# DCS and Reverse Loops



## Tom Bray (Jan 20, 2009)

I have gone through the list looking for some good information related to implementing reversing loops but I haven't found what I need. Most of what I have found seems to be focused on LGB system, controls, and their accessories. While I do have a LGB trolley, the bulk of the rail system will probably be powered by MTH locomotives and ultimately their DCS system. The track is Aristo-Craft SS and most likely the switches will be too.


In the process of designing my layout I am trying to decide whether or not to include a reversing loop in the system. I like the idea of being able to turn the a train around and have it go the other direction but I am concerned about the mess this is going to make out of the controls. Regardless, I may want to run trains in the opposite direction. 


It appears that using DCS, the polarity of the track voltage and the polarity of the control signals must be matched to the direction the train is facing. I assume that all I need to put a double pole double throw (DPDT) switch into the system to deal with trains running in different directions, regardless of whether I do it will a loop or manually pick the locomotive up and turn it around. Correct?


Can the track controllers, particularly the MTH ones, assist in automating this activity? Is there a way, using sensors, to tell the track controllers to do this automatically? Is there a controller that would adapt to this environment from another manufacturer? (I know I can do this pretty easily with an independant controller, such as a Basic Stamp or other micro controller but ... at least for now, I would rather not go that route)


----------



## Torby (Jan 2, 2008)

Sorry, I have to say it










Reverse loops don't bother battery powered locos.


----------



## John Allman (Jan 2, 2008)

Tom - if you send a DCS controlled loco through a reverse loop, the engine will continue on exactly the same speed and direction as before. But you are correct that the DCS signal would not be getting to a PS 2.0 equipped engine. So to regain command control, you need to reverse polarity. You can do that with a DPDT switch. You could also connect that switch to the AIU connected to the TIU, and control the polarity from the remote.


----------



## Greg Elmassian (Jan 3, 2008)

No you don't have to say it Tom. 

DCS does not need a battery car, or drilling holes in your loco for a charging plug, or recharging when it's most inconvenient, or chargers for that matter, and DCS users can run smoke and lights all day without worrying about running down the batteries faster. There's other advantages. 

Now when I say "sorry I have to say it".... that makes it reasonable and helpful? 

Back to the subject, I'm not a DCS expert, but cannot you run DCS on AC? If so, possibly a DCC autoreverser would work. 

Maybe Chuck or Raymond know. 

Regards, 

Greg


----------



## Tom Bray (Jan 20, 2009)

I thought about running the system on AC but based on reading the MTH online manual, it appeared that I still need to have the DCS signal going to the correct set of wheels which negates the advantages of AC. So it came back to the need to swap the signals regardless of whether or not I ran AC or DC. Is that correct?


I also see the there is an opinion that AC has more noise, or whatever, and that the DCS systems have more trouble communicating. I have no idea if this is a totally valid view or not or if it is a carryover from the O Guage community.


The other problem with AC is that if I want to be able to run guest trains, I may need to be able to switch to DC power and run the whole thing on manual mode.

Batteries aren't really an option right now. I am trying to control how much technology and cost I throw at this thing to get my feet wet. My goal is to get a basic layout functional, then add DCS, and finally add any additional automation that I can dream up.


----------



## John Allman (Jan 2, 2008)

Yes, AC will not work in the way you want it to. It works for 3 rail as you desire. Stick with a method of reversing the polarity. You could even use an LBG accessory switch motor to automatically change the polarity. I think your idea of getting the RR up and running is a good idea. I have found that once the RR meets up with outside conditions, it's best to keep things simple. Therefore, if you don't need the reverse loop, don't use it. If you need it but are able to create a loop in addition to the reversing path, do that.


