U Shaped Layout Wiring

[thecheesemiester]

Hi all,

I'm in the process of turning an existing end-to-end layout into a 'U' shaped loop (see picture below). The central station/yard section is already laid so it is theoretically just a matter of adding the two end loops to allow continuous running, with locomotives passing through both platforms in one circuit. However, I'm struggling to figure out how to wire it up so that the passing loop in the station still works; unless i'm mistaken, when the points are changed to allow locomotives to move between the two lines there will be a short circuit between the two points (see my beautiful illustration). However, if I add an insulating fishplate between the two, the locos will change direction as they switch between the two tracks. Is there a way to get around this so a train could say go out of a platform in one direction, around the loop, and then through the points to run back through the same platform?

 

[jpendle]

Is this Dc or DCC? With DCC you would use reverse loop modules/frog juicers for the two loops and polarity would change automatically.

With DC you would need to isolate the 2 loops run a train into the loop, switch the loop's polarity with a switch and the loco's direction, then you can continue round the loop.

I'm not aware of any automatic methods using DC as you have the issue of changing the loco's direction "on the fly", which DCC decoders deal with automatically.

 

Regards,

 

John P

[thecheesemiester]

Thanks. I'm currently moving to DCC but still have a large number of DC locos (and can switch to a DC controller) so sounds like it might be easiest to get on with switching to DCC. Presumably I'd need one at both ends?

 

Guessing it would be wired up like below

Edited June 19, 2023 by thecheesemiester

[RobinofLoxley]

Not like that. The module is wired to opposite ends of the same loop as you have it. Switching occurs between a section where the power doesn't need to be switched such as the station section and one that does, i.e. a loop

There is a requirement for insulating joiners on the four turnouts and individual power droppers as well if DCC is used

One or two suggestions about the track plan might be forthcoming too

[thecheesemiester]

Thanks. I found this diagram which I think is comparable to my layout. May I ask why I will need insulating joiners on those points if the whole loops are isolated and the central section is all the same polarity?

[jpendle]

Yes that's  what you need.

 

BUT please take note that the polarity of the non-loop tracks has been changed from what you would see in a DC dogbone where the outermost rail would always be the same polarity.

 

Also if you plan on using live frog (Electrofrog) points you will need to isolate the rails at the 'heel' end of the points.

 

Regards,

 

John P

[RobinofLoxley]

Part of the reason is simply good practice, part is the avoidance of risk. Your proposal and the reverse loop 'tutorial' aren't identical. In yours it would be easy to produce unexpected short circuits without some protective measures.

[Chimer]

16 hours ago, RobinofLoxley said:

Your proposal and the reverse loop 'tutorial' aren't identical. 

 

I think they are, in practical/electrical terms.  But of course with electrofrog points the frogs have to be protected with IRJs as usual where necessary - four on the crossovers, and a bunch more in the top yard because of the additional feeds required to get power into the kickback sidings.  Not necessary with insulfrogs.

 

The tutorial solution works for DC too, provided you're happy to stop trains in the loop sections and flip a DPDT switch to change the polarity of the loop rails.  Simple and cheaper ...

 

And incidentally, if the station area represents a double track main line, which it seems to, both crossovers really should be reversed to be trailing rather than facing.  But I'm a bit confused by your reference to a "passing loop", which would normally imply a single track line.

 

Trying to be helpful 🙂

[thecheesemiester]

Thanks that's great. I'm planning on reversing the direction of the points at the left end of the station section, but the track plan currently represents the centre section of the layout as it is now (built many years ago without much thought!)

[DavidBird]

Another method for DC/analogue control is this. Wire your reverse loops through a bridge rectifier. As the train travels around the loop, hit the reverse switch on the controller. The train will continue in the same direction.

The disadvantage is that trains must always go round the loops in the same direction and you cannot reverse a train in a loop.

I'll do a wiring diagram tomorrow.

 

[DavidBird]

21 hours ago, DavidBird said:

Another method for DC/analogue control 

...

I'll do a wiring diagram tomorrow.

 

[DavidBird]

Another idea is this.

Think of the dog bone shape as a squashed oval, with the outside rail having the same polarity all the way round.

The lower section of track through the station is completely isolated in both rails. All 4 points in both crossovers are operated from the same switch, (each with its own motor or a single motor for both points in each crossover, it doesn't matter). 

If you use a style of motor with auxiliary contacts, use these to drive a DPDT relay which switches the polarity of both rails in the lower section.

In this setup a train will run round continuously without the need to change the direction switch on the controller.  If you need to shunt a train from one line to the other in the station area, when the points are thrown the train can just be driven across. The train will swap direction when the points are switched back to normal (or continue in the same direction if the direction switch is changed). Diagram (very rough, sorry) attached. 

This method is a lot more involved to wire up than the "bridge rectifier" method, but more flexible.