[R-390] Question about VARIAC

[rbethman]

Sheldon & Barry,

*IF* that was what Barry had in mind, then I would agree that it is a 
REAL concern.  I CERTAINLY would NOT wire one up THAT way!

My view was based on the thought that the INPUT would be connected to 
the intended locations.  If you then turn the wiper to one or two turns, 
the you just get whatever voltage you see.  The current is limited by 
wire size and load applied.

I was primarily addressing the issue of "impedance".  At 60 cycles, 
impedance doesn't "usually" get into the act unless a short-circuit 
situation is calculated and/or actually occurs.  That is why circuit 
breakers are tested and built to do what they do.

Just my $0.02 worth!

Bob - N0DGN

sdaitch at kuw.ibb.gov wrote:
> Bob and Barry,
>
> Looking at Barry's concern again, 
>
> "If I were to tap the input at one turn 
> (or two or three), then I assume this 
> would appear as a very low impedence 
> and wouldn't work very well (most likely 
> incurring a very heavy current draw and 
> hopefully trip the circuit breaker before 
> burning out the transformer."
>
> I am almost thinking Barry is looking at
> running the INPUT to the variable transformer
> in the first few turns, making it a quite
> large step-up transformer.  Short (and pun 
> intended) of either modify the unit to do 
> so, or feeding the input into the variable
> contact (not normally recommended, I beleive) 
> there isn't enough winding in the transformer
> to make it operate as a transformer, but more like
> a very low inductance coil.
>
> Certainly that isn't the way the variable transformer
> is designed to operate, but when Barry discusses
> a few turns, "very low impedance" and high current
> draw, it is almost like the discussion is on the
> theoretical, "if you used only a few turns" on
> the variable transformer as the primary.
>
> Barry, correct me if that is not where you were
> thinking.
>
> 73
> Sheldon
>   

-- 
Bob - NØDGN