Well, it was there a minute ago. Anyway what is a DCC reversing loop? Why would you need one, especially with dcc.?
Thanks,
JaRRell
When the loco crosses the border of the reversing section, at on end or the other there is going to be a short, where the left track is shorted to the right track. So, the reverser senses the short, and swaps the polarity of the reversing section so that the left and right track are the same. Nothing else has to happen, because the direction of travel in DCC is independent of the polarity of the rails.
If you have a reversing loop and use DCC, you will need a circuit to reverse the polarity of the pwer as engines exit the loop. These special circuits do this automatically without disrupting the DCC activities such as speed, direction, and sound.
Bob Boudreau
Okay, imagine a loop in your head. No not in your head, on the track. It goes out and come back around on itself. Now trace your finger around the outside of that loop and you see that what was once one side of the track is now the other. So you have to isolate the loop from the rest of the track. Now the loco really doesn’t care about how the current is running except that when it crosses where the two tracks meet, the front truck is one polarity and the rear is the other. This causes the track to short out.
So what the reversing circuit does is flip the circuit while the loco is in the loop so that the current is running the right direction when the loco crosses back to the main track.
Clear as mud?
Dang, two people were quicker than me.
DCC is no different that DC when it comes to wye’s or reversing loops - A ‘short’ is a short. You still have to ‘gap’ the rails. The various reverse loop controllers detect the short as the engine bridges the gap and reverses the polarity in the reverse section to ‘match’. We have a Digitrax AR1 controlling a reverse loop on the club layout and it works great. The only problem is adjusting the ‘sensitivity’ for BLI sound equipped engines(current hogs).
Jim Bernier
Hmmmm… I think I don’t understand. Do you guys mean like a figure 8 where you have say… a 45 degree crossing? No… the outside track would still be the outside track. Ok, I’ll admit it, I don’t understand.
Jarrell
One tracks comes into a loop and the track comes back to rejoin the single track from which it came. Think of a needle and the eye as the loop.
And I was about to ask what is the best products on the market are for someone new to DCC and now this? Argghhhhhhh…
Jerrell,
A reverse loop actually comes back onto itself. It doesn’t cross. If you
have a wye turnout and the track from one leg circles around and comes back to the
other leg. The outside rail is now the inside rail… you see? Dave
Opps. Sorry Chip. I see you already explained it.
it isn’t really a loop, because that makes you think of a circle, which would have correct polarity. Think of the shape like a teardrop, with the pointy end being where the track meets, and it continues upwards. You can see if you made this shape into two rails going around, and you colored the outside one red and the inside blue, you would see that the red line when it returns to the point would hit the blue, which means that a negative current and postive current have met, causing the short. By using a reverser to flip the red and blue line when the train passing over is past the switch, it rematches the red and blue, forming a connected current.
And it can be disguised, like a cutoff across an oval (or similar, but hidden in the trackplan 'til you can’t see it without real study.
This is harder in DC. IN DCC, the loco does half the work.
Not sure if you understand yet, but here’s something else to think about. I asked someone at my LHS when I first heard about this. They told me to take one switch. Now, loop the straight through track back around and connect it to the switched track. You’re not using any other switches or any cross overs. Just loop one leg of the switch back to the other leg of the switch.
Hope that helps (and hope it didn’t confuse you more)
Kevin
Oh yes, that makes sense! I’ve got it now. The straight leg goes out curves around and if you connect it back to the ‘turnout’ portion of the switch the current collides with itself so to speak. What was a positive runs back into a negative.
Thanks to all of you for trying to get me to see this. Thanks Kevin for giving me the example that lit the bulb!
Jarrell
Nope, it’s still on the outside. (draw it and see) the problem is that the left hand rail going out of the wye becomes the right hand rail when it enter the wye, looking at it from above the wye.
i surely cant explain it like you guys but i do understand now . thank you
Ok. So the current that is going up that left hand rail meets the current going up the right hand rail when the left becomes the right. Right?
Jarrell
Yes, that is my understanding, & = “poof”. Hence, the requirement to gap both rails as they leave the wye. And you still need to throw a switch when the loco traverses the out-going rails and back through the wye (I’m a little fuzzy on this and the actual timing), or pay for and install the auto-reverser.
Personally, I think the AR has a better memory than I do, so I’d let it do the work.
And because you can arbitrarily change the polarity of the DCC at any time, one reverse module can theoretically be used for more than one reversing section, as long as locos are not straddling two sections, or both ends of one section, at the same time. Depending on your configuration you can be pretty sure of this, or get multiple auto-reversers.