Double Reverse Loop and DC/Analog Advice?

[Rrock1211]

Novice level - pretty new to model RR.  Question: we have an old Bachmann Hershey "Diesel" engine, which I assume is analog and are using a Railpower 1300 controller, which appears to be DC.  1 train set running on EZ track.  We were looking at setting up a double reverse loop (similar to "dogbone" layout, but with a main line connecting to loops via turnout switches.)  Question is: what is easiest way to make that double loop work.  Looked at Bachmann's auto reverse loop module, but that's DCC only, so would either have to convert analog to DCC and system to DCC - sounds time consuming and pretty expensive.  Is there another, easier way?  Would purchasing a DCC ready/capable engine solve it since just 1 train set running at this time?  Sorry if any of my lingo is off-still learning the very basic.  Any help is appreciated!! thank you!

[Waikiki968]

I don't know if it works with EZ track, but azatrax.com offers a Reversing Track solution that will do what you want without DCC.

[Rrock1211]

Many thanks!

[Maletrain]

If you want to make it reverse automatically, then DCC is the easiest (not cheapest) approach, because there are devices already made to do that for you and throw the switches on the splits for your two reversing loops while the train is in a loop.

But, if you want to do it by hand, each time the train enters a loop, then all you need is a simple double-pole/double-throw electrical switch.

The wiring for the simple hand operated layout is different from the DCC layout.  With DCC, sections of each loop get their rail phases switched automatically, while the train is in the loop, by an electronic device that senses a short circuit when the train bridges an insulated track joint where the rails are out-of-phase across the joint.  That happens so fast that the sound on the locomotive does not even notice it.  And, that same electronic device can make the turnout at the end of the loop throw when the phases reverse, so that the train does not derail when it gets to a turnout that is set against it.  So, with a set-up like that, you could just start the train and let it run, unattended, without it stopping or derailing on a layout that is basically a single track that connects 2 reversing loops. 

But, with DC, if you are going to throw the turnout of a reversing loop by hand whenever a train has gone into that loop (so that it can come out without derailing), then it is not much additional work to also throw an electrical switch that reverses the polarity of the rails on the section of track that connects the two loops while the train is completely in a reversing loop.  That is what the dp/dt electric switch is for.  You feed the section between the twp reversing loops through the dp/dt electric switch so that it can be made to match the polarity of one end of a reversing loop or the other end of that loop, instead of switching the polarity of the loops.  That way, your train is not on the section of track while it changes polarity, so even if the locomotive has sound, the slow manual switching process will not affect it.

[jward]

One way to do this on DC is to wire a bridge rectifier between the controller and the track. AC leads go to the controller, Dc to the track. You'll still have to gap both rails at each end of the loop, and you'll only be able to travel in one direction around the loop. But it works like a charm and is as simple to wire as any other method. Make sure your rectifier is rated at least 3 amps.

[Maletrain]

One way to do this on DC is to wire a bridge rectifier between the controller and the track. AC leads go to the controller, Dc to the track. You'll still have to gap both rails at each end of the loop, and you'll only be able to travel in one direction around the loop. But it works like a charm and is as simple to wire as any other method. Make sure your rectifier is rated at least 3 amps.

Frankly, I don't understand how what you posted would work to prevent a short circuit at one end of the loop or the other.  Please explain. 

Keep in mind that a bridge rectifier will put only + on one rail and only - on the other, and that those two opposite polarity rails will be connected with each other at the turnout for the loop.  Yes, you can isolate both sides of the turnout from the rest of the loop, but, at those isolation points, there must be a mismatch in polarity across on set of gaps or the other.  There will be a short circuit when a train bridges the gap with the polarity mismatch.  So, something must reverse polarity between the time that the train crosses the first set of gaps and the time that it reaches the second set of gaps.  The options are to either reverse the section of rail in the loop (typically done for DCC set-ups), or reverse the mainline (and switch) often done with DC analog set-ups).

[Len]

If you're only running one train using a DC power pack why go to all the hassle of double reverse loops? Why not just a dogbone to get the same general look without the complications?


If you really, really want the double reverse loop, I would suggest getting a DCC controller and autoreverse module. Then stick a decoder in your loco.

Len

[jward]

One way to do this on DC is to wire a bridge rectifier between the controller and the track. AC leads go to the controller, Dc to the track. You'll still have to gap both rails at each end of the loop, and you'll only be able to travel in one direction around the loop. But it works like a charm and is as simple to wire as any other method. Make sure your rectifier is rated at least 3 amps.

Frankly, I don't understand how what you posted would work to prevent a short circuit at one end of the loop or the other.  Please explain. 

Keep in mind that a bridge rectifier will put only + on one rail and only - on the other, and that those two opposite polarity rails will be connected with each other at the turnout for the loop.  Yes, you can isolate both sides of the turnout from the rest of the loop, but, at those isolation points, there must be a mismatch in polarity across on set of gaps or the other.  There will be a short circuit when a train bridges the gap with the polarity mismatch.  So, something must reverse polarity between the time that the train crosses the first set of gaps and the time that it reaches the second set of gaps.  The options are to either reverse the section of rail in the loop (typically done for DCC set-ups), or reverse the mainline (and switch) often done with DC analog set-ups).

