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>
How about a switchable type variac (auto transformer) instead of a
continuously variable device? It's simpler to design a switch vs. a
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
> I can't afford to buy a variac but I need some way to vary the
>voltage... So, I decided to build one. I'm pretty sure I can get my
>some 10 guage magnet wire, however, I still need to find a suitable
>a variac basically a bifliar-wound 1:1 turns ratio transformer? If so,
>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
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