I’ve been thinking about getting an “auto-reversing” unit for my layout. I’ve had a reversing section of isolated track on my layout ever since it’s creation 13 years ago, but occaisionally I still “forget?” to manually switch polarity in time to avoid tripping the breaker on my DCC unit. I have read somewhere that tripping the breaker in these things is not always a good thing, so I have recently installed an inline fuse that trips before the unit does. Anyway, sometimes I run some old STRAIGHT DC locos on my tracks. What would I do with the “Auto-reverser” in this case? Would I have to elecronically ISOLATE it in DC, and go back to manual switching?
The only reverser I know of for DC is the DPDT switch.
Rich
So, you’re running a DC locomotive on your DCC layout, right? And you want to use an auto-reverser instead of a toggle?
It won’t work. An auto-reverser works by flipping the polarity of the reversing section. A DCC engine will keep right on going when you do that, but a DC engine running as “Engine Zero” on your DCC system will reverse direction. If you just let it run, either the engine will “ping-pong” between the ends of the reversing section, or it will get stuck at one end and short out.
I don’t think this is what he is asking. I believe that he is saying “I want to run a DC loco with a DC power supply. Do I have to electrically isolate the DCC auto-reverser?”
I agree with you, maxman, that he is running DC locos with a DC power supply on a DCC layout.
I cannot answer his question except to say that since the AR unit will not work, he is creating an unresolved short and may be damaging the AR unit. On the other hand, if the AR unit doesn’t work on a DC powered track, it may not be damaged if it is inoperative to begin with.
Let’s see if someone can answer this question.
Rich
There are two problems. It’s not necessarily that the autoreverse won;t work in DC, it’s more like it won;t have the expected results. The all-electronic type may not work at all on DC. The relay type, all teh really are is a DPDT switch that is automatically operated.
Problem is - it reverses the wrong section of track. With DC, when you enter a reverse loop off the main, you then change the polairty of the MAIN to match the exit side of the loop so the train can continue on. With DCC, you are changing the polarity of the loop track since the polarity (really phase since it’s a bipolar square wave) has no bearing ont he direction of travel of the loco.
So even if the autoreverser would detect the short and operate, what would happen is you train would instantly reverse direction. Until it tried to back over the gaps at the entrance of the loop, in qhich case it would instantly change direction again - poor man’s back and forth shuttle.
If the track is a simple balloon loop, it is entirely possible to make it ‘automatic’ in a way that would work with DC and DCC. It requires that you always traverse the loop in the same direction though. Track polarity would eb controlled by switch machine contacts (or for more current carrying capcity, a relay triggered by the switch machine contacts). Instead of the typical DCC method of feeding the loop itself through thise revesing ‘switch’, you would feed the main. Thus the polarity will match for the train entering the loop. Once within the loop, the turnout needs to be thrown, and the main line polarity will flip to match the exit side fo the loop.
This can also be made to work with a wye.
–Randy
The AR unit will be “locked” into one position - the DC supply / engine won’t make it work, but it won’t hurt it either. The simple solution would be to add a DPDT reversing switch between the AR and the track. Use the DPDT switch when operating DC, on DCC, the AR will work normally as it should and just feed through whatever position the DPDT switch was left in.
Mark.
My layout operates DCC and DC via a selector switch. I run mostly DCC, but I occaisionally want to run “the old stuff”. From what I’m reading, I probably need to install some switches so’s I can isolate it during DC operation. I kinda figured that…thanks fot the input!
If I understand correctly what Mark recently replied, you won’t need to “isolate” it. Just install it as you would for a strictly DCC powered layout.
Rich
Hi, newbie here. I’ve been looking for the mythical DC auto reverser for a looong time and every one I found was for DCC, even digitrax AR1. I just found another and was wondering if any has experience with it:
Oops! I just read the ad again. I think this a trolley type reverser that just goes back and forth. Sorry, remember I am a newbie.
1 Like
Yep, you beat me to it.
First, let me say that Circuitron makes quality products. My layout (DCC) is littered with Circuitron devices.
Second, the AR-2 is designed for DC operation, but it is primarily intended for point-to-point operation since it reverses track polarity causing the motive device to reverse direction. That said, it will work as an “auto-reverser” if your layout has a true “reverse loop” as opposed to a “reversing section” by reversing polarity in the non-reversing section adjacent to the reverse loop.
Rich
The best DC wiring schemes are designed to have the operators think in terms of “East and West”, not forward and reverse.
So think of a single track mainline connected by two loops. Your primary reversing switch for the main line should reflect your direction of travel. Then each loop needs its own separate direction switch connected to the throttle “before” the mainline direction switch.
The loops should be marked to match the loop polarity with the position of the turnout entering the loop. In other words let’s call going clockwise around the loop “West” and counter clockwise “East”.
So then you set the turnout to enter clockwise into the loop, and set the loop reverse switch to “West”. The polarity is now correct for the West bound train to enter the loop in the clockwise direction.
Once the train is completely inside the loop, you switch the turnout to let the train re-enter the mainline. And you reverse the mainline direction switch to East - because that is the direction the train will now be traveling.
The train then exits the loop and continues to travel now going East on the mainline.
So more effectively described, the loops are a place to “hold” the train (even if it is moving) while you reverse the direction of the mainline.
For this reason, any scheme to automate this process is full of problems.
One other way to approach this is to wire the loop so it’s polarity is the same as the mainline using a relay or contacts on the switch machine. Using this method the loop will always be the same polarity as the mainline based on the turnout position.
The loop is still isolated, and its polarity changes when you throw the turnout.
So you drive the train into the loop. You cannot change the turnout with the train running, it will stop and go in reverse. But, if you stop the train, reverse the mainline polarity, throw the turnout, you can now restart the train and proceed out of the loop.
Advantage? you don’t have to make sure the loop is preset correctly. Disadvantage? you have to start and stop the train.
In both cases you are reversing the mainline, not really the loop.
You can use this method with a dead end Wye as well, West bound train drives into dead end leg, turnouts switched to exit via leg opposite the one entered from, train moves in reverse now but still West bound out of other leg. Train stops, turnouts set to the direction the train came from. Mainline direction changed - train proceeds forward and has been turned around and mainline direction switch now reflects “East” bound travel.
Sheldon
Thanks Richotrain
Thanks AC it’s gonna take a long time to digest
Sheldon has the logic of the reversing circuits down pat, especially the part about “east vs west” instead of “forwards and backwards” as the direction the train travels depends on the polarity of the track and not how the train is pointed.
Don’t worry about needing to take time to digest.
Yep, that is the right way to reference direction in DC. 
Rich
it’s better to have separate reversing switches for both the reverse loop and mainline. The mainline reversing switch needs to be toggled after the train enters the reversing section.
the trick is making sure the reversing section polarity matches the mainline polarity depending on the turnout position. An LED/resistor wired across one of the gaps would be ON when they are not
1 Like
Greg, that is EXACTLY what I described. I clearly stated that just like your drawing the loop feed needs to be ahead of the mainline reversing switch.
There is no “trick” to matching the polarity, that is why for 70 plus years DC modelers have used the conventions “East” “West” and “clockwise/counterclockwise” to define mainline direction and direction thru the loop.
Sorry my explanation did not fit into a sound bite number of words and cute graphic.
Sheldon
1 Like
One more note, back in the day, a great many modelers were not using “off the shelf” “power packs” with built in reverse switches. Many where building their own.
So there was no “built in” reverse switch to consider.
Those who did use power packs knew that once they introduced a reverse loop, that the built in reverse switch would be rendered unused.
Even the inexpensive Atlas wiring components clearly explained and provided for this.
Sheldon
1 Like