Transformer current rating calculation

[Roy3932]

Hi,
l would like to custom-made a toroidal power transformer because my old transformer broken. This power transformer is multi secondary output and center tapped winding (sec 1=0-9vac and sec 2= 71vac-0-71vac). Primary voltage is 230v with power rating @ 30va. The transformer dimension is 70mmx25mm.
I'm not sure how to calculate the current ratings? If I want to change the power rating to 50va, what should be the current? Can someone help. Thanks.

Rgrds/Roy3932

[multi-volti]

Without knowing how much current each of the existing secondaries had to deliver, you can't know how the VA rating was shared by the multiple windings, only that increasing your VA rating will increase the proportional capacity of each of the windings in a higher rated xfmr.

There may be some merit in picking apart the bad xfmr and measuring the diameter of the the magnet wire (not the external leads) for each secondary. From this we could estimate typical design current density used in xfmrs. (worst case 250-300 circular mils/A, conservatively perhaps 1000 CM/A).

Regardless of what current density the designer assumed, we could estimate the load ratio between the two secondaries and work backward to determine currents.

It would be an educated guess, perhaps better than having no info.

Is there any way for you to estimate what each of the the windings has to accomplish?

I wish I knew why it take 2-3 attempts for me to post. I'm always told I'm not logged in the first try.

Murray