Large Scale Central

Reverse Loop

Track and Trestles
#1

I have been working on the old mountain pass, reducing the grade, putting in a new tunnel and increasing the track curves from a tight 4’ diameter to a better 5’.

I have been trying different track arrangements to get the most bang for the buck and I’m looking into a reverse loop.

The hitch is I also want this to be a continuous circuit to the main with the option of reversing a trains direction by taking another switch to head back the way it came.

I have limited funds and I want to keep this simple. I have a WYE and a turntable that uses DPDT switches to change the polarity. Engine goes on, stops I flip the switch and off it goes. Can I do the same thing with a reverse loop? A train enters the loop and instead of continuing on the main I decide to send it back the way it came. the engine enters a section of isolated track, stops I flip the DPDT switch train moves off in the correct direction.

Could it be that simple or should I look into getting a LGB reverse loop automatic setup? This of course is track powered and outdoors.

Thanks.

#2

Todd Haskins said:

I have limited funds and I want to keep this simple. I have a WYE and a turntable that uses DPDT switches to change the polarity. Engine goes on, stops I flip the switch and off it goes. Can I do the same thing with a reverse loop? A train enters the loop and instead of continuing on the main I decide to send it back the way it came. the engine enters a section of isolated track, stops I flip the DPDT switch train moves off in the correct direction.

Could it be that simple?

Thanks.

If the proper wiring precautions are taken, yes.

Basically the LGB system just automates this for you so that the dpdt throws with the turnout that is triggered by a magnet under the engine, but you could certainly slow/stop the trains and do this by hand.

#3

I have this exact scenario on the balloon loop of my indoor division. There is a section of the loop that is isolated (both rails) from the rest. It is fed with a DPDT switch wired the same as you would for a wye or a turntable. Stop the loco on the isolation section, flip the switch and reverse the power pack polarity. Then continue on in the same direction. It does not matter which direction you enter the isolation section from so long as the switch is set properly.

With a train that is longer than the isolation section you will get a small bit of arcing as the wheels short the gap between tracks with opposite polarity. You can avoid this if your isolation section is as long as any train you wish to run. Lighted passenger cars with pick-ups on both ends are a problem across this polarity gap.

#4

John, lighted passenger cars would be an issue, but to stop that arcing for freight cars, I put a short, maybe 1/2 inch piece of rail in my gaps, and used plastic rail joiners on both ends of the short rail. So that short rail is dead, and because its shorter then the wheelbase of any of my trucks, I don’t have any arcing issues.

#5

Good idea David. I just didn’t worry about it! For the passenger cars there are solutions too, but I never went down that road.

#6

John, I only worried about it after my power supply reset itself because it saw a short circuit. I could not accelerate the train fast enough to keep the next set of wheels from shutting it down again. But then I do tend to run my trains a bit slow, and that is probably why the power supply tripped the first time.

#7

Arcing? I don’t have that problem on my WYE unless I forgot to switch the DPDT the right way then I blow a fuse. When a train comes in I flip the switch in the direction it is entering hit stop on my TE flip the DPDT switch, apply power and off the train goes on the opposite leg of the WYE.

Do you guys have arcing if there is a wheel straddling the insulated joiner? I still don’t understand because with mine all voltage is off, I flip the switch then apply voltage again. I don’t have any arcing.

Here is a photo of my proposed plan. the track to the bottom right is the main, the track heading off left is the main, and what can’t be seen is the bypass trestle track so my trains have an option to either go up the mountain or take the bypass.

From what you guys have posted I think I will need to extend the section that makes this loop a reverse loop so an engine will fit on it.

If my thinking is correct I will wire an insulated section inbetween the 2 switches. If a train approaches from the left the DPDT switch will need ot be thrown to match. Engine stops on the insulated track I throw the DP switch apply voltage and the train moves along down the main. Sounds simple enough but stretching that insulated spot will be tough. I like the way it looks in the photo.

