I have been sitting here reading a number of posts about the non-DCC indexed Walthers turntables and assuring others that the turntables have a built-in auto-reverser because the Walthers installation instructions say so.
However, something has haunted me for years since I first installed the Walthers 130' indexed turntable back in 2004. Back then, I was into model railroading less than one year and knew a heck of an amount less about model railroading electronics and wiring than I do now (not that I know that much now).
I installed the turntable on my layout and wired it up. I had an approach track on either side of the turntable, so the approach tracks accessed the turntable at the 9 o'clock position and the 3 o'clock position. Since both approach tracks came off the mainline track, both approach tracks were wired in phase with one another and with the mainline track. I just re-checked this wiring today and I am certain that this statement is accurate.
When I ran an engine onto the turntable from the 9 o'clock position, all went well. However, when I tried to exit the engine from the turntable at the 3 o'clock position, the system shorted. I re-checked the wiring at that point and all was in good order. So, I isolated the approach track on the 3 o'clock side of the turntable and installed an auto-reverser. It worked, so I left well enough alone.
Recently, I went back and re-read the installation instructions for the turntable. Here are the relevant instructions:
Your new turntable automatically reverses track polarity when turned.
Wiring - Connection points are marked on the underside (of the control box) as follows: B1 and B2 connect to rail power supply; powers bridge rails.
After the HO scale turntable was released, Walthers later issued an N scale 130' turntable. The installation instructions were the same as the HO scale turntable but with the following additional statement:
To match radial tracks, you can reverse polarity by interchanging the B1 and B2 wires.
I have not taken the control box off the layout to examine my additional wiring. But, did I reverse the wires on the control box, thereby defeating the built in auto-reverser and necessitating the installation of a separate auto-reverser? Could I have avoided the problem by reversing the two wires connected from the turntable to the control box? If so, I sure wish that Walthers had included that additional statement on the HO scale turntable.
Any thoughts, comments, suggestions?
Rich
Alton Junction
Sounds like you're confusing a DCC type auto reversing circuit with the mechanical reversing mechanism in the turntable. The rails on the bridge are fed through the center pivot of the table. If you lift the bridge out of the pit, you can see the wipers in the hole in the pit and rings on the base of the bridge. Two of these rings have a pair of gaps in them, offset by 180 degrees, which are the feeds to the rails. This is very simply how the rail polarity reverses at a certain point, and it will give you a dead spot as the bridge rotates through this point. There is a pair of areas marked on the bottom of the lip of the pit section that says "no track.," which is where this dead spot will occur. Putting tracks in this dead area MAY work, but can give you all kinds of funky problems with polarity. You may have to figure out where these "no track" areas are in relation to your 3 and 9 o'clock positions.
Also, since it works from one approach track to the bridge, but not off the bridge to the opposite approach track, you have a crossed wire somewhere. When you say the tracks are wired "in phase" with each other and the mainline, added to the statement that they both come from the mainline on opposite sides of the turntable, it begs the question "do you have a reverse loop arraingement in your mainline?"
TomDiehl Sounds like you're confusing a DCC type auto reversing circuit with the mechanical reversing mechanism in the turntable. The rails on the bridge are fed through the center pivot of the table. If you lift the bridge out of the pit, you can see the wipers in the hole in the pit and rings on the base of the bridge. Two of these rings have a pair of gaps in them, offset by 180 degrees, which are the feeds to the rails. This is very simply how the rail polarity reverses at a certain point, and it will give you a dead spot as the bridge rotates through this point. There is a pair of areas marked on the bottom of the lip of the pit section that says "no track.," which is where this dead spot will occur. Putting tracks in this dead area MAY work, but can give you all kinds of funky problems with polarity. You may have to figure out where these "no track" areas are in relation to your 3 and 9 o'clock positions. Also, since it works from one approach track to the bridge, but not off the bridge to the opposite approach track, you have a crossed wire somewhere. When you say the tracks are wired "in phase" with each other and the mainline, added to the statement that they both come from the mainline on opposite sides of the turntable, it begs the question "do you have a reverse loop arraingement in your mainline?"
