[sdiy] How to predict a tansformer's current capability?

[Glen]

I have some assorted used power transformers that have been removed from
various types of equipment. I'd like to use some of these for projects, but
how do I predict what the maximum safe output current would be for a
transformer that I have little or no information about? I can determine the
primary and secondary windings with no problem. I can hook them up and
determine the output voltages with no load, but how do I determine the
maximum load the transformer should be subjected to? I'm more interested in
a "continuous use" specification, instead of a peak current rating, but a
peak current rating might be useful for some things as well.

The transformers are a varied assortment. Some have multiple secondaries,
perhaps a few have multiple primaries. Some transformers have "step-up"
secondaries, but most are the "step-down" style.

Do I just power one of them up, while increasing the load on the secondary,
and monitor the secondary's output voltage? (Perhaps I would stop
increasing the load, when the output voltage has dropped by some calculated
"safe" amount, whatever that amount might be, and declare the amount of
current flowing at that moment to be the maximum rating.)


Thanks for any assistance,
Glen Berry