Common return using two different types of controllers?

[Demondrille Junction]

Hi all. I've a basic question with regards to common return track/controller wiring.  Do the controllers have to be the same type or brand? 

From searches in the past I know that each controller must connect to separate transformers but I've not been able to find any mention of the subject relating to controller compatibility.  Maybe it doesn't matter, but I don't know.

 

My situation is I have a GM UDS panel controller which has two track outputs with switchable inertia/brake and a newly acquired Morley Vector Zero Two.  Thanks to Mikesndbs thread I knew about the different waveforms of the two controllers and I'm worried if one might damage the other through a common return. Any thoughts?

 

 

[RobjUK]

As long as neither controller is connected to anything else - or the low voltage side of the transformers earthed - in any way, it should be OK.

 

The critical part is that the only possible current path between the two controllers is through the track.

eg. If they use metal enclosures and have an internal connection to the enclosure, the enclosures would have to be mounted on insulation rather than being possibly interconnected.

 

Edited July 15, 2019 by RobjUK

[Demondrille Junction]

Thanks very much Rob, that's reassuring.  Despite my research I couldn't see this scenario covered but it makes sense re current path, and isolation/insulation of transformers will be no problem.  I'll proceed with some testing, cheers.

[34theletterbetweenB&D]

8 hours ago, Demondrille Junction said:

...My situation is I have a GM UDS panel controller which has two track outputs ... Any thoughts?

While the principle outlined is correct, two separate transformers,* one per track output, (or two completely independent low voltage windings on a common transformer frame) are required for this device, if both track outputs are to be connected to a common return system (before even considering any other controller being added to the common return system).

 

*I believe that is what is specified for this Gaugemaster product.

 

Just to avoid anyone reading this as 'a controller with two track outputs can be connected to a common return wired layout' without that qualification.

[Demondrille Junction]

Ah yes, I should've clarified there.  Reading my first post again I feel I should add a little more detail.  The two transformers for the Gaugemaster panel controller are wall warts, fully enclosed plastic, not the T1 open frame type and the Morley has two track outputs supplied by two independent inbuilt transformers.

[cliff park]

There is one situation it would be best to avoid. Let's assume a straight piece of track. One half controlled by Controller A the other by Controller B. A common technique is to set both controllers to a similar setting, say half way, and drive the train across the join. Momentarily the engine wheels will bridge both controllers, and may cause problems. In the good old days of simple rectified AC this would not have mattered.

[kevinlms]

13 hours ago, cliff park said:

There is one situation it would be best to avoid. Let's assume a straight piece of track. One half controlled by Controller A the other by Controller B. A common technique is to set both controllers to a similar setting, say half way, and drive the train across the join. Momentarily the engine wheels will bridge both controllers, and may cause problems. In the good old days of simple rectified AC this would not have mattered.

Then your wiring is wrong, it's best practice to have a movement done using one controller only. Look for references for block switching or cab control.

 

Simple 'AC rectification' has nothing to do with it. 

[PatB]

8 hours ago, kevinlms said:

Then your wiring is wrong, it's best practice to have a movement done using one controller only. Look for references for block switching or cab control.

 

Simple 'AC rectification' has nothing to do with it. 

 

True, it's not ideal, but I've seen it described as acceptable in a number of older books covering layout wiring, so presumably there have been a few layouts set up like this. 

 

I suspect it's not so much the "simple rectified AC" that rendered such arrangements tolerable, as the fairly basic transformers and controllers of decades ago, with big, robust resistance mat throttles, chunky, slow acting thermal cutouts (or car indicator bulbs for the homebrew enthusiast), etc. that would take no hurt, nor stop a train, in the event of a momentary short. Even moving into the electronic era, the favoured 2N3055 output transistor of many, many controller circuits would likely survive such abuse for quite a while. 

 

Like I said, not ideal, but much older model railway practice could be described as such. 

[5050]

I'm sure that in the past I've also put my point motor AC returns through the 'common return wiring' - or am I suffering a delusion?

Edited July 17, 2019 by 5050

[Brian]

So long as the AC is taken from a totally separate transformer or separate transformer winding, then no problems. However, you may need to increase the wire size of the common return wire.

