Re: Arc Welders as Rheostats??

["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: "Barton B. Anderson by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <tesla123-at-pacbell-dot-net>
> 
> Bill -
> 
> The variac is the ballast. Think of ballast as a current limiter. It can be
> resistive,
> inductive, or capacitive. Inductive current liminting is the norm where
> typically variacs
> or welders are used as they can be hooked up without modification.
> Alternating current
> flowing in an inductor causes inductive reactance which is an opposition to
> current flow.
> As the wiper is moved, the number of windings between legs changes,
varying the
> inductance, varying the inductive reactance, limiting available current the
> load will
> attempt to draw.
> 
> Take care,
> Bart

	Not that simple by any means.  When the voltage across the portion of
the winding being used exceeds the voltage in normal "variac" operation
the core will saturate, and moving the brush only affects at what point
in the cycle saturation will occur.  Of course, if the variac core is
gapped appropriately, this won't happen but it's real tough to cut those
wraps of thin core steel.

Ed