Re: Potting Diode Strings - yes!

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

Original poster: "Kevin Ottalini by way of Terry Fritz <twftesla-at-qwest-dot-net>" <ottalini-at-mindspring-dot-com>

All:
    It is very important to pot the diodes in something not because each
diode only sees 1kv but because the far end diodes see 15kv or more.

The corona and leakage to the air alone can eventually cause arcing
and failure (I've done it, I've seen it, it happens .. the cascade arc was
wonderful to behold).

The AC end sees 0 to 7.5kv too on a 15kv nst and that means the first
diode off the AC side really sees ~1kvdc to ~7.5kvac potentials ... any
leakage there and that diode or the next is history
(contamination = leakage from dust, finger oils, coke, cat hair, that
meter lead, your finger, etc etc).

Not to speak of how to keep the whole chain isolated from everything
around it as well.  Putting the whole string in a pvc tube is a good idea
(Brian Basura did this).  Building each leg separately is a very very
good idea.

Potting is a very good idea and wax isn't great but much better than
nothing at all.  I've used jewelry wax, which is a dry hard smooth wax
(available in several hardnesses ... it even smells good).

I successfully did some small HV parts in normal as well as vacuum
encapsulating with this wax too up to 24kv in one case and 90kv in
another (but I have a vacuum oven!).

I did not do an exhaustive study of how the wax compares to the
normal HV epoxy that I typically use.  However ... the epoxy costs
$15 / 200ml, and the wax is $4.50 / lb or less.

If there is interest in this wax, let me know and I'll do some real
leakage testing and post the results back to the list.

Kevin

----- Original Message -----
Sent: Tuesday, March 19, 2002 7:01 AM
Subject: Re: Potting Diode Strings

> Original poster: "Jeff Kamla <jeffk-at-sinclair-dot-net>
>
> Hi  All
>
>   so if you pot your strings with anything you are going to have fun
getting
> them apart if one diode blows and you have to replace it, as Gary said you
> are going to develope less than 1kv across each diode so whats the big
> deal.....
>
>                                                           jeff......
> ----- Original Message -----
> Sent: Monday, March 18, 2002 6:17 AM
> Subject: Potting Diode Strings
>
> > Original poster: "Matthew Smith" <matt-at-kbc-dot-net.au>
> >
> > Hi All
> > Can anyone comment on using PARRAFIN WAX for potting diode strings? I
> > don't know what it's electrical properties are like, but it is certainly
> > easy to pour when molten...
> >
> > Cheers
> >
> > Matthew Smith