The Z4000 uses a much more expensive digital sine wave generation approximation to give what is close to a pure sine wave. It has a pure sine wave output at all voltages and currents.

I posted some waveform pictures in the past for various transformers, don't know what the thread name was.

Robert,

The z500/1000 type controllers, in the process of reducing voltage, alter the wave form, which has an effect on motor operation apart from the voltage change and can't be fed to a TIU.

That's  not exactly correct.

In fact, the output of a Z-Controller as fed by an MTH Z-Brick (Z500, Z750, Z1000) can be used with a TIU Fixed channel input, although not with a Variable channel input.

The difference is that chopping the sine wave (which is what the Z-Controller and the Variable TIU channels do) once is not all that big a deal. however, chopping it twice is a big deal.

The difference is that chopping the sine wave (which is what the Z-Controller and the Variable TIU channels do) once is not all that big a deal.

That's not exactly correct, either, Barry.  I had a PS2, 3-volt, which would not operate correctly on a variable circuit when the input was 22 volts pure sine and the output in the 15-volt range.  The once-altered wave affected it.  Our mutual friend at MTH couldn't figure it out.  The board was replaced and the issue never redeveloped on that or any other loco.

The small Type R was handy on my workbench.  I guess I'll use a Z500 I have, and if there is a rare occasion when I want to use a variable, just feed it full voltage.

I have an old 1033 on my workbench with a little breaker box on the side and a 2A breaker.  That's sufficient for any bench work I do, and I don't risk high current's smoking something.

Robert,

That's not exactly correct, either

On the contrary, it is correct.

I had a PS2, 3-volt, which would not operate correctly on a variable circuit when the input was 22 volts pure sine and the output in the 15-volt range.  The once-altered wave affected it.  Our mutual friend at MTH couldn't figure it out.  The board was replaced and the issue never redeveloped on that or any other loco.

Your engine that couldn't deal with it was obviously defective, i.e., it worked fine when its board was replaced.

So on the modern power supplies which vary the voltage by modifying the wave form, do they have a transformer and a DC link, or they just modifying the 120 volt input voltage?

I would hope they all have step-down power transformers, to assure the layout is isolated from the power lines in event of an internal malfunction.

All the modern supplies are totally isolated from the 115V line using a transformer, then they do their "magic" to vary the voltage.

why do we need to change the sine wave in the first place?

I assume model train power supply designers want to get away from the mechanical system of tapping off the transformer secondary winding and go to an electronic system, to get away from the maintenance problems of the mechanical systems (a roller or slide running over the wires).

The cheapest approach apparently is a design that in reducing voltage alters waveform.  Reading a post above, the Z4000 uses a more expensive design which apparently does minimal alteration of the waveform; as I read that post, there is still some distortion.

I'll leave it to the electronics experts to answer the technicalities of your question.  I'll also pose a question for transformer electrical experts:  Looking at my ZW or R Transformer secondaries, the roller (ZW) or slider (R) moves over the secondary windings and obviously makes electrical contact with them, so they are not insulated.  Yet since the coil windings are in contact with adjoining coils of the winding, why don't they short? 

If each coil is touching the one next to it, it's the same as if the coils at each end of the winding were touching, correct?

The reason they alter the waveform for electronic controls is the easiest by far method of varying the power from a fixed voltage source is by using the chopped waveform.  Here's a sample of what that looks like.

The Z4000 uses a more expensive method that actually synthesizes a sine wave at full power, takes a lot more parts to do that.

FWIW, here's the thread I posted on the topic.

MTH Z4000 Waveform Pic

 Correct, that's why they use carbon rollers or wipers.  It has a higher resistance and doesn't directly short the windings.  The carbon actually erodes a bit under the high current short so that the windings are not shorted.  It's also why the rollers wear out.

Thanks, GRJ.

I'm not stating the question clearly.  Let me try again.  Forget the roller or slide, why don't the individual coils of wire short out to one another all across the secondary winding.  Or are they varnish-insulated except where roller or slide runs?

They are all varnish coated, then the tops of them are sanded to remove the insulation.  If they do get shorted, say when the roller wears down and the arm scores the wire, the transformer is usually toast. 

I rescued a ZW that had this happen. I first cleaned out the copper residue and then varnished the whole area a couple of coats, and finally sanded the tops again.  Worked like new, but it was more work than I'd like to do for the payback.  I was just curious if it would work, and it worked out fine.

Thanks again, GRJ.  Interestingly, I can't see where there's varnish and where it's sanded.

The varnish is the red coating that the wire has, it's pretty standard magnet wire, just a really heavy gauge.  The sanded part is copper colored and is easily seen.  See the lighter color in this shot on the surface where the rollers are contacting the coil.

Here are some photos of the inside of a 1941 Type R.  Instead of rollers, it has copper sliders than rub along the coils.  The photos show the sliders, what the coils look like after almost 75 years of use, and the condition of some of the internal wires, where it looks like heat or age (?) has caused some swelling of the insulation.  The insulation is not crumbly.  The resistor is between the outputs of the two circuit breakers; tapped off in the middle is the red short light.

I've seen worse that were still in use.

The question is whether to replace the internal wiring or say goodbye to my childhood companion.

Good idea Dale.  You can even use plain insulation stripped from scrap wire the same way.