Common return issues

User avatar
steve howe
Posts: 911
Joined: Sun Feb 01, 2009 10:16 pm

Common return issues

Postby steve howe » Mon May 01, 2023 4:21 pm

Evening chaps,

I just had this question from my club colleague who is designing the circuits for the next section of our Watermouth project. Broadly we have a terminus (Watermouth) with two controllers wired for 'cab control', leading to a second station (St David's) which will have one controller. The terminus panel has rotary switches enabling either of its dedicated controllers to be switched in, with a third setting linked to the junction controller allowing the Junction operator to drive a train through from cassette deck to terminus on their controller. The question posed is this:

I envisage certain sections of track being switchable between the Junction operator and the Terminus operator. If the two controllers are powered by separate transformers, can they both be connected to a common return or do the two returns have to be kept separate from each other?

Can anyone throw any light on this that I can pass onto him?

thanks

Steve

User avatar
grovenor-2685
Forum Team
Posts: 3918
Joined: Sun Jun 29, 2008 8:02 pm

Re: Common return issues

Postby grovenor-2685 » Mon May 01, 2023 4:29 pm

steve howe wrote: If the two controllers are powered by separate transformers, can they both be connected to a common return


The answer to that question is YES, and it also applies to any other controllers, eg all the 3 you mention.
The 'separate transformers' is important.
Regards
Keith
Grovenor Sidings

User avatar
Tim V
Posts: 2868
Joined: Tue Jul 29, 2008 4:40 pm

Re: Common return issues

Postby Tim V » Mon May 01, 2023 4:31 pm

Yes, you will need separate transformers to run separate controllers for common return wiring.

However, if your 'designer' is asking these questions, I would be wary of their capability of designing a new wiring system.
Tim V
(Not all railways in Somerset went to Dorset)

User avatar
Noel
Posts: 1976
Joined: Wed Jun 23, 2010 1:04 pm

Re: Common return issues

Postby Noel » Mon May 01, 2023 4:43 pm

steve howe wrote:with a third setting linked to the junction controller allowing the Junction operator to drive a train through from cassette deck to terminus on their controller

It depends to an extent on visibility for the operators, but the convention is usually that you drive towards yourself, not away, so that, in this case, arrivals at the terminus are driven by the terminus operator and departures from it by the FY operator. It makes it much easier to see what you are doing.
Regards
Noel

davebradwell
Posts: 1174
Joined: Fri Jan 18, 2019 3:48 pm

Re: Common return issues

Postby davebradwell » Mon May 01, 2023 4:52 pm

Yes, Tim it does raise some doubts when querying a fundamental point like this. You can also have completely separate windings on the same transformer, of course.

But seriously and I'm not trying to be funny, have you sat down and thought about using DCC? You can drive anything anywhere at any time, loco conversion isn't difficult or expensive (although the system can be considered a significant purchase) and the control is wonderful as long as you buy decent decoders. Once you start inventing unusual 3rd positions of switches, somebody is going to leave one on with possible bad consequences.

DaveB

martin goodall
Posts: 1425
Joined: Fri Oct 02, 2009 6:20 pm

Re: Common return issues

Postby martin goodall » Mon May 01, 2023 7:04 pm

If you wish to stick to analogue (DC) control, you can use one transformer to power two or more controllers, but only if you have BOTH a separate feed AND a separate return for each track section. This requires DPDT switches to select the relevant controller to each section. Rotary switches can be wired to act in effect as DPDT switches.

This is the way I have wired my own layout. Each section has a three-way rotary switch which will switch that section (i.e. both feed and return) to (a) Controller A, (b) Off or (c) Controller B. Ordinary DPDT toggle switches could equally well be used to perform these same functions. The switches connect/disconnect both the feed and the return for each section to the chosen controller. In this way, you avoid any problems you would get with anomalous electrical paths through the controllers if you were to wire the layout simply for Common Return (with only the feeds, but not the returns, separated by the section switches).

User avatar
grovenor-2685
Forum Team
Posts: 3918
Joined: Sun Jun 29, 2008 8:02 pm

Re: Common return issues

Postby grovenor-2685 » Mon May 01, 2023 7:43 pm

Using seperate transformers (or just secondary windings) you don't get problems with common return and it halves the amount of switching and wiring. Its not much of an issue on a very simple layout such as the Burford Branch but as layouts get bigger so do the benefits of common return, if you want to stick with DC analogue control.
Regards
Keith
Grovenor Sidings

User avatar
steve howe
Posts: 911
Joined: Sun Feb 01, 2009 10:16 pm

Re: Common return issues

Postby steve howe » Mon May 01, 2023 8:25 pm

Tim V wrote:Yes, you will need separate transformers to run separate controllers for common return wiring.

However, if your 'designer' is asking these questions, I would be wary of their capability of designing a new wiring system.


That's unfair and unnecessary Tim.

He happens to be a retired S&T engineer of the Southern region and before that a design engineer for British Aerospace. He happens to be a DCC modeller and not so familiar with 'old school' DC wiring. :shock:


Return to “Control Concepts”

Who is online

Users browsing this forum: ClaudeBot and 0 guests