From your description this sounds like a 'reverse loop'. Google will provide plenty of solution descriptions which fall into two categories - one for DC and one for DCC.
David
David
Turnback chord : impossible on a model railway ?
I suspect this question is just as relevant in any of the gauge forums, but since it is an N Gauge layout here goes !
I am renovating my 1970s N Gauge layout basically two loops (inner and outer) plus sidings inside the inner loop and a terminal station out side the outer loop. Remembering the wooden railway systems I have been creating with my son, I decided to extend one of the sidings inside the inner loop so that it became a turnback chord, i.e. that entering the chord (from the inner loop) in one direction it would exit it going in the other direction.
However......
Almost immediately I switched on I realised this may not actually be possible because the polarities on the rails would be reversed !
Am I right ?
And if so is there anything I can do ?
I had considered an isolating section (both tracks) at one end of the chord but even that has problems because a loco could, at a certain point, be picking up current with opposite polarities at each of its ends as it travels over the gap in the tracks (!) Could that not do significant damage to it ?
I am renovating my 1970s N Gauge layout basically two loops (inner and outer) plus sidings inside the inner loop and a terminal station out side the outer loop. Remembering the wooden railway systems I have been creating with my son, I decided to extend one of the sidings inside the inner loop so that it became a turnback chord, i.e. that entering the chord (from the inner loop) in one direction it would exit it going in the other direction.
However......
Almost immediately I switched on I realised this may not actually be possible because the polarities on the rails would be reversed !
Am I right ?
And if so is there anything I can do ?
I had considered an isolating section (both tracks) at one end of the chord but even that has problems because a loco could, at a certain point, be picking up current with opposite polarities at each of its ends as it travels over the gap in the tracks (!) Could that not do significant damage to it ?
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^Wot they said^ 
To add to David's comment, the following links have some guidance for DC and DCC systems.
For either system on a turnback chord/turning triangle/turning wye (all different names for effectively the same thing) I would probably treat one of the "Y" sections as the reversing section (i.e. the bit referred to as the 'loop' on the above links.). You could also do so on one of the chords, but I personally feel this is slightly less elegant.
(After clicking 'post', I scrolled down slightly further on the DCC link, and there is an example of this arrangement there)
Regards,
Cameron.
To add to David's comment, the following links have some guidance for DC and DCC systems.
For either system on a turnback chord/turning triangle/turning wye (all different names for effectively the same thing) I would probably treat one of the "Y" sections as the reversing section (i.e. the bit referred to as the 'loop' on the above links.). You could also do so on one of the chords, but I personally feel this is slightly less elegant.
(After clicking 'post', I scrolled down slightly further on the DCC link, and there is an example of this arrangement there)
Regards,
Cameron.
It doesn't damage the loco, or at least none that I have seen it happen to...I had considered an isolating section (both tracks) at one end of the chord but even that has problems because a loco could, at a certain point, be picking up current with opposite polarities at each of its ends as it travels over the gap in the tracks (!) Could that not do significant damage to it ?
For DC the loop is made into a fully isolated section, with switching to reverse polarity once the train is fully in the isolated section. Then the train runs in on matched polarity, stops fully in the isolated section, polarity is switched and the train then resumes movement with matching polarity as it leaves the isolated section.
For DCC a very rapid switch (in a 'return loop module') takes care of switching over rail supply when the short circuit is detected as the wheels pass over an insulated break in the loop, loco keeps moving throughout. Just one of many good features that the expense of DCC provides.
Thanks.For DC the loop is made into a fully isolated section, with switching to reverse polarity once the train is fully in the isolated section. Then the train runs in on matched polarity, stops fully in the isolated section, polarity is switched and the train then resumes movement with matching polarity as it leaves the isolated section.
For DCC a very rapid switch (in a 'return loop module') takes care of switching over rail supply when the short circuit is detected as the wheels pass over an insulated break in the loop, loco keeps moving throughout. Just one of many good features that the expense of DCC provides.
It's a DC layout BTW.
I thought of having two isolating points at each end of the loop, then stopping the train in the middle and switching which end is on "through power". What concerned me is if my lad was operating it and switched the isolaters in the wrong order, though my AGW PE404 controller seems to be able to cope with that, the overload light just illuminates !
I would have to use non conducting rail joiners though because I have not been able to find an isolater track with "breaks" on both tracks, am I right that would be needed ?
One of my Locos is a Farish Deltic with all axle drive and all axle pick up, and as such it runs far better than any of my other locos........ Would it be possible to have one bogie motoring one way and the other bogie (at the other side of the isolater) in the opposite direction ? ! ?It doesn't damage the loco, or at least none that I have seen it happen to...
It would be interesting to know how the wiring of each loco would cope with some of the wheels having 12V one way and some of the others 12V of the opposite polarity.
You can't run the bogies in opposite directions - there is only one motor in the model, and it uses a worm drive to the bogies. So, they all must run in the same direction.One of my Locos is a Farish Deltic with all axle drive and all axle pick up, and as such it runs far better than any of my other locos........ Would it be possible to have one bogie motoring one way and the other bogie (at the other side of the isolater) in the opposite direction ? ! ?
It would be interesting to know how the wiring of each loco would cope with some of the wheels having 12V one way and some of the others 12V of the opposite polarity.
The loco will cause a short-circuit in the situation you describe. (There are ways to damage the loco if using two independent power sources, as the loco might, sometimes, experience the combined voltage (nominal 24 volts, in practise probably well over 30 volts) . But this needs two power supplies and a certain amount of stupidity in the wiring of the layout.
You could "protect" things on the loop, with DC running against mistakes. Depends what level of doing things you're willing to undertake. Could be switches (which also throw turnouts), which also isolate sections of track (so they're dead if switch not correctly thrown). Or there are more advanced methods.
- Nigel
Thanks Nigel. I haven't stripped down my Deltic, thus showing I don't know how it is constructed ! As I said it runs the best of any of my locos.You can't run the bogies in opposite directions - there is only one motor in the model, and it uses a worm drive to the bogies. So, they all must run in the same direction.
Good to know, and I assume the short circuit would "just" cause the overload lamp to light on the AGW controller and, one assumes, cut out the power.The loco will cause a short-circuit in the situation you describe. (There are ways to damage the loco if using two independent power sources, as the loco might, sometimes, experience the combined voltage (nominal 24 volts, in practise probably well over 30 volts) . But this needs two power supplies and a certain amount of stupidity in the wiring of the layout.
When you say two independent power sources, does a twin controller count as that ?
Things are complicated by the fact my 9 year old sometimes plays with the layout, and I want him to really, that's one of the main reasons I renovated it. Thus I am "cautious" about any solution which requires switches to be operated in a certain order etc. Use of a 4 pole (or 8 pole for completely isolating two lengths of track) may be fool proof (?), but awkward to wire up and I'd have to find one !You could "protect" things on the loop, with DC running against mistakes. Depends what level of doing things you're willing to undertake. Could be switches (which also throw turnouts), which also isolate sections of track (so they're dead if switch not correctly thrown). Or there are more advanced methods.
- Nigel
TBH I am considering, for now anyway, just having a length of permanently isolated track at one end (just past the last pair of sidings), though that would mean any train traversing that section would have to be pushed..... It wouldn't actually be that inconvenient as its an N gauge layout and not too far to reach !
Yes.Good to know, and I assume the short circuit would "just" cause the overload lamp to light on the AGW controller and, one assumes, cut out the power.
When you say two independent power sources, does a twin controller count as that ?
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