DC wiring Block control or conventional isolating sections

[AndyID]

Common return can be complimentary to Cab Control but is not a necessity.  I did use  common return but have since abandoned it in favour of feeding both sides of sections from two pole switches as this means my individual isolators to allow moves such as attaching a pilot loco can go in either rail which simplifies wiring in some situations.  Sectioning the layout is just as important with DCC unless you want to cut and resolder lots of dropper wires every time you have a fault.

 

Hi David,

 

I've noticed before you don't care for common return, but it improves reliability, reduces cost and simplifies wiring. It would be a pity if you put other modellers off the advantages of common return for the wrong reasons.

 

I'm not saying you didn't experience a problem but I would really like to understand exactly what was causing the problem you ran into. Can you please be a bit more specific about the particular issue?

 

Regards,

 

Andy 

[Ron Solly]

HI , I was wondering if many people used the concept of " block switching" for DC wiring, which seem more common in the US.  This where the layout is divided into electrical blocks and each block ( and its corresponding trackwork ) and then switch to an appropriate controller.

 

The advantages are the removal of the issues of synchronising controllers when running trains from one track controlled by a controller to another, as is common with the more conventional " isolating sections" , form of wiring we then to do on this side of the pond 

 having been reading all this thread, I am wondering where the concept  of  more conventional " isolating sections" , form of wiring came from?  While I know some UK modellers use that possibly antiquated method, Cab control as used in many parts of the modelling world, was used by the late Rev Edward Beal on his West Midland layout during the 1940-1950's. Even when I stared modelling in 1957, I used cab control straight away.

[Junctionmad]

 

 

Sectioning the layout is just as important with DCC unless you want to cut and resolder lots of dropper wires every time you have a fault.

not to derail this thread, but better to install district cutouts in DCC to do that , but the simplest is to just disconnect inter baseboard connectors rather then introducing more switches 

[Junctionmad]

 having been reading all this thread, I am wondering where the concept  of  more conventional " isolating sections" , form of wiring came from?  While I know some UK modellers use that possibly antiquated method, Cab control as used in many parts of the modelling world, was used by the late Rev Edward Beal on his West Midland layout during the 1940-1950's. Even when I stared modelling in 1957, I used cab control straight away.

 

My experience is that many average modellers started with simple ovals, often driven by something like a H&M Duette etc ( our club still has several ).  This tended to be connected to the up and down loops and then as the need to isolate locos became apparent, isolating sections were added.  Modellers then stayed with what they " knew " 

[Junctionmad]

Hi David,

 

I've noticed before you don't care for common return, but it improves reliability, reduces cost and simplifies wiring. It would be a pity if you put other modellers off the advantages of common return for the wrong reasons.

 

I'm not saying you didn't experience a problem but I would really like to understand exactly what was causing the problem you ran into. Can you please be a bit more specific about the particular issue?

 

Regards,

 

Andy 

 

 

Just my twopence , cause Im not a fan either . My experience is (a) the need for isolated supplies is often problematic,, especially where the DC output of wall warts is tied to earth ground with is common 

(b) users get confused  when adding more wiring 

 

my own preference , having debugged several Dc layouts , is DPST feed switching , far less likely to get confused and the additional wiring is actually not that great at all. in reality compared to costs elsewhere on the layouts the addition costs are negligible 

[ejstubbs]

Just my twopence , cause Im not a fan either . My experience is (a) the need for isolated supplies is often problematic,, especially where the DC output of wall warts is tied to earth ground with is common 

(b) users get confused  when adding more wiring 

 

my own preference , having debugged several Dc layouts , is DPST feed switching , far less likely to get confused and the additional wiring is actually not that great at all. in reality compared to costs elsewhere on the layouts the addition costs are negligible 

 

I tend to agree.  I certainly regard the cost issue as negligible compared to the reduced risk of confusion: "how does the return for this bit run, exactly?"  If you have two wires to every section then the answer is right there in front of you.  Power feeds on my layout use black 6A flat twin-core speaker flex with a white tracer on the insulation of one core for power feeds.  That way the two wires are always routed together, and I always know where the electrons are going.  Enough wire for the whole layout cost less than one streamline point.

 

My view is that common return is a bit of a "cunning trick" that doesn't have any significant benefits and does have non-negligible potential downsides.  I wouldn't set out actively to discourage others from using it but I wouldn't want to have to try to fault-find the result if it went a bit pear-shaped.

