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Reversing section advice
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Hi folks
I've posted a sketch for a tricky bit of trackwork I have (it's in the files section, called Reversing Sketch.pdf). Here's the accompanying text, and questions. Electrically, A, A', and A" are the same bus. B and B' could be the same bus (and will be until Santa delivers a booster), or originate on a separate one, but neither are expected to be reversing sections. My original thinking was to put L, the reversing loop, on a PM42 reversing section, and put the short segment at Y on another PM42 reversing section (Y and L could actually be reversed by aux contacts on SW1 and SW2, but I digress). The loop is long enough to hold my longest train (26'), but the segment at Y is not (only long enough for a four-diesel consist). This would not be a problem as I understand it, unless I were to run trains with power requirements that are train-long, like lighted passenger consists. Unfortunately, one of the signature trains expected to traverse from A to A', and/or to traverse the loop, is the circa 1985 CP Canadian; two diesels and a passenger car just won't do. Sigh. So back to the wiring plan. My proposed solution for the problem is to make Y extend all the way to X, including both 3-way switches. Alternatively, I could extend Y out through A along the main line beyond A. Either solution means the reversing section Y will see a lot of action, whereas I could see the original X not being used very often. Any other alternatives I'm missing? Thanks in advance. Blair Smith |
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Vollrath, Don
Hello Blair. I see 3 Options:
1. Use a standard A-R unit at loop L as you propose. Use Loy's Toys ARSC at section Y. This unit requires extra rail gaps but can handle trains that are longer than the reversing track section, as long as Y is longer than the powered loco consist. It does work, even with a long train of lighted passenger cars, but the location of rail gaps and their width are important, particularly on curves. I can send you more data if you are interested. I also have an improved version that you can build yourself for a lot less $$. Send me a private e-mail. [need 1 A-R unit, 1 Loy's Toys ARSC or equal] 2. Use a conventional A-R unit for track Y, but extend the effective length out to SW1, SW2 and X as you propose by use of a relay sensitive to throwbar position of SW1, only when it is set for track Y. SW1, SW2 & the track leading to X should always be at the same rail polarity as you have indicated. However, Loop L still exists, and it should be possible to pass a train from either side of L to Y through SW2 & SW1. But L itself is a reversing loop and it is not wise to connect two A-R controlled track sections end to end... so control the polarity of track L with yet another relay operated from the exit throwbar position of SW2, from the polarity of the SW2 track, which may be powered from the A-R unit of Y if SW1 is set that way. Photo sensors near SW2 can be used to automatically flip SW2 from either direction, but thats a whole 'nother matter. [1 A-R unit, 2 relays] 3. Use a standard A-R unit at track section Y and extend the effective length of isolated A-R track out into track A via a relay controlled by the throwbar at switch. The isolated extension into A must be long enough to hold an entire train. Leave tracks of SW1 & SW1 at the fixed polarity of B and B'. Use a 2nd standard A-R unit for track L. This can work, but you must also consider available track length of A beyond what is shown in your sketch. If it is long enough to avoid yet another complication of train length or passing restrictions this option may be easy to implement. [1 a-R unit, 1 relay] With options 2 & 3, you must use DPDT relays (or toggle switches) to control rail polarity. DPDT contacts on most switch machines are break before make and can interrupt rail power on moving locos for too long of a time as throwbars change positions. Are my explanations clear enough? DonV |
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Vollrath, Don
Oops.
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My option 3 requires 2 A-R units and 1 relay. DonV -----Original Message-----
From: WiringForDCC@... [mailto:WiringForDCC@...]On Behalf Of Vollrath, Don Sent: Wednesday, November 16, 2005 11:06 AM To: WiringForDCC@... Subject: RE: [WiringForDCC] Reversing section advice Hello Blair. I see 3 Options: 1. Use a standard A-R unit at loop L as you propose. Use Loy's Toys ARSC at section Y. This unit requires extra rail gaps but can handle trains that are longer than the reversing track section, as long as Y is longer than the powered loco consist. It does work, even with a long train of lighted passenger cars, but the location of rail gaps and their width are important, particularly on curves. I can send you more data if you are interested. I also have an improved version that you can build yourself for a lot less $$. Send me a private e-mail. [need 1 A-R unit, 1 Loy's Toys ARSC or equal] 2. Use a conventional A-R unit for track Y, but extend the effective length out to SW1, SW2 and X as you propose by use of a relay sensitive to throwbar position of SW1, only when it is set for track Y. SW1, SW2 & the track leading to X should always be at the same rail polarity as you have indicated. However, Loop L still exists, and it should be possible to pass a train from either side of L to Y through SW2 & SW1. But L itself is a reversing loop and it is not wise to connect two A-R controlled track sections end to end... so control the polarity of track L with yet another relay operated from the exit throwbar position of SW2, from the polarity of the SW2 track, which may be powered from the A-R unit of Y if SW1 is set that way. Photo sensors near SW2 can be used to automatically flip SW2 from either direction, but thats a whole 'nother matter. [1 A-R unit, 2 relays] 3. Use a standard A-R unit at track section Y and extend the effective length of isolated A-R track out into track A via a relay controlled by the throwbar at switch. The isolated extension into A must be long enough to hold an entire train. Leave tracks of SW1 & SW1 at the fixed polarity of B and B'. Use a 2nd standard A-R unit for track L. This can work, but you must also consider available track length of A beyond what is shown in your sketch. If it is long enough to avoid yet another complication of train length or passing restrictions this option may be easy to implement. [1 a-R unit, 1 relay] With options 2 & 3, you must use DPDT relays (or toggle switches) to control rail polarity. DPDT contacts on most switch machines are break before make and can interrupt rail power on moving locos for too long of a time as throwbars change positions. Are my explanations clear enough? DonV Yahoo! Groups Links |
