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Re: Rotary Arc Gaps



In a message dated 99-02-18 01:59:13 EST, you write:

<< Original Poster: "Harvey Norris" <tesla4-at-excite-dot-com> 
 
> I have several questions regarding rotary arc gaps. Is not its purpose to be
> able to allow for the short on the arc gap contained in the tank LC primary
> to be timed so that this occurs precisely when the AC voltage input is near
> zero, thus negating the problem of the arc representing a short to the power
> supply? If such is the case this would be 120 shorts per second based on 60
> hz. Why do some designs than use 720 bps which I assume must mean 720
>bursts

Harvey,

The purpose you mention is one possible purpose of using a rotary,
but often it is used simply as a timing device.  When the gap fires,
in general, it's not really too much of a short to the power supply,
because of the reactance of the ballast which limits the current.
By using a high break-rate, you're able to process more power than
at a lower break-rate with a given sized tank capacitor.  Often the
ballast is adjusted to be resonant at the power mains frequency,
which means the current limiting will be in effect *only* when the
gaps fire.  The current limiting will be "canceled" during cap
charging (which is when you need a lot of current).  Often some
resistive ballasting is used to prevent excess transformer saturation.

> or shorts per second? Also can I expect to pay around $500 just for a
> synchonius motor to make a Rot. arc gap? I assume this must be purchased.
> Are dc motors also used with many poles or shorts per revolution to
> circumvent this cost? Thanx for any info.

You can find a sync motor at a hamfest, or surplus store,etc, for 
maybe $5 to $30.  Or you can modify an induction motor to make
it synchronous.  Induction motors are a dime a dozen and often free.
I've posted the method for modifying these motors on this list in the
past a number of times, it's in the archives.

John Freau

> HDN
  >>