Model Railway Forum

Go Back   Model Railway Forum > Model Railway Construction > Wiring & Electronics


Reply
 
Thread Tools Display Modes
Old 30-12-2017, 01:34 PM   #1
Wolseley
Junior Member
 
Wolseley's Avatar
 

Join Date: Jun 2017
Location: Hills District, Sydney, Australia
Posts: 21
Wolseley is on a distinguished road
Default Common Returns

I am in the process of planning a layout that will be, basically, a double oval of track with two stations (one terminal and one through) and some passing loops and sidings. As everything I have built up to now has been rather small and a pair of wires (or sometimes two pairs) to the track have always been sufficient, my background in the electrical side of things is not quite up to the job.

I have been reading C J Freezer's Book of Model Railway Wiring, in an attempt to get my knowledge up to scratch and it is, generally, a pretty easy book to follow, but I am finding a bit of trouble coming to terms with the need for a common return. If CJF said that it was the best way, then I'm sure it is, but why? Why not just a pair of wires to the track (or several pairs of wires if the position of the points necessitates a few more). And with two controllers, do the returns go go one only, both, or just the one that the relevant feed came from?

I should add that I am using Hornby Dublo 3 rail equipment in which I believe the track acts as a common return, so do I really need to worry about this?
Wolseley is offline   Reply With Quote
Old 30-12-2017, 03:20 PM   #2
4VEP
Hornby Collector
 

Join Date: Jan 2016
Location: Rye East Sussex
Posts: 549
4VEP is on a distinguished road
Default

With 3 rail the centre rail is the feed and the outer rails are the common return. With 2 rail when a track goes round a loop the positive and negative are transposed causing a short, but you don't need to worry about this with 3 rail because the feed is always the centre rail and the common return is always the two running rails.
__________________
Railway Modelling is about life, the universe and everything.
4VEP is offline   Reply With Quote
Old 30-12-2017, 04:17 PM   #3
yelrow
Senior Member
 
yelrow's Avatar
 

Join Date: Dec 2013
Location: burgandy france
Posts: 817
yelrow is an unknown quantity at this point
Default

Wolseley, hi, i run a big 3 rail Dublo layout. You are over complicating the thought process, by your book reading. My track is 60 years old, and each circuit, only needs 2 wires, normally using the little screw terminals, on the feed rails. Unlike modern track, the rails joining process, is so good, that no extra feeds are needed. I have 6 running loops, each with their own controllers. The main problem, you will have , is the controllers, in that 3 rail locos, draw a lot more. I use Hamment and Morgan, clippers, and Duettes, that are easily obtainable from ebay. I appreciate your location, but the extra postage will ensure they run perfectly. The modern controllers, Guagemaster, and Morley. apart dont have the grunt, in my view. If you have no feed rails, just solder 2 wires, one to middle rail and tother to any side john
yelrow is online now   Reply With Quote
Old 30-12-2017, 06:01 PM   #4
Suzie
Senior Member
 
Suzie's Avatar
 

Join Date: Sep 2013
Posts: 377
Suzie is on a distinguished road
Default

With 3-rail you have a common return on the outer rails. Just make sure that your controllers are happy with common return and you will be fine.
Suzie is offline   Reply With Quote
Old 30-12-2017, 06:19 PM   #5
yelrow
Senior Member
 
yelrow's Avatar
 

Join Date: Dec 2013
Location: burgandy france
Posts: 817
yelrow is an unknown quantity at this point
Default

its the controllers, being under powered, that may effect future running. Mine struggled till i changed th H&M. May be aussie ones have more power
yelrow is online now   Reply With Quote
Old 30-12-2017, 09:29 PM   #6
Mountain Goat
Senior Member
 
Mountain Goat's Avatar
 

Join Date: Mar 2011
Location: UK.
Posts: 1,642
Mountain Goat is an unknown quantity at this point
Default

The principle of common return is to link all the return wires together to save on wiring and it also allows the use of just one pole of a switch, while normal non common return wiring will use two poles of a switch, so one can use a two pole switch and keep the second pole for panel lights etc.
For two or more controllers to be wired with the common return method, all controllers used have to either have separate transformers or if they share one transformer, the transformer must have totally separate windings for both outputs rather then have a single winding shared with two outputs. (If you are unsure, use two separate transformers). The most common controllers have transformers built in. If it is a twin (Or more) track controller you need to know how its transformer is wired before you use common return.
The reason why each controller needs a separate transformer (Or separate independent windings for each controller) is that under certain conditions where a short circuit can occur, the controllers overload cut out can be bypassed and send the short direct to the transformer should two controllers share the same windings.
This is the main consideration to bear in mind when wiring a layout for common return wiring.

Hornby Dublo 3 rail is basically wired as two rail but one can look at it as the feed being the central rail, and the return being the two outside rails, so basically it can be wired as common return or not. If you have to wire without common return bear in mind you have to isolate the central rail of the feed, and also totally isolate both rails and the metal bases as the return. Why for HD 3-rail, it is much easier to wire cab control sections using the common return method as all one has to isolate it the centre rail between sections and not the base or the two outer rails.