#8

I think you also may need insulators on the two rails of the diverging path on the turnout to the left. If I understand your track plan, this curve on the left is part of the main line and will reverse polarity when the mainline reverses. Without the insulators here also, this “reverse polarity” will find its way into the loop creating a short.

#9

Todd Brody said:

I think you also may need insulators on the two rails of the diverging path on the turnout to the left. If I understand your track plan, this curve on the left is part of the main line and will reverse polarity when the mainline reverses. Without the insulators here also, this “reverse polarity” will find its way into the loop creating a short.

Hmmm the only spot which is a reverse loop is where the 2 switches connect to each other. I was going to insulate that entire section that is inbetween the switches. If a train makes the regular loop up the mountain without reversing course through the reverse loop all should be OK if my brain is functioning properly. otherwise if the train does want to go back the way it came I will have to switch the turnouts have the DPDT switch set the for the proper direction, drive the train onto this isolated section, stop it, flip the DPDT the other way apply power and off the train goes.

I think if I insulate both ends of that one section between the switches I will be OK.

#10

Todd H - You are correct - Todd B has it wrong IF you are only going to change polarity on the short section between the switches that forms the loop.

BUT - Unlike your Wye, you will need to flip your DPDT switch AND reverse direction on the main, Otherwise your engine will reverse. The DPDT is only matching the polarity to a section of the loop - it isn’t changing the trains direction on the loop. In the Wye situation, you want to change the direction of travel, so only the DPDT needs to be flipped.

Re Arcing: In your situation this will be an issue. When you flip the DPDT, the insulated joint where the engine entered the reversing section will have opposite polarity. Metal wheels will bridge the small gap and cause arcing and a lighted car with power pick ups at both ends will cause a dead short as the leading truck crosses the joint.

The best way to visualize this is to draw it out with red and black rails. You will instantly see where the polarity conflicts are.

#11

Yes, John, my arcing was caused by each metal wheel bridging the air gap between the rails of opposite polarity, I have 2 reverse loops.

What I did, is I set the polarity of the loops as a constant, and used a relay to “reverse” the polarity of the mainline. So my trains don’t have to stop, the locomotive trips the relay on or off when its a certain distance through the loop. Then the power on the main swaps polarity, so that when the locomotive exits the loop, the polarities match. So I have non stop, roundy roundy running, on a single track, bi-directional mainline.

#12

Daktah John said:

Todd H - You are correct - Todd B has it wrong IF you are only going to change polarity on the short section between the switches that forms the loop.

BUT - Unlike your Wye, you will need to flip your DPDT switch AND reverse direction on the main, Otherwise your engine will reverse. The DPDT is only matching the polarity to a section of the loop - it isn’t changing the trains direction on the loop. In the Wye situation, you want to change the direction of travel, so only the DPDT needs to be flipped.

The best way to visualize this is to draw it out with red and black rails. You will instantly see where the polarity conflicts are.

I know that Daktah John sounds like he is disagreeing with me, but he is not.

If you just isolate and reverse the section between the turnouts, eventually, the train gets back to the main line and unless you flipped its polarity also, your train will try to run backwards when entering it UNLESS you change the DPDT switch for the short section and the main polarity for the main line past the turnout…, which is twice the effort.

So basically, you are looking at an ordinary reverse loop that just happens to have a turnout in it that takes you back to the main line. And, that being the case, what I said before still goes.

If you draw out the remainder of the track plan, maybe this can be better visualized.

#13

Todd B -

Where we disagree is the polity of the main. I’ll re-post the photo for refresher…

If I understand correctly, both the track exiting on the left and the one entering at the bottom are both the main line.

Once you have exited the short section when doing the reverse you are back on the main. That is why, when you stop to flip the DPDT you also need to change direction on your power pack. So, now that power direction has changed, when you return to this spot the main (and your direction of travel) is correct.

Assume train is entering from the bottom. Switches are thrown to reverse. Loco enters the reversing block and stops. DPDT is thown. If you throttle up, engine will try and back out until it hits the gap; will short and stall.

