Jerry Flanders <jflanders2@home.com> asks:
>For "ordinary" old power transformers:
>
>Is there a rule of thumb to help estimate transformer KVA capacity from the
>iron (or total) weight? If not, why?
>
>Prior to hypersil, weren't most transformers made from similar iron in
>similar configuration? If so, wouldn't capacity be directly related to core
>weight?
The older ARRL handbooks used to show an estimated KVA capacity based on
core cross-sectional area. There are too many variables to give a rule of
thumb, except that if you can't pick it up, it's big enough. 4 KVA CCS is
about 150 lbs., 4 KVA ICAS about half that. 2 KVA ICAS is somewhere around
45 lbs.
Those are probably reasonable numbers for most transformers. The
transformers that are more efficient and have a better match between core
saturation and maximum primary / secondary current capacity will weigh less
per watt, obviously.
Transformers from old vacuum-tube TVs were very conservatively rated, and
are well worth collecting. Transformers from most low-end amateur gear and
ALL CB amplifiers carry very optimistic ratings for current capacity.
FWIW, the previous owner of my Heath HA-10 (4 - 811As) blew the palte
transformr, and replaced it with a unit from a 300 watt Motorola base
station. Result? With an extra 200 volts and probably 400 mA more
headroom on the plate, about 35% more power.
Jim N6OTQ
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