[DCB]

Sooner or later you will connect both controllers to the same bit of track, usually a loco will bridge the insulated joiner, this has become more likely in recent times as bogie pickups and tender pickups have become popular.  This could cause issues as Morleys don't have an "Off " position.  You could end up with one controller set forward and the other set backwards and the loco and controller electrics slowly cooking as you struggle to figure out what is going on. Driving from one controller to another over a section break will inevitably give power from both controllers momentarily. .  . I use Morley, OnTrack and H&M controllers, 7 in total of which 4 can operate 90% of the layout , selected through double pole rotary switches and if I need to change controllers I just change the section selector and with most locos Bachmann etc you barely notice the jerk

I regard common return as a complete PITA. Much easier to run pairs of wires to each section, and isolate each section. so  Our layout has gradually gone from common return to the other thing, variable return? with some areas having the return switched as weird complications creep in with complicated pointwork and live frogs.  

Edited July 18, 2019 by DavidCBroad

[Sol]

And I run DCC, DC  & AC on common return without any problems - of course each supply has its own transformer.

No different than old style telephone exchanges with 3 different DC volts -ve & +ve  & the same common return.  SWER   https://en.wikipedia.org/wiki/Single-wire_earth_return     AC mains also uses the  Earth as the return as did microwave transmissions.

[PatB]

37 minutes ago, Sol said:

And I run DCC, DC  & AC on common return without any problems - of course each supply has its own transformer.

No different than old style telephone exchanges with 3 different DC volts -ve & +ve  & the same common return.  SWER   https://en.wikipedia.org/wiki/Single-wire_earth_return     AC mains also uses the  Earth as the return as did microwave transmissions.

Not to mention vehicle electrical systems, which, even pre-electronics, might typically have had ~5V regulated DC for instruments, 12V DC for general power, the AC output from the alternator, and a zillion volts intermittent for the HT side of the ignition , all finding their way home quite happily via the vehicle structure.

[Crosland]

3 hours ago, PatB said:

Not to mention vehicle electrical systems, which, even pre-electronics, might typically have had ~5V regulated DC for instruments, 12V DC for general power, the AC output from the alternator, and a zillion volts intermittent for the HT side of the ignition , all finding their way home quite happily via the vehicle structure.

 

Different situation entirely. Ultimately all of those supplies come from the one battery. 

 

In MR common return we are connecting together (or commoning) two or more independent supplies, e.g., two transformer windings.

[Junctionmad]

Personally I avoid common return as I’ve seen to many issues as a result of unintended interconnected supplies 

[kevinlms]

31 minutes ago, Junctionmad said:

Personally I avoid common return as I’ve seen to many issues as a result of unintended interconnected supplies 

Yes, although it needs to be said that the troubles usually relate to breaking the rule of seperate power supplies. It's all too easy, to tap into an existing power supply, thinking this device, doesn't take much power.

[AndyID]

As we are experiencing the normal topic drift I'd point out that you can use common-return with a two DC supplies powered from a single center-tapped transformer. You'll have to make your own push-pull controllers that can swing the outputs positive and negative.

 

Has anyone seen it done like this?

[Nearholmer]

Split-potential supply was considered quite a normal way of going about things on model railways until possibly as recently as the early-1950s.

Edited July 19, 2019 by Nearholmer

[Clive Mortimore]

8 hours ago, Junctionmad said:

Personally I avoid common return as I’ve seen to many issues as a result of unintended interconnected supplies 

Wow Junctionmad and me are in agreement about common return.....best avoided.

 

I have had to try and debug a layout where the problem was solved by getting rid of the common return.

 

In addition when I worked for Guagemaster back in the 80s, Neil Collins who designed the Guagemaster controllers recommended, more like insisted, that common return was not to be used.

