I guess the only dumb question is a question never asked. Background:Mrr-ing for 25 years but my current layout is the 1st w/ an engine terminal. Still using DC cab control and trying to figure out the wiring for a hopefully temporary Atlas turntable. The wiring instruction sheet doesn't have a schematic for my situation that I can see. For simplistic reasons think of this: What works is that an engine can travel out of the stalls onto and thru the tt bridge, out on the departure track, travel around the layout wherever I please and come back onto the arrival track and to the tt.
At this point, as the loco's wheels cross over onto the bridge, a short happens and the engine screeches to a pitiful halt. If I try it again with the bridge rails reversed 360 degrees, the same thing happens.
I'm sure there is some easy "should have known that" reason but me and electricity get along about as well as me and combustion engines. Not at all. I can figure out the common rail, assign and insulate and wire various blocks and/or tracks and that's about all I've done. Never wired a wye, or reversing loop or anything else out of the most simple type of arrangement.
Would someone be able to draw a simple schematic that would enable me to fix this issue? I will be eternally grateful!
Matt
Matt, what happens when you rotate the TT 180 degrees. It seems to me that, if your TT doesn't have auto revers like the Walthers, then you need to reverse the TT or reverse the rail polarity. But then you would need to reverse the rail polarity in the stalls too. You might consider going to DCC
73
Bruce in the Peg
180 degrees shorts as well. Picture: out on length of track and returning to tt via the same piece of track. (DCC is coming at some point but not until scenery is 99% complete.) Due to the size of the layout -28' x 14' that won't be for approx. 5 years. In the meantime DC it is.
The Atlas TT has built-in wiring to cross-over the polarity of the bridge when it spins. This simplifies the wiring in one way, but a by-product is that the lead tracks around the turntable are at different polarities. If you look around the edge of the turntable, there will be probably be little "A"s and "B"s molded-in to show the tracks that are at the same polarity. I'll bet that your arrival track and departure track are not connecting to the same polarity (same letter, "A" or "B").
If you can, re-orient the turntable so that the "arrival" and "departure" tracks are both the same, either "A" or "B". If you can't arrange the turntable to do that, you'll probably need a reversing switch to flip the polarity of the tracks leading into and out of the turntable.
Did you see the discussion of the "A" and "B" tracks in the instructions?
ByronModel RR Blog
Layout Design GalleryLayout Design Special Interest Group
You need to add a polarity reverse switch to the TT and house tracks. Hook up a DPDT switch to line that feeds the TT and house tracks. Try Googling Polarity Reverse for schematics.
Jay
C-415 Build: https://imageshack.com/a/tShC/1
Other builds: https://imageshack.com/my/albums
As mentioned, your Atlas TT has a built in 'reverser' - Spin the TT 180 degrees and it will reverse the polarity for you. Lets do some basic hook up:
Jim Bernier
Modeling BNSF and Milwaukee Road in SW Wisconsin
Ahem. I didn't see or quite grasp the A and B idea very well. Now, thanks to you I am further ahead in my muddled brain than what I was!!!
I will see which avenue is the one that works best in the morning. I believe Jim's post is where I will start if I can relocate the departure track to an A slot for the TT. This may require a day of re-arranging terminal trackage and structures 1st.Though I may not get to the wiring part again until Wednesday or Thursday. I will let you know and ask more if I encounter further annoyances. Give me a paintbrush over a soldering iron anyday!
Thanks much,
salt water cowboyAhem. I didn't see or quite grasp the A and B idea very well. Now, thanks to you I am further ahead in my muddled brain than what I was!!!
Hey Cowboy,
Instead of A and B polarity, think of the two rails as red and blue (see my crude drawing which follows:
As the engine leaves the round house and reaches the turntable, polarity matches as long as blue rails and red rails line up (this is always a question of matching wires soldered to the rails so you don't cross polarity). As the engine leaves the turntable for the tracks to the main line, polarity continues to match (assuming departure on the curved rails at the bottom portion of the drawing. But, assuming a loop of your mainline, note the rails at the top right of the drawing, you have created a different situation.. As the turnout send the track down to the turntable, there is a reverse polarity situation since blue and red rails don't match up. To avoid a short due to reverse polarity, you need to either throw a manual switch or install an auto reverser. To do this, you need to gap the rails and at both ends of a section of track long enough to hold the entire length of the engine (and tender). This reverse polarity problem can, and will, also occur when the turntable track is turned 180 degrees. For this reason, an auto reverser is preferable to a manual switch because you will forget which 180 degree position the turntable is set at any given time. Hope this helps.
Alton Junction
It may be as simple as just reversing the leads to the contacts on the turntable.
Disconnect the wires that connect from the rest of the track to the turntable. Reverse their positions. Reconnect them.
