I’m new to this and a little confused. When your running two trains on ona layout and one enters an auto reversing section of track and triggers the polarity reversing, what happens to the other train?
Will be DCC if it makes a difference
Not a dumb question at all. Even after using DCC for two years, I still have questions.
The other train will not be affected. The decoder tells the locomotive which direction to go, regardless of the polarity of the track.
If the other train remains outside of the reversing section, it is unaffected. However, if the other train is entering or exiting the reversing section, it may trigger the auto-reverser depending upon whether or not the polarities are matched or mismatched.
Rich
you probably know that DCC track voltage alternates (AC). The decoder rectifies it and then controls the polarity of the rectified voltage to the motor to control it’s direction
but just because the track voltage alternates doesn’t mean the that the polarity of adjacent rails can be different because a short will occur when a metal wheel bridges the gap.
an auto reverser controls the polarity of the rails on one side of the gaps to a reversing section so that when there is an inevitable short at one end of the reversing section or the other, the reverser very quickly reverses the connections between the rails in the reversing section so that there is no short.
frog juicers do a similar think, changing the polarity of an all metal frog if there is a short across the gap to the diverging rail.
“Auto-reversers” do not reverse the direction of the train. They do not reverse the direction on the engine’s DCC decoder. They reverse the polarity of the track in the reversing section.
Just for info, note that you can edit your posts as needed. You will see an edit button on your own posts that others do not see. You can even edit the title.
But sometimes a subsequent reply is a better update. Just fyi.
Some DCC systems allow you to run a single DC locomotive along with the DCC fleet. It will run poorly, but it will run.
But, it will NOT work properly across a reversing section, because the DC engine will reverse when the polarity flips, unlike a DCC engine. It could actually ping-pong back and forth, but will probably eventually just short out with an unresolvable polarity conflict.
bear in mind, the track voltage/polarity is still DCC. As soon as metal wheels bridge the gaps of a reversing section, the auto-reverser flips the polarity on the rails of the reversing section to “match” the mainline rail polarity.
if the polarity of the rails and average DC is now the same on either side of the gaps, why would the DC loco change direction?
The average DC isn’t the same - that’s how zero stretching works, it makes the average DC different instead of net 0, so the DC motor can turn one way or the other.
–Randy
i take back what I said earlier, i think you may be right
so the average DC on the mainline has a polarity, let’s say positive is forward and negative is reverse.
on the mainline, the loco travels from left to right , “>”, toward a reversing section. It crosses into the reversing section gaps and continues to travel “>” until it loops around and is now traveling right to left, “<”, ready to come out of the reversing section.
as it crosses the reversing section gaps at the opposite end the auto-reverser swaps polarity to match the mainline, reversing the polaity of the DC average and the loco reverses direction. It is now traveling “>” again.
The operator now needs to reverse the direction of the loco so it travels “<”. Changing the direction if the DCC control reverses the polarity of the DC average. the loco crosses the same reversing section gaps again and continues on the mainline traveling “<”
on a DC layout, doesn’t the operator reverse the direction on the mainline block when leaving the reversing section?
thanks MisterBeasley
Yeah, I tried the edit button and it acted like it didn’t go through. Hence the duplication
Let me see if I got this right…
- Loco enters auto reversing zone thinking it’s s going forward.
- Auto reverse switches track polarity.
- Decoder tells loco motor it is now running backward.
- Loco continues on thinking backwards is forwards.
?
No. The digression to DC operation on a DCC layout caused unneccessary confusion.
3 & 4 are wrong if we are still talking about DCC. The decoder tells it to go forwards.
To prove it put your loco in the track and tell it to go forward, it does.
Turn in 180 degrees and tell it to go forward, it does. Which is the real forward?
There is no absolute forward based on DCC wiring. The reality of foward is based on the nose of the loco. There is no logical process in the docoder that tells it backwards is forwards.
How do we get ourselves into these situations? Initially, the OP merely asked how a second train reacts when the first train enters a reversing section on a DCC-powered layout.
Rich
I believe people want to be helpful and they also what to show what they know or what might be related to the OP’s question and be helpful to someone else. I’m guilty of both.
Henry, I wasn’t directing that comment at anyone in particular. It just seemed to me that the thread has taken an unintended turn in direction away from the OP’s initial inquiry.
Rich
DCC track voltage does not control the direction of a loco with a DCC decoder. The decoder rectifies the alternating track voltage producing DC within the decoder. DCC commands to the decoder determine the voltage polarity and direction of the motor.
when a train enters a reversing, the reverser swaps the polarity if it needs to, maintaining the polarity as the loco crosses into the reversing section. If this happens, it happens so quickly that any momentary drop in voltage because of the short seems like dirty track to the decoder. There is no change in polarity as the loco enters the reversing section.
at the opposite end of the reversing section, the polarity is changed to match the mainline polarity but has not affect on the decoder because it rectifies the track voltage and is unaware that polarity (phase) changed.
the loco moves in the same direction, forward, as it enters and exits the reversing section.
Think I get it now.
Thanks everybody
Be aware that only one train at a time can cross the gaps at the ends of the reversing section. If a train is crossing the gaps at both ends at the same time the autoreverser will try to match the polarity at both ends, which is impossible, and you will get a short. This can also happen if a single train with metal wheels is longer than the reversing section.
Mark Vinski