Re: Home Made Variac

• To: tesla-at-pupman-dot-com
• Subject: Re: Home Made Variac
• From: wwl-at-netcomuk.co.uk (Mike Harrison) (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
• Date: Sat, 05 Feb 2000 08:25:30 -0700
• Approved: twftesla-at-uswest-dot-net
• Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

On Fri, 04 Feb 2000 06:35:06 -0700, you wrote:

>Original Poster: "J. B. Weazle McCreath" <weazle-at-hurontel.on.ca> 
>
>At 04:22 PM 03/02/00 -0700, you wrote:
>>Original Poster: "Michael Novak" <Acmnovak-at-execpc-dot-com> 
>>
>> 
>>     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
>
>Hello Michael:
>
>I think you'd have a pretty hard time home brewing a variac if for no
>other reason that finding the circular core material.  However, there
>is another approach you might take.  You could wind a conventional
>auto-transformer with many taps to provide you with a stepped range
>of outputs as opposed to the smooth afforded by a variac.

You could  have coarse and fine taps, so you could get fine adjustment
without too many taps. - corase taps at one end of the winding, and ,
say, five 2-volt taps at the other. 
Remember to use break-before-make switches if you want, say, rotary
switches to select the tap, otherwise the momentary shorts when
switching will kill the switch. Even then, inductive arcing could
possibly be a problem on the switch.

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