Re: Disassembling transformers

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Bob (R.A.) Jones" <a1accounting@xxxxxxxxxxxxx>

Hi all,

I tried depotting a small 6kV/30mA NST about 6 weeks ago.

I put it on a small single electric hot plate on the lowest setting.
After about 0.5 hr the top was not perceptible warmer.
So I covered the NST with aluminum foil down to the hot plate.
I left it for at least a further 2hr.

It was now significantly hot (too hot to touch for more than about 0.5s).
The potting material that looks and smells like bitumen had bubbled up at
one side of the case.
Though the bitumen was soft  it was not runny so it was impossible to pour
it out.
I don't know if  higher temperature would have allowed me to pour it out.
But I don't think so as even the bitumen at the bottom which presumably was
the hottest still had the consistence of say speckling.  It looked like it
was poured in originally but perhaps with age (it may be 20 years old) it
has set to some extent.

I was forced to allow the transformer with the majority of the potting
material to fall out of the case which ripped out the high voltage leads
from the secondaries.
I was able to remove the majority of the potting with a screw driver as it
was soft.

Its now been in white spirits for six weeks. The remaining bitumen has not
dissolved but it can be brushed away from most areas. It looks like it will
be impossible to remove it all. So if I put it in oil the oil will go dark
with time due to the contamination by the remaining bitumen.
The next step is to wash it with clean white spirits. Then let it dry so I
can attempt repair of the primary coil  and HV leads.

Incidentally the reason I even attempted this was because NST was dead o/c
input.
Apparently the primary had arced across and down two or three  of the outer
layers as evidenced by the blobs of copper at the end of the broken wires.
It probably not recoverable and approximately 20% of the primary will have
to be removed to get down to undamaged turns.
My question is can I use polyurethane vanish to glue new output leads down.
and to stabilize the sides of the coils where the coil former cheeks have
broken off.
I have adhesive glass fiber tape but a suspect the adhesive will be softened
by oil.
i.e. what can I use to stabilize the paper insulation of the windings.
Silicon rubber is the only thing I am certain will not soften in oil.



Robert (R. A.) Jones
A1 Accounting, Inc., Fl
407 649 6400
----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Friday, February 10, 2006 2:14 PM
Subject: RE: Disassembling transformers


> Original poster: "Lau, Gary" <Gary.Lau@xxxxxx>
>
> Since it's current-limited, running an NST with the secondary shorted
> won't draw any more power than its faceplate rating.  So I don't know
> how that could result in melting of the tar.
>
> I used an enclosed Weber BBQ grill to cook my NST and melt the whole
> stinkin' mess - a process I hope I never have to repeat!  I used paint
> thinner for the final dissolve.  If someone had poured that mess onto my
> driveway, they would definitely be off my Christmas card list.
>
> Regards, Gary Lau
> MA, USA
>
>
>  > Original poster: "Dave Halliday" <dh@xxxxxxxxxxxxxx>
>  >
>  > Richard Quick suggested freezing but then running the transformer with
> a
>  > short across the HV output for an hour or two.  This will warm the
> core
>  > enough so that the chunks of frozen tar can be pulled away without
>  > damaging the windings.
>  >
>  > He used kerosene (a lot less dangerous) and mentioned that the
>  > tar-kerosene mixture was an excellent sealer for asphalt driveways if
>  > you have one.
>  >
>  > Dave
>  >
>  >  > -----Original Message-----
>  >  > From: Tesla list [mailto:tesla@xxxxxxxxxx]
>  >  > Sent: Thursday, February 09, 2006 9:13 PM
>  >  > To: tesla@xxxxxxxxxx
>  >  > Subject: RE: Disassembling transformers
>  >  >
>  >  >
>  >  > Original poster: "Robert Hanford" <pomnept@xxxxxxxxxxx>
>  >  >
>  >  > Hi,
>  >  > I froze my NST, chipped away some or the tar, then soaked it
>  >  > in gasoline til
>  >  > almost all the tar was gone. Don't remove all of the shunts.
>  >  > There is good
>  >  > internet material on this. I think a lot of us have stories about
> this
>  >  > particular aspect of coiling.
>  >  > Good luck,
>  >  > Robert Hanford
>  >  >
>  >  > -----Original Message-----
>  >  > From: Tesla list [mailto:tesla@xxxxxxxxxx]
>  >  > Sent: Thursday, February 09, 2006 10:38 PM
>  >  > To: tesla@xxxxxxxxxx
>  >  > Subject: Disassembling transformers
>  >  >
>  >  > Original poster: norman@xxxxxxxxxxxxxxxxxxxxxxxxx
>  >  >
>  >  > Has anyone tried to open up an OBIT or NST and dissolve the
>  >  > potting material
>  >  > in
>  >  > order to remove the magnetic shunts?  If so, could you explain how.
>  >  >
>  >  >
>  >  >
>  >  >
>  >
>
>
>