Andrew Gabriel wrote:

In article ,
(Roger Hayter) writes:
Johnny B Good wrote:
I can imagine the need for a 10A rated 240v supply which would require a
400VA auto transformer in this case (40v difference at 10A) which could
easily weigh some 16 to 20 Lbs. Just as you described, not a lightweight
item. :-)

My knowledge of transformer theory was never very clear, but why is it
not rated for the total output, which might well be something like 10A
at 200v, 2000VA?

An auto-transformer has just one tapped winding.
The core only has to cope with the VA of the voltage difference.
The common part of the transformer winding can be thinner too,
although that depends on the no-load inductance and the harmonic
component of the load.

Thanks. I must make the effort to read a fuller explanation some time
so I understand it. But the point is noted.



--

Roger Hayter