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A question about Automatic Loop Reversers

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Posted by Mmbushnell on Thursday, May 23, 2019 11:27 AM

RR_Mel
That’s the way I run my layout, with the block switches.  I might not need a auto reverser, my 11 year old great grand daughter was reading my posts and said that I could teach her how and that she could teach her 5 year old sister how to flip the toggles.

Your grandkids may be more clever and astute than you'd imagined.  I'm impressed that the elder one read the posts.  So teach the young lady how to work the toggles, and why.  She'll catch on and teach her sister.  You may well have a budding engineer on your hands, or two.  

And, as for the grandchildren, you GO, girls!   

//  Michael 

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Posted by gregc on Thursday, May 23, 2019 8:27 AM

mfm37
For DC operation the block ahead of the train must have its polarity changed before the engine enters.

that's what i ment by using block detection.   I guess it wasn't clear that it could be used with a circuit breaker to detect the crossing and using the block detection to determine whether to reverse the polarity of the reverse or mainline sections.   (yes, it may need to keep track of which block is occupied just before the crossing).

greg - Philadelphia & Reading / Reading

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Posted by mfm37 on Wednesday, May 22, 2019 8:40 PM
A DCC auto reverser swaps polarity (Phase) right under the engine as it enters the reversing section. For DC operation the block ahead of the train must have its polarity changed before the engine enters.
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Posted by RR_Mel on Wednesday, May 22, 2019 7:54 PM

gregc

 

 
MisterBeasley
The polarization flip that allows autoreversers to work on DCC will just cause a DC engine to reverse, not continue through the loop at the end.

 

seems that with block detection, you would know whether to reverse the polarity of the reverse or mainline sections

 

That’s the way I run my layout, with the block switches.  I might not need a auto reverser, my 11 year old great grand daughter was reading my posts and said that I could teach her how and that she could teach her 5 year old sister how to flip the toggles.
 
 
Mel
 
 
My Model Railroad   
 
Bakersfield, California
 
I'm beginning to realize that aging is not for wimps.
 
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Posted by gregc on Wednesday, May 22, 2019 7:14 PM

MisterBeasley
The polarization flip that allows autoreversers to work on DCC will just cause a DC engine to reverse, not continue through the loop at the end.

seems that with block detection, you would know whether to reverse the polarity of the reverse or mainline sections

greg - Philadelphia & Reading / Reading

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Posted by RR_Mel on Wednesday, May 22, 2019 1:07 PM

The main large oval has 8 block switches and they have to be thrown in the correct sequence or it’s a no go, that’s a bit tough for a 5 year old even on my easy to run control panel.
 
 
 
 
Mel
 
 
My Model Railroad   
 
Bakersfield, California
 
I'm beginning to realize that aging is not for wimps.
 
 
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Posted by Mmbushnell on Wednesday, May 22, 2019 12:35 PM

Mel, 

I see your point.  

My dad's American Flyer (AC operation) was a simple 4' X 8' oval with a reversing crossover leg, plus a couple of sidings.  The crossover leg was powered through a slide switch, which we kids were supposed to operate while the locomotive was on the crossover leg.  I'm not sure how he had it wired.  If we were agile and attentive, and got the slide switch thrown at the right time, the loco would go through to the main without stopping.  Otherwise, if would just stop when it got to the gap.  

It would be good if your grandkids could operate on the crossover by themselves.  If I think of something else, I'll let you know.  

Best //  Michael

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Posted by RR_Mel on Wednesday, May 22, 2019 11:47 AM

Sorry, I figured that by saying I used DPDT center off toggles that everyone would know that I manually control the track polarity which really isn’t that big of a problem for me.  My layout has been dual mode since 2006 and I can operate both DC and DCC modes quite easily using the toggles. 
 
I have an auto interlock that controls the DC and DCC power pack operation to the track preventing any problems.  When the DC power pack is turned on the Accessory voltage activates a relay switching the track power from the DCC controller to the DC power pack.
 
My great grand daughters like to run my trains occasionally and having an auto reverser would give them more options.  They finally got the hang of turnout control but the reverse polarity thing is out of the question.  Right now they just don’t do the loop back operation.  My passenger station is on the pair of angled tracks and they just do the two circle things right now, CCW.  When they ask to reverse the train direction (CW) I set it up for them.
 
I guess if a DC reverser isn’t available I might give it a go and make my own, I was just thinking a store bought might be easier than trying to reinvent the wheel.
 
