Wiring a Reverse Loop in DC - not DCC

[CRL]

I know this is primarily a DCC section, but I couldn’t find anywhere else to post this question, so if there is, please have Mods move it.

I’m aware the conventional method of wiring a reverse loop is to switch the DC polarity on the main line while the train is transiting the loop. This presents problems for any other trains operating elsewhere on the mainline unless you have multiple main line blocks — each with its own directional toggle switch. Our NTrak reverse loops dealt with this problem by placing the directional toggle switch on the reverse loop. The train operator would flip the loop directional toggle switch at the same time as the controller directional toggle switch while the train was within the reverse loop. However, if the switches were not changed simultaneously, the results were not pretty but this was the only reasonable method to not disturb the mainline polarity.

I’m not aware of any “auto-reverse” circuitry that doesn’t disrupt the mainline polarity. I’m wondering if you could wire  a double reverse loop layout for a continuous run option to JFRT if you have a multi-block mainline between the loops.

Any suggestions?

[learmoia]

I guess it's one of the unsung advantages of DCC.. is that it's really AC and the decoders dont care about polarity..

Anyways.. for DC.. what you described.. (doule switch) Track Reverse+ Throttle reverse is the only way to do it in DC... 

The only way to get around it is to put the auto reverser on 'the rest of the railroad'  (autoreverse everything but the loop itself. )

Or..Auto Reverse every block.

But it only works if your the only operator.    Any other train would be affected by the reverse.

[CRL]

Thanks. I was afraid that would be the answer.

[learmoia]

I was thinking more last night, and the unless someone else has an idea.. the only way you can get away with it is if your the sole operator and put every block on an auto reverse.

... What you could do is make the process more prototypical.. is have the loop with a signal at each end of the loop, that displayed red if you were reverse polarity and green for correct polarity.. (Signal is powered by track voltage). With a DPDT switch to manually change the polarity.  Used in conjunction with an auto reverse.. the following would take place.

Pull onto loop (Auto reverse would set your polarity as needed.)
Pull around the loop to the red signal.
Stop.
Switch the throttle and throw the DPDT switch - Signal turns green (when voltage turns on).
Continue as normal.

~Ian

[peteski]

Yes, since the direction of DC model's travel is polarity-dependent, when the train exits the reverse loop back onto the main track, it is traveling in reverse direction. So the polarity of the main track has to be reversed too (or the loco would try to back into the reverse loop again).  Even if the block preceding the reversing loop was separate from the rest of the layout (and automatically reversed), then once once you came to the end of that block, the rest of the layout would still be wrong polarity.

[CRL]

Basically, imagine the direction switch on the throttle to reflect the direction of the train. Toggle left moves train to the left, toggle right moves train to right. Train goes around loop (wired to change polarity) throw the loop throttle in unison with the throttle direction switch. This leaves the main line blocks unaffected. The other approach is to wire each block with a direction polarity switch, but that seems like a pain in the butt unless an automated circuit could flip the polarity as the train approaches the block boundary.

[peteski]

Think about it.  The train is on the main line going towards the reverse loop.  Enters the reverse loop which has the same polarity as the main line.  You make a circle and when you come back to the main line, the polarity is now wrong on the main line and you have to flip it so the train can now go away from the reverse loop.  The main line polarity *HAS* to change somehow.

[CRL]

Not if you make the polarity change on the reverse loop. Trust me on this... it worked on our N-Trak club loops back when we were all running DC. You flip the reverse loop and the throttle direction at the same time. Train keeps rolling back onto the unchanged main line.

[peteski]

Not if you make the polarity change on the reverse loop. Trust me on this... it worked on our N-Trak club loops back when we were all running DC. You flip the reverse loop and the throttle direction at the same time. Train keeps rolling back onto the unchanged main line.

Going back in the main line in the direction reversed of when it arrived with no main line polarity change?  You must have invented new type of DC trains.

Whatever . . . 