Tom,
Thanks for that reply.
When I set up the turntable, I was careful not to place track in the dead spot. No problem there.
I was afraid that you would accuse me of mis-wiring the tracks. LOL. Always possible, but I am sure that the wiring is correct. The mainline track feeds approach tracks to the TT on the left side of my freight yard and on the right side of my freight yard so that engines may approach the turntable from either side. I have always followed a convention of wiring the outside rail with blue colored wire and the inside rail with yellow colored wire. When I first wired that approach track on the right side at the 3 o'clock position, engines ran fine right up to the TT. However, when I first tried to exit an engine from the TT onto that right side approach track, a short occurred.
"Sounds like you're confusing a DCC type auto reversing circuit with the mechanical reversing mechanism in the turntable". Not sure what you mean by that statement.
My first TT was the Walthers motorizable one that came as a kit, motor separately. I got it to work eventually, but not through a full rotation of the bridge...it would bind due to the pit wall not being circular. I merely lined to the radials in each bay by swinging the bridge through a narrow arc of about 40 degrees...so no reversal, and I didn't have to wire in a DPDT. Erecting the kit, it was obvious that no provision was designed into it for reversing the polarity if the bridge swapped ends to rotate an engine 180 degrees.
Thankfully, the newer indexed version has the "split rail" design where the wipers cross a small gap (sound engines die momentarily and then restart), and then encounter the next rail that has the same polarity as the rail just left!!! Meaning, nothing changes as far as the engine/decoder are concerned, just a momentary break in the current. The bay radials, all radials, are wired the same as the lead to the bridge on the opposite side of the pit. If you turn an engine entirely 180 deg, the same thing happens, except the polarity is still correct for the radials. Just as is the case when an auto-reverser quickly reverses polarity under your wye or reversing loop, the decoder doesn't care. It just won't accept crossing a gap where the rails are switched, which is what the split rail and the AR rectify in due course.
Crandell
If you want/need true autoreversing, then put the an autoreverser between the track power and b1 and b2 terminals.
You really shouldn't have to do this however, unless you are creating some type of s-loop cross over.
Don - Specializing in layout DC->DCC conversions
Modeling C&O transition era and steel industries There's Nothing Like Big Steam!
richhotrain TomDiehl: Sounds like you're confusing a DCC type auto reversing circuit with the mechanical reversing mechanism in the turntable. The rails on the bridge are fed through the center pivot of the table. If you lift the bridge out of the pit, you can see the wipers in the hole in the pit and rings on the base of the bridge. Two of these rings have a pair of gaps in them, offset by 180 degrees, which are the feeds to the rails. This is very simply how the rail polarity reverses at a certain point, and it will give you a dead spot as the bridge rotates through this point. There is a pair of areas marked on the bottom of the lip of the pit section that says "no track.," which is where this dead spot will occur. Putting tracks in this dead area MAY work, but can give you all kinds of funky problems with polarity. You may have to figure out where these "no track" areas are in relation to your 3 and 9 o'clock positions. Also, since it works from one approach track to the bridge, but not off the bridge to the opposite approach track, you have a crossed wire somewhere. When you say the tracks are wired "in phase" with each other and the mainline, added to the statement that they both come from the mainline on opposite sides of the turntable, it begs the question "do you have a reverse loop arraingement in your mainline?" Tom, Thanks for that reply. When I set up the turntable, I was careful not to place track in the dead spot. No problem there. I was afraid that you would accuse me of mis-wiring the tracks. LOL. Always possible, but I am sure that the wiring is correct. The mainline track feeds approach tracks to the TT on the left side of my freight yard and on the right side of my freight yard so that engines may approach the turntable from either side. I have always followed a convention of wiring the outside rail with blue colored wire and the inside rail with yellow colored wire. When I first wired that approach track on the right side at the 3 o'clock position, engines ran fine right up to the TT. However, when I first tried to exit an engine from the TT onto that right side approach track, a short occurred. "Sounds like you're confusing a DCC type auto reversing circuit with the mechanical reversing mechanism in the turntable". Not sure what you mean by that statement. Rich
TomDiehl: Sounds like you're confusing a DCC type auto reversing circuit with the mechanical reversing mechanism in the turntable. The rails on the bridge are fed through the center pivot of the table. If you lift the bridge out of the pit, you can see the wipers in the hole in the pit and rings on the base of the bridge. Two of these rings have a pair of gaps in them, offset by 180 degrees, which are the feeds to the rails. This is very simply how the rail polarity reverses at a certain point, and it will give you a dead spot as the bridge rotates through this point. There is a pair of areas marked on the bottom of the lip of the pit section that says "no track.," which is where this dead spot will occur. Putting tracks in this dead area MAY work, but can give you all kinds of funky problems with polarity. You may have to figure out where these "no track" areas are in relation to your 3 and 9 o'clock positions. Also, since it works from one approach track to the bridge, but not off the bridge to the opposite approach track, you have a crossed wire somewhere. When you say the tracks are wired "in phase" with each other and the mainline, added to the statement that they both come from the mainline on opposite sides of the turntable, it begs the question "do you have a reverse loop arraingement in your mainline?"
