On Friday 04 July 2008 21:40, Tony Duell wrote:
Roy J.
Tellason wrote:
If you're talking about a full-wave (4-diode)
bridge across a 9V
winding you can get the same result by using two diodes with an 18V
winding. For the other, where what you want is only 9VAC, you can
use half the winding, just one end and the center tap and not use the
other end.
That would be ideal. Just remember that the 18V winding will be rated
for half the current that a 9V winding would have been, and that still
applies even if you only use half the winding. In this case I'd
Now, this is more your filed than mine, but the rating of a transformer
is determined by at least 2 things :
1) 'Copper losses' due to the resisance of the secondary winding
2) Ditto for the primary winding
3) The size of the core / the flux density in the core.
Now, I think that (2) and (3) would be the same whether you used the
whole winding or half the winding at twice the current. And for small
transformers, the copper loss in the secondary is rarely the limiting
factor (For example it's very rare for the seocndary to be the winding
that fiales on a burn-out).
I'd tend to agree with this.
Soe while I'd not try and use half the secodnary
at twice the rated
current, I think you would get away with rather more than the current you
could draw if you used the whole winding.
Yup.
But then again I like over-rating transformers, so
I'd probably not do
this anyway.
If I'm going to spec one, yeah, but more often than not if I'm building
something from scratch I'll end up using some transformer I salvaged
somewhere, and mostly it works out.
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
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