Re: Arc Welders as Rheostats?? Variac Mod Question

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

Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>" <davep-at-quik-dot-com>

Tesla list wrote:
 
> Original poster: "Jack King by way of Terry Fritz
><twftesla-at-qwest-dot-net>" <speakernut-at-yahoo-dot-com>
 
> Anyone out there have data on how "wide" the air gap needs to be?

	Near as thin as you like.

>My gut says something like .75-1"

	MASSIVE overkill.
	I Took a course in mag design, once, decades ago.
	'any' air gap is as effective as a huge one.
	(roughly speaking.  There is math, could be found in
	any engineering handbook.  But the above captures the
	useful bits...)
   
> should be sufficient to interrupt the flux travel...any
> thoughts?

	Thoughts don't count.  8)>>
	This is physics.  Known physics.  8)>>

> I'm toying with "modifying" a 7.8 kva unit for use as a series reactive
> ballast, and would like additional insight before i dig out the band
> saw.

	Cut a thin slot.  Easier to widen it if more is needed.
	(it won't be....)

> Also, does one need to replace the removed section with epoxy or something
> along those lines to maintain structural integrity?

	I'd think not.  Could do, but I wouldn't.

	(If someone asks, I'll try to dig out the maths.  But.
	'trust me', an arbitrarily narrow slot is fine...)

	best
	dwp