----------



## Rayman4449 (Jan 2, 2008)

It is true that polarity need to be correct for the engine to operate right but once you have it running you will follow the same rules after that as any track power based engine... You have to flip the polarity on the return track to keep the engine from shorting out when it re-enters. So, if you put the TIU between your power source and the reversing loop controller it will work fine as the signal will always be on the + lead. The only question would be would the reversing loop electronics negatively impact the DCS signal. My guess is probably not but it is a possibility. If it does I think I know of a way to fix it, just report back. Actually report back anyway, I will be interested to hear of a successful implementation and would like to document it on my website for other users.

That is an interesting idea Greg as on a DCC reversing loop setup. Something to look into. 

I like John's suggestion too, get up and running and see if you really end up wanting or needing it. 

On the difference between AC and DC power and it's effects on signal strength, the opinions I've heard so far indicate there isn't a difference. (But that doesn't mean there isn't. I've heard some good reports from AC users on long linear feet loops.) The biggest impacts I have seen so far that impacts DCS signal is 1) Stainless steel track over Brass. I think the electrical resistance of the SS rail is detrimental to the signal over longer runs or higher amp levels. Good feeder lines really help with this. Folks using brass rail can run long loops with no feeders and never seem to have track signal issues. 2) is power supply type. If you are using what I hear are called a 'linear' supply (which are more expensive and are heavier[from the large copper wound transformer inside]), you will get better track signal than if you use the much cheaper and lighter 'switching' type supplies. 

If you know you're going track power then I highly suggest you do it right from the get go and use all direct to rail stainless steel railclamps (I like splitjaws) and add your feeder wires. On my DCS tips page on my website I have information on the type of wire I used and how often I connected the feeder wires. I did a buss configuration so I only had one set of wires going from the house to the track then ran jumps every 24 feet or so from that point till I made a complete loop. If you do it right from the start, you will save yourself aggravation and time. With my setup, I haven't had to mess with anything and I'm going on 3 years now. 

Good luck and let us know how you make out.


Raymond


----------



## Enginear (Jul 29, 2008)

I run my MTH on AC. It has many advantages and no noise problems. AC packs are cheaper! A good DC pack is required or you'll suffer. There are rules on the wiring and it would be easier to direct you to the correct site. I have been told that dcs will operate on a reverser but I've never tried it. Ray's site is excellent for startup info on dcs. http://www.rayman4449.dynip.com/ look at the dcs pages and save this site. For great help in any DCS problem got to http://ogaugerr.infopop.cc/eve/forums/a/frm/f/93360682
these guys will answer and help out future problems.
For wiring remember to break up loops, only connect one feed to each block of track so the dcs signal does not double back on itself, and connect a light bulb or resistor to clean interference as needed. Joe


----------



## Rayman4449 (Jan 2, 2008)

Yeah I would read the info I have on my site so you can see what my experience has been too. I've found that us in G scale don't seem to have the same issues regarding maximum feet of rail that can be served per block. I've heard of G scale folks with 230+ ft loops with brass track and clamps and have power wires going to only one spot on the loop and they have perfect 10s all the way around. From all my testing and experimentation, I went with a buss feeder wire configuration which does go against the conventional wisdom on the O gauge forums but I've gotten mine to work great. That is just my experience.

Very interesting on being able to use cheaper style AC power supplies, I hadn't heard that and will need to try that out when I have time. If we can in-fact just use cheap regulated AC power supplies with no negative effects or even better results then this is really great news! Joe, how many amps is your power supply and about how much did it cost? Is it a constant voltage AC power supply?


Raymond


----------



## Rayman4449 (Jan 2, 2008)

Can someone suggest a good source for cheap AC regulated power supplies? I'd be looking for a 24v - 30-40 amp.


Raymond


----------



## Greg Elmassian (Jan 3, 2008)

Ahh!! you will not find a regulated AC supply, they are pretty expensive... 

The upside of regulated supplies is that voltage (and thus the running speed) will stay constant under load... so 2 more locos are started, and the rest that are running are not affected. 