Now I understand what you mean by "Sounds like you're confusing a DCC type auto reversing circuit with the mechanical reversing mechanism in the turntable".
Hmmm, so far no one has commented on Walthers statement in the installation instructions that says,
If I wired the B1 and B2 wires in reverse, could that be why I apparently defeated the system and had to install my own auto-reversing unit?
Walthers statement about reversing the B1 and B2 wires is so that the bridge will be wired the same way as the approach tracks. On inital installation it is possible to have the bridge wired backwards.
You say you use blue wire on the outside rails and yellow on the inside. That would mean the 'blue' rail is closest to you. Then if the dead spots are at 12 o' clock and 6 o' clock, the rail of each track closest to the 12 o'clock position will have a yellow wire regardless of whether it approaches on the left or right side of the TT. Blue wire goes to every rail closest to 6 o'clock.
A loco that enters from 3 o'clock and exits at 9 o'clock will always have a blue wire under the left side. A loco that enters from 3 o'clock and turns around and exits the same track will have the blue power changed to the right side as the bridge passes the dead spots. No reversing unit is required.
Hope this helps.
Dave
From Mt Pleasant, Utah, the home of the Hill Valley and Thistle Railroad where the Buffalo still roam and a Droid runs the trains
Dave Merrill Rich Walthers statement about reversing the B1 and B2 wires is so that the bridge will be wired the same way as the approach tracks. On inital installation it is possible to have the bridge wired backwards. You say you use blue wire on the outside rails and yellow on the inside. That would mean the 'blue' rail is closest to you. Then if the dead spots are at 12 o' clock and 6 o' clock, the rail of each track closest to the 12 o'clock position will have a yellow wire regardless of whether it approaches on the left or right side of the TT. Blue wire goes to every rail closest to 6 o'clock. A loco that enters from 3 o'clock and exits at 9 o'clock will always have a blue wire under the left side. A loco that enters from 3 o'clock and turns around and exits the same track will have the blue power changed to the right side as the bridge passes the dead spots. No reversing unit is required. Hope this helps. Dave
Well, sorry to say, I still needed to install an auto-reversing unit even though all of my track was all wired the same way, and no shorts occurred from either direction on the approach tracks right up to the edge of the turntable. The only time that a short occurred was when a loco crossed the gap on the right side of the turntable (the 3 o'clock position), either entering the TT from the right side approach track or exiting the TT from the right side onto the approach track.
To this day, years later, it remains a mystery to me.
I will buy a six pack to the man who proves me wrong or tells me with certainty why I needed to install an auto-reverser to avoid shorts in my particular situation.
Let me see if I got this straight from the description. If you went from say a stall track at 9 o'clock onto the turntable bridge, no short, but if you went from the approach track at 3 o'clock it shorted? What about if you rotated the bridge around 180 degrees? DId it then short on the stall but not on the approach, or did the short remain on the approach side?
In either case, you had the feeders flipped somewhere, but if the second case was ALSO true you would need an autoreverse as the bridge pickups did not reverse the polarity.
