinner to drop it
into. Reattaching
connections to the severed secondary connections was like brain surgury,
even 30 gauge wires
were huge compared to the tiny secondary windings. I had to open up one of
the secondary
windings to find the free end.
>2. Can I do this without stinking up the house?
Do it outdoors, and be patient, waiting for everything to melt. Also beware
of the flamable vapors
generated by the hot core going into the paint thinner. Do this downwind
from the house and
away from the BBQ grill!
>3. How do I remove the shunts?
>4. How do I identify the shunts?
>5. How many can I remove without toasting the thing?
Jefferson NST cores are unique in an unfortunate way, they do not have
removable shunts.
You may be able to cut the laminations, but I made no attempt to do this.
>6. If Vasoline is used, how do I make sure to fill all the air spaces?
Melt the vasoline first in a pot. It will pour like water and you should
have no problems with trapped air.
Also beware that if Vasoline touches the burner, the vapors will be
flammable. Just make sure that
your secondary windings are as clean as possible (i.e. many paint thinner
baths).
And don't buy the cheap thinner, get the "odorless" type.
I assume you plan to re-use the original case as I did. You may need to
plug some of the 120V bushing
holes with putty while the vasoline gels. I thought that the outside of the
secondary windings were closer
to the NST case than I thought was good, so I added a couple layers of LDPE
between the windings and
the case to fortify the insulation, prior to the repotting.
>7. What are other good potting compounds? I would prefer something easy to
>work with, and not liquid.
>8 Is it better to keep it in it's original case, or would somehting like a
>5Gal bucket be better?
If you can reuse the case, it will be far more compact and look much better.
I'm glad I did.
It's just a bit (!) more work to clean out the case and figure out how to
remove and reinstall
the insulating bushings.
>9. Can wooden forms be used to place and center the core in a bucket? (I
>have seen this done with BIG transformers in oil)
I don't recall if I did anything, I think I just relied upon the solidified
Vasoline keeping things in place.
Nothing wrong with dry wood though, as long as it doesn't float in the
liquid Vasoline.
Gary Lau
Waltham, MA USA