If I have a reversing loop controlled by a DPDT switch, and the engine is across one gap and a powered car is across the other, won't there be a short either way the switch is thrown? Is there anything you can do about it or do you just have to make your trains the right length? Will this also happen with a DCC auto reverse loop system?
Modeling the Maine Central in N scale.
I can only speak for DCC, but there a short will occur if the engine bridges one gap and a powered car bridges the gap at the other end, regardless of which way the turnout is thrown. Your best bet is to make the reversing section longer than your longest train.
Rich
Alton Junction
In all articles about reversing loops DC or DCC all explain that the reversing loop should be longer then you longest train!
Johnnny_reb Once a word is spoken it can not be unspoken!
My Train Page My Photobucket Page My YouTube Channel
For DC running, the only way to wire a reverse loop is to use two dpdt switches; one for the reverse loop and one for the main line. There is a Model Railroader issue September 2003 that explains all this. Or you could read Kalmbach's Easy Model Railroad Wiring book. Hope this helps.
-Paul
The situation you describe will cause a short in both DC and DCC. If the powered car or engine is wired so that each truck only gets power from one rail, though, you might get away with this. I have some passengers cars that are wired this way.
Even an unpowered caboose at the tail end of the train can cause this problem if it has metal wheels, which will briefly bridge the gaps, but for a shorter time than an engine.
A DCC auto-reverser, particularly one of the fast-acting solid-state ones, might let you get away with this sometimes. As long as the train is moving, the condition is dynamic and might only persist for a moment. So, you might get to "coast" over the problem while that poor auto-reverser is trying frantically to resolve it.
It takes an iron man to play with a toy iron horse.
Question from the clueless: Could this situation be (sort of) resolved by having separate circuit breaker protected sections before the reverse loop, in the reverse loop, and after the reverse loop? The assumption being that unless the train is incredibly long, and many trailing cars will be shorting the track, the engine being in a section protected by a circuit breaker couldn't it just drag the one or two trailing/shorting cars through the short? Like I said, I'm clueless, so be kind...
Sean
HO Scale CSX Modeler
Colorado_Mac Question from the clueless: Could this situation be (sort of) resolved by having separate circuit breaker protected sections before the reverse loop, in the reverse loop, and after the reverse loop?
Question from the clueless: Could this situation be (sort of) resolved by having separate circuit breaker protected sections before the reverse loop, in the reverse loop, and after the reverse loop?
If the existing reversing section takes up the entire reversing loop, then the section before the reverse loop and after the reverse loop are one and the same.
If the reversing section does not take up the entire reversing loop, the solution is to enlarge the reversing section until it either a) is longer than any train to be run through the reversing section; b) takes up the entire reversing loop - which ever of the 2 is shorter. Obviously, if the reversing section is as long as the reversing loop, you can't' physically run a train longer than the reversing section through it, and there is no issue with both gaps being bridged at the same time.
The same is true with the wye tail. Make the reversing section the entire wye tail including the wye turnout. Then you can never have a train too long for the reversing section.
I don't understand the aversion to making the reversing section as long as possible to avoid this known situation. It may take a few more gaps to accunt for all the branches of the reversing section, but it will prevent short circuits.
my thoughts, your choices
Fred W
fwright I don't understand the aversion to making the reversing section as long as possible to avoid this known situation. It may take a few more gaps to accunt for all the branches of the reversing section, but it will prevent short circuits. my thoughts, your choices Fred W
Me too.
Jim Murray The San Juan Southern RR
fwright ...If the existing reversing section takes up the entire reversing loop, then the section before the reverse loop and after the reverse loop are one and the same...
...If the existing reversing section takes up the entire reversing loop, then the section before the reverse loop and after the reverse loop are one and the same...
Doh! Thanks, for the simple explanation for the simple-minded, Fred.
fwright I don't understand the aversion to making the reversing section as long as possible to avoid this known situation. It may take a few more gaps to accunt for all the branches of the reversing section, but it will prevent short circuits.
