RE: NST secondary (OBIT secondary?)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "McQuay, Michael by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Michael.McQuay-at-wcg-dot-com>


>>I'd like to resurrect that OBIT especially since it belonged to a friend
:-)


Years ago, a friend and I were playing with my 15kv/30ma NST (with no
protection of course) when one of the HV terminals of the transformer became
severely impaired in how much spark it would make.  I figured we had burned
up that side or had an internal arc so I depotted the thing.

I put the transformer in an oven at about 200 degrees F for about an hour.
This was enough heat to make the tar soft, but not melt it.  It also made
the tar "sweat" an oily substance.  I then used a screwdriver to dig out the
potting tar from about the transformer core and was able to remove the core
from the case this way.

The advantage to doing it this way as opposed to actually melting the tar
was that it was a lot less messy and thanks to the "sweating" effect, the
tar fairly cleanly separated from the transformer in big chunks rather than
melting to it and coating it.  I then used kerosene and a toothbrush to
clean the residual tar from the core and windings. I also cleaned the tar
from the metal case, then sealed the low voltage and High voltage feed
throughs into/out-of the case with blue RTV.  I put the transformer back
into the case, hooked everything up, and filled the case with kerosene.  (I
know, I know.  Flammable liquids, High voltage, bad idea, but it's cheap and
seems to work well.)  I've ran it than way (under kerosene) for a long time
with no problems and it restored the functionality of my transformer.

When I was digging the tar out, I found the carbonized place where the
secondary winding was shorting to the case.  However, during digging I
accidentally jabbed the screwdriver into one of the secondary windings,
damaging some of the wires.  That's the disadvantage to the screwdriver/dig
method.  You have to be careful not to damage windings.

I hooked up the transformer while it was depotted and could see small arcing
within the winding where I had jabbed the screwdriver, but after putting it
back in the case and submerging in kerosene, the transformer appeared to
work normally and still does.




-----Original Message-----

From: Tesla list

To: tesla-at-pupman-dot-com

Sent: 2/15/2002 4:21 PM

Subject: Re: NST secondary (OBIT secondary?)



Original poster: "Chris by way of Terry Fritz <twftesla-at-qwest-dot-net>"

<chris-at-atomic-pc-dot-com>



Hi all,



I'm looking at a lifeless 10/23 OBIT that I burned up just as the coil

was 

sending the wildest-looking, seething and dancing purple streamers off

into 

the air from the brass andiron sphere I had set atop it as a secondary 

terminal... it was... it was ALIVE!!!  then it was, uh... quite dead...

and 

the OBIT just made a soft buzzing sound...



So (total clueless newbie question here:)  will depotting and immersing

in 

oil be good also for an OBIT?  I didn't notice a center tap point on the



OBIT, but maybe I just don't know what to look for.  I'd like to

resurrect 

that OBIT especially since it belonged to a friend :-)



What kind of oil do you use / where do you buy your oil?  I'm interested

in 

hearing different responses of what people are trying these 

days.  (Household-available, etc.?)



Canola (rapeseed) oil:  I don't know much about the dielectric

properties 

of it, but I know the particular   fatty acids in this make it much less



suitable for human consumption than for industrial use... so now I have 

like 2 gallons of the stuff sitting around which I've decided not to use



for cooking, ever...  wait, I'm just thinking aloud here- is transformer



oil just a pure hydrocarbon oil, or is it a "fatty" oil?  Probably

devoid 

of -O-OH groups which I'd imagine would make the stuff break down at HV 

(just a guess, never tried it).  But then, I just found Fuji Electric

and 

Kansai Electric Power are using a rapeseed-based transformer oil...

http://www.japancorp-dot-net/Article.Asp?Art_ID=1758



Thanks,

Chris





>Running a depotted NST under oil is a good procedure. There

> > is the advantage of increased insulation and heat sinking. When a

NST 

> is put

> > into tesla service, it can output much more power than its normal

rating.

> > The extra heat sinking will be appreciated.

> >

> > Godfrey Loudner

> >

> >