Phasing transformers and using a common ground.

[mikemc52]

I recently retired and now have time to get back to finishing my layout.  I haven't touched it in years!     I also have inherited a couple of postwar transformers from my father in law (ZW and Z).  I currently run the layout with my postwar ZW.  I would like to use the Z for accessories and lights and use the ZW to run my trains ( I can only run one train at a time on my layout).  Can I use a common ground between these transformers?  I think the answer is yes is I phase the transformers correctly.  I know the question of phasing transformers has been answered hundreds of times, however I can't remember the correct way to do this for sure.  The reason I ask these questions is that I am currently using my ZW for accessories as well as running the trains and I want to use it only for running the trains.  I have several blocks set up only to activate signals which is what I would like to change over to the Z,  therefore I wonder if I can use a common ground.  I hope this is somewhat clear. Thanks for any advise and help.

[lionelsoni]

Yes, you can connect the common terminals (U) of the Z and ZW together.  (Strictly speaking, they are grounds only if they are actually connected to the earth, which, however, is a good thing to do for safety.)  But it doesn't matter whether they are in or out of phase, are at the same or different frequencies (or even DC), or have the same or different waveforms (like the CW80).

Actually, if the accessories, like the lights in a turnout, use the outside rails for their return to the transformers' common, then having the two transformers out of phase lets the return currents cancel and reduces somewhat any voltage drop in the outside rails.

To determine whether transformers 1 and 2 are in phase, connect their U terminals together (U1-U2).  Then set one of the outputs (for example A1-U1 and A2-U2) of each transformer to the same voltage.  Then measure the voltage between the two transformers' outputs (A1-A2).  If the voltage is close to zero, then they are in phase.  If it is about double the individual voltages, then they are out of phase.  If you don't have a voltmeter, you can use a lamp and just set the controls for about the same brightness, then look for a much dimmer or brighter light when you connect the lamp between A1 and A2.  Use a fairly low voltage to start with so that you don't burn out the lamp when you double the voltage.

If the result is not the way you want it, in or out of phase, unplug one of the transformers, rotate the plug to swap the pins, and plug it in again.  It's a good idea to use one of those power strips so that the transformers can stay plugged into it while power is off.

[wyomingscout]

lionelsoni

If the result is not the way you want it, in or out of phase, unplug one of the transformers, rotate the plug to swap the pins, and plug it in again.  It's a good idea to use one of those power strips so that the transformers can stay plugged into it while power is off.

 

That's what I did, but I had to replace the wiring on my old 1033.  I used a three prong male I had.  My ZW still has the original 2 prong male.  I marked one side of the ZW prong with duct tape (nail polish works, too) & the corresponding female side on the  power strip.  That way, if I unplug for any reason, I don't have to recheck the phasing.

Charlie

[mikemc52]

Thank you very much for the quick and very helpful reply.

Mike