Question on how accessory voltages work on KW Postwar Transformer

The KW is a multi-tap secondary power supply. There is potential(voltage) between any two points on the secondary which can be used for any suitable application, the C-D posts are taken from two points in the middle of the secondary.

@steam posted:

Also, if I used an odd combination like C and D...  I guess there isn't a way to have this connected to a common ground with a second transformer?  Thanks for any help.

Not really.

Thanks for the reply!  Is it ok to use the A and B posts for different things, while connecting the U terminals to a common ground with a ZWL?  I did verify that both transformers are in phase but using a light-bulb to confirm which way it shines bright or dim when connecting positives from the 2 transformers together.

The U terminals are offset from the C terminal by the 6V secondary winding.  If you do not need 6-20V for any purpose, you can use the C terminal as common, D for 14V fixed, A & B for 0-14V variable, and U for 6V fixed.  Note that there's a fair bit of resistance in the A & B pickup rollers, so the voltage at A & B will drop somewhat under load.

The reason Lionel starts the trains moving at 6 volts is to get the e-unit to operate before the train starts to move. If you have the conventional electro mechanical e-unit, the 6 to 20 volt connection is correct for your train. If you are using the more modern electronic e-unit, the 0 to 14 volt connections will give smoother operation. Same goes for the 5 volt boost.  That is needed for a motor driven whistle to compensate for voltage drop when the second motor cuts in. For electronic horns and whistles this boost is not needed.

I guess I'm not much of an electrician so I might not ever understand how all the different combinations work haha!  I am used to always having a positive and negative and they were attached it would trip the transformer's breaker.  Anyhow, Just to clarify that my setup is ok...

On the ZWL I am using all the outputs, A,B,C,D.  The U is connected to the outside rail and ground.  

My KW I will just use the A and D posts to power accessories.  The U I will connect to the same terminal strip that the ZWL ground is attached to.  

I marked the cord on the KW so it is only plugged in the way that it is "in phase" with the ZWL.