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Re: Pri-Sec Phasing





---------- Forwarded message ----------
Date: Sun, 05 Oct 1997 23:17:32 +0000
From: Greg Leyh <lod-at-pacbell-dot-net>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Pri-Sec Phasing 

Bert Hickman wrote:


> Greg and all,
> 
> Interestingly enough, when I first looked at this from strictly a
> hand-waving basis, I initially drew the same conclusion. However, I then
> began thinking about how an autotransformer works (see sketch below).
> Both portions of the winding definately have the same winding sense, and
> yet the induced voltage, Vx, must be in phase and additive to Vin. I
> suspect there's either a polarity reversal due to Lenz's law, or perhaps
> in the definition of the directions of primary and secondary current
> flow. It sure can get confusing, can't it...! :^)
> 
> Anyway, "same winding sense, same polarity", is at least easy to
> remember!
> 
>                  O
>                  O<----------------------
>                  O  +          +        |
>                  O  Vx      ------>     |
>                  O  -        Iout       |
>     -------------*                      |
>     +  ----->    O                      |
>          Iin     O            Vout     LOAD
>                  O                      |
>     Vin          O                      |
>                  O                      |
>                  O                      |
>     -            O             -        |
>    --------------*-----------------------

I agree that your variac should work as advertised, but, but...
what about the 'Right Hand Rule'?  Can't it be applied here???

My confusion is further compounded by my copy of the "Practical
Transformer Design Handbook", by E. Lowdon.  On p.366 it says that
in a xfmr where the windings are wound in the same direction,
(and most are so that the bobbin doesn't have to be removed)
the start of the primary winding has the same polarity as the
end of the secondary winding.  This confirms the Right Hand Rule.

Perhaps their definitions of start and end are different.


-GL