Dave H. Painted side goes up. My website : wnbranch.com
Thanks guys. (Richotrain) I will study your drawing a bit more as I have to get ready for work shortly. I am off on Thursday so I will finalize my conundrum then. (I hope). This morning I did some temporary wiring using the Atlas Controller in front of my Selector block switches. (The layout is wired for DC 2 cab control with two powerpacks.) (bear with me here DCC folks! I'm sure I'll need your assistance also when I get to it in a few years!).....anyways, I wired the Controller exactly as the diagram in the TT instructions showed for 2 cab control. Now I use the direction switch on the Controller instead of the direction switch on the power packs. The rest of the layout and all the blocks work fine. A common wire runs from the Controller to the common rail on the mainline and also from there- to the lefthand screw on the TT. A wire also runs from the right hand screw on the TT to one of the Selector block switches essentially making the TT it's own separate block. Forget about stall tracks for a minute as they are not laid yet. My next question I think would be this...As the loco travels off the main and onto the arrival track, I must flip the direction switch on the Controller exactly as soon as the front trucks reach the bridge track. If I don't flip the switch exactly on time the short occurs and the five fingered crane from the sky must bump the loco ahead a bit to get it going across the TT. Is there a way to reverse the polarity in the TT rails before the loco reaches it so there is smooth continuity off the arrival track? You guys might have answered my question already but I will re-read/study your posts tomorrow when I have more time.
Thanks again for all your help!
I was thinking the same thing, Dave, but I didn't feel confident about it. I hope you have the right solution and can get the "credit" for helping this gentleman out.
-Crandell
richhotrain Instead of A and B polarity, think of the two rails as red and blue (see my crude drawing which follows:
Because of the way the Atlas Turntable is pre-wired internally, one can't ignore the "A" and "B", unfortunately. Depending on how the turntable is oriented, your diagram does not match how it is wired. The issue is specific to the Atlas TT, not turntables in general. That's why they go to the trouble of molding the "A" and "B" designations right into the plastic of the TT itself.
The problem specifically is that I don't believe there is a "straight through" path that has the same polarity as you have drawn on the Atlas TT (again, because of the way it is pre-wired internally).
I believe that the original poster could solve this problem in one way by offsetting the two entry paths to the TT so that they can both be the same polarity, either "A" or "B".
All right, forget this I'm taking the turn table out of my plan .
cuyama richhotrain Instead of A and B polarity, think of the two rails as red and blue (see my crude drawing which follows: Because of the way the Atlas Turntable is pre-wired internally, one can't ignore the "A" and "B", unfortunately. Depending on how the turntable is oriented, your diagram does not match how it is wired. The issue is specific to the Atlas TT, not turntables in general. That's why they go to the trouble of molding the "A" and "B" designations right into the plastic of the TT itself. The problem specifically is that I don't believe there is a "straight through" path that has the same polarity as you have drawn on the Atlas TT (again, because of the way it is pre-wired internally). I believe that the original poster could solve this problem in one way by offsetting the two entry paths to the TT so that they can both be the same polarity, either "A" or "B". ByronModel RR Blog
Cuyama, I hear ya, but isn't the principle still the same? If polarities are mismatched, he is going to get short. When Cowboy responded to the inquiry about turning the TT position 180 degrees, he said that the short still occurred when the engine returned to the TT on the same track from which it left so, of course, he will now get a short. If he returned the engine on the other track (arrival versus departure) as he first indicated, then no short should occur when the turntable is flipped 180 degrees (unless you are indicating that special Atlas internal wiring anticipated the rotation and reversed polarity automatically). In that case, he needs to isolate a section of track and wire that section with a manual switch or an auto reverser, no ? Simply reversing the feeder wires just reverses the problem.
I just checked my Atlas turntable ( will be using 2 of them as stand in turntables until I get my "real" ones built.)
They do NOT need a polarity reversing switch.
If its wired correctly there is NO need to flip a switch as the train enters the turntable.
If wired correctly the turntable will AUTOMATICALLY align the polarity to match the polarity of the track entering the turntable.
Assume the turntable will be a "normal" engine terminal installation. There will be one or more tracks leading in from the west end of the yard and maybe one or more tracks leading in from the east end of the yard. The rest of the tracks will be stub ended storage tracks.
Critical item # 1 : The change between the "A" tracks and the "B" tracks must fall between the west leads and the east leads. It CANNOT fall between the leads on any one side. So if there are two leads on the west side, it can fall to either side of the two leads but NOT between them.
Critical item # 2 : The change between the A and B tracks marks the point where you have to change the rails to which your power feeds connect.
Example :
Assume you are the engineer on an engine and you are running forward. As you approach the turntable on a lead the red feeder wire is connected to the right rail and the black feeder wire is connected to the left rail (from the point of view of the engineer facing forward.)
Connect the feeders to the turntable so that the engine can pull onto the turntable without shorting. If the engine shorts out, simply swap the feeders on the terminals on the turntable.
Without turning the turntable, AT ALL, the track opposite the lead will have the same wiring polarity as the lead onto the turn table. So for the point of view of the engineer pulling onto the turntable if right is red, then leaving the turntable the track will have the right rail connected to the feeder.
