[R-390] Was variacs, now bucking transformers...

[Drew Papanek]

Dave Kamp wrote:

  "I've got a 1A SOLA here, that I've used on my HQ-140X, and found that it
   cuts down power-line pops, clicks, and a 'little' drift (usually when the
   AC compressor kicks on).

   I can understand how it 'bucks' a change in voltage, but how does a
   bucking-transformer prevent a 130v input from creating more than 115v 
output?"

A bucking transformer does not "buck" a change in voltage.  All it does is 
reduce the voltage by connection of the secondary in series opposing (or 
bucking) the input voltage.  If the phasing of the windings were reversed, 
the transformer would aid or "boost" the voltage.  With either connection, a 
variation in input voltage will affect output voltage by essentially the 
same percentage.

Sola is perhaps best known for their constant voltage transformers.  Is your 
Sola unit just a bucking transformer or is it a constant voltage transformer 
which also includes a Bucking Function (say that three times fast!).

The constant voltage transformer regulates its output voltage by way of 
resonance raising the magnetic flux peaks high enough to clip the sinewave 
peaks via magnetic saturation.  There is an extra winding connected to a 
large oil filled capacitor to establish resonance.  They work quite well if 
you don't mind the increased harmonic content of the output voltage, the 
sometimes loud (mechanical) hum and the heat.  Their primary (no pun 
intended) advantage over the power conditioning UPS is simplicity, low RFI, 
and extreme robustness.

Drew

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