changing polarity

[Anonymous]

   

 

     i have  an O scale layout in my back yard that has a loop at each end that is connected with a single track connecting the two loops.  I know at a certain point i need to change the polarity coming out of the loops to get the train to run continuously around the layout.  what is the best way to get this accomplished?

[challenger3980]

Hi TJ,

    If your O Scale layout is 3 Rail O-Gauge, rather than 2 rail O Scale then there is NO PROBLEM and NOTHING needs to be done, other than use either non-derailing or spring switches so that the train doesn't derail coming back through the same switch from the other side. Again if it is 3 rail track, You don't have to do anything to reverse the polarity, the center rail is the "HOT" rail, and will ALWAYS be the center rail. The two outside rails are the common ground rails, both outside rails will always be outside rails and are both ground rails.

   A nice feature of 3 rail track is that with both outside rails being ground, you can insulate one with plastic rail joiners at each end ( I am assuming that being outside, you are not using track with metal ties, if so you need to insulate the rail from the ties in a insulated track section) then you can use the train itself to turn on accessories such as crossing signals or track signals or anything else that you would want to activate when the train is in a certain location. Just put your insulated rail joiners where you want the accessory to begin and end operating. Then hook up your accessory with the red or hot lead to your transformer just like you normally would, the instead of hooking up the other lead to the transformer, hook it up to the insulated rail and the train itself will act as a switch and turn it on, this is exactly how non-derailing turnouts (switches) work.

   If your layout is 2 rail, then for unattended running you would insulate both rails of both tracks on the diverging side of the switch at each end and then use a n automatic reverse detector. This will detect when a train crosses over the shorting connection and reverse the polarity of the section that the train is entering to correct it, this happens very quickly and shouldn't be much more noticeable than a small hiccup for DC powered trains. You will probably need one at each end loop, I don't know if one unit would be able to control both ends or not. The automatic reverse modules are very common to HO, which would also work for N Scale, I don't know if those are heavy enough for O Scale Volt/Amp loads or not, or if they are available for O Scale power loads. This is something that if someone else here in the forum can't answer your LHS (Local Hobby Shop) can answer, especially if it is a train specific shop.

                                                      Hope that Helps More than it Confuses,

                                                                                      Doug

[Anonymous]

 

 

    you mean something like this

 

http://www.railclamp.com/displayCategory.jsp?categoryId=32&vId=53891

[challenger3980]

Hi Trader Joe,

   That Split jaw device is something different that I am not familiar with, but reading the description it is for linear point to point reversing not loop reversing. This unit works by sensing a loss of current flow ( it uses diodes to insulate rails at each end) what you need is a unit that senses the short circuit, and reverses the polarity to correct that.

   Are You running 3 rail AC powered trains or 2 rail DC powered trains? it makes a HUGE difference in what You want to do.

                                                                         Doug

[Anonymous]

 

   2 rail DC is what im running.

[challenger3980]

Hi Again TJ,

    You might want to ask this question on the Garden railways forum, most large scale stuff that is track powered is DC, they would be more familiar with the larger power requirements and also the weather proofing needed for an outdoor layout. Those are the kind of things that they deal with on a regular basis, as opposed to to indoor modelers, which don't have to worry about the weather (if it is bad, that is a good reason to go in and play with trains )

                                                                              Doug

[challenger3980]

Hi Again Trader Joe,

    Another solution to your problem would be to remove the turnouts and do a "dog-bone" track layout. Instead of using turnouts to return the train to the same single track, would it be possible/practical to put in "S" curves at the ends of the loops and essentially Double Track the center portion of the layout. this would be the equivalent of a loop, just in a different shape. This would be a simple solution to the need to reverse the polarity, would still use your end loops, with only slight modification, then a new parallel straight center section. Give this some thought, it may be the most practical and trouble free way to accomplish what you want to do.

                                                                                           Doug

[lionelsoni]

The lowest-tech solution is to use three double-pole-double-throw switches to be able to reverse the polarity of all three blocks while the train is running.  Each of the loops, except for the turnouts, would be a block.  The single-track main line, including the turnouts, would be the third block.  You would use the DPDT switches to make the polarity of the block ahead agree with the block that the train is in, before it gets to it.

Otherwise, an alternative to a double-track main line would be 4-rail gantlet track.  You would need a frog at each end; but it wouldn't have to be insulated, since both of the rails that cross would be permanently connected to the inner rails of the loops.  You could also use a three-rail track, not the usual kind, but with the rails spaced out to make two O-gauge tracks.  Either of these would be a bit of trouble to build unless you're into hand-laying.