Re: Reversing loop with multiple trains in the loop


In case it matters to anyone, I believe the OP is using Digitrax, as he posted this question to that list as well, and is now receiving advice on both lists.

Even this analogy is flawed, but it's useful most of the time. If you really want to know polarity/phase/amplitudes, get an electronics friend who owns an oscilloscope to make a measurement of Rail A and Rail B simultaneously, both referenced to the "ground" screw terminal in the seven pin connector. Do this both

- with "analog" mode disabled

- with "analog" mode enabled, and address zero set to some decent throttle position, say 50%.

Have him/her explain what you're seeing in both cases.

Then think about what happens to those signals when they are processed by the onboard full wave rectification in a decoder.

To the OP:

If you do this, you'll benefit more than anyone just explaining what's going on with analogies.


On 17/06/25 10:23, Ed S [WiringForDCC] wrote:

I am not an expert in DCC, but I did stay at a
Holliday Inn once. So I will throw in my .02
cents worth. The DCC voltage does not have
polarity. It is AC as in alternating current; but
not like the AC in the wall of your house. DCC is
a higher frequency and a lower voltage.

So what is the problem with reverse loops? Well
the two rails carry different thing. One rail
carries the commands from the command station and
the other rail is more like a neutral rail. If
you make a loop and it comes back on itself the
neutral rail touches the command rail and that is
the problem. Most layout programs will show one
rail as red and the other as green and the rule
is a red rail should never connect to a green rail.

Now the really interesting part is the decoder,
once it is set to tell the motor to run forward,
it does not care if it crosses over and insulated
section and the rails switch from red to green.
The decoder/motor will still run forward.

So stop thinking in DC….. There is no positive /
negative rail in DCC. (But the locomotive motor
is still DC but the decoder takes the AC from the
rails and turns it into DC for the motor.)

In addition; thinking more about the analogy of
house AC wiring you would never connect the black
wire (hot) to the white wire (neutral) in a house circuit.

Now the experts should chime in and clear up any of my faulty logic.

Ed S

At 12:21 AM 6/24/2017, you wrote:

Now that I better understand it I have more questions:

· Exiting the loop the polarity is
reversed, but the next turnout can route the
train to another power district (same booster)
is something needed at every point where this
can occur or does the polarity reversal apply to the booster.

· Same question except the turnout leads to a different booster.

Posted by: Ed S <>

Yahoo Groups Links

Join to automatically receive all group messages.