Find low voltage trnsformer amperage rating.

[electronics-whiz]

I have been dismantling old UPS units for a while. A lot of them were older and used 60HZ transformers. I just too apart one the other day that was rated 550VA output. I intend to use as a step down transformer putting in 120V to the old 120V output. The old primary was 3 wires between the ends is about 16V and it has one center tap lead. These wires appear to be 10AWG.

Wondering if there is a way to find the max amperage for the larger secondary winding. I don't know if it would still be 550VA,  if so how do I convert that to Amps? I also saw one unit that was like a 2500VA and had 2 transformers in series on the drive side each appeared to be 24V. How would I find the rating on those?

I did try to Google on occasion, but they seem to be off brands that all I get info on is people fixing or taking apart UPSs with questions on windings, etc.

[jeroen79]

VA stands for Volts * Amperes or apparent power.
Note: VA is not Watts real power.

So if you have 550VA and 16V then you could get 34A out of it.
At 110V it would deliver 5A.
The VA rating may apply to the whole transformer.
If there are several secondary windings they may share the rating.
Also, a lower voltage tap may have the same rating as the whole winding.

The size and weight of the transformer and the gauge of the wire can also give an idea of how much current it can deliver.

If you really want to squeeze the last Ampere out of it without doing damage you should test it.
Apply more and more load and observe the output voltage and temperature.