[learmoia]

The other approach is to wire each block with a direction polarity switch, but that seems like a pain in the butt unless an automated circuit could flip the polarity as the train approaches the block boundary.

Yes.. you could implement an Auto Reverse circuit for this... that gets you into the loop.. but to get out.. you still need to do the double switch because your changing the polarity under the loco (same as changing the direction)... thus changing the direction to compensate.


The Key is to find a way to always flip the polarity of the block your NOT on..

Has anyone tried 2 blocks together - with both protected by an auto reverse?
... That would be the only solution that wouldn't require you to switch both items at the same time..

In theory, as you come into each block, the AR (auto reverse) in the next block switches the power ahead of you...

But if all blocks have an AR.. which one triggers.. or does it find an infinite loop of shorts as each one tries to correct itself to match the other.. 

If it worked.. and you had every block on an auto reverse, then any block you enter would flip to match you.. thus you don't have to flip the direction switch.

If your running a multi throttle situation with DPDT or Rotary switches.. as long as the AR is between the Throttle Selector switch and the track.. your good (the AR doesn't care what throttle your using.). it just wants the polarity of it's block to match the polarity of the block next to it.. when a locomotive is bridging the isolated gap.

... The wiring it would take to make this work, or the cost of ARs for each block... you might as well buy some decoders and a DCC system..

*But I want to run my DC engines that can't take a Decoder...

Put ARs on the loops, and you can use a 3-5A Decoder and use the motor leads to one of your throttle selectors and run DC through DCC (without using 00)... but no other DCC locos would run on those block because it's straight DC power coming from the motor leads.

~Ian

[peteski]

Never mind - deleted.

[CRL]

@peteski, you’re forgetting the throttle direction switch is thrown at the same time.

[peteski]

@peteski, you’re forgetting the throttle direction switch is thrown at the same time.

I guess I have hard time understanding this.  The DC stuff is way too complicated.  I'm not throwing any manual toggle switches.  I'm sticking with DCC. 

[CRL]

Yes.. you could implement an Auto Reverse circuit for this... that gets you into the loop.. but to get out.. you still need to do the double switch because your changing the polarity under the loco (same as changing the direction)... thus changing the direction to compensate.


The Key is to find a way to always flip the polarity of the block your NOT on..

Has anyone tried 2 blocks together - with both protected by an auto reverse?
... That would be the only solution that wouldn't require you to switch both items at the same time..

In theory, as you come into each block, the AR (auto reverse) in the next block switches the power ahead of you...

But if all blocks have an AR.. which one triggers.. or does it find an infinite loop of shorts as each one tries to correct itself to match the other.. 

If it worked.. and you had every block on an auto reverse, then any block you enter would flip to match you.. thus you don't have to flip the direction switch.

If your running a multi throttle situation with DPDT or Rotary switches.. as long as the AR is between the Throttle Selector switch and the track.. your good (the AR doesn't care what throttle your using.). it just wants the polarity of it's block to match the polarity of the block next to it.. when a locomotive is bridging the isolated gap.

... The wiring it would take to make this work, or the cost of ARs for each block... you might as well buy some decoders and a DCC system..

*But I want to run my DC engines that can't take a Decoder...

Put ARs on the loops, and you can use a 3-5A Decoder and use the motor leads to one of your throttle selectors and run DC through DCC (without using 00)... but no other DCC locos would run on those block because it's straight DC power coming from the motor leads.

~Ian

I think that the CTI Electronics Train Brain system works by essentially having a computer controlled block assignment system that assigns a throttle to the occupied block and the one ahead. It tracks the direction of travel by monitoring the polarity of the track, but it’s basically an on/off relay coupled to a throttle routing relay... if I understand the literature.

[Mark W]

@peteski, you’re forgetting the throttle direction switch is thrown at the same time.

Flipping the track polarity AND the throttle polarity will cancel each other out.  Your reverse loop polarity would be unchanged.