MTH Z Controller puzzle - Question

A couple of thoughts.  It's likely your meter is not a True RMS voltage meter.  Since you didn't mention it, I'm also guessing you're not measuring the controller output voltage with any significant electrical load on it, other than a high impedance meter.  Some sort of load (like an incandescent bulb in parallel with the meter) will make the measured AC voltage out of the controller read higher on your meter.

A word of caution with this 24V brick is that it exceeds the recommended 19 volts Lionel recommends for LionChief and it's other command controlled locomotives.

With these considerations in mind, this Topic may help you understand these mysteries a bit better.

Chopped wave transformers: How much voltage is really going to your engines electronics?

Thanks Steve for your response.

I did have an engine moving slowly on the track while I took readings. 

What I have not seen before is this MTH set up where they used a Z controller 750 paired with a 24 VOLT brick.  This Z controller does not behave like the two I already have.  It only puts out about half the voltage (at full throttle)  when paired with one of my newer MTH bricks.  When the 24 VOLT brick is paired with it's mate,  they run a basic train fine (no electronics).  I was wondering if the controller was somehow "governed" inside to put out only the 12.5 volts regardless of the 24 VOLT brick.   

Any idea why MTH produced this arrangement?

As you mentioned, 24 VOLTS is too much voltage for our O guage  trains.

Thanks Dave

It sounds like your controller is suspect, especially because you say that it doesn't behave like the others you have.  If you put your meter on the raw output from the brick, what do you get?  What happens if you plug the 24V brick into one of your other controllers??

It's true that Lionel warns against putting more than 19V on the rails for Legacy and LionChief, and I'm careful not to push it.  But I will call them out here for a shortsighted design decision.  Many existing prewar transformers put out 24V, as did the Right-of-Way transformer circa 1990.  Some conventional locos need that much!  The venerable ZW puts out 20V, and the Z-4000 21-22V at open circuit.   So Lionel imposed this arbitrary lower ceiling sometime in the last 20 years, giving us one more thing to worry about.

It frustrates me, because using 24V motors combined with a higher track voltage would have yielded a small performance improvement and lower current draw, relative to the 12-15V can motors found in premium steam since the mid-1990s.