Transformer current

[Jimbz]

Hello all, question:

How do you calculate the maximum current able to draw in a transformer primary without getting voltage drop ? I assume this has to do with the amount of windings, the more windings, the greater the power you can carry on to the secondary.

What is the exact maths behind it ?

[fcb]

Ohms Law basically.

You'll always get some drop with ANY load, you need to define how much of a drop is acceptable.

[Psi]

If you have no specs on a 50/60Hz transformer and it's a simple Primary:Secondary arrangement then the quickest way to get an approximate max current is to use the core size to estimate power, then you can get current from P/V.




Note: If the transformer has multiple winding then knowing the total power doesn't really help. You could have one thick high current secondary winding plus one thin low current secondary winding.

[digsys]

And there waaaaay more involved. You have to calculate temperature rise at max load, usually max at 75C-85C, which also depends
to excitation current and saturation (1.5-1.6 Tesla, 1.7+ is pushing it).

[Jimbz]

The power is dependant on the core cross section ? We can have say a single winding on the primary with a 4 inch core and it can give us 500 watts without any issues ?

[IanB]

The power is dependant on the core cross section ? We can have say a single winding on the primary with a 4 inch core and it can give us 500 watts without any issues ?

This will be true as a rule of thumb, but it assumes that the rest of the transformer is properly designed as well (right number of windings, right flux density, right window area, right primary and secondary wire gauge, and so on...).