Edited September 13, 2017 by ejstubbs

[Crosland]

Sectioning the layout is just as important with DCC unless you want to cut and resolder lots of dropper wires every time you have a fault.

 

You've said you do not use DCC, yet you persist in making ill-informed comments like this.

 

A well wired DCC layout will simply not fall into the "every time you have a fault" scenario you describe. Faults are actually quite rare if care is taken with the wiring, no more than you would with DC.

 

You do not need to cut and resolder any droppers to fault find a DCC layout. Simply breaking the bus in a few strategic places is sufficient to section the layout.

[Ron Solly]

It appears that many are concerned about common return (which simplifies wiring) because of possible confusion re power supplies & interconnecting of same.

 

Well. for many years telephone exchanges had 3 voltages 50, 24v & 130v and all three used a common earth/return    and also transmitted over single wire earth return was mains power for farms & remote homes and known in Australia as SWER  https://en.wikipedia.org/wiki/Single-wire_earth_return

[kevinlms]

It appears that many are concerned about common return (which simplifies wiring) because of possible confusion re power supplies & interconnecting of same.

 

Well. for many years telephone exchanges had 3 voltages 50, 24v & 130v and all three used a common earth/return    and also transmitted over single wire earth return was mains power for farms & remote homes and known in Australia as SWER  https://en.wikipedia.org/wiki/Single-wire_earth_return

Yes, but once it left the exchange it was (and still is, even for Fibre to the Node - a pox that BS is!) MOST CERTAINLY a pair of wires for each phone service. Customer equipment too, is always in pairs. The only time that was broken, was for an additional wire for Earth Recall on switchboards, which deliberately provided an unbalanced circuit, to activate a relay to enable calls to be transferred.

 

Not sure that we should be bringing mains electricity into the conversation, when discussing model railways. Not saying you're wrong, it just seems inappropriate.

[Junctionmad]

It appears that many are concerned about common return (which simplifies wiring) because of possible confusion re power supplies & interconnecting of same.

 

Well. for many years telephone exchanges had 3 voltages 50, 24v & 130v and all three used a common earth/return and also transmitted over single wire earth return was mains power for farms & remote homes and known in Australia as SWER https://en.wikipedia.org/wiki/Single-wire_earth_return

The problem with model railway common return , is the problem of the reversing switch , when switched in essence converts one controller into a common feed and the other remains a common return. For this " trick" to work the two controllers must having floating power supplies, hat are isolated from one another . If it remained a " common return " system it would be acceptable , but it's nothing of the sort.

 

The confusion can be considerable , in order to save what , a few metres of cheap wire and the negligible cost of adding another pole to the section switch

 

Furthermore where cab control is added on single track isolating sections are subsequently added , common return coupled with common feed, can generate funny results.

 

The DPST feed is easier to debug and conceptualise for most people

Edited September 13, 2017 by Junctionmad

[Silver Sidelines]

More misinformation

.., is the problem of the reversing switch ..

My layout is essentially a dumbell with reversing loops at both ends.  Common return works fine and trains traverse the layout without halting.  The reversing loops are divided into three 'Blocks' each fed by their own dedicated double pole double throw centre off switches.  Yes the up line is fed from one cab and the down line from a second cab.  All that is required is to operate the DPDT switch as the train negoitates the reversing loop changing the supply from the first cab to the second.  There is an old YouTube video taken from a Camtruck as it negotiates the layout.  I doubt you can spot where the DPDT switches are operated!

 

Regards  Ray

Edited September 13, 2017 by Silver Sidelines

[AndyID]

So far the justifications for not using common return seem flimsy at best. It would be a shame if wavy arm descriptions of "potential" problems discourage others from adopting a perfectly good system.

 

Yes, the DC feeds to the controllers should be floating. (Actually, that's not true either. They really don't need to be, but I probably should not go into that in this topic.)

 

Yes, reversing loops need to be handled carefully, but that has little to do with common return wiring.

 

Yes, you need a convention for which rail is common - something like "the rail nearest the the operator is always common" usually works. Also, if you use a substantial uninsulated copper conductor as the sub-baseboard return it's pretty obvious where the common return is.

 

Two-pole switches are more expensive, they take more time to connect, there are twice as many connections that can fail, and the the switch contacts are twice as likely to fail compared with the contacts on single pole switches.