For a turntable that does NOT reverse polarity with the bridge one way you should be able to drive right across it without a short if all your feeders are positioned the same. The short happens when you drive on to the bridge, rotate 180 degrees and try to back off - now the polarities will be reversed.
For a turntable that DOES reverse the polarity as it rotates, assuming you've correctly aligned the gaps in the wiper system that does the reversing, and you have your feeders correct, you should eb able to drive on and off with no shorts at any time. If it shorts then you have the feeders backwards, either th ones to the turntable bridge do not match the approach track or the bridge does not match the stall track.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Rich,
I'd like to work on this 6-pack challenge, and it may take a few posts to get there. Please humor me with the answer to a few questions.
At what clock position are the 'dead spots' on your TT? At what clock position is the sensor that is used to 'zero' your bridge? When you stand in front of the TT where is the TT in relation to the mainline? Do you happen to have a layout diagram in electronic format? If so could you insert it or email it direct?
Regards,
Dave Merrill Rich, I'd like to work on this 6-pack challenge, and it may take a few posts to get there. Please humor me with the answer to a few questions. At what clock position are the 'dead spots' on your TT? At what clock position is the sensor that is used to 'zero' your bridge? When you stand in front of the TT where is the TT in relation to the mainline? Do you happen to have a layout diagram in electronic format? If so could you insert it or email it direct? Regards, Dave
I have attached a photo of the turntable on the layout. The dead spots are at 9 o'clock (the track where the yellow/green C&NW tender and crane are sitting) and 3 o'clock. The sensor that is used to zero the bridge is at 12 o'clock right below the third roundhouse stall from the right. When I stand in front of the TT, the double mainline is right in front of the turntable coming from the left, past the TT, and then turning right down the right side of the photo. Incidentally, the TT approach tracks are at 8 o'clock and 4 o'clock. Those two approach tracks are the bottom most tracks at the turntable.
The diagram that follows was the original wiring setup that produced the short when engines arrive at or exit the TT on the track at 4 o'clock. There was no short when engines arrive or exit the TT on the track at 8 o'clock. I have noted the rails, the feeder wires and the bus wires.
The next diagram is the wiring setup with the AR-1 auto-reverser that was necessary to eliminate the short on the 4 o'clock approach track. I gapped the approach track as shown and connected this reversing section to the AR-1.
I look forward to your comments.
WHat about the feeders for the turntable? There should be a spot underneath marked "no track" - this is where the reversing gaps are in the turntable. That should be somewhere about 90 degrees away fromt he approach tracks. Since the turntable reverses the polarity of the bridge track, if it shorts with the turntable in one poaisiton, rotating it 180 degrees should make it work without shorting. If not, you have the dead spot in the wrong place. If the upper bridge rail was red and the lower one blue, there is no short in the diagram you have drawn.
Bingo!!
The answer to your problem is in the text of your last post. The 'dead zone' is at 9 o'clock under the yellow crane and straight across between two tracks at 3. Your approach tracks are at 8 o'clock and 4 o'clock. That puts both approach tracks on the same side of the 'dead zone'. On the left 8 o'clock approach track the red feeder is closest to the 9 o'clock dead spot and on the right track 4 o'clock the blue feeder is closest to the 9 o'clock dead spot.
Hence both approach tracks approach the same half of the TT with the feeders on the right approach track reversed in relation to the left approach track. A short every time.
The dead zone divides the TT into two electrical components. All tracks approaching each half must be wired the same. If the 'dead zone' (no-track) was between the roundhouse and engine shop you would have no reversing issue. Probably not worth the effort to rotate the TT or re-route the right approach track to be at the 2 o'clock position, either of which would eliminate the reversing issue.
That explains why the AR is needed. By the way, in what part of the world is your layout located?
Thank you for providing these diagrams and photo. Love a challenge. Keep up the good work and drink the 6-pack for me as you ponder the solution to this 6 year old mystery.
