Dropper wires; continuity question.

[Mallard60022]

I have been reading a website that gives some really useful information on 'conventional' layout wiring but am a little confused about one diagram*.

I am aware of the need to take care when using 'droppers' (for track power control) that + and - need to always be to the 'same' rail; even I can cope with that.

I also remember reading somewhere that using a wagon with some + and - labels on opposite sides and moving it around the layout gives an indicator of where + and - minus power droppers need to go. That seems like a very good idea.

So, on a continuous single circuit (oval) depicting British practice, + should/could be the inside rail if trains ran forwards in a clockwise direction if the convention for + being on the right side of the loco (looking forwards from the cab) for standard Power Controllers  is adopted.  Is this correct?

My confusion comes thus. Having stated this 'convention' on the site, the informer goes on to show a typical roundy roundy oval layout with 'up' and 'down' tracks (no links between circuits AFAICR). Presumably the layout owner would then run trains 'up' and 'down' i.e. clockwise on the outer circuit and anti clockwise on the inner circuit.

If one then sticks to the suggested convention, when fitting droppers to this layout, the + needs to be on the 'inner rail' on the outer circuit, but on the 'outer rail' on the inner circuit.

However, the diagram* shown on the site shows the inner rail also as + on the inner circuit. That's where I'm confused, but I don't mind being seen as being daft as I don't understand as this seems to contradict the right hand side + supply to the locomotive.  This diagram suggests that the circuits would run either both clockwise or both anticlockwise and that seems daft.

 

On my own layout, that is really two roundy roundy ovals but linked at both ends and including Xovers, I have already started to place droppers and I was going to use the + or - on the rail furthest away when standing inside the oval method. I'm now worried that's wrong.

Can someone clarify what's what please with this dropper fitting if it is possible and I apologise for not being able to create super layout diagrams.

Many thanks,

Phil                    

[HeeleyBridge]

I've always wired with + furthest away from me on both ovals. Then use the controller on either circuit to drive the loco through the crossover.  Wiring the ovals in opposite directions would result in the magic smoke escaping from something when the crossing was used.

[Brian]

Doesn't the polarity reverse with direction of travel.

I feel the use of two colures in a drawing is perhaps the confusion, but any colour could have been used - Yellow and Blue, Green and Grey etc The drawings just show wire connections not polarity even if red and black colours are used, as at some stage the red wire will carry black power!!! OK I know there is no Black power but Im trying to illustrate the fact that the colours used are not necessarily those for the polarity flowing on the wires! 

[kevinlms]

Using + and - is the real cause of the issue, that you correctly are questioning. Yes, when the right hand rail is positive & left hand rail is negative will go forward (in relation to a model driver), is true (except Z gauge, I think for some obscure reason).

 

However, that doesn't take into account the direction switch of the controller. If you have 2 controllers (one on each circuit), both should be wired so that when the direction switch is set to the right, both trains will go to the right (clockwise on an oval), the reverse is true, if the direction is set to the left. That is what you should be trying to achieve, the actual means (designation of the rail polarity) is irrelevant.

 

 

As HeeleyBridge has suggested, making both outer rails the same, will work. But if you connect them together (both outer rails), that is a Common Return condition & your controllers MUST be Common Return compatible.

 

 

Its easier to test than describe, so make up a small sample of track (a complete circle isn't required) with a crossover (insulation gap in both rails) & attach them electrically with some alligator clip test leads & place a low current draw loco on the track. Now with a couple of fresh 9 Volt batteries, observe what happens. You can try changing the wiring to see what difference it makes, by swapping the alligator clips around. Try reversing the batteries too.

 

Its easier to use the batteries, as they have the voltages marked on them, thus making identification of what's occurring easy - the batteries, won't LIE. Make sure you observe what way round the batteries are when you go over the crossover. Write down what combination(s) works, so you can repeat it!

 

I hope you find this useful & helps to understand, exactly what 'polarity' & 'direction' really means. Perhaps, you'll agree that they aren't the same thing!

[Mallard60022]

That's really helpful chaps. I hasten to add that the site I was looking at has been excellent for loads of other stuff, especially wiring points. The real problem is my inexperience with large layout wiring. Experimenting is a sound idea and I shall try that, however i am fortunate in having a couple of friends that can assist but only occasionally and I need to get cracking with the layout.

Phil.

[HeeleyBridge]

 

As HeeleyBridge has suggested, making both outer rails the same, will work. But if you connect them together (both outer rails), that is a Common Return condition & your controllers MUST be Common Return compatible.

 

 

'Tis true, 'tis true. My H&M Powermaster and Safety Minor were quite happy together. Centre off too. Are more modern (hehe) controllers not happy with common return?

 

I ask because I am sure Mr Duck will be interested too.

