[Boatanchors] 120 vac Variac

[John Lawson]

  Many variacs (and powerstats, and 'x'-stats) have multiple tapped 
windings. So instead of just common - wiper - end, they have taps, at 
say, 15% of input volts, 100% of input volts, and 130% of input volts.

  If you use the 'bottom' of the coil for "common", and apply your mains 
voltage to the 100% tap, and you have a 130% winding extension, then with 
the wiper as 'output' you will be able to dial up more than the input 
voltage - the wiper goes 'past' the 100% point and now the variac is 
acting as a step-up autotransformer.


   Depends on the hook-up of your particular unit - sometimes its actually 
diagrammed on the faceplate, other times you will need to see the docs - 
but if your variac has more than three terminals then it's pretty certain 
you can go above your input volts.



Cheers

John KB6SCO




On Fri, 10 Jun 2011, John King wrote:

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> Checking my Variac as referenced above, I notice that my line voltage tonight
> is
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> about 118 volts at the wall plug. My Variac  reads from 1 to 130 AC on the knob
> but only from 0 goes to 118 Vac.