Running an unregulated supply can make a noticeable difference in speed when you change the load a lot... notice the words "can" and "a lot" 

I noticed a difference on my DCC layout but I run consists all the time 2-6 locos. 

Talk about varying load! 

I still think that I would try AC and various DCC autoreversers. 

Question, when running on AC, does a DCS loco not care about track "polarity", i.e. it will go forward, no matter what way it is placed on the track? 

Regards, Greg


----------



## Enginear (Jul 29, 2008)

Hey Ray, it took so long to type, you replied before me. Anyway all I use is a Lionel 180 power brick that's under $80.00!!!! It's only going to give about ten amps so I'll need to buy another one soon. I thought it was the best value for the buck. You could hook up one to each of the four channels of a TIU I'm told. Ray, I know you run passive so your not concerned with TIU amp capacity. An electrician at work said a good computer supply might have worked also. Joe


----------



## Enginear (Jul 29, 2008)

Gregg, with AC you still have to "worry" about polarity. I don't know if the engines will short or just run without dcs signal. I'm told that DCC reversers will function with dcs. Joe


----------



## Rayman4449 (Jan 2, 2008)

Ok. Thanks Greg and Joe. 

You do still have to get the polarity correct even on AC. Of course the polarity switch on the engine makes correcting the polarity quick and easy.

That Lionel 180 I bet is a 180 watt (~ 10amp at max 18 volt output?) 

Hmmm.... I'll need to look more into the AC power supply thing. Thanks for the info.


Raymond


----------



## Greg Elmassian (Jan 3, 2008)

If the polarity matters, then you may need something more sophisticated, entering a reversing loop means the loop might have to reverse... leaving the loop, the main line HAS to reverse. if you put an autoreverser on the main line, and then set the switch entering the reverse loop to SELECT the route that "matched", then when you exited the reversing loop, the autoreverser would change the main to match your polarity. 

I could make this work... 

Regards, Greg


----------



## Rayman4449 (Jan 2, 2008)

Oh and the computer power supplies I think are going to be just like any other standard switching power supply I bet (as far as impacts to signal strength) and we are talking DC power now with that. Another issue with the computer power supplies is that they have constant 12v and 5v outputs. 

Thanks for the confirmation too on the DCC reversers, good to know! 

Would a DCC reverser need to be used with AC track power only or could it work under DC?


Raymond


----------



## Greg Elmassian (Jan 3, 2008)

I have been unable to find an autoreverser that works on DC... I have looked several times. 

Regards, Greg


----------



## Rayman4449 (Jan 2, 2008)

Posted By Greg Elmassian on 01/21/2009 8:46 PM
If the polarity matters, then you may need something more sophisticated, entering a reversing loop means the loop might have to reverse... leaving the loop, the main line HAS to reverse. if you put an autoreverser on the main line, and then set the switch entering the reverse loop to SELECT the route that "matched", then when you exited the reversing loop, the autoreverser would change the main to match your polarity. 

I could make this work... 

Regards, Greg


I don't know much about how auto reversers work, but I agree with that. You would have to reverse the main line polarity. If you put the TIU between the power supply and the autoreversing unit then you hopefully shouldn't have any issues.

Isn't that how they normally work, the engine enters the loop and when the last car enters the loop the main line polarity flips?


Raymond


----------



## Enginear (Jul 29, 2008)

Hey Greg, Ray and all, look at this comparison page if you want, maybe smaller scales but good info on protection!
http://www.tonystrains.com/technews/dcc_autoreversers.htm
Joe


----------



## Tom Bray (Jan 20, 2009)

I have a feeling some poor beginner looking at this thread is going to run away screaming ...

Lets clear a couple of things up.

When running on AC, there isn't polarity. The train isn't going to be able to tell which track is on which side of the AC power. It does swap the relative phase of the AC signal but I don't know of any motor that will run on 2 AC wires that is sensitive to this difference (with 3 phase, that is a different story but we only have 2 rails). Most likely the motors are really DC motors and there is a full wave bridge rectifier built into the motor controls to convert the AC into to DC.


