I understand transformer operation quite well. MY question was very specific in stating that it was about a transformer, such as a standard current transformer, connected so that the entire DC output of the alternator passed through it This would happen if a clamp-on ammeter were clamped around the single DC line from an automotive alternator. Given that the ripple voltage is present at the output terminal, then the current variation produced by that voltage variation would also be present, in addition to the DC voltage and the nominal 50 amp DC current.

A similar example may be seen in the class "A" output transformer of an audio amplifier, where there is both a constant DC current and an additional varying current. with the AC voltage being produced in the secondary. The DC component does cause a constant magnetization at some level. In adequately designed transformers it does not result in non-linear operation.

 

MY question was very specific in stating that it was about a transformer, such as a standard current transformer, connected so that the entire DC output of the alternator passed through it This would happen if a clamp-on ammeter were clamped around the single DC line from an automotive alternator.

I don't understand why you are referring to a current transformer, which has nothing to do with the TS's question, and just muddies the waters.
Where was this mentioned elsewhere in this thread?

 

No, there was no prior reference to a current transformer in the thread. My question was relevant to the issue of if there could be alternating current in a circuit such as the one presented, when diodes will not allow any current flow in the opposite direction.

Evidently I should have given a much more detailed explanation along with the question that I proposed.
What I was proposing was the fact that certainly, IF there can be an alternating current in the secondary winding of a transformer with DC and varying DC flowing in the primary, then possibly we should be able to describe that varying DC current as containing an alternating component.

 

Is the question now "can pulsating DC in the primary coil of a transformer induce AC in the secondary coil of said transformer"? Interesting.

 

Yes.

Because the Ripple variation will induce changes in the Magnetic-Field connecting the 2 Windings.

All of the Ripple, and none of the DC, will be seen at the Secondary-Winding.
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IF there can be an alternating current in the secondary winding of a transformer with DC and varying DC flowing in the primary

I still see muddy water.
Please explain where this "If" DC is coming from in the windings of a transformer with a full-wave rectifier bridge on the secondary and a DC output as a load, which is the circuit posted in this thread.

 

I still see muddy water.
Please explain where this "If" DC is coming from in the windings of a transformer with a full-wave rectifier bridge on the secondary and a DC output as a load, which is the circuit posted in this thread.

To view the waveform I am referencing, please look at the non-sine waveform on post #14. That clearly shows a voltage variation with a repetitive waveform. And the fact is that with a constant load, a voltage variation will produce a current variation, usually with a similar wave-shape.
In the real world, many transformers have both AC and DC flowing in at least one of the windings. It was especially common in the vacuum tube era, both in audio output transformers and in MODULATION transformers for AM transmitters. Mostly, modulation transformers had DC current flowing in both the primary and secondary, usually from independent sources.

 

And the fact is that with a constant load, a voltage variation will produce a current variation, usually with a similar wave-shape.

Of course, it's obvious there is a current variation, since it's an AC circuit.
But the average (DC) current from the transformer is zero in the circuit here.
Are you trying to say it isn't zero?

 

Of course, it's obvious there is a current variation, since it's an AC circuit.
But the average (DC) current from the transformer is zero in the circuit here.
Are you trying to say it isn't zero?

NO, the AVERAGE value of the DC portion si nominally constant. BUT the instant value is affected by whatever the ripple or the modulation signal amplitude is. The ripple is that constantly changing value of the peak, which is not the same as the instant ,value. So there is the variation on top of the constant value. The mechanical ammeter will show an accurate average current, while the scope connected to the series shunt resistor will show the AC part along with the DC offset to the reading. Likewise, the scope voltage trace will show the large DC offset and the smaller signal on top of that.

 

NO, the AVERAGE value of the DC portion si nominally constant. BUT the instant value is affected by whatever the ripple or the modulation signal amplitude is

I guess the confusion is that you are referring to the the output current from the rectifiers, which has a large average DC component.
I thought was clear that I was referring to the output current from the transformer secondary, which has zero DC average current..
Obviously they are not the same.

This conversation started because you originally stated there could be a problem with DC current in the transformer secondary, and somehow it segued into the rectifier output current.

 

This is leading me to believe that a diode is not 100% effective in blocking reverse current flow. I was thinking that the voltage downstream of the diodes was all DC. That the ripple was pulsating DC.

It sounds like you need to be very explicit about what YOU mean by the terms you are using, because you are trying to get at concepts that are very sensitive to that.

I don't think I have every seen the phrase "pulsating DC" in any engineering textbook or paper in over forty years of experience. But my dad (who had a mechanic's level understanding of electric machinery, and was quite proficient in that realm) used that to describe things to me at a very early age.

From an engineering perspective, you have DC, meaning signals that have ZERO frequency in theory, and less than some relatively-low bandwidth in practice, and you have AC, which is anything else. Real signals are then combinations of the two. Thus, anything that someone describing things at a "technician-level" (and please do NOT read ANY kind of pejorative intent in that label) would describe as "pulsating DC" is simply a mixed AC and DC signal in which the DC component is sufficiently large to prevent sign reversal of the overall signal.

 

OK, and probably "pulsating DC is also correct,but usually called ripple because that is what it looks like.