 

Common return effectively halves the required number of insulated rail breaks/joiners. (In my opinion that's more than enough justification for using it.)

 

Common return substantially reduces the number of connections you have to make. That saves time and makes for a more reliable layout.

 

Common return prevents stalling at a section break when you try to hand-off a train between controllers "on the fly".

 

I'm not suggesting anyone should convert a layout back to common return. I just want to make sure we are not putting other people off it for the wrong reasons..

[Ron Solly]

I am sure I did say that for common return, every controller has its own power supply connected as per Fig 3 of http://rail.felgall.com/crw.htm

also previously discussed http://www.rmweb.co.uk/community/index.php?/topic/58713-common-return-wire/

 

And telephone exchanges in the days of magneto, were often one wire with earth return to subscribers. The internal component of telephones exchanges used 50 volts for switching; 24 & 130 volts for valve operated transmission equipment all with the same common return - earth.

[AndyID]

And telephone exchanges in the days of magneto, were often one wire with earth return to subscribers.

 

Commonly (sorry!) used by the GPO in the UK until quite recently. They would convert a two-wire line into a party line by sending the ring current down one or other wire and return the current through ground.

[Junctionmad]

More misinformation

My layout is essentially a dumbell with reversing loops at both ends.  Common return works fine and trains traverse the layout without halting.  The reversing loops are divided into three 'Blocks' each fed by their own dedicated double pole double throw centre off switches.  Yes the up line is fed from one cab and the down line from a second cab.  All that is required is to operate the DPDT switch as the train negoitates the reversing loop changing the supply from the first cab to the second.  There is an old YouTube video taken from a Camtruck as it negotiates the layout.  I doubt you can spot where the DPDT switches are operated!

 

Regards  Ray

 

you miss my point, the issue is that common Return is nothing of the sort , because when the reversing switch is activated, you get common feed not common return 

[Silver Sidelines]

Hello JM

you miss my point, the issue is that common Return is nothing of the sort , because when the reversing switch is activated, you get common feed not common return 

To put my Common Return into perspective I have over 100 Blocks / Sections each with single pole section switches and three double pole switches at both ends to cater for changing polarity over the reversing loop.  Common Return 'saves' me 100 odd lengths of return wire.

 

Regards

 

Ray

[Junctionmad]

So far the justifications for not using common return seem flimsy at best. It would be a shame if wavy arm descriptions of "potential" problems discourage others from adopting a perfectly good system.

 

Yes, the DC feeds to the controllers should be floating. (Actually, that's not true either. They really don't need to be, but I probably should not go into that in this topic.)

 

Yes, reversing loops need to be handled carefully, but that has little to do with common return wiring.

 

Yes, you need a convention for which rail is common - something like "the rail nearest the the operator is always common" usually works. Also, if you use a substantial uninsulated copper conductor as the sub-baseboard return it's pretty obvious where the common return is.

 

Two-pole switches are more expensive, they take more time to connect, there are twice as many connections that can fail, and the the switch contacts are twice as likely to fail compared with the contacts on single pole switches.

 

Common return effectively halves the required number of insulated rail breaks/joiners. (In my opinion that's more than enough justification for using it.)

 

Common return substantially reduces the number of connections you have to make. That saves time and makes for a more reliable layout.

 

Common return prevents stalling at a section break when you try to hand-off a train between controllers "on the fly".

 

I'm not suggesting anyone should convert a layout back to common return. I just want to make sure we are not putting other people off it for the wrong reasons..

 

 

Two pole switches are more expensive 

 

MTS-103 3-Position SPST Latching Mini Toggle Switch 6A 125VAC 3A 250VAC 10PCS - Aliexpress.com £2.17 for 10 

 

VENSTPOW 10pcs MTS 202 Minitoggle switch ON-ON rocker switch 6 pins lever 6mm

 

( DPDT ) Aliexpress.com £2.27 for 10 .   SO you are right , 1 penny extra per switch !!!!!!!!

 

Common return substantially reduces the number of connections you have to make. That saves time and makes for a more reliable layout.

 

 

The fact is that the common return has to be wired and interconnections made as the returns  are commoned under the board , the net reduction in connections in reality very little 

 

 

Yes, the DC feeds to the controllers should be floating. (Actually, that's not true either. They really don't need to be, but I probably should not go into that in this topic.)