Either way it means another control panel overhaul, I just went through one.  I have 24 blocks, all homeruns to the control panel so the reverser will have to feed the individual blocks, I don’t intend to give up my individual block control.  Every layout since 1951 has had individual block control.
 
 
Mel
 
 
My Model Railroad   
 
Bakersfield, California
 
I'm beginning to realize that aging is not for wimps.
 
 
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Posted by Mmbushnell on Wednesday, May 22, 2019 11:07 AM

Hello, Mel, 

What you don't say in your post above, is how you're presently dealing with reversing on the crossover leg, when you're operating DC.  There are a variety of approaches, which I'm not going to discuss right now. 

However, for DCC operations, it's simple enough.  

  • Double insulate the crossover leg at all 3 turnouts, so that it's electrically isolated from the rest of the layout. 
  • Power each rail of the crossover leg from one of the two outputs on a Frog Juicer Dual reverser (i.e., green leg to one output terminal, orange leg to the other). 
  • For best results, the insulation gaps should be slightly offset from one another (+/- 1/8"); see Frog Juicer installation instructions (downloadable) for more details.  
  • There are other electronic auto-reversers that will work equally well.  I mention Frog Juicers because I've used them and am familiar with them and how they work (flawlessly). 
  • The longest train that you run through the crossover leg should be shorter than the length between electrical gaps, especially if you have lighted cabooses.  Otherwise, the auto-reverser will try to fight itself at both ends of the crossover leg.  

For dual DC/DCC operations, I would envision you'd need to have two separate feed systems to the layout.  I wouldn't expect the auto-reverser to work very well, if at all, on DC.  

I hope this helps.  

//  Michael

 

 

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Posted by gregc on Tuesday, May 21, 2019 1:35 PM

an auto-reverser is essentially a circuit breaker with the added capability of reversing the polarity of the output.

it monitors the current to either rail.  It recognizes a "short" if the isolation gap at any of the boundaries of the reversing section is bridged and the polarity doesn't match.   It quickly reverses the polarity to the reversing section so that there is no longer a "short"

either mosfets or DPDT relays can be used to reverse polarity.   It may also use mosfets with a relay to disable power if there is a persistent short.

here's an example of a circuit breaker controlled by a processor (not shown) that can be used to reverse the polarity to the rails using a relay (not shown)

there is a 0.22 Ohm resistor in each path that is used to detect a short.  when there is enough current, the voltage across it is sufficient to cause the (Q1) transistor conductor and alert the processor using the opto isolator (U1a).

The processor can momentarily disable the bias to the back-to-back mosfets to momentarily disable power to the rails while it changes the state of a relay.   The back-to-back mosfets allow current to flow in both direction.  a mosfet behaves like a diode (conducting) when the polarity across it is reversed.  The other mosfet needs to be biased to conduct.   This allows it to control the alternating DCC voltage.

A short can be detected in either rail and either/both rails disconnected from power using the mosfets.   An additional pair of back-to-back mosfets could be added to replace a relay.

greg - Philadelphia & Reading / Reading

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Posted by MisterBeasley on Tuesday, May 21, 2019 12:11 PM

A DCC autoreverser will not work on DC, or on a DC engine running on address zero on those DCC systems that allow it.  The polarization flip that allows autoreversers to work on DCC will just cause a DC engine to reverse, not continue through the loop at the end.

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

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A question about Automatic Loop Reversers
Posted by RR_Mel on Tuesday, May 21, 2019 10:47 AM

My layout is wired for DC operation with 24 total blocks each on a DPDT center off toggle switch.  I run dual mode DC & DCC, one at a time.  My layout functions great with no problems in either mode.
 
I have never used or thought about using an Automatic Loop Reverser until last weekend.  I have absolutely no knowledge on how they perform.  I do have an electronics background and could figure it out but I’m curious about what is available that would work out of the box.
 
I drew up a very basic color coded track drawing with two “Power sections”.  I’m not locked into any particular method, I’m merely showing how I would start the planning.
 
 
 
As always you can click on the picture to enlarge
 
As I said above I don’t have a clue how the reversers work but my layout will have to function in both DC and DCC modes.
 
EDIT:
 
I added a couple of sidings to my drawing.  The length of the oval is 120', the long siding is 13'.
 

 
I welcome any and all input.   
 
 
Mel
 
 
My Model Railroad   
 
Bakersfield, California
 
I'm beginning to realize that aging is not for wimps.
 

 

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