The old Hornby Dublo controllers had their own built in transformers per unit, so were suitable for common return.

In theory one could get in to trouble if one ran a slave controller (Which were normally powered by old 12v batteries) via the 12v accessory connections on the HD controller if these are not internally taken from separate independent windings on the transformer. I dont know if they are or not. So best not to try until one knows!
One of the issues with old Hornby Dublo controllers is the old rubber type mains lead which could look good on the outside but have the rubber breaking down on the inside and be a potential hazard, so it is best to have them checked by a professional to ensure they are safe to use, especially as they have a metal case to them. In the UK there has already been one fatality from a modeller who was using an old H&M controller. (It was either a clipper or duette). What had happened is the rubber grommet had broken and come away from the metal case, and the mains wire over time had rubbed on the case and worn through causing the metal case on the controller to become live and electrocuted the poor man. So it is why it is a good idea to carefully examine the mains lead of older controllers, or better still, have them checked professionally. This is not to put anyone off using old controllers as some, like the old H&M's were excellent controllers and can be bought at very good prices today. Is just that one has to make sure they are safe before use.
I'm certainly no expert, so I can only advise from the fringes of what I know. I hope it helps someone.

Last edited by Mountain Goat; 30-12-2017 at 09:53 PM.
Mountain Goat is offline   Reply With Quote
Old 31-12-2017, 01:53 AM   #7
Wolseley
Junior Member
 
Wolseley's Avatar
 

Join Date: Jun 2017
Location: Hills District, Sydney, Australia
Posts: 21
Wolseley is on a distinguished road
Default

Interesting. For what I am proposing to do it seems that I wouldn't get the full benefits that come from using the join all the common returns method.

I am using two controllers each with their own transformer but I have no intention of using vintage equipment for that. I have found that a Gaugemaster Combi (available here at a price not much higher than the UK price) has enough power to start and run my locomotives, even the Trix and the pre-nationalisation Dublo ones. I am using one in conjunction with an older (1980s) Australian built unit, which I am going to bin once I get another Combi, as it has sliding controls (which I don't like anyway) that have a tendency to stick.

Last edited by Wolseley; 31-12-2017 at 03:37 AM.
Wolseley is offline   Reply With Quote
Old 31-12-2017, 12:42 PM   #8
Mountain Goat
Senior Member
 
Mountain Goat's Avatar
 

Join Date: Mar 2011
Location: UK.
Posts: 1,642
Mountain Goat is an unknown quantity at this point
Default

Quote:
Originally Posted by Wolseley View Post
Interesting. For what I am proposing to do it seems that I wouldn't get the full benefits that come from using the join all the common returns method.

I am using two controllers each with their own transformer but I have no intention of using vintage equipment for that. I have found that a Gaugemaster Combi (available here at a price not much higher than the UK price) has enough power to start and run my locomotives, even the Trix and the pre-nationalisation Dublo ones. I am using one in conjunction with an older (1980s) Australian built unit, which I am going to bin once I get another Combi, as it has sliding controls (which I don't like anyway) that have a tendency to stick.
Surprised the Combi will run Hornby Dublo locos. Yours must be running well.
I prefer either panel mounted controllers or hand held ones if on a larger layout, though these do need a separate cased transformer. The Combi is basically a hand held of sorts. Not quite as flexible as a handheld which one can plug in and out along the layout but almost as flexible in use.
Panel mounted controllers do tend to look nice set into a control panel.
Controllers that have gone past their useful life I've used for the wire in the transformers... Useful for modelling use. The transformers core is sometimes made from thin metal segments which make useful weights for wagons and coaches.
Mountain Goat is offline   Reply With Quote
Old 01-01-2018, 07:45 AM   #9
Wolseley
Junior Member
 
Wolseley's Avatar
 

Join Date: Jun 2017
Location: Hills District, Sydney, Australia
Posts: 21
Wolseley is on a distinguished road
Default

Quote:
Originally Posted by Mountain Goat View Post
Surprised the Combi will run Hornby Dublo locos. Yours must be running well.
I have 27 (I think - there might be one or two more) Dublo locos and two Trix Twin (12v DC of course). I also have a few Tri-ang locos and a DMU I am in the process of converting to 3 rail. The Tri-ang locos and DMU are not finished yet, so I haven't tried them out and three of the Dublo locos are in various stages of repair, but all the others run well with the Combi. I haven't had any problems, but then all my locos have been cleaned, serviced and lubricated before I give them anything more than a test run. I have replaced magnets on five of them, as they were running slowly, but those ones ran slowly with both the Combi and my old controller, which had an output of 1.6 amps.
Wolseley is offline   Reply With Quote
Reply

Bookmarks



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump



All times are GMT +1. The time now is 07:24 AM.


Powered by vBulletin® Version 3.8.3
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.