Same scenario; Train stops with loco in reverse section. DPDT is thrown AND power pack is reversed. Throttle up and train continues forward clockwise around the loop and back down the main the opposite direction (to the bottom). You also need to flip the switches back to 'Main Line" before the train gets around the loop. Eventually the train will arrive back here entering from the left and travel around the loop.

At this point, in order to reverse again, the train needs to proceed clear of the switches, then back the train through the reversing section being sure the DPDT is aligned to the bottom part of the main. Once the loco is in the reversing section Stop and flip the DPDT and change direction on the power pack. Continue to back clear of the switch and stop. Throw the switch, change direction on the power pack and exit forward to the left of the photo.

#14

Right. I was considering using a bridge rectifier in the loop so it always entered from the same direction and could proceed around the loop back to the main or out to the main from the other side. Actually, using some creative wiring, reed switches, and an LGB EPL DPDT connected to a turnout (or a dpdt switch thrown with the turnout), the rectifier could be made to change polarity so that the train could enter from either direction with the turnout selecting the correct polarity through the loop. The dpdt is to throw the polarity to the main (we are not in disagreement), not the loop. Just another way to do it.

But Cliffy’s concern seems to be keeping this transition track short, just as in the picture. Too short to park a train or even big engine on. And to do that it could be wired as a typical reverse loop without a separate transition section, and that being the case, it seems that insulators would be required on the diverging path of the left turnout to keep the mainline from interferring with the operation of the loop and that’s what I was envisioning.

#15

Your explanation Daktah John is a mouthful… LOL but I think you are on to something.

the optional main line up the mountain does come from the right makes a loop through the tunnel then curves back around to meet the mountain bypass mainline on the left.

What I will need to do is lengthen the reverse loop connecting track and isolate both rails on both sides. Train comes in from the top the DPDT is switched to correct polarity, train stops, DPDT switch is thrown to reverse polarity and I will need to reverse direction on my TE as well because the DP switch is only controlling the track in that connects and makes up the reverse loop.

Now I understand why the WYE is different, it is because the one leg of it is a dead end. It ends in my main yard but still a dead end. If all 3 legs of the WYE were connected to the main THEN I would have problems.

SO now what to do about arcing as metal wheels go over the insulated joiners? I could go back to plastic wheels… nope. Maybe once the engine clears the insulated track I can flip the DPDT to the center position and kill the power to the track.

There is still much to do on the mountain before the track goes back down but it is coming along.

Thanks guys

#16

Sorry my explanation was so long winded. I needed to talk it out to be sure I had it right. I’ve been doing this on an indoor reverse loop for a long time, but it only has a single entrance and exit.

Early on David had a solution to the arcing: Two sets of insulated joiners at each “gap” with a short piece of dead rain in between, just long enough for the wheel to clear one polarity before touching the other.

#17

P.S.

I found this in my freight shed - it might help. It shows using a Bridge Rectifier in place of the DPDT for semi-automatic operation. I’ve never tried it.

#18

Whew, sure am glad I run DCC! One autoreverser hooked to the loop, powered from the main, done.

Greg

#19

Todd Haskins said:

Your explanation Daktah John is a mouthful… LOL but I think you are on to something.

What I will need to do is lengthen the reverse loop connecting track and isolate both rails on both sides. Train comes in from the top the DPDT is switched to correct polarity, train stops, DPDT switch is thrown to reverse polarity and I will need to reverse direction on my TE as well because the DP switch is only controlling the track in that connects and makes up the reverse loop.

Thanks guys

Or…,

Instead of using a dpdt switch, use a 4pdt switch and reverse the loop and mainline simultaneously (as two dpdts thrown at the same time) with one switch without bothering with the TE. Then you could even throw it all at once without even stopping in the loop.

#20

Yep, of course all the other locos on the mainline will now take off in reverse!

I know, Todd is probably only running one loco at a time on the track, so reversing the main line does not matter. (for those who do not know, reversing the “polarity” of the rails does not change the speed or direction of a DCC loco)

Greg