I share your view. Once you realize that you have a reverse polarity situation, make the reversing section as long as possible, at least as long as your longest train. That sure seems simple enough.
fwright Colorado_Mac: Question from the clueless: Could this situation be (sort of) resolved by having separate circuit breaker protected sections before the reverse loop, in the reverse loop, and after the reverse loop? I don't understand the aversion to making the reversing section as long as possible to avoid this known situation. It may take a few more gaps to accunt for all the branches of the reversing section, but it will prevent short circuits.
Colorado_Mac: Question from the clueless: Could this situation be (sort of) resolved by having separate circuit breaker protected sections before the reverse loop, in the reverse loop, and after the reverse loop?
If the reversing loop turnout is controlled by a Hare set for auto-throw, then gapped *throw and clear* trigger rails must be put in (at least) two seconds of travel away from the turnout, that along with the fact that DCC Specialties recommends that the trigger rails and auto-reversing gaps *not* be adjacent to one another, pretty much means that the reverse loop gaps can *not* take up the entire reverse section.
I am currently pondering this exact problem, i.e., I either run with a reversing section that is smaller than my largest train (I guess I'll try the different districts on each end of the reversing section), or my trigger rails will be much closer than *two seconds of travel to the turnout*, which means my engines will halt while the Hare moves the tortoise's turnouts.
Or I guess an earlier poster suggested making sure that any powered trucks only receive power from one rail at a time ... if that works, that would probably be the best solution?
-aka
WWtrain If I have a reversing loop controlled by a DPDT switch, and the engine is across one gap and a powered car is across the other, won't there be a short either way the switch is thrown?
If I have a reversing loop controlled by a DPDT switch, and the engine is across one gap and a powered car is across the other, won't there be a short either way the switch is thrown?
Yes.
Is there anything you can do about it or do you just have to make your trains the right length?
The only way to "fix" this is to prevent it from happening by not allowing any train to be longer than the reversing section.
Will this also happen with a DCC auto reverse loop system?
Chris van der Heide
My Algoma Central Railway Modeling Blog
Colorado_Mac Question from the clueless: Could this situation be (sort of) resolved by having separate circuit breaker protected sections before the reverse loop, in the reverse loop, and after the reverse loop? The assumption being that unless the train is incredibly long, and many trailing cars will be shorting the track, the engine being in a section protected by a circuit breaker couldn't it just drag the one or two trailing/shorting cars through the short? Like I said, I'm clueless, so be kind...
Probably not. The auto-reversor should still flip the voltage polarity as soon as it detects the short, and the circuit breakers will flip off. When they come back on, the train is still bridging both ends, so they short again. The auto-reverser keeps trying to switch its polarity to fix the short, but either way it's still shorting.
The number of cars that are trailing beyond the end of the reverse loop doesn't matter. The thing that will cause the short is an engine at one end with some of its wheels on either side of the gap, and another engine or car with electrical pickup (lighted caboose or passenger car) across the gap at the other. Having them both bridge at the same time will cause a dead short and kill the system (i.e. trigger the circuit breaker protection).
Another simple-minded Coloradan has a simple-minded question/solution:
Isn't the issue the electrical length of the consist?
Why not put plastic wheelsets on your last few cars (and use battery light if you have to have lights in those last few cars)?
Problem solved, right?
The St. Francis Consolidated Railroad of the Colorado Rockies
Denver, Colorado
St Francis Consolidated RR Another simple-minded Coloradan has a simple-minded question/solution: Isn't the issue the electrical length of the consist? Why not put plastic wheelsets on your last few cars (and use battery light if you have to have lights in those last few cars)? Problem solved, right?
That's sure one way to do it.
akadams Or I guess an earlier poster suggested making sure that any powered trucks only receive power from one rail at a time ... if that works, that would probably be the best solution?
That will help somewhat with the reversing section, but it certainly isn't something you want to do. The whole idea of all-wheel pickup is to improve power distribution, so by using fewer wheels for pickup, overall engine performance would suffer. You would see more flicker on lighted passenger cars, too.
It will also not completely eliminate the problem. Even a single truck will still bridge a gap for a short time. A single metal wheel will do this in some circumstances. If you use insulated rail joiners, some of them have a center nub which reaches up just above the rail, and that may lift a single wheel enough to avoid the gap, but the other situations are unavoidable.