Re: Arc Welders as Rheostats?? Variac Mod Question

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

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

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? My gut says something like .75-1" should
> be sufficient to interrupt the flux travel...any
> thoughts? 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.
> Also, does one need to replace the removed section
> with epoxy or something along those lines to maintain
> structural integrity? Lastly, might anyone know off
> hand if cores on these older, larger dogs are silicon
> steel strip or scintered iron encapsulated in epoxy?
> 
> Cheers,
> 
> Jack King

	That sounds like way too much gap, but I'm not an expert on calculating
magnetic circuits.  Someone else here probably is and can give you an
answer.  I would suspect the actual value should be of the order of
0.050", depending on the core area and the number of turns.

	Don't think any 60 Hz transformers use anything but silicon steel for
the cores, with the exception of very recent ones which use some of the
"matallic glasses" for ultra-low loss cores.

Ed