 

My present layout has four controllers. Each section has a roatary switch, 4 way 3 pole (I think that is what they are called) and a double throw double pole switch.  All the rotary switches are wired up in parallel, the positive wire from controller one goes to pin one on every rotary switch, the negative wire goes to pin 5. Controller two positive to pin 2, negative to pin 6, and so on. Pin A is the positive pin for that switch, it is then wired to the positive side to the DTDP switch and Pin B is wired to the negative side. Wires to the track are then run from the DTDP to the track, remembering to keep the positive and negative the same sides on all sections. The reason for two switches per section is to ensure when dialing through the rotary switch I do not accidentally power a train. Unless a section is going to be used the DTDP switch is in the off position. 

 

I hope the sketch explains it a wee bit better than my waffle.

 

 

 

I am sure there are many out there who will say , go DCC it might be easier.

 

 

Edited July 19, 2019 by Clive Mortimore

[Theakerr]

If your going to the trouble of common return wiring, suggest it is just as easy to use cab control with DPDT switch centre off and both wires cut and block sections,

[Demondrille Junction]

On 20/07/2019 at 06:06, Clive Mortimore said:

 

I am sure there are many out there who will say , go DCC it might be easier.

 

 Oh I hope not. This subforum seems to be the most DC friendly place there is with a knowledge base to suit. It's refreshing not to have to justify why one wants to meddle with at times complicated DC problem solving when asking questions.  

 

Thanks to all that have responded.  I believe my biggest problem will be me implementing common return correctly so far as poor planning and making silly mistakes is one of my attributes .  So I'm leaning towards running pairs of wires where needed and implement cab and block control with appropriate switching to create some interlocking.  I started with an interesting perhaps  complicated prototypical track plan without any circuitry or electrics included in my interpretation.  I threw down flex track and modified electrofrog points to match the plan then soldered every join with the aim of cutting in isolating, expansion and block sections later, some of which I've done.  Needless to say there's been a lot of short circuits up to this point.  To move forward I'm going to have to do what I'm not good at, a proper plan and implement some order and neatness.  I've not used uniform colour codes for wires either and I've recorded nothing so far on what I've done, just keeping it in my head and it's getting crowded in there.  I still think common return will have a place in regards to the Seeps and later signalling plus relays I plan on installing but every system will have it's own common return except the controllers which will all be separated. 

 

There's a simplified, condensed plan of the layout below, basically highlighting the points and crossings involved. Minimum of three controllers for starters with one for Up Main, Down main and Branch.  Where one controller hands off to another, say when a train traverses down main to down branch, I'll just have to bring the train to a stop before the swap is made.

 

 

Edited July 22, 2019 by Demondrille Junction
trying to make image legible but failed

[Sol]

Even old modellers like the late Rev Edward Neal used common return  and cab control on his West Midland Lines back in the 1940-50's.

A modern version  http://www.rail.felgall.com/cc.htm

[Clive Mortimore]

1 hour ago, Sol said:

Even old modellers like the late Rev Edward Neal used common return  and cab control on his West Midland Lines back in the 1940-50's.

A modern version  http://www.rail.felgall.com/cc.htm

If the bloke who designed Gaugemaster controllers said don't wire them in in common return, then I would suggest to Demondrille, as he has a Gaugemaster controller, to take his advise before something goes bang or worse becomes unsafe.

 

On the packaging of Gaugemaster controllers there is a diagram explaining why they should not be used with common return.

On 19/07/2019 at 21:06, Clive Mortimore said:

.

 

In addition when I worked for Guagemaster back in the 80s, Neil Collins who designed the Guagemaster controllers recommended, more like insisted, that common return was not to be used.

 

 

 

Neil Collins wasn't always the easiest boss to get along with but I wouldn't question his advice when it comes to safety with model railway controllers.

 

[Sol]

Without seeing the circuit of the Gaugemaster unit, one can only assume then that it was one secondary coil of the mains transformer serving both controllers circuitry.

 

Common return wiring can only be used with separate windings of transformers and have a understanding of electrical interconnections . I have used common return wiring for 50 plus years with both DC & DCC with no problems - granted my career path in telephone exchanges may have helped.

[AndyID]

1 hour ago, Clive Mortimore said:

 

On the packaging of Gaugemaster controllers there is a diagram explaining why they should not be used with common return.

 

 

That's odd because Gaugemaster says the UDS is suitable for cab control and common return.

 

http://www.gaugemaster.com/instructions/uds.pdf