Subject: Re: Neon Xfmr: electrical model?

From: [email-masked] (Charles R. Sullivan)
Date: 27 Jul 1995 01:17:07 GMT

[email-masked] (Wesley Brzozowski) writes:

>In trying to use a neon sign transformer for purposes other than its intended

Don't hurt yourself!

>one, I'm trying to understand how it performs the way it does. The internal
>magnetic shunt is there to perform a current limiting function, of course. But
>does the shunt provide an effective series inductance to limit the secondary
>current? Is the effect of the shunt more complex than this? Any enlightenment
>would be appreciated.

Exactly.  If you operate somewhere other than the intended voltage,
frequency, current, you might have parasitic capacitances, and magnetic
saturation to worry about, but those are not essential parts of the
intended function.

Charlie Sullivan

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From: [email-masked] (Wesley Brzozowski)
Date: 27 Jul 1995 17:37:18 GMT

In article <[email-masked]>, [email-masked] (Charles R. Sullivan) writes:
|> [email-masked] (Wesley Brzozowski) writes:
|> 
|> >In trying to use a neon sign transformer for purposes other than its intended
|> 
|> Don't hurt yourself!

<sigh> Thanks for the vote of confidence :-). Actually, I've been an electrical
engineer for more than 20 years, and have enough high voltage work under my 
belt to have some chance of survival on this. The use of a neon sign 
transformer is common in certain homebrew electrical projects which tend to
get constructed by rule-of-thumb, rather than any real design. The engineer in
me says that there's gotta be a better way and I'm trying to find it. 

|> >one, I'm trying to understand how it performs the way it does. The internal
|> >magnetic shunt is there to perform a current limiting function, of course. But
|> >does the shunt provide an effective series inductance to limit the secondary
|> >current? Is the effect of the shunt more complex than this? Any enlightenment
|> >would be appreciated.
|> 
|> Exactly.  If you operate somewhere other than the intended voltage,

A comedian, eh? Well, I wouldn't quit that day job just yet! :-).

|> frequency, current, you might have parasitic capacitances, and magnetic
|> saturation to worry about, but those are not essential parts of the
|> intended function.

Aw, c'mon Charlie; I'm looking for some information here. With all due respect,
you're just stating that information exists. I'm sure that there are some
decent numbers available on neon sign transformers, but they're hiding awfully
well from me. Even a couple of excellent technical libraries available to me 
have little more than vague information on the technical details of these
suckers. If you've got something concrete, I'd _really_ be interested 
in hearing what you've got to say. 

Parasitic capacitance will play a considerable part in my results, but I
didn't expect to find anything on that here, as folks using 'em for their
intended purpose are unlikely to need that information. I'm pretty sure I can
get some ballpark measurements on that, but if you have some numbers, I'd be
immensely grateful.

As far as saturation goes, the end use will have a 60 Hz transformer being 
driven at its usual 60 Hz. If there's any way to saturate one considering their 
internal current limiting, (say, with a capacitive load, just to toss out an 
idea) I'd once again be very glad to hear about it.

But my original question, which I guess I can ask again, involves the internal
magnetic shunt. While I've not had the best time finding a basic  analysis of 
a transformer with such a core, one fields text did start with a
transformer/magnetic circuit with a shunt. It then used one of those
"and-then-a-miracle-occurs" handwavings to end up with a model that 
involved the equivalent of series inductance. I'm interested in knowing wether
such a model is realistic for a neon sign transformer, even in its intended 
usage. (I'll deal with the more perverse usages of such a device later on).

I intend to take a lot of data on such a transformer in-situ, and will
be building and refining my own model of the beast, but right now, a little 
preliminary information on the things would be very helpful. I'm doing this 
at my own cost and on my own time, and any hints that would make the journey
a bit easier and less costly to traverse would be immensely appreciated.

Does anyone out there see these things as more than just a black box? (Yeah,
yeah, I've seen blue ones, too. :-)

Wes B.

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*  Wes Brzozowski      *        Nothing is a waste that makes a memory        *
*  [email-masked]   *                                - Ned Rorem           *
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