Phasing AC with DC on a TMCC layout

Dennis,

I run TMCC on my layout with a separate regulated DC power supply for signals.  Simply connect AC common to DC minus and all is well.  The wire from the TMCC Command Base is also connected to AC common.  I've been running TMCC since 2002 and added the signal system in 2018.  I've seen no changes in TMCC signal strength.

I operate S gauge with Legacy. The track is powered with two ZW-L's. I have three separate DC supplies for accessory items. While possible to share a common return modern transformers are not pure sine wave output in most cases so there are significant harmonics in the output. Also we would need to check the internal wiring of the selected DC supplies to assure isolation. I feel it is a really bad idea to do this just to save $50 of wire. Also keep in mind you will have better signal reception if the Legacy (or TMCC) signal is on both rails, this is done with .1mF ceramic capacitors.

I would run separate ground wires for the AC and DC power supplies if for no other reason than to help simplify future troubleshooting, should the need ever arise.

The quick answer (and the only answer needed) to the OP's questions is - YES. You can connect the common sides of both the DC and AC circuits together so that you can run only one common wire around the layout.

As to your phasing question, DC doesn't have a "phase." Just connect the DC negative to your AC Common Ground and you're done.

Don't give over-complicated answers to simple questions!

Well, depending on the amount of current the accessories draw, I think a slightly more complicated answer may be warranted.  One issue of running a single common is the current carrying capability of that single common.  You're asking it to carry all the current for both the track and the accessories.  This may not be an issue, but without more details, it's difficult to be sure.

The original poster said:

"I also have a 12v DC regulated power supply dedicated to my various trackside signals and other low power DC needs."

I better add another complication to my answer for the benefit of the 3 railers. The OP has S gauge which is 2 rail. In 2 rail layouts with reverse loops as a train goes in and out of a reverse loop each rail is alternately connected to different posts of the power supply. Trying to keep all this sorted as the track feeder wires enter and leave reverse loop controllers with a common connection to a DC accessory supply is way more trouble than it is worth. In 2 rail even our turntables and crossing diamonds must be powered through reverse loop controllers.

Thanks to all of you for your comments and suggestions.  After considering these, I’ve decided to use a separate AC transformer for my accessories and the DC power supply for my trackside signals (and other LEDs) and connect the two commons together.  I’ll keep track power from the 180w Powerhouses and TPC400 completely separate from these other circuits.  I believe this will answer the concerns voiced by some of you.  (Especially regarding the reverse loops, of which I have three!). Thanks again for your advice!

Dennis

The concern is only that your common's wire.gauge is sufficient for the added current. You haven't metioned wire gauges, supply specs, etc.. Without enough info, you get vague answers.

It's hoped you are going to grab the common from a non-switched, non track source. If complex, your track system is obviously near 100% isolated from most accessories already, and this new dc loop is pretty safe in concept... we don't really know your skill level ,until you let us know yourself.