[kevinlms]

'Tis true, 'tis true. My H&M Powermaster and Safety Minor were quite happy together. Centre off too. Are more modern (hehe) controllers not happy with common return?

 

I ask because I am sure Mr Duck will be interested too.

No, it has nothing to do with the age of them. What common return requires is separated power supplies and not a common power source. As the two devices are quite independent, your two existing controllers are common return compatible.

[Dunsignalling]

Two tips

 

However you do it - TEST - immediately after you make each and every connection, then you know straight away if you got it right and don't have to check back through lots of them to find the odd one you get wrong (which you inevitably will).

 

If you are wiring common return, it is less confusing to think of the common rail as 0v and the other as +/-12v (or neutral and live if you prefer) rather than positive and negative, which change as you reverse your controller.

 

John.

[Mallard60022]

Excellent stuff. In theory my main line runs are quite simple with sidings off. It is only really the bidirectional fiddle(s) and the possible swap from up to down for operational reasons that could cause problems. All this, bar one trailing main line cross over that will actually be used 'on stage', is off stage so can be tested and jiggled about as it won't be 'pinned' until all is working! I've also got to do everything so it could be DCC later.

I've always hated doing wiring like this and avoided it as far as possible. Other stuff I can muddle through.

Many thanks again.

Phil

[BR60103]

In North American layout diagrams, the rails are labelled North and South, usually with North being away from you.

 

+ and - will be confusing; I thing they are making the symbols do extra duty, for which they should receive extra pay.

[DCB]

The whole point about common return is that the common wire can be both positive for one circuit and negative for another,   The use of  + and - is inappropriate except when crossing from one circuit to the other       The the tracks must be arranged + - + -  or North South North South  or you will get a same side dead short half way across a crossover        The fact the wires can be both negative for one circuit and positive for the other  is why the controllers need to be electrically isolated, if they are not there is a dead short.

 

Quite honestly the concept is out of date.  Use four bus bars one for each rail not three with one bus serving two rails, the saving in wire is minimal and the increase in potential mistakes massive.  I always recommend almost the same isolated sections for DCC as DC, not the segmentation of loco sheds etc but 5 or 6 points and some plain track, with double isolators. This aids fault finding, a layout with 50 plus points and 50 locos can be a nightmare to find fault on even with 30 odd sections, and even when isloated to a segment of maybe 6 points and a few yards of track fault finding can still be time consuming.  Especially on the newer and less robustly constructed locomotives

[AndyID]

Quite honestly the concept is out of date. 

 

Hi David,

 

Perhaps not that out of date. I don't think there are too many computers on the planet that don't make extensive use of a common-return.

 

Of course it's a matter of personal choice, but I much prefer the common-return method. There are a lot fewer connections to make, switches/relays are less expensive, voltage drops are reduced and fewer insulated rail-joiners are required.

 

Andy

[RAF96]

My convention has always been red for outside rails and black for inside rails with any reverse loop sections clearly tagged at the crossover point. The exception is the turntable bed where I have 3 colours - purple being for the common of my led 'polarity' indicators.

 

As stated above the colours are of no consequence nor which is + or - as long as some convention is adopted outside of pot-luck birds nest wiring.

[Crosland]

 I don't think there are too many computers on the planet that don't make extensive use of a common-return.

 

Of course it's a matter of personal choice, but I much prefer the common-return method. There are a lot fewer connections to make, switches/relays are less expensive, voltage drops are reduced and fewer insulated rail-joiners are required.

 

Other things being equal, voltage drop will be worse with common return as the common is carrying all the return current for each controller. 

 

To use your example of computers you have to be very careful when mixing the "returns" from different circuits, especially logic, power and analogue. Connecting the return from the CPU power supply to the return from the audio circuits would be a disaster for sound quality. What computers, and much other complex electronics, use is a ground plane, even then it will often be split into different regions. Think of it as covering the underside of the layout with copper sheet and using that as the common return

 

Andrew

[AndyID]

 

Other things being equal, voltage drop will be worse with common return as the common is carrying all the return current for each controller. 

 

To use your example of computers you have to be very careful when mixing the "returns" from different circuits, especially logic, power and analogue. Connecting the return from the CPU power supply to the return from the audio circuits would be a disaster for sound quality. What computers, and much other complex electronics, use is a ground plane, even then it will often be split into different regions. Think of it as covering the underside of the layout with copper sheet and using that as the common return

 

Andrew

 

Gosh! All those years designing computers and I never knew that 

 

I use heavy (uninsulated) copper wire for the common - not a lot of voltage drop.

[BR60103]

Slightly OT (and I've told it before)

An engineer I worked with told me that during the war he worked on radio for one of the armed forces. They had a wiring colour code for the different circuits, say, blue for heterodyne, black for power, red for ...  The one that exasperated him was orange for "modifications". He said that sometimes you'd open the back of a set and see nothing but orange wire.

