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Power Transfer in Multiple Secondary TRF

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pawan kumar

Member level 4
Jan 31, 2012
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Hi Friends,

I accept that the law of conservation of energy can never go false. I got this doubt, if answered, many like me may get benefited.

Consider the image below, Case 1: 10W is transferred ideally agreed.

In case 2, is there any way magnetically to prove that since the power input = power o/p, the current gets halved?

What if there is another secondary winding close by... How can the coils understand that and divide current accordingly?

Has this something to do with Mutual inductance? if yes, please guide me on where to read further..


When you apply load to a secondary, its effect is to try to LOWER the flux in the core, lowering the back EMF generated in the primary winding and causing more current to flow in the primary as more voltage appears across the primary winding resistance.

So yes, you can prove such a thing. For an ideal transformer the flux in the core is proportional to the sum of the products of the turns and the currents in each winding, and the back EMF is proportional to the flux * number of turns.
Assuming equal numbers of turns and eliding some annoying constants (Because electromagnetism was a lot of years ago, and I cannot remember the appropriate magic):

So: Flux is proportional to Iprim - Isec1 - Isec2.
V is proportional to flux.

Hence with a constant voltage applied to the primary, Iprim must equal the sum of the secondary currents, as the applied voltage is constant implying constant core flux.

Obviously real transformers have resistance and iron losses, as well as all sorts of other infelicities, any good EM text book will go into details of the maths.

Regards, Dan.
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