If you take a Lionel train set to go forward and you swap the wires going to the rail, it still goes forward. Additionally, the center rail is used on the Lionel as one half of the signal and both outside rails for the other half, turning the train around still has the positive DCC signal in the center and the negative on the two ouside rails, so there isn't a problem there either. One thing this approach does is that it makes doing a reverse loop a piece of cake because there is no way to short out the power through the trucks as locomotive goes across the turnout.


Now back to the more realistic stuff we run with only 2 rails. If doing a reverse loop, we still need to somehow swap the AC signals so that the engine trucks don't short out the power as it goes across the turnout. It is possible to switch the polarity within the loop as the turnout changes position but that requires dropping the power momentarily during the turnout transition. The transition must be what is called a break before make action which means that power goes to zero for an instant on the loop track. The engine electronics may not like that, then again maybe it will just deal with it because there are already going to be small interruptions in power as the locomotive moves around an imperfect set of rails. 


So can someone illuminate this loop controller or whatever it is called, that has been mentioned and where can I find more information on it?


Thanks

Tom


----------



## Greg Elmassian (Jan 3, 2008)

I was sitting here saying to myself "I cannot believe DCS would not be phase-sensitive" when running on AC... That's the reason DCC runs on AC (square wave yes, but Alternating Current). 

So, I pose the question again: you have an AC DCS layout. You tell the loco to go forwards and it goes forwards. You switch the leads to the track, does the loco still go in the same direction? 

In DCC the answer is yes. 

In DCC the autoreversers trip pretty quickly, and the locos do not glitch. 

I don't know if loop controller means autoreverser, since you are the only person to use that phrase in this thread, but if it does, many of them are made. 

Tony's train exchange sells one that is great, made by DCC specialties (owned by Tony's Trains), I have the PSX-AR. Digitrax makes them, MRC, Lenz, basically anyone who makes a DCC system. 

My DCC booster also has one built in. 

Regards, Greg


----------



## Enginear (Jul 29, 2008)

Yes I believe you are correct also that most trains do have a bridge rectifier to convert to dc for their motors. I am not an electronics guru. The DCS signal is polarity concius though and needs to get to the engine on one rail and returns info on the other. 
The link I showed above points to Tony's train EX for comparisons on some popular dcc reversers and breakers. Hope that helps. Go to their main page and products for more, Joe


----------



## John Allman (Jan 2, 2008)

Greg - the answer to your question is yes. A DCS engine set in forward goes forward, no matter what the polarity. It is not necessary to have AC power for a reverse loop using DCS commmand control. 
Imagine a DCS controlled locomotive running down the track to a reverse loop. The engine operates normally with complete control. Once inside the loop, the engine would still be under DCS control, because the polarity has not changed. The mainline polarity is reversed once the train is inside the loop. Command control is not lost, and all is well. 
You do not need anything special to reverse the polarity. You can do it with a LGB accessory switch, or DPDT switch of your choosing. I guess an DCC autoreverser would work too, but that seems more than required. 

Now suppose when you placed the loco on the track, you put it on facing the "wrong" direction, so that the polarity was backwards and the DCS system can not "see" the locomotive. Power up the track and what happens? The locomotive starts up normally, and runs like a conventional engine. (Meaning, in this case, it goes forward) Reverse the power, without waiting for the engine to shut down, and the locomotive will go in reverse. Now, for fun, push the "start up" button on the remote and what happens? The locomotive is again under command control. However, it does not stop just because you put it in command mode. It continues on doing whatever you had it doing before, until or unless you send it a new command signal. 

I have run the system exactly this way around my Christmas tree. Creating a reverse loop for DCS is exactly the same as creating it for conventional track power. It may be simpler in DCC, I don't know. But I do know it is not required. It makes no difference to the system or the MTH engine if you use AC or DC.