 

 

The feeds have to be isolated, otherwise when you reverse one controller and in reality make it common feed, you then have a common return, connected to a common feed, aka a short circuit .

 

 

Common return prevents stalling at a section break when you try to hand-off a train between controllers "on the fly".

 

huh, its irrelevant, in cab control.  in conventional DC wiring ( have we a name for this ) irrespective of common return or DPST the issues of transferring from one controller to another remain , common return does nothing for this 

 

 

Common return effectively halves the required number of insulated rail breaks/joiners. (In my opinion that's more than enough justification for using it.)

 

yes but the fact that once you switch the reversing switch on the controller, effectively you mix single isolated sections where the isolation is now in the return and not the feed, with two breaks , this confusion is removed . The section is dead electrically , irrespective of the position of the reversing switch 

 

 

 

The fact remains, common return saves very little money in any typically layout, is harder too debug , creates confusion, can have funny side effects , requires isolated supplies 

 

There is really no redeeming factors in real life 

Edited September 15, 2017 by Junctionmad

[AndyID]

you miss my point, the issue is that common Return is nothing of the sort , because when the reversing switch is activated, you get common feed not common return 

 

Say what? That's an interesting exercise in semantics, but it makes no sense. The "common" refers to the wiring that forms a return path for multiple controllers. It has nothing to do with the polarity of the individual controllers.

 

But it tends to confirm my suspicion that there is a deep-seated distrust of common-return in the community because there is something "unnatural" about it.

[Junctionmad]

Say what? That's an interesting exercise in semantics, but it makes no sense. The "common" refers to the wiring that forms a return path for multiple controllers. It has nothing to do with the polarity of the individual controllers.

 

But it tends to confirm my suspicion that there is a deep-seated distrust of common-return in the community because there is something "unnatural" about it.

When you flip the reverse switch on one controller , which is connected via the common return , if effectively , ie that controller, is in effect a common feed ( ie the designated + feed ) rather then a common return., the trick only works because it relies on floating power supplies, a legacy of the type of transformer supplied systems of early simple controllers.

 

The reality is it leads to confusion , saves little money in reality, limits the type of controllers and generally adds few benefits for its limitations

[AndyID]

When you flip the reverse switch on one controller , which is connected via the common return , if effectively , ie that controller, is in effect a common feed ( ie the designated + feed ) rather then a common return., the trick only works because it relies on floating power supplies, a legacy of the type of transformer supplied systems of early simple controllers.

 

 

 

Excuse me, but that's complete nonsense. There is no concept of "feed" or "return" at the terminals of a floating controller. The output terminals can be positive or negative relative to each other. That's all.

 

Your use of the pejorative term "trick" only reinforces my impression that you don't like common-return because you don't really trust that it works. There is no "trick". It's all really basic electrical theory.

 

As I mentioned before, there is no need to rely on separate transformers, but I suspect you really don't want to know that.

[Ron Solly]

 

 

huh, its irrelevant, in cab control.  in conventional DC wiring ( have we a name for this ) irrespective of common return or DPST the issues of transferring from one controller to another remain , common return does nothing for this 

 

 

 

 

 

er...  with cab control. it is NOT normal to transfer control of a train from one controller to another - it is the process of that cab controlling the train over the entire layout so that one driver has full control of the train in its operation.

 

Common return is used outside of our hobby without problems and I like many with DC or DCC, use that concept without any hiccups.

 

My common return is used not only for track connections but other power suppliers. 12v DC for LEDs; 15AC for CDU,s;16c DC for Kadee Electromagnets; 40vDC for relays - each with their own transformer - two large bared copper wires ex 240power cable  run around\d my 12 x 20ft room as the common return  and the other 5 heavy wires for DCC track power, etc to cater for the 5 trains moving around at the same time in a normal operating session.

 

Of course it may have helped me as I was a telephone technician in the exchanges for 25 years. I have the impression that electrics do scare many but don't be scared, read and experiment slowly if in doubt.

[Pete the Elaner]

We seem to have drifted a little from cab control to common return.

With the latter, it may be useful to think of voltage by another term I was taught: Potential Difference. If you use separate transformer windings to supply each controller, then you are applying a separate difference to each circuit & can therefore return (or feed) them all through a common connection.

I don't use it because I don't know if an older controller (H&M Duette for instance) uses 2 windings or just the 1 for both regulators. If you or someone else in the club connects something like this to the layout, it is nice to know it will not cause an issue.

