"Daniel T. Burrows" <danburrows(a)mindspring.com> wrote:
The only safe way is to use a transformer that is
correctly wired. US mains
is
120 - neutral - 120. which gives 240 between the 2 hots. European mains are
240 - neutral. Both expect the neutral to be at / near ground potential. If
you wire it to US 240 directly what was neutral in Europe will be at 120v. I
have several isolation / step up transformers that I routinely use to
accomplish
this. You need to be careful how they are wired in order to have both primary
and secondary tied correctly to neutral and the grounds MUST be kept separate
from the neutral to meet US electrical code.
Hi
When using an isolation transformer, the transformer needs
to handle the entire power. If you use an auto-transformer
arrangement, you only need half as big a transformer.
What I have done in the past is look for supply transformers
that have configurable AC for 110/120. I save these from
old supplies that would otherwise be scrap. When I need a
boost or dropping transformer, I just wire up the primaries
as an auto-transformer. I compare the core volumes of the
units transformer with the transformer that you are using
as the auto-transformer. If the core volume of the auto-transformer
is 50% as big as the units, you should have no problems with power.
You can just leave the secondaries open.
Dwight