----------



## Rayman4449 (Jan 2, 2008)

I think John covered it well.

Just to summarize for newbies reading this, you can run a DCS engine under:

Analog AC power (with a manual throttle type power supply and no TIU or remote) Note: if throttle power supply has whistle and bell button you can trigger those sound with the transformer. Also has a reverse button
Analog DC power (with a manaul throttle type power supply and no TIU or remote) Note: no DC throttle power supplies have a whistle or bell button. To reverse just flip the forward/reverse switch on the transformer to reverse the polarity.
With TIU and remote (Command control with constant track voltage) under AC power
With TIU and remote (Command control with constant track voltage) under DC power

You actually can also run your trains under Analog AC power WITH the TIU and remote. You can apply a fixed voltage (say 18-24v) to the input Var1 or Var2 ports and vary the voltage output on each port Var1 and Var 2 output ports with the remote. You can't vary the voltage output under DC power and of course the output power from the TIU is AC if the input power is AC.

Oh and when running your engine under command control, the speed of the engine won't vary even if the track voltage varies. If you have your engine(s) dialed in to run 26 SMPH on your remote and you have 24v voltage applied to the track and then lower the track voltage to 18v the engines will maintain the same speed. The speed control for DCS is controled by the optical reader and as soon as it detects a slow down in speed it will increase power to the motors to keep it going at the dialed speed. I've tested it and it does work that way. Now running at 18v as opposed to 24v will lower your max top speed and lower the total amount of torque the motors will have but that's it. (I've found this out through testing also)

Raymond


----------



## Greg Elmassian (Jan 3, 2008)

Yes, an autoreverser is a nice convenience, and since DCC (unlike DC) can reverse any section of track at any time with no disruption, it a nice deal. 

What happens if you reverse the track polarity "under" a DCS locomotive while it is running? (AC on the rails) I would hope it would ignore it, like DCC does. 

If so, then using an autoreverser on DCS (running AC) would function just like DCC, and it's operation would be transparent, and no other hardware would be involved. 

If it does not work this way, then the way I suggested might work with an autoreverser, but reversing the main line would mean other locos on the main line would be affected. 

This is interesting, I never hear of how DCS handles reverse loops. 

Regards, Greg


----------



## adelmo (Jan 2, 2008)

I was always told that reverse loops are out for DCS operation. 
Another reason I hope next run of MTH One Gauge will have DCC option.
I am happy with DCC and will wait for Proto 3.0
Alan


----------



## Rayman4449 (Jan 2, 2008)

Yeah as John said, there's no reason it can't be setup to work.

I wouldn't think anyone who has already committed to a control system like DCC would be interested in switching to something else anyway. If something with twice the sounds or features came out tomorrow, I wouldn't switch from what I use (DCS) either. It's not likely to be worth the effort or expense if you are happy with what you have. 

Current estimates are late 2009 for the DCC control option in the DCS boards but that date could get pushed out.


Raymond


----------



## Greg Elmassian (Jan 3, 2008)

Is it going to be a firmware upgrade, or new boards Raymond? 

And I agree with the rest of your posts, and as I have stated before, if MTH was online with all their locos when I started, I might be 1:32 today! (and DCS). 

Regards, Greg


----------



## Rayman4449 (Jan 2, 2008)

I've been told by MTH that it will be a hardware change. 

It's going to be really interesting to see where the state of digital control will be in the next 10-20 years. What we have already in DCC and DCS really bring our trains alive.


Raymond


----------



## Torby (Jan 2, 2008)

Actually, the reason a lionell can reverse loop is the center rail is "hot" and both outsides are neutral. He designed it this way so it could do reverse loops and the like 'cause the right rail never goes to the center rail.


----------



## Greg Elmassian (Jan 3, 2008)

Yep, a very smart idea that has worked for years. Also, people who run from catenary can enjoy the same simplicity. 

Regards, Greg


----------

