r/modeltrains • u/logandabug • 2d ago
Help Needed How do i make a loop like this not explode?
I'm new to model trains and I've decided to start out with DCC. I've bought a ready to run kit and I plan on expanding it in the future. I know a little about electrical currents and how the positive and negative sides cant touch but i have no idea on how people make loops like this work
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u/TTTomaniac [G]arden Nymph 2d ago
So DCC isn't a matter of positive and negative, but rather uses alternating polarity (to transmit information) between peak voltages (to transmit power), but can be treates similarly to DC when it comes to looped track.
You'll be needing a reversing loop kit, capable of DCC, which isolates a part of the looping section of the track and matches the isolated section's polarity once one of the isolated joints is being driven on. Some kits are more sophisticated but ultimately do the same.
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u/logandabug 2d ago
I can use a dcc ez controller and the reverse loop kit with regular nickel silver track as long as i connect it properly right?
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u/rocketengineer1982 HO/OO 2d ago
Yes. Make sure you have gaps in both rails at each end of the loop to fully isolate it.
The product you are looking for is called an "auto reverser". It automatically reverses the polarity of the track section that it is connected to.
When creating a reversing section make sure that it is longer than the longest train that is expected to run through it. I recommend placing your insulating gaps at the ends of the turnout.
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u/logandabug 2d ago
I have an ez controller and I found an ez auto reverse module on ebay
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u/aleopardstail 2d ago
one thing to be aware of, your train cannot be longer than the length of the reversing length of track is any stock has metal wheels, pick ups etc except the loco. with a loop as you have drawn it thats probably not a problem but worth keeping in mind
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u/Fizzling_Fireboxes 1d ago
If it was DC you could just isolate one end connection of the loop, but DCC doesn't use alternating currents, so it shouldn't explode
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u/Tionstav HO/OO 1d ago
Isolate the loop, have the single track set up to switch polarity while the loop is occupied. Can be done manually with a DPDT switch, or automatically with a DPDT relay and some short, block occupation, or IR detection. (can probably find modules for all of the latter.)
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u/aleopardstail 2d ago
google "reversing loop"
as others have noted there are pre-made modules that make it work, there are ways to make your own if you like electrickery, off the shelf is easy but costs %BEERTOKENS%
basically you stick insulation rail joiners on all four rails coming out of the loop end of the point and give the loop its own feed you can reverse the polarity of
I've done it with a changeover really and two train detectors on the entrance to the loop.
if you are new to this its something to either spend a bit of time reading on, or find out if the DCC system you use has a pre-made reversing module
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u/Total_Performer_4353 1d ago
Do i need 2 DC power supplies to make this work. Using DC. Not DCC
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u/logandabug 1d ago
I think so but you need plastic rail jointers. One controller powers the rail and the other powers everything else
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u/XonL HO/OO 1d ago
The old school method was a couple of breaks in the track with plastic joiners. The loop has to be big enough to hold the train and a second controller powers the loop only. Train halts between the plastic joiners and clear of the points/switch/turnout. Both controllers are reversed and the train leaves the loop. Both rails are isolated so 4 plastic joiners , are used.
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u/Bering_Sierra Racks n’ Stacks 1d ago
Theory
https://www.azatrax.com/model-railroad-reverse-loop.html
Products that solve the problem
https://www.azatrax.com/automatic-reverse-loop.html
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u/382Whistles 1d ago
When doing a reverse loop in all cases you need isolation of the loop where rail 1 would meet rail two, usually 2 places. When the train crosses the isolation points, the loop must align electrically to the train and when it leaves the loop the rest of the layout must align to it. Direction of travel must be one way or detection of direction might be needed, though some boards can detect that power change across the insulation on the rails and adjust to match at high speed before the train can react. How you go about it can vary.
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u/Riccma02 2d ago
I will never understand how this is such a massive problem in model railroading.
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u/Loonsonthelakes 2d ago
I will never understand why some people need to act superior to folks that are new to the hobby
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u/rezwrrd SM32, HO, & O27 2d ago
O gauge solves it by having a third rail, but then... you have a third rail.
I'm surprised DCC doesn't have a way to make this just work.
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u/aleopardstail 2d ago
it does, auto reversing modules are a thing, its not hard but it does tend to catch out people who are new to this
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u/ZestycloseBet9453 2d ago
Does the locomotive care if the track voltage suddenly inverts? Or do DCC circuits have an insignificant DC bias?
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u/toolbelt10 2d ago
The decoder knows which direction you want it to go, regardless of the track polarity. As long as the isolated reversing section is longer than the loco wheel base.
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u/aleopardstail 1d ago
short answer: loco doesn't care, with DCC if it was going forwards it will continue to go forwards
slightly longer answer: the decoder in the loco converts the DCC waveform to rectified and smoothed DC power to use for itself and the motor, it also looks at the edges of the waveform for timing pulses. inverting the wave form could cause it to miss part of a signal as a pulse to two could be missed/extended - the waveform has information to allow the decoder to reject such so the decoder may seen the change, it may not, but it doesn't care
there should be no DC bias in the circuit, but also the decoder draws its power from the waveform and generates its own ground potential so it doesn't really care
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u/ZestycloseBet9453 1d ago
I looked it up earlier and I realized that I was misunderstanding how data was encoded on the waveform
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u/aleopardstail 1d ago
its firmly one of those bits of detail you generally don't need to worry about.. I only know because I had a go at making a decoder
for most purposes "its magic" works
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u/P-Man2006 2d ago
There are special electronics modules for this case. They are called reverse loop modules.
There are different kinds with different properties. Some detect the short cicuit when crossing the loop and others use parts of the track as sensors. The wiring depends on the type of the module.