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DCC Reverse Loop Short Circuit?

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  • Member since
    August 2003
  • From: Collinwood, Ohio, USA
  • 16,367 posts
Posted by gmpullman on Friday, December 5, 2014 3:33 PM

peahrens
When installing track, IIRC I've seen comments that it's good practice to stagger slightly (1/8" or so?) opposite track joints at the entry / exit points of the loop as in some cases (can't remember the issues) some reversers can be confused.

I have done that on my reverse loops, Paul. I think the issue is with metal wheels crossing (making contact) with all four points {zone 1 & 2 / rail A & B} AND if the exit side were bridged at the same time, as when the locomotives are bridging the gap at the other end (or even on another track within the reverse section) it would see it as a true short circuit, not just a reverse phase.

I have an interchange track that's about seven feet long and it is a reverse section protected by a PSX-AR. I learned that I can not run an eight foot long passenger train through it Confused at least the lighted cars since they act as 85' long jumpers that will bridge the gap. Even the trucks have continuity from wheel to wheel on each side and that's around 6-8 scale feet!

As they say in the London Tube... Mind The Gap! Ed

  • Member since
    September 2004
  • From: Dearborn Station
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Posted by richhotrain on Friday, December 5, 2014 2:47 PM

I never had problems with mechanical relays such as the AR-1 until I decided to create power districts and add PSX circuit breakers.  Once I did that, the AR-1s proved too slow such that the PSX units reacted first, cutting power to my reversing sections.  So, I had to dump the AR-1s on eBay and buy PSX-ARs to remedy the problem.

Rich

Alton Junction

  • Member since
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  • From: Bedford, MA, USA
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Posted by MisterBeasley on Friday, December 5, 2014 2:32 PM

Be aware of the current requirements of what's in the loop and the current allowed by the auto-reverse unit.  While my DCC system puts out 5 amps, my auto-reversers only support 2.5 amps, as I recall.  That should still be plenty for most applications, even 3 trains worth, but make sure the auto-reverser you buy has enough power.

My reversing sections are not nice "classic" loops like yours.  One is large and oddly shaped, and the other is a crossover within an oval.  Neither of them begins and ends at the same point, so it is quite possible for a train (sometimes the same train) to enter and exit the loop at the same time.  Still, I don't have a problem, most of the time.  I think it's because I use solid-state auto-reversers, and they can flip polarity many times a second.

It takes an iron man to play with a toy iron horse. 

  • Member since
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  • From: Dearborn Station
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Posted by richhotrain on Friday, December 5, 2014 2:12 PM

cacole

A auto reverser with a mechanical relay, such as the Digitrax AR-1, may not switch fast enough to prevent problems.

Interesting point, but the AR-1 would work just fine.  While it might take a fraction of a second longer than a solid state unit such as the PSX-AR to react, the polarity flip is instantaneous so no loss of track power.

Rich

Alton Junction

  • Member since
    January 2010
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Posted by peahrens on Friday, December 5, 2014 12:00 PM

It helped me to understand that when the autoreverser flips the polarity in a section, the locos in the section all still use the available power as instructed (e.g., continue going forward at speed "x") so they simply immediately use the changed power appropriately to accomplish their prior (curent) "instruction".  This is one reason it's ok to have yards within a reversing section, even with lots of locos in the section. 

In my case I used OG-ARs for my two reversing sections.  They are not expensive ($32) and work consistently.  When installing track, IIRC I've seen comments that it's good practice to stagger slightly (1/8" or so?) opposite track joints at the entry / exit points of the loop as in some cases (can't remember the issues) some reversers can be confused.  I'm rusty on what I read on this but maybe someone can comment if needed.

http://www.tonystrains.com/products/dccspecialties.htm

Paul

Modeling HO with a transition era UP bent

  • Member since
    October 2002
  • From: City of Québec,Canada
  • 1,258 posts
Posted by Jacktal on Friday, December 5, 2014 10:35 AM

In a simple loop like your drawing,the trains already inside the loop won't be disturbed any when a third train crosses the gaps.The trick is to not have two different trains crossing different gaps at the same time wich is impossible in your drawing.

  • Member since
    July 2003
  • From: Sierra Vista, Arizona
  • 13,757 posts
Posted by cacole on Friday, December 5, 2014 10:30 AM

As long as you don't have two trains simultaneously crossing the rail gaps near the turnout, there should be no problem with an electronic DCC auto reverser switching the phase to the other locomotives within the loop; however, the loop would have to be a really long one to fit 3 trains on it at one time.

A auto reverser with a mechanical relay, such as the Digitrax AR-1, may not switch fast enough to prevent problems.

 

 

  • Member since
    August 2014
  • 122 posts
DCC Reverse Loop Short Circuit?
Posted by KisNap on Friday, December 5, 2014 9:43 AM

Hi Everyone.  I am unfamiliar with the limits of automatic reversers and am hoping someone can help me out whether or not the situation below would be an issue for trains inside the loop.

Situation 1: Train 3 enters loop with trains 1 & 2 inside

Situation 2: Train 1 exits loop with trains 2 & 3 inside

Would everything be fine or would the automatic reverser flip when a train exits causing another one to stall.  Thanks for your input

The N scale section of my website is now uploaded with a lot of various things.  Check it out: www.CarlettaTrains.com

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