Another time, they were working on designing a set and one of the engineers said they could do a better job if they didn't have the 50 lb limit for any component. A bit of digging and they found that the 50lb was the load limit for one side of a mule in the Himalayas.

[DCB]

I'm not sure if my understanding of common return is the same as other contributors, to me it means connecting on of the output wires from two or more controllers together, or permanently linking them so section switches can be single pole rather than double pole.  The defining feature is that the wire can carry both positive and negative currents at the same time.  

 

This was a great system in the 1950s when switches were either domestic or government surplus from Spitfires and telephone exchanges and a 00 tank loco cost a weeks wages so we only had about a dozen locos and two controllers and used 2 amp twisted twin lighting wire for the layout, but that was about the time I was born, and with much layout wire being marginal for 1 amp, a vast range of cheap switches just an ebay click and 2 month wait away it does not seem that useful.    A common ground system, like a car earth or the return side of a diode matrix is different as the common wire only conducts in one direction.

 

Personally I wired the rails on a large layout with a common return wire within each section and individual switches for the isolators, side A is Pink, Side B is Brown.   However as I have Live Frog points the outer rail on the inner circuit and inner rail on the outer circuit have to be the common feeds or bus bars, with the isolators on the inner rail of the inner circuit and outer rail of the outer circuit.    Even then I had to put isolating micro switches on some of the points.  Full common return would have been a total wiring nightmare, especially with 4 controllers each able to operate 95% of the layout, and 3 more local zone only controllers.

 

I have never really bought the voltage drop argument, in my experience voltage drop is usually poor fish plate connections or point blade tags, or even those screwed wiring connectors but there is less drop in 30 feet of fishplated steel code 100 than in 20 feet of layout wire as our trains slow appreciably on entering the lifting section fed only by wires and speed up again when back to the fishplate fed track.

 

As regards computers they are a wonderful source of motors magnets, wires diodes plastic sheet etc etc  and the funny thingies on the circuit boards make great 00 wagon loads. 

[AndyID]

Hi David,

 

I don't really want to confuse the OP with too much information, but my main point is there is nothing wrong with a common return system. Personally, I prefer it because it has higher reliability, it's simpler, and it's less expensive. (Others my not agree.)

 

The common return doesn't really carry positive and negative currents at the same time. What happens is that it carries the sum of the currents. If it so happens that there are two locomotives that each draw 0.3 amps, but they are going in opposite directions, the net current in the common return is zero (although that does depend on where it's measured.)

 

There is a misconception that all the controllers on a common-return system have to be "independent" which usually means that they have their own mains transformers, or at least their own secondary windings on a common transformer. In fact it's quite practical to power an entire DC layout with as many controllers as needed with only two power supplies - one that sources around +12 volts, and anther that sources around -12 volts.

 

Andy

[LNER4479]

Another vote for the common return system here. I was brought up on it (by my father), have wired all my layouts via this method, continue to do so and have never had a moment's problem with it. It works for me. (accepting that there are alternative conventions that can work just as well, if the builder / owner is more comfortable with them)

 

Personal convention is common return on the inside rail of a roundy-roundy and use of white wire (using coloured wire for the electrical sections on the outer rail), although there's nothing that says it has to be like this.

[dhjgreen]

I don't know about you Phil, but all this advice is terrifying me.

 

 

And I'm a qualified electronics engineer!

[DCB]

Where common return does not work is where a controller with a 12 volt DC or 16 volt AC uncontrolled output taken from the same secondary winding on the transformer as the 12 volt controlled output is used to feed a separate circuit controller. Connect them to common return and you get a short when the controllers are turned in opposite directions.     Many double controllers have separate windings for each side,   My Duette appears to have 16v unconrolled and 12 v controlled on one winding and thermal breaker and 12 v controlled and 12 v uncontrolled on the other.   I use a Playcraft diode based controller with the Duette to give controlled voltage 

[AndyID]

I don't know about you Phil, but all this advice is terrifying me.

And I'm a qualified electronics engineer!

There was a very good booklet put out by th RM years ago. "Wiring the layout" or something?

[St Enodoc]

There was a very good booklet put out by th RM years ago. "Wiring the layout" or something?

There was, and another on Cab Control. Between them they tell you just about everything you need to know for non-DCC wiring. In them, CJF uses the terms "Feed" and "Return" for the two wires connecting the controller(s) to the track, to avoid any confusion between positive and negative.

[Mallard60022]

Nah, I'm not terrified as my CCE seems to know what he is going to tell me  (Notice I said CCE and not CEE......that's because he does both by the looks of it)

Thanks again everyone. I have certainly learnt a lot (so far).

Phil

[Silver Sidelines]

Another vote for 'common return'.  It has been around for a long long time. I was converted by the Rev Edward Beale

 

Ray