Re: [TCML] TAR

[Phillip Slawinski <pslawinski@xxxxxxxxx>]

Ed,

I guess you haven't worked with tar before.  I have, and from my experience
I can tell you that it is a royal pain.  You have to get tar extremely hot
to make it fluid (500F) if I remember correctly.  When you get the tar hot
enough to pour it gives off vapors which smell awful, and are probably not
very good for you either.  Something else to consider is that since the tar
is black, and you will not be able to see if the coils are sparking.  So you
may think that the coils are better insulated until they let their smoke
out.  That being said, I'm no expert in this matter.  If it were up to me, I
would do everything I could to avoid using tar.

-Phillip Slawinski

On Sun, Jan 18, 2009 at 10:01, Ed Phillips <evp@xxxxxxxxxxx> wrote:

> Hi Ed,
>
> What was your technique when you tried the Paraffin? I have used Paraffin
> on 10 kV strobe trigger coils.  I submerged the coils in the hot Paraffin
> for a long time.
> At first there was a steady stream of bubbles, but eventually they stopped.
>  But I left the coils in much longer after that,
> like 1/2 hour.  The Paraffin is really thin at high temp and it wicked into
> the multilayer coil really well.  It is important that the entire coil get
> up to temperature so that the Paraffin does not solidify and trap air
> anywhere.
> These coils I had originally came from the manufacturer with Paraffin
>  insulation, but it looked like they had only been dipped while the coil was
> cold so there was only a outer coating of  Paraffin.  There was sparking
> under the Paraffin on the first one I tried.  After the thorough soaking
> there was no problems.  If they ever got too hot though, it would be a
> problem as the Paraffin would run out.
>
> Jeff"
>
>   I did something different and probably not as good but it was easier.  I
> wasn't trying to impregnate the coils but just to insulate them to increase
> the external breakdown voltage.  I put the coil assembly in the oven and
> heated it up to about 220° F.  At the same time I melted the paraffin in a
> can and got it about as hot I thought I dared.  Then put the hot coil
> assembly in the mold and poured the paraffin over it.  Clearly the coils
> were above the melting point of the paraffin.  I filled the mold with the
> hot was and in the beginning it was pretty well bubble free but as it cooled
> and the stuff shrunk on top it began to turn milky white and then eventually
> there were some pretty big bubbles.  I can't see the coils of course and
> don't know what the paraffin looks like around them but when I run the coil
> with sparks of 4" or more [that's from two coils in series] I see light
> through the paraffin from the sparking so it's pretty obvious there are
> voids or more probably big bubbles at the surface of the coils.  I have
> considered putting the whole assembly back in the oven and letting it sit
> for a few hours but haven't done that since the coil assembly immersed in
> oil works just fine and the "potting" was just an experiment.  I do want to
> repeat it with the "tar" if I can get some.
>
>   Since the GMHEI coils are potted to begin with the sparking has to be
> from the HV terminal of the coil to the core so no permanent damage occurs.
>
> Thanks for the note,
>
>
> Ed
>
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