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will my house burn down?

Unless it is DC. The DC component of the secondary current adds a DC component to the core magnetization, but is not reflected by any primary current to cancel its effect on core magnetization.

Try putting a resistor or an incandescent lamp in series with a diode, with a jumper across the diode, and power that with a transformer. Put a resistor in series with the primary so that primary current can be shown on an oscilloscope. Watch what happens when you unshort that diode.

Magnetization is caused by difference between primary amp-turns and secondary amp-turns, times core permeability. Volts per turn is proportional to time derivative of this times core cross section area.

A DC component of current in either winding will add magnetization to the core without causing any induced voltage.

- Don Klipstein ( snipped-for-privacy@misty.com)

Reply to
Don Klipstein
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Correct.

During the 1/2 cycle when the diode conducts, the A*T in the pri and sec balance each other out (almost). In the 1/2 cycle when the diode doesn't conduct the A*T in the pri and sec again balance each other out (almost).

I agree with what John said above about the flux walking due to the imblanced AC voltage on the primary caused by the primary resistance, but what you are saying is something more fundamental and completly different and I don't agree that it applies in this case.

Mark

Reply to
Mark

It looks like John was doing a transient analysis, analyzing what happens step by step starting at the moment power is first applied. I was doing a steady state analysis of what occurs once things other than effects of varying temperature have stabilized.

I do see how the primary current could have a DC component for a little while. I expect that to fade, maybe with a time "constant" along the lines of L/R, where L is the primary's inductance and R is the primary's resistance. L is going to be messy, nonlinear and non-constant with the core's permeability being non-constant.

- Don Klipstein ( snipped-for-privacy@misty.com)

Reply to
Don Klipstein

(snip)

How does primary current during any during any given half cycle of voltage know whether there will be secondary current the next half cycle, ahead of time, so it knows whether or not to cancel the secondary ampere turns with its own?

Transformers have no trouble passing DC pulses from primary to secondary, as long as you make sure the volt seconds over a whole cycle add up to zero.

Reply to
John Popelish

I am doing steady state analysis, with primary and secondary carrying DC currents with canceling ampere turns. Any forward converter transformer does exactly that.

Reply to
John Popelish

Yes, and I hearby apologize profusely for spoiling the atmosphere of this newsgroup by posting this sort of thing.

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Paul Hovnanian     mailto:Paul@Hovnanian.com
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Reject nihilism!
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Paul Hovnanian P.E.

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