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Re: Home Made Variac



On Thu, 03 Feb 2000 16:22:33 -0700 Tesla List <tesla-at-pupman-dot-com> writes:
>Original Poster: "Michael Novak" <Acmnovak-at-execpc-dot-com> 
>
> Michael

  How about a switchable  type variac (auto transformer) instead of a
continuously variable device?  It's simpler to design a switch vs. a
wiper/brush assembly.  

  Transformer silicone steel is not that important (to a point) for a
device that will be operated intermittently for short periods.   Eddy
currents & hysteresis will exist, but not a problem unless you are
designing a transformer with a high duty cycle.  Don't just wind wire
over a piece of pipe though, this would be inefficient to the max.

 I have used galvanized antennae guy wire rolled into a toroid, wound
over it with # wire, tapped at 29 positions & switched with a homemade
switch that runs over 10 kW for more than 4 years.  Its maximum
inductance is 8 mH, and can be used for varying voltage, or as a variable
inductor for current limiting.

 Another design used steel strapping in a toroid core wound with romex
house wiring paralleling all 3 conductors, and tapping at different
points.  These items are shown on my web page at
www.flash-dot-net/~kreld/kevin's.htm.  They work & work well.  Overheating
has never been a problem with them.

Hope this helps

Kevin E.


>     I can't afford to buy a variac but I need some way to vary the 
>line
>voltage... So, I decided to build one. I'm pretty sure I can get my 
>hands on
>some 10 guage magnet wire, however, I still need to find a suitable 
>core. Isn't
>a variac basically a bifliar-wound 1:1 turns ratio transformer? If so, 
>does
>anyone have some sort of formulas on the subject?  What would be the
>disadvantages of having a core which is not laminated such as the kind 
>found in
>transformers?
>Any thoughts?
>                                                            -Michael
>
>

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