Hi
I Have question that i wouldlike to get answered. If you have a DCC system and there is a point on my railroad where the polarity changes like in a turnaround or a P shaped end line. Does the polarity have to be reversed or will the engine automatically correct the polarity reverse and continue at same speed and direction.
Simple Answer:
The polarity has to be reversed. Also, the P section (loop section) of your track would have to be isolated at each end from the main section. You can do this by hand using a throw switch, but using an auto reverser is much much better. You lower the risk of burning something out because of a short.
Use an auto reverser for polarity issues on loops etc. I have one on my loop and one on my turntable. They are very easy to wire in to the feeder wires and switch the polarity without any engine hesitation.
Just curious - which polarity gets flipped when you use an auto-reverser - the loop or the main? In a DC arrangement, you’d run the engine into the loop, flip the polarity on the main, and then run the engine out. What’s the sequence for DCC?
The polarity in the loop gets reversed, so fast the train never notices. I’ve got three of them and it’s great to just fly around the reverse loop and not worry about it.
With an auto-reverse, it’s the loop that gets flipped. If you wire in toggle switches and work it manually, it really doesn’t matter, as long as SOMETHING gets changed so the polarity across the gaps matches. It’s easiest to switch just the loop. The beauty of DCC is the track ‘polarity’ (technically, the phase, since it’s a square wave signal, not DC) does not matter as far as teh direction the loco moves. If you say go forward, it’s going to go forward no matter what you do with the track polarity.
–Randy
67297[#welcome],
Welcome to the forum. You will find a lot of knowledgeable and experienced people here. Help is usually only minutes away.[tup]
With DCC use an Auto-Reverse module. They are relatively cheap and easy to install. They make reverse loops and turntables transparent to the rest of the layout. The loop must be isolated from the rest of the layout and allow for your longest train, just like for DC. [:I]
I have one, MRC Auto-Reverse Module, on my BRVRR. It took about two minutes to install and has worked flawlessly for more than a year.[:)]
I don’t know the technical side of the system, just that it works.[:D][:D]
Good luck and remember: It’s your railroad.
Beginner, possibly dumb, question here: By “longest train” do you mean the loco plus the entire consist, or just the loco? If it is the former, why would the the consist have to be inside the isolated section too?
Getzen
There are cases when the wheels of the cars can also cause a short when crossing the gap, especially if you’re using metal wheels (though most don’t cause a problem). It’s really a problem if you have lighted passenger cars (or cabeese) that draw power from the track, since that’s also a circuit that can cause a short.
If you’ll never do either of the above, and use metal wheels that don’t short out on the gap, you could get away with making the reversing section only long enough to hold your longest loco or loco consist. But, since there’s no real penalty to making the reversing section as long as possible when using a DCC auto-reverser, might as well do it to avoid future problems.
I too, have an MRC auto-reverser and have found that it only works one way. Have any of you had this experience or am I doomed to one way traffic through my reverse loop? For 67297 this could have more meaning than we realize.
Archie
It’s either defective, or one of the gaps in the rails is closing on you and causing it not to react. Another possibility is that its delay or sensitivity is set too high, so it’s not reacting properly when the train goes through the “wrong way”. I’m not familiar with the MRC reverser, but just about all of them have the ability to change the delay time – check the programming manual that came with it.
Your one way issue does sound like its not an isolated loop. With the MRC module there is no programming that I am aware of. I agree to check the track to make sure both rails are gapped at both the begininng and the end of the loop.
As for having the loop long enough, what is meant is anything that is drawing power, several engines, lighted passenger cars, etc. must be able to be on the isolated loop section before they cross out of the loop or a short will occur.
Just an additional note on reversing loops. I have a short reversing section on my 4x8 layout. It is isolated from the main on both ends and has an MRC auto reverse module installed.
Since it is a fairly short section of track, I have to be aware of the distance between my locomotive and lighted caboose when going thru. It doesn’t matter what length train I pull through, as long as the locomotive clears the isolated section on one end before the lighted caboose enters the other.
I use Kadee metal wheelsets that have plastic axles and all my trucks (so far) are delrin so they are all insulated when going thru the reverser.
My MRC reverser is almost 2 years old and works flawlessly. I think it cost about $30 and is a simple 4 wire hook up. 2 wires to the main and 2 to the reverse section.
thanks alot you guys it is all very interesting. The auto reverse modul sounds great.