Transformers, sine waves, need clarification

For my clarifications please also include the lionel ZW to the list, full or chopped, avoid?..thanks

Frankly it matter much less when running LC+ or Command engine where you have the transformer near full voltage.  At that point the chopping effect is not much.  Additionally, for Lionel, they are chopped output and the engines are fine with it.  MTH units prefer a smoother normal AC wave, but nothing will hurt it if chopped.  Just might not operate with bell and whistle functions.  G

Some generalizations with out getting too awful technical:

1. You won't fry any AC locomotive regardless of wave pattern (pure sine wave or chopped sine wave).
2. Any older transformer (pre/postwar) such as the 1033, LW, KW, ZW and such are pure sine wave transformers.
3. Most modern transformers are chopped sine wave transformers. This includes the CW, GW, ZW-C, ZW-L, TPC and PowerMaster units.
4. There is most power delivered with the chopped sine wave transformers which can be deemed beneficial for smoke unit performance.
5. I recall some very early MTH ProtoSound locomotives have difficulties with chopped sine wave transformers.

In reading a john galt  post about chopped waves, its my understanding that if transformer is capable of 20 volts even tho you set it up to 12v or 18volts, the electronics can still see the max, 20v ??

@Squirrelstrains, You would never feed more than 18VAC to modern O Gauge Equipment. Therefore your premise of feeding 20VAC is invalid and should not be done. That is because the peak voltage, even if throttled, is still 20VAC (see the chopped AC waveform above).

AC meters are used to measure the RMS value of sine waves. True-RMS meters are required to measure the RMS value of complex wave forms, such as chopped sine waves generated by a triac. Non-true RMS meters actually measure the DC voltage and multiply it by .707 (appropriate for the pure sine wave) to get the AC voltage. Think of RMS as related to the measure of area between 0 and the wave. The more pronounced the chop, the less area and therefore less apparent RMS voltage.

My understanding is that as long as you stay away from the CW80 and a couple of MRC transformers, you shouldn't have any problem.

Most people think they have to get a newer model transformer. As I'm planning on going to digital this year, I'm messing around with upgrading my old Z. The Z has almost as much power as the older ZW's (250W vs 275W). Once I get things spec'd out and tested, I'll do a post on it. Some of the info I got from people telling me about modifications, the others I couldn't find much info on. So if anyone wants to PM me some links or info, I'd be grateful.

I'm also going to dig out my old tektronix o'scope and do some signal analysis as I'm curious about a couple of things. it's been sitting for so long though, I'm hoping it still works.

Upgrades in mind so far:
Voltage limiting diode on the output to prevent spikes. On order, haven't got here yet.
Thermal circuit breaker sized to trip on a short but hang in under 6 amps. These are mini button breakers and the idea is to mount it inside the transformer casing. So far the 10 and 15 amp I tried will not trip. Have a 5 and 7 amp on the way.

If I can't get reliable operation out of the thermals, will look for a fast acting. Already tried an in line fuse but 10 amp blows too easily on an RW and 15 doesn't blow. The idea for using the thermals is if something develops causing a current draw that's not expected, it will trip before a fire starts, yet the breaker will allow for smaller fast surges that will blow a fuse. (The fire is something I read about that happened recently to an O gauger, a current draw that didn't trip the old lionel CB on the transformer was still enough to melt layout wiring insulation due to heat and start a fire). The rating would be easier to figure out if my DMM did AC & DC current, instead of only DC current .

Also ready to convert a 167 Whistle controller to a solid state 6 amp diode. Will be curious if it changes the voltage drop. With the diode disc, there's a 3.2 to 3.5V drop across the controller terminals. This is not an issue in conventional for the Z because you can crank it up to almost 24V, so even with the voltage drop, you can easily hit 18V to19V no load at the high end. But I'm curious if I'll see a change in the drop with the new diode.

bmoran4 posted:

@Squirrelstrains, You would never feed more than 18VAC to modern O Gauge Equipment. Therefore your premise of feeding 20VAC is invalid and should not be done. That is because the peak voltage, even if throttled, is still 20VAC (see the chopped AC waveform above).

AC meters are used to measure the RMS value of sine waves. True-RMS meters are required to measure the RMS value of complex wave forms, such as chopped sine waves generated by a triac. Non-true RMS meters actually measure the DC voltage and multiply it by .707 (appropriate for the pure sine wave) to get the AC voltage. Think of RMS as related to the measure of area between 0 and the wave. The more pronounced the chop, the less area and therefore less apparent RMS voltage.

So your saying an mth z4000 capable of 22v output should not be used even if thottled up to 18 and double checked with a rms meter

I believe a Z-4000 is a pure sine wave Transformer. No issues there as if it is set to 18Vac, your peak is 18vac.

Okay great, i think i understood the original john galt post more clearly now, wish i could find it..anyways thank you, as long as i meter each time if using full wave im good with LC+ set at 18v.

if using chopped wave as long as its max voltage is 18v or under, im good, avoid any chopped wave with max output higher than 18v  irregardless of handle position, due to thats what loco will see...max output

Squirrelstrains posted:

Okay great, i think i understood the original john galt post more clearly now, wish i could find it..anyways thank you, as long as i meter each time if using full wave im good with LC+ set at 18v.

if using chopped wave as long as its max voltage is 18v or under, im good, avoid any chopped wave with max output higher than 18v  irregardless of handle position, due to thats what loco will see...max output

 

You've got the general gist of things!

Thank you so much, my lionel VW is full wave, over 20v output max,  so setting with a meter is required there as well, looks like my next project is to install a few meters, seen on another post. Since an rms handheld meter is required, should that be considered when purchasing a panel mount?

Really glad i finally joined this forum, ive read for years and always have found good info here, sometimes these go down the rabbit hole a tad deep so taking the time to clarify and respond is greatly appreciated!

When measuring a pure sine wave transformer, any AC voltmeter will do. You don't necessarily need a true RMS voltmeter. Non RMS voltmeters take a shortcut of measuring the DC voltage and then multiplying it by .707 to derive the RMS value for a pure sine wave. True RMS meters are needed only when measuring complex waveforms that are not a pure sine wave.