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Hello Don
Thanks for the informative and very useful response; yes the explanations are excellent. As an electronics tech, everything makes sense. Your comments about relays (and switches) make me think that although that will accomplish what I want electrically, I will pay an unacceptable price in performance if the train is visible. Since the reversing section trackage in question is all staging, however, I wonder if I will even notice a stagger, if that is the only effect. Are there other drawbacks you can identify to solutions 2 and 3? Regardless, I am extremely interested in your offer of more data in solution number 1, as my section Y is only longer by about one inch than my longest conceived locomotive consist; the power on my longest lighted passenger train would be shorter, but some of the long freights will likely be 4 SD40-2 units, which fit with an inch to spare. The flawless performance of this hidden trackage is important to me, as it will be central to the operation of both my main line and one of the two primary interchange railroads on my layout. Regards Blair Smith |
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Vollrath, Don
Blair,
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My solutions 2 and 3 using relays do not have any real drawbacks. You simply add more insulating rail gaps in the appropriate places and wire up a DPDT relay(s) to control power to those sections of track. If you use Tortoise switch machines for turnout control this is simple to do. [Wire a 12Vdc relay coil in parallel with the Tortoise motor, but add a diode so that the relay coil gets energized with the tortoise in only one direction.] If you plan on using manual throws, add a DPDT toggle sw to do the same thing manually. Small electromechanical relays and toggle switch contacts change state in milliseconds. Any sound decoders on your locos won't even notice that track polarity has changed. Slide switches or 2 separate SPDT contact sets or microswitches or the contacts internal to a Tortoise may interrupt track power momentarily causing an annoying re-start of loco movement or sound. The advantage of using a relay is that the cost of relay or two is far less than any Auto-Reverser. Loy's ARSC is ~$80 USD. Solution 1 with the Loy's toys ARSC may not be totally workable as your own words indicate that track section Y space may be slightly too short. It needs to be longer than the active wheelbase of your longest loco consist PLUS about 2 more inches at each end for what L-T calls portals. Each of these need to be slightly longer than a 3 axle passenger truck, but no longer. See my short track reverser explanations in the files section of this forum. One other comment - For almost any A-R units, You may have difficulty starting up your DCC system if locos are bridging the isolating gaps at a reversing section of track. This occurs because the polarity detecting mechanism needs power to select the proper state and there is no power until the booster gets going. But if there is an instant track short on power up, the booster can't provide power to the relay or A-R unit for self correction...Catch 22. A manual toggle switch system, or one using a separate power source for relays can avoid this problem. A simple way is to simply avoid leaving locos bridging A-R rail gaps when you suspend operations. DonV -----Original Message-----
From: WiringForDCC@... [mailto:WiringForDCC@...]On Behalf Of Rasa and Blair Smith Sent: Wednesday, November 16, 2005 7:28 PM To: WiringForDCC@... Subject: RE: [WiringForDCC] Reversing section advice Hello Don Thanks for the informative and very useful response; yes the explanations are excellent. As an electronics tech, everything makes sense. Your comments about relays (and switches) make me think that although that will accomplish what I want electrically, I will pay an unacceptable price in performance if the train is visible. Since the reversing section trackage in question is all staging, however, I wonder if I will even notice a stagger, if that is the only effect. Are there other drawbacks you can identify to solutions 2 and 3? Regardless, I am extremely interested in your offer of more data in solution number 1, as my section Y is only longer by about one inch than my longest conceived locomotive consist; the power on my longest lighted passenger train would be shorter, but some of the long freights will likely be 4 SD40-2 units, which fit with an inch to spare. The flawless performance of this hidden trackage is important to me, as it will be central to the operation of both my main line and one of the two primary interchange railroads on my layout. Regards Blair Smith |
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Vollrath, Don
Blair, One more thought.
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If some of your track is hidden, it one more reason for making track polarity reversals and switch controls occur automatically. For example: a train exiting out of loop L should automatically throw SW2 as it approaches the exit...and correct the track polarity of L to match. If you can't see the train, it will be difficult if not impossible to throw toggle switches manually to do the job. There is an example of how to do this using an auto-reverser and relay at DonV -----Original Message-----
From: WiringForDCC@... [mailto:WiringForDCC@...]On Behalf Of Rasa and Blair Smith Sent: Wednesday, November 16, 2005 7:28 PM To: WiringForDCC@... Subject: RE: [WiringForDCC] Reversing section advice <U said> The flawless performance of this hidden trackage is important to me, as it will be central to the operation of both my main line and one of the two primary interchange railroads on my layout. |
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