Your friend in railroading,
Dave Merrill Rich, Bingo!! The answer to your problem is in the text of your last post. The 'dead zone' is at 9 o'clock under the yellow crane and straight across between two tracks at 3. Your approach tracks are at 8 o'clock and 4 o'clock. That puts both approach tracks on the same side of the 'dead zone'. On the left 8 o'clock approach track the red feeder is closest to the 9 o'clock dead spot and on the right track 4 o'clock the blue feeder is closest to the 9 o'clock dead spot. Hence both approach tracks approach the same half of the TT with the feeders on the right approach track reversed in relation to the left approach track. A short every time. The dead zone divides the TT into two electrical components. All tracks approaching each half must be wired the same. If the 'dead zone' (no-track) was between the roundhouse and engine shop you would have no reversing issue. Probably not worth the effort to rotate the TT or re-route the right approach track to be at the 2 o'clock position, either of which would eliminate the reversing issue. That explains why the AR is needed. By the way, in what part of the world is your layout located? Thank you for providing these diagrams and photo. Love a challenge. Keep up the good work and drink the 6-pack for me as you ponder the solution to this 6 year old mystery. Your friend in railroading, Dave
Well, I'll be. I am a six pack poorer, but I can rest well for the first night in six years. Mystery solved, thanks to Dave Merrill. I suspect from the other recent reply that Randy was hot on the trail as well.
I pulled out the Walthers installation instructions after reading your post, Dave, and here is a little more that had been written for Installing The Pit: "Your new turntable automatically reverses track polarity when turned. As a result, the unit has two electrically insulated areas where the track on the bridge is not powered. These are indentified on the underside of the lip by the "NO TRACK" lettering. Working approach and fan tracks must be installed away from these areas - we suggest placing them at 90 degrees to the approach tracks."
Well, excuuuuse me. I thought that warning was just a guide not to place approach tracks in the NO TRACK area so that they would not access the bridge track at a point where there was no power. I did not interpret that warning to mean that approach tracks close to the NO TRACK area would cause a short because the turntable could not rotate far enough to activate the built-in reversal of track polarity - - the split ring, or whatever.
Well, I feel good about one thing. My wiring was fine from the outset. It was the approach track placement that was at fault. I assume that the stuff about reversing the TT wires at B1 and B2 on the Control Box would not have made any difference.
In any event, as you say, I see no reason at this point to re-route the approach track on the right side of the TT. There isn't any room anyhow.
I guess that I cannot fault Walthers. After all, they did suggest placing the dead zone at 90 degrees to the approach track. But, they could have been more explicit, IMHO. If you look at my photo, I have tracks coming up to the TT from all directions, so when I first installed it, I was hard pressed to find a good spot for the dead zone. I just thought I had to avoid the immediate NO TRACK area.
Dave, you are the man! Thank you, and thanks to all the others who offered their advice and comment on this issue. It really has haunted me for the last 6 years why I had to install an external auto-reverser to make this thing work.
Heck I nailed it in my first post BEFORE the diagram was posted: "Assuming you've correctly aligned the gaps in the wiper system that does the reversing"
Thanks for the kind words. Enjoy the trains. That is what this is all about.
Randy, you did get it right. Just needed to clarify everything.
rrinker Heck I nailed it in my first post BEFORE the diagram was posted: "Assuming you've correctly aligned the gaps in the wiper system that does the reversing" --Randy
OK, here is how I am going to resolve this apparent conflict. I bought a case of Sam Adams and huge bag of Tostidos, complete with salsa and a selection of melted cheeses.
We meet tomorrow night at my place, Randy Rinker, Dave Merrill and me and we don't leave till we finish the treats. Agreed?
Seriously, folks, for all the rest of you out there in the Peanut Gallery viewing these proceedings, isn't this the greatest set of forums in the model railroading world?
Has any one you ever asked a question that you didn't get answered?
You guys are all wonderful.
Sounds good to me - and darn if you didn't actually get good beer, too! I'll bring a couple of locos over, maybe we can give one of my T-1's a spin on the turntable.
Oh yeah, Historical Society meeting tomorrow night, bummer. No beer but there will be a slide show on those wonderful T-1's. I refer of course to the BEST T-1, the Reading 4-8-4's. Not those silly PRR or C&O ones