[AMPS] High Potential Tester (high-pot) Components

[Dave Kirkby]

> >Hmmmm...  I measure 12.7 ohms across the primary.  A true center tap
> >should be 9 ohms.  Maybe something is wrong with mine.
> Due to the current requirement difference, the two windings probably
> have
> unequal resistances.   There are three color coded pri. wires.  What
> are
> the resistances?
> Rich...
>
> R. L. Measures, 805-386-3734, AG6K
>

It *not* true to say that a centre-tap will be half the resistance of
the full windings. I hit this once when making resistnace mesurements on
a 1800-0-1800V tranny. Once half had about 30% (from memory) more
resistance than the other. At first I thought that some part of the
windings were shorted, but then I realsied this is not so. Since the
winding diameter gets bigger the more turns on the core, the second half
wound must have a higher resistance, as its on a bigger mean diameter
and so the wire is longer. When I applied power to the transformer, both
halves gave the same voltage, although the DC resistances were unequal.

--
Dave Kirkby G8WRB
Department of Medical Physics,
University College London,
11-20 Capper Street,
London,
WC1E 6JA.

Tel: 0171 209 6406 (International +44 171 209 6406)
Fax: 0171 209 6269 (International +44 171 209 6269)



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