Look at the letter on that track. Doesn't matter if that track is an A or a B. Find the location where the A and B tracks change. So if the track opposite the lead is an A, find the location where the first B track is. All of those tracks (in this case a B) will have the polarity "reversed" FROM THE POINT OF VIEW OF AN ENGINEER ON THE TURNTABLE. So if you are the engineer on the engine sitting on the turntable, for this example aas you leave the turntable on ANY "A" track the red wire will connect to the right rail. As you leave the turntable on ANY B track the red wire will be on the LEFT rail.
If you follow those conventions then every track will have the correct polarity, the olnly switches you will need are those to turn the power off and kill the tracks. You will need NO DPDT reversing switches, you won't need to throw ANY switches just as the engine reaches the turntable. The polarity will AUTOMATICALLY be aligned for EVERY track.
Guaranteed.
"If wired correctly the turntable will AUTOMATICALLY align the polarity to match the polarity of the track entering the turntable."
OK Dave...it's late and I will delve into your post tomorrow. But in regards to your quote above. How would the turntable "know" what the polarity is to be if the arrival and departure tracks don't touch the bridge track? On my layout the 2 tracks out from the TT hit the same main line and return on the same. The positive and negative rails stay exactly the same out and back. The engine travels from the RH over the bridge, onto the departure track, out to the main, does it's loop and goes off the main and onto the arrival track and then shorts as it hits the bridge.
I think I'll have a beer before bed.
I think Dave's right. I had goofed up my explanation earlier ... to drive straight through, you need one track on an "A" and the other on the "B" (and yes, Rich, that part works like your diagram).
But now I don't understand Matt's explanation of the way the tracks connect to the TT. Could it be that the addition of the turntable and connecting tracks has created a way for the engine to now turn itself end-for-end as it travels around the layout? IF that's the case, you may have created another return loop, and that could be the reason for the trouble.
A sketch of the way the turntable connects to the rest of the layout would help.
cuyamaA sketch of the way the turntable connects to the rest of the layout would help.
A sketch of the layout would definitely help. I agree with others that a throw switch should not be necessary as the engine moves onto the turntable. But, it may be that the approach/departure track on one side of the TT may need to be isolated (gapped) if shorts are occurring. I am not as familiar with the Atlas TT as I am with the Walthers TT, so other may have a point that the problem-causing side of the A/D track to the TT may need to have it wires reversed as they connect to the TT. I suppose it could be that simple. Weird !
salt water cowboyOK Dave...it's late and I will delve into your post tomorrow. But in regards to your quote above. How would the turntable "know" what the polarity is to be if the arrival and departure tracks don't touch the bridge track?
Its the wiring method that has been in use for at least the last 50 years, split ring contact. The concept is that there is a contact area that is circular and split into two halves, then there are two wipers that touch the contact area and are positioned so that each wiper touches only one contact area at a time and the opposite contact area from the other wiper. Doesn't matter whether the feeders connect to the contact area or to the wipers.
On the Atlas turntable the contact areas are two currved strips of nickle silver sheet metal that connect to the feeders. The wipers connect to the rails on the turntable and rub on the contact strips. The gap between the two contact areas is at the spot where the tracks change from A to B.
Lets say the turntable is positioned so the AB split is vertical (N-S), so the contact area has an east half and west half and the inbound track is from the west. The wiper for Rail #1 on the turntable (currently the north rail) is connected to the west contact area and Rail #2 on the turntable (currently the south rail) is connected to the east contact area.
As you rotate the turntable around the rails on the turntable stay connected to thier respective contact areas, UNTIL the turntable is due N-S. At that point tracks change from A to B, what that really means is the wipers are going over the gap between the two halves of the contact area. So when the turntable is directly in between the A and B tracks the rails on the turntable aren't connected to either contract strip.
As soon as you pass due north, the wipers are on the contact strips again. Only this time since you have turned the turntable past the midpoint, The #1 rail on the turntable is now the SOUTH rail and connected to the east contact strip and the #2 rail on the turntable is now the NORTH rail and is connected to the west contact strip.
So for ANY track connecting to the turntable the north rail always remains connected to the same feeder and the south rail always remains connected to the same feeder.
YAY! It's done...It works...Thanks to everyone for all their help in this and I am now in business and will start to get stall tracks laid (and wired correctly I hope!)
All I had to do, since the approach and departure tracks are essentially the same track is have one go from the A slot and the other to the B slot. I had them laid into 2 B slots before... That simple....geeeeez! I will keep my Atlas component switches wired up as explained above as the Controller will be used to send power to the motor as soon as I get one. I now am more knowledgeable than I was on wiring issues and if ever I can help anyone with painting, weathering, structure building, scenic effects and the like please let me know. That stuff I CAN do without filling up my head full of plusses, minuses, polarities, reverses, circuits and the like!! My secondary project underway is an operating wigwag signal kit that I may have to tap into some brains here when I get to the "operating" part of the instructions!
Thanks again everyone...Y'all are super folks.
Just a quick apology for not including a track plan. If I had done so in my initial post it may have saved some time, consternation and "gosh-darning" on my part!
salt water cowboyThanks again everyone...Y'all are super folks.
Glad to hear that you got that worked out. The guys on this forum are all very knowledgeable and helpful and have provided me with invaluable assistance many times as well.