It is very simple. As your train traverses the reversing loop, you merely throw the direction switch on your controller. your polarity will then match the track you exit to. Which is exactly what you'd be doing under any other method of controlling a reversing loop.

[Len]

Jeff,

If the output of the power pack is wired to the AC side of a bridge rectifier, and the DC side of the rectifier is wired to the tracks, it doesn't matter what you do with the power pack directions switch. The DC polarity to the track will not change. The output of the rectifier would have go through a DPDT switch wired for direction control.

Like I said earlier, this is a bit of an ambitious project for a DC layout if the idea is to have things switch automatically, without human intervention.

Len

[jward]

If the output of the power pack is wired to the AC side of a bridge rectifier, and the DC side of the rectifier is wired to the tracks, it doesn't matter what you do with the power pack directions switch. The DC polarity to the track will not change. The output of the rectifier would have go through a DPDT switch wired for direction control.

Exactly. The direction of the train won't change regardless of how you throw the direction switch, AS LONG AS THE TRAIN IS IN THE LOOP. Once it exits the loop, you've already set the proper direction to eliminate a short circuit. This eliminates the need for the second direction switch traditionally needed when wiring the loop for DC. The only direction switch you need is the one built into the controller.

[Maletrain]

If the output of the power pack is wired to the AC side of a bridge rectifier, and the DC side of the rectifier is wired to the tracks, it doesn't matter what you do with the power pack directions switch. The DC polarity to the track will not change. The output of the rectifier would have go through a DPDT switch wired for direction control.

Exactly. The direction of the train won't change regardless of how you throw the direction switch, AS LONG AS THE TRAIN IS IN THE LOOP. Once it exits the loop, you've already set the proper direction to eliminate a short circuit. This eliminates the need for the second direction switch traditionally needed when wiring the loop for DC. The only direction switch you need is the one built into the controller.

OK, now that he has added the use of the direction switch on the controller, I think I understand what Jeff means, but he is not describing it properly/adequately in his posts.

What I think he means is that you can take the DC (not AC) output of a controller and run it through a bridge rectifier and it won't matter which way the direction control switch is set, because the bridge rectifier will take any (constant or alternating) input polarity and convert it to one specific DC output polarity.  So, for the section of rail that is connected through the rectifier, the train will only go in one direction, no matter which way the direction switch on the power pack is set.

He is suggesting that the isolated sections of the loops be fed from the controller through bridge rectifiers, so that the center section of the layout between the two loops can have its direction of travel reversed by the usual direction control switch on the controller.  That much is true.  It does force trains to travel the loops in only one direction, which may or may not matter to this particular original poster.  And, it also requires human attention and action to throw an electrical switch while the train is in each of the loops, otherwise, there will still be a short circuit when the train exits a loop.

Another element of the scheme Jeff is proposing has to do with the alignment of the turnouts at the entrance/exit of a loop.  If it is set for the "wrong" direction for the direction of travel in that loop, there will be a short circuit when the train enters the part of the loop fed by the rectifier.  One way to handle the turnouts would be to use "spring turnouts" that always point in one direction, held there by a rather weak spring, so that when the train comes back into the turnout with it set against it, the train itself can push the turnout to the other position and the train can pass through it without derailing.  That actually works, so, with 2 bridge rectifiers and 2 modified turnouts, an operator needs to only throw the controller reversing switch twice as a train completes a full trip around the layout.  The need to throw the turnouts is removed, at the expense of limiting the direction of travel to just one way in each loop.

But, that is still not an automatic setup for a train to make a complete trip around the layout without human attention and action.  To turn it into an automatic layout, it would still be necessary to add equipment to sense where the train is and throw the controller direction switch (or a dp/dt switch between the controller and the track) at the 2 necessary times per trip.

So,  Jeff's suggestion to use the bridge rectifiers is really no different for the operator than what I posted to begin with for a DC system that allows the operator to reverse the mainline between the loops (and the turnouts that start the loops) with a dp/dt switch between the controller and that section of track.  It does make it simpler for an operator to know which way to position the dp/dt switch as the train approaches each loop, because it removes the option of the train traveling around the loop in either direction.  And, using spring turnouts removes the operator's need to keep track of which way those turnouts are directing the train into their respective loops.

But, getting this approach to full automatic would require more equipment and some complicated reasoning to set it up, properly.  

To do it with DCC instead of DC is logically much more simple for the beginner layout builder.  That is because there are already available DCC components that are purpose designed to reverse the phase (not "polarity") of the electrically isolated sections of the loops as soon as a short circuit is detected, so fast that it does not affect the train at all.  And, those DCC components can also send a signal to automatically throw a turnout whenever they reverse the phase on a section of track.  So, a train could enter a loop in either direction, and the DCC automatic reverser component would allow the train to go around the loop without stopping due to a short circuit and without derailing at the turnout when it gets back to it.  

A DCC system would also allow 2 or more locomotives to be operated independently on the same (electrical) section of track.  So, for instance, a train could stop on the mainline, and a switch engine could come out of a siding with some cars to add to the train and take some cars from the train back into the siding, before the mainline train moves on down the mainline.  As needed, both engines could be moving at the same time in the same or opposite directions at different speeds to break the train, move the cars, and reassemble the train on the same electrical section of track.