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Re: Protecting a potential transformer
Ted-
In both cases when I blew up the 15/60 I had a dual safety gap from each HV
terminal of the transformer to Gnd, and a series choke on each HV leg going
to the spark gap. I think the chokes were about 4mH based on a crude
measurement w/ a signal generator and an oscilloscope.
The first time the xfmr failed, I think I had opened up the safety gap
rather wide. It seemed to be limiting my performance and I got a little
caught up in the quest for longer sparks... I also had a static gap which
was not quenching well which also lead to a wider main gap opening to try to
get better output.
Since I had purchased the 15/60 new when I could not find a used one, I was
able to return it to be replaced under warranty. By the time I got the
replacement a week later, I had gone to an air blast gap which worked much
better and allowed a main gap opening of closer to 1/4 inch rather than
around 1/2 inch. I also adjusted the safety gaps just wide enough not to
fire with only the transformer connected, and promised myself I would leave
them there. At some point I also eliminated the chokes, but it resulted in
much more frequent firing of the safety gap, so I put them back in. This
worked for some time but the xfmr eventually failed again and I don't think
the place I got it from is too likely to replace it under warranty again.
Anyway, based on my experience, I think the RC filter and MOVs sound like a
really good idea w/ NSTs.
Jay
----- Original Message -----
From: Tesla List <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Monday, May 15, 2000 10:35 AM
Subject: RE: Protecting a potential transformer
> Original Poster: "Ted Rosenberg" <Ted.Rosenberg-at-radioshack-dot-com>
>
>
> Jay:
> A bit of post mortem for us all...please.
> When expensive 15/60's go, I want to know what NOT to do.
> Did you use a safety gap? Did you use a Terry type MOV-R-C network (see
his JPG
> drawing
>
<http://users.better-dot-org/tfritz/NSTFilt.jpg>http://users.better-dot-org/tfritz/N
> STFilt.jpg
>
> The details could benefit us all. Thanks.
>
> Ted R
>
> -----Original Message-----
> From: Tesla List [<mailto:tesla-at-pupman-dot-com>mailto:tesla-at-pupman-dot-com]
> Sent: Sunday, May 14, 2000 1:27 PM
> To: tesla-at-pupman-dot-com
> Subject: Protecting a potential transformer
>
> Original Poster: "Jay Stone" <jaykstone-at-home-dot-com>
>
> Hello fellow coilers!!!
>
> Having recently blown up my second 15/60 neon on my 6" coil, I have
decided
> it's time for something different. I have recently acquired a transformer
> which I am told is rated at 20 KV, 2 KVA. I am trying to get more info
about
> this xfmr such as BIL rating etc which I don't currently have. I think it
is
> some sort of potential transformer. It has multiple taps on the 120VAC
side
> for +/-5% and 10%, and a large, round epoxy sealed winding. One side of
> the HV
> winding is tied to gnd and the other to a single terminal on the top.
Does
> anyone know what this is?
>
> Since one side of the HV winding is tied to gnd, I believe I will have to
use
> an Oudin coil configuration w/ one side of primary tank coil at gnd. I
plan
> to use an unmodified 20A variac in series with the 120VAC side of the
> transformer for ballast at least to start with. I know it will probably
> saturate and tend to overheat but I hope this will be ok for short runs.
Will
> this work?
>
> The other question I have is about protecting the HV side of the
transformer.
> Should I use a safety gap and a choke or some sort of RC filter like one
might
> use on a NST? Any recommendations would be greatly appreciated.
>
> Thanks ,
>
> Jay
>
>
>
>