[Junctionmad]

Excuse me, but that's complete nonsense. There is no concept of "feed" or "return" at the terminals of a floating controller. The output terminals can be positive or negative relative to each other. That's all.

 

Your use of the pejorative term "trick" only reinforces my impression that you don't like common-return because you don't really trust that it works. There is no "trick". It's all really basic electrical theory.

 

As I mentioned before, there is no need to rely on separate transformers, but I suspect you really don't want to know that.

By convention we assign positive and negative , ie feed and return. When you flip the reverse switch you invert the connections from one controller

 

I never said , you need transformers , I said you need floating supplies ( and that's the " trick" ) , in effect the supplies must be isolated so that source current can return to the originating supply ( you can obviously use non floating supplies where no polarity reversal occurs of course )

 

I'm not disputing it's not " electrical theory" , after all I'm a professional electronics engineer. I'm remain unconvinced of its benefits either in wiring or cost, and where I've seen it used ( by non professionals, like railway modellers etc ) , it can lead to confusion and issues. ( and I'm not alone in this thread in this view )

Edited September 17, 2017 by Junctionmad

[Junctionmad]

er... with cab control. it is NOT normal to transfer control of a train from one controller to another - it is the process of that cab controlling the train over the entire layout so that one driver has full control of the train in its operation.

 

Common return is used outside of our hobby without problems and I like many with DC or DCC, use that concept without any hiccups.

 

My common return is used not only for track connections but other power suppliers. 12v DC for LEDs; 15AC for CDU,s;16c DC for Kadee Electromagnets; 40vDC for relays - each with their own transformer - two large bared copper wires ex 240power cable run around\d my 12 x 20ft room as the common return and the other 5 heavy wires for DCC track power, etc to cater for the 5 trains moving around at the same time in a normal operating session.

 

Of course it may have helped me as I was a telephone technician in the exchanges for 25 years. I have the impression that electrics do scare many but don't be scared, read and experiment slowly if in doubt.

I say again , all over electronics , we have the concept of " common return " , it's called the ground plane for example.

 

This is not what " common return " is on a model railway. It's a trick that REQUIRES floating power supplies , the that's not a common concept in ordinary electronics , in fact , in good design separate currents from separate sources are largely returned via separate paths.

 

Again DCC does not have reversing switches in its feed to the tracks. And as such by and large DCC is bus based with droppers , or both a common feed and common return and has no relevance to this discussion

 

My common return is used not only for track connections but other power suppliers. 12v DC for LEDs; 15AC for CDU,s;16c DC for Kadee Electromagnets; 40vDC for relays - each with their own transformer - two large bared copper wires ex 240power cable run around\d my 12 x 20ft room as the common return and the other 5 heavy wires for DCC track power, etc to cater for the 5 trains moving around at the same time in a normal operating session.

Again , I fully understand the theory. However I regard it as extremely bad practice to return currents from different isolated sources along a common wire, especially AC and DC sources. There is also the risk of safety from having fully floating supplies ( have a look at medical devices protection ) , and it's the same safety reasons that an oscilloscope has its probe GND referenced to mains earth.

 

In my case all feeds are earth referenced, which means that any part of my track work etc ever got elevated to high voltage , the safety earth would do its job.

 

I have also debugged layouts where multiple controllers with DC wall warts that had earth referenced outputs were inadvertently used and common return wiring

 

NOTE: I have no issues with common returns used in areas other then TRACK wiring, because polarity reversals dont generally occur ( i.e. where for example different DC voltages might be used etc ) 

Edited September 18, 2017 by Junctionmad

[Junctionmad]

We seem to have drifted a little from cab control to common return.

With the latter, it may be useful to think of voltage by another term I was taught: Potential Difference. If you use separate transformer windings to supply each controller, then you are applying a separate difference to each circuit & can therefore return (or feed) them all through a common connection.

I don't use it because I don't know if an older controller (H&M Duette for instance) uses 2 windings or just the 1 for both regulators. If you or someone else in the club connects something like this to the layout, it is nice to know it will not cause an issue.

Sure sure we all know electrically why it works. The problem is exactly as you lay out , it requires isolated supplies to each controller, and that's one of its issues , especially for certain layouts where controllers are interchanged ( like some club layouts )

 

And no the Duette, is a single Transformer from memory