Chopped wave add-on circuit for old transformer

Just curious but WHY?

I'll echo that query, why?

I will double down and say why.  There is no benefit to a chopped wave sine output that I know of, and in fact chopped wave sign causes problems problems with some  engines. The old transformers had some shortcomings, but being pure sine wave wasn't one of them. 

I enjoy working on electronic projects, and I'm thinking it could be less expensive than a new CW-80??

I mostly have post war engines, and I heard or read somewhere that a chopped sine wave makes post war engines (including AF) smoke better and makes the light brighter and is not as dependent on the locomotive speed.  

@Drummer3 posted:

I enjoy working on electronic projects, and I'm thinking it could be less expensive than a new CW-80??

If you have an old ac transformer, why not just use that? Emulating chopped wave would be an engineering exercise, but it doesn't emulate any functionality, using a CW80 doesn't give you any kind of access to features, etc, functionally it operates identically to an old AC transformer with pure sine wave.  As far as cost, assuming the old transformer is in good shape and doesn't need updating (and if it does, you would have to do that anyway for safety reasons), the only extra cost of using the old transformer would be getting a fast blow breaker (and tvs's, but you you should use them with any transformer). 

Dave is actually somewhat correct in that the chopped waveform does offer a small benefit to "some" conventional locomotives.  Specifically, they will smoke slightly better at a given voltage setting with the chopped waveform than with the pure sine wave.  However, if I wanted to improve the smoke vs. the speed of one of these, I'd add some series diode pairs in a motor lead, it can have a much more dramatic effect on the smoke.  As for lighting, a simple conversion to a nice amber or warm white LED will give you tons more headlight brilliance without having to design a new transformer.  It'll also look way better than the incandescent will every look even with a chopped waveform.

I remember a little time after the Z-400 came out (before Lionel's new ZW), I believe it was CTT had an article about repairs to some engines that were coming in to his shop were all with people using the NEW transformers and the one that wrote the article advocated the old transformers. After reading that article I thought it was funny that there was still the big switch!

Redball342   

Yes John, on several of my Lionel and AF engines I have added a bridge rectifier before the motor so more voltage gets to the smoke element and light.   Works very well.   Now I need to add to my project list installing LEDs.   

I remember purchasing a pre-owned Lionel 2055 at a local shop, and we did a test run on the store layout to verify its operation.    The transformer was a CW-80 and I noticed the engine  smoked very well.  When I got home to my old transformer, I noticed it smoked about 1/2 as well, and the light was not as brilliant.   That's what got me thinking about the chopped sine wave transformers.  

Dave, in your case, a chopped waveform may actually make sense if you don't want to mod the locomotives.

You know you can buy the MTH Z-Controller and handle up to 100 watts to the track. MTH 40-1000B Z-Controller

That should be more than sufficient to handle your needs.  It'll sure be a lot cheaper than designing/building one.  I see several on eBay right now, search for MTH Z-Controller.

Here's one at TrainWorld for $50: MTH 40-750C Z Controller Set Includes Z-750 Controller w/Lockon & Wire

Your thought is to chop the pure wave to test how your electronic projects behave with chopped power?

As for a module that is designed to do this specifically, I don't know of any.  However, you can get an MTH Z-Controller (Z500, Z750, Z1000 & Z-Controller) that will take a perfectly good pure wave from any transformer and chop it for you.

Great - I will look into getting a z-750 from train world.    I don't need to re-invent the wheel.

A Lionel PowerStation Controller, BW(or GW) Controller, or a PM-1 will do this for you as well.

Now if only someone would devise a simple circuit to do the opposite: smooth a chopped wave into a sine wave...

Ain't no simple answer to that one!  The reason the MTH Z-4000 has so much electronics is the issue of handling high power sine wave synthesis.

@gunrunnerjohn posted:

Ain't no simple answer to that one!  The reason the MTH Z-4000 has so much electronics is the issue of handling high power sine wave synthesis.

GRJ~

Somewhere in the past I ran across the patent for the Z4k.  This may sound crazy but the size wave is generated by pinging a large inductor with a power MOSFET and using the sinusoidal ring to create the sine wave.

Lou N

I have all the schematics from the patent, they're actually useful in figuring out issues with the Z-4000.  I noticed the oddball circuit, didn't actually analyze it to see exactly what they were doing.  I know there's a lot of parts in there to generate the sine wave.

I did something similar on a lower power scale in the late 1970's, I was synthesizing 400hz sine waves in an air data computer for synchro based panel instruments for the 727.  It was all done using 10 bit ROM tables and the TI 9900 16 bit uP.