Re: Ballasting question

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

Original poster: "Gregory Hunter by way of Terry Fritz <twftesla-at-qwest-dot-net>" <ghunter31014-at-yahoo-dot-com>

Hi Mike,

I'm kind of weak on theory but I'll take a swing at
the practice of it.

In the context of Tesla coil usage, ballast is
resistance or reactance (or both) used to limit AC
current from the wall outlet. Certain types of high
voltage transformers will draw virtually unlimited
current in a short circuit condition, causing the
breaker to trip instantly the first time the spark gap
fires.  Examples of this type of transformer include
the pole transformer, the vacuum tube plate
transformer, and the potential transformer. All of
these transformers require external current limiting.

Examples of practical inductive ballasts include AC
arc welders, large variacs (either "gapped" or
"stock"), and commercial or home built slide chokes. A
few coilers are using saturable reactors, but these
are pretty rare. Count yourself fortunate if you can
find a surplus one for less than an arm and a leg.

Examples of resistive ballast include large power
resistors, electric stove elements, hot water heater
elements, space heaters, etc.  Resistive ballast is
pretty inefficient, and tends to drop the output
voltage as well.  It's better than nothing, but not
much.

Ballast is not required when using shunted
transformers, such as OBITs or NSTs. Microwave oven
transformers are shunted, but still draw so much
current that many hobbyists use ballast with them
anyway.  I've used MOTs without ballast, but I had to
abandon 120v operation in favor of heavy duty 240v
outlets.

Are you OK on all the "alphabet soup" acronyms?  If
not, see my glossary at: http://hot-streamer-dot-com/greg

Hope this helps,

Greg


--- Tesla list <tesla-at-pupman-dot-com> wrote:
> Original poster: "Michael O. Poley by way of Terry
> Fritz <twftesla-at-qwest-dot-net>" <mpoley-at-mindspring-dot-com>
> 
> Okay, since I got such a fast response on the other
> question, let me ask 
> this...
> 
> Can someone explain the theory and practice of
> "ballasting"?  I'm familiar 
> enough with the physics behind the Tesla coil, but
> the term has been 
> bandied about a lot and I haven't seen anything
> explaining what exactly 
> ballasting is nor when it should be done, and when
> it is acceptable to 
> overlook it.
> 
> Mike
> 
> Michael O. Poley
> mpoley-at-mindspring-dot-com
> 
> 
> 


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