If I create a reverse loop on my DCC layout, does that create a electrical short and what do I need to do to overcome the short?
Yes, it creates a short. You use insulating rail joiners on all four rails leading to the turnout creating the loop. You can then reverse the polarity of the rest of the layout manually be feeding its power through a DPDT switch. Or you can do it automatically using any one of several manufacturers’ auto reverser units. Power from the bus to the reversing unit and then on to the loop.
Good luck!
I picked up a reverse unit made by MRC for $20.00. Yet to hook it up, but my LHS runs them and said they are great. All the other DCC stuff on the layout is Digitrax, only MRC item they use.
Yeah, amazingly the MRC reversing units are quite reliable and inexpensive, I’ve used a lot of them on custom layouts.
I have been using TCH for several years. The price is right and their service great. Verry happy with their products and prices. Small Guy Company. Give them a try. www.tchtechnology.com
Grandpagator
You can also just reverse the reversing section. Yet another cool feature of DCC!
Reversing just the polarity of the reverse loop is the preferred way of doing it in DCC. It’s the opposite of the way it must be done in DC.
The “low-tech” approach of a DPDT toggle may be acceptable, but a toggle is a mechanical device, and there is always a “dead spot” in the center where there is no power being applied to the track. This causes a momentary interruption in the DCC signal. Depending on the locomotive, this may be enough to reset the decoder, causing it to stop and then restart, or it may simply “recycle” the on-board sound.
Auto-reversers are much faster. The lower-budget ones are generally relay-based, so they still have a “dead spot” or “switching transient,” but the interruption should not be serious. The high-end autoreversers, like the Tony’s Trains models, use all solid-state switching which results in no perceptible dead spots.
The only downside to the MRC one from what I’ve heard is that they’re not adjustable. The Digitrax one allows you to adjust the setting so it will work every time. Apparently some folks have had trouble getting the MRC one to work right all the time.
As noted a DPDT switch will work too. I converted to DCC while I still had my previous layout that was DC. Inside of a reverse loop was a station and water tank, so I just had all trains stop there (passenger trains for passengers, freights to take on water or pick up orders) so I used the DPDT reverse switch while the engine was stopped. Pretty basic but it worked on DC or DCC just fine. But the automated one was nice once I hooked that up, nice to be able to go thru the loop without having to stop.
hi,
in the good old days we used two DPDT switches. One for the reverse track or loop and one for the rest of the layout, so you can take the loop clockwise and counter clockwise. I never stopped the engine, just flipped the switch. But entering the loop I had to watch out.
How does it work with an automatic device? Can the loop be still be used bi-directional? Do I need some extra wiring?
Paul
The reverser can be used to reverse the reversing section only. You can change the polarity right under the train, part of the beauty of DCC.
The loop will be bi-directional, the wiring will most likely be less than with DC.
correct me if I m wrong ,the reverser changes the polarity (phase) twice a train ? (once entering & once leaving the loop) is this correct?..Jerry
It depends.
If the polarity is right when the train enters the loop (which would be the case if it enters the same way the previous train exited), then the polarity will only have to change upon exiting the loop. Otherwise, yes, it will change on entry and on exit. But you’ll never know it.
thanks Jeff,now I get it . Jerry
hi,
but can some one explain what is happening?
The automatic reverse device (ARD) must know the position of the switch, must know when the whole train is on the reverse section and act correspondingly.
I assume an extra pair of wires from the switch are going to the device. So the ARD knows if it has to adjust polarity. Then when the whole train (or the engines, incl. helpers) are on the reverse track it can change the polarity (under the train). Or is this done by setting the turnout in the proper direction? Do I have to do it, or is this done by the ARD?
Paul
Paul,
The ARD doesn’t need to know the position of the switch at all. All it has to do is sense a short between the entry track and the loop, and flip the polarity of the loop track to correct the short. The MRC autoreversers have four wires coming off of them. Two go to the entry track (or mainline, if you prefer), and two go to the loop/wye track. Very easy. I can’t comment on any other ARD because I have no experience with them.
Several people have had trouble with auto reversers that have been hooked to the tracks where the circuit breaker tris before the reverser. Generally this is solved by connecting the non reversing loop side of the reverser to the shortest bus back to the command station or booster. For example I have a main bus for the power and sub-busses for each section/power district of the layout. When I connected the reverser to the entry track, a train entering the reverse loop would short out the system, so I connected the reverser to the main bus and it resolved the issue.
Simply, the reverser is wired in concert with the bus, and the bus is wired to the main tracks on the layout. So, the two share that commonality.
Regardless of which end of the loop the engine encounters, the reverser is happy as long as there is no disparity between the polarity the engine passes through as it crosses the gap. If there is a short, there is a change that the reverser detects and neutralizes immediately via a polarity change, but it does this only via its outputs which provide power solely to the loop portion that is isolated for that purpose.
There is no double switching of polarity…not under any circumstances. The reverser only has to switch at one end of the reversing section, unless the main feed it gets is also reversed during the train’s transit of the reversing loop…and why should that ever happen? Instead, your main layout bus feed is constant, and that is what anchors the reverser in terms of a reference for detecting shorts.
If there is no polarity disparity, the engine passes over the initial gaps without incident. We know, logically, that it can’t be the same case at the other end; we would expect a short to take place at that other end, except that the digital reversers effect it seamlessly…no discernible switching…ever.
I use the PSX-AR, a very good investment for my own way of enjoyment.
-Crandell
I use Digitrax DCC on my layout and a PM42 to handle the auto reversing and also power districts. I like the PM42 because it is programable and versital. it has 4 “channels” that it can run off of and those 4 channels can be set for power districts or auto reversing or both. Right now I have 3 districts and one reversing loop configured. You set the type of device it is by the poles you solder your wiring to and you set the delay and pause via the loco bus on with your throttle. I have both my reversing loop and short circuit detection set to the fastest setting and so far no problems. I dont know how the PM42 would react to several sound powered locos all powering up at the same time, I have had 5 on my rails in one district at one time and it powered up just fine. This is not the cheapest device for reversing out on the market but it does have more versitility than most other devices.
My rev. loop is connected to the DCC bus through the one small electronic board, divised and done by my friend, electronic wiz. [;)]
There is no need to sensing short circuit in the loop, because I have (on the both ends of the loop) small, cca. 10 milimeters isolated gap in the track, which works as a signaling sensor. When locomotive or car wheels carry dcc signal to the “sensor track”, electronics decides does the segment needs to change polarity. Polarity is reversed only on the loop segment, never on the rest of the layout.
It performs flawlessly ever since I installed it, tested with the 2-axle locos - no problem. Price of the electronics was maybe 15$.
Negative is that you need to cut your track on four places, and wiring can be little more complex than “short reversers”…
Hi Crandell,
so when I understand you right:
when a train is entering a loop and makes a short (due to polarity disparity) the polarity is changed with the “speed of light”; that fast that nobody noticed.
Sounds logic.
Paul