Is this complex reverse loop possible? (DCC)

[kevlarcat]

Hey all, I've been doing much research about reverse loop wiring in dcc, I understand the basics but the way my yard is designed I can't tell if i'm overthinking it or there's no way it will work.  The real confusing point for me is the crossovers in the top left of the actual loop.  They are there on the prototype and would like to have them in the yard if possible.  I could make the entire yard one giant reverse loop but does that work when there are multiple trains parked or even moving around the yard, all while a train or maybe even two is going through the loops?  The real life the loops are coal dumpers on a port, and multiple trains are moving around different parts of the yard at once.

Hoping I'm overthinking it and missing something obvious. 

Thanks

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[Chris333]

Wouldn't one of these work?
https://www.tamvalleydepot.com/products/dccfrogjuicers.html

[ednadolski]

Electrically it looks to me like a single reversing loop with multiple parallel paths.  I don't think the crossovers change that, just be sure to isolate the reversing section at all the proper places.

WRT multiple trains, I think that should work as long as (a) you don't overload the reverser with too many locos; and (b) only one train at a time can enter/exit the reversing section.

Ed

Edit - be sure to isolate the live frogs too.

[C855B]

Crossovers change nothing, it's still just one ginormous reverse loop.

As far as multiple units within the reversing section, there is nothing to prohibit boosters or multiple power districts on the output side of the reverser provided that the DCC feed is the output of the reverser and not something direct from the command station or in the case of Digitrax, fed from LocoNet.

If I were implementing this, it would be a Tam Valley Dual Frog Juicer configured as a reverser with the output feeding three Tam Valley boosters, the plan divided into three power districts, one for each yard.

[GaryHinshaw]

I agree that it's just one big reverse loop.  I think you can just put gaps at the red ticks here:



Then feed the entire yard off of any auto-reverse circuit.  It's very unlikely that you'll overload something like a DCC Specialties PSX-AR.

[kevlarcat]

Ok clearly I was overthinking it.  I was thinking I had to run 3 auto reversers, one for each loop and cutting in the insulators on the end of the yard tracks on the right side.

What I don't understand is if an engine is traveling left to right on one section of the tracks and another loco enters the yard off the main and the auto reverser flips polarity how is every engine moving in the yard not affected by that?

Would things still work as you guys say if I was using wheels with resistors on them throughout the trains for block detection?

[peteski]

Ok clearly I was overthinking it.  I was thinking I had to run 3 auto reversers, one for each loop and cutting in the insulators on the end of the yard tracks on the right side.

What I don't understand is if an engine is traveling left to right on one section of the tracks and another loco enters the yard off the main and the auto reverser flips polarity how is every engine moving in the yard not affected by that?

Would things still work as you guys say if I was using wheels with resistors on them throughout the trains for block detection?

In DCC, the track polarity has no effect on the travel direction of the loco, so all the locos inside the loop will not behave any differently, regardless of the reversing section's phase.  Remember, DCC track power is a voltage that flips polarity many times a second.

Resistor wheels should not matter either.  What flips the polarity of a reversing section is the instant short when a metal wheel shorts the gap between the mainline and the reverse section while they are powered by out of phase voltage.  The reverse senses that short, and flips the reversing section to be in phase with the mainline.

[GaryHinshaw]

Yep.  All you need to worry about in this case is having trains cross the gaps at both ends of the AR section simultaneously.  I my sketch above, I placed the gaps where it is very unlikely that trains would cross both gaps at the same time, since they would basically foul each other if they did.

[C855B]

... Then feed the entire yard off of any auto-reverse circuit.  It's very unlikely that you'll overload something like a DCC Specialties PSX-AR.

The reason I suggested power districts on the output side of the reverser is we're dealing with yards here. In a multi-operator situation*, likelihood of somebody running into the backside of a misaligned turnout is high a certainty. We shan't have one person not paying attention taking down everybody else. 

* - Or, in my case, a single-operator situation.

Now... speaking of derailments, etc., let's talk about all those curved turnouts. 

[ednadolski]

What I don't understand is if an engine is traveling left to right on one section of the tracks and another loco enters the yard off the main and the auto reverser flips polarity how is every engine moving in the yard not affected by that?

DCC decoders take the DCC voltage from the rails and put it thru a bridge rectifier circuit, which feeds constant power to the rest of the decoder regardless of the phase of the rail voltage.  So you can invert (ie, reverse) the phase of the rail voltage and the rest of the decoder does not notice it.  The decoder keeps sending voltage to the motor the same way, regardless of the track 'polarity'  (quotes there because polarity is not an accurate term in that context, it's more just to give the idea.)  Hence the motor does not change direction when the voltage on the rails changes.

Ed

[mmagliaro]

In DCC, the track polarity has no effect on the travel direction of the loco, so all the locos inside the loop will not behave any differently, regardless of the reversing section's phase.  Remember, DCC track power is a voltage that flips polarity many times a second.

Resistor wheels should not matter either.  What flips the polarity of a reversing section is the instant short when a metal wheel shorts the gap between the mainline and the reverse section while they are powered by out of phase voltage.  The reverse senses that short, and flips the reversing section to be in phase with the mainline.

I always wondered about this, as in, why is an auto-reverser even needed with DCC?  So this is the trick?  It's just a matter of the two sections being out of phase?  And all the auto-reverser does in a DCC system is align the two phases?

[Jbub]

I always wondered about this, as in, why is an auto-reverser even needed with DCC?  So this is the trick?  It's just a matter of the two sections being out of phase?  And all the auto-reverser does in a DCC system is align the two phases?

That's one way to look at it. The two rails touch each other in a loop and they always carry a different portion of the signal so when something bridges the isolation gap you get a short.

[CRL]

I agree that it's just one big reverse loop.  I think you can just put gaps at the red ticks here:



Then feed the entire yard off of any auto-reverse circuit.  It's very unlikely that you'll overload something like a DCC Specialties PSX-AR.

Gary - I think it’s not one big reverse loop. I think there is a second reverse loop you’re not recognizing located inside the big one. I think you need to slide the upper gap in the diagram from the point end of the turnout to the frog end of the turnout. Otherwise, you’ve got a short caused by that turnout.

[GaryHinshaw]

CRL, I don't think so, but it might be that my gap drawing was not clear enough.  Here is a blow-up showing that there are two gaps in the upper section, past the frog of the lead turnout:



I don't see any way for a train to reverse direction in this yard without having to cross one of these gaps.  I am also assuming that two trains will never cross two gaps simultaneously, lest they foul each other.  Strictly speaking you could voilate that if a loco sneaked out beyond one of the paired gaps while a train was crossing the outer gap, but that's always a risk.

The reason I suggested power districts on the output side of the reverser is we're dealing with yards here.

I agree that it's nice to have, but it's not a requirement for this situation if, for example, cost is a factor.

[DKS]

Now... speaking of derailments, etc., let's talk about all those curved turnouts. 

Correct me if I'm wrong, but they look like Peco turnouts. In which case, the derailment rate would be greatly diminished.