Wiring protocol for DCC

[RobinofLoxley]

I may have missed this, but I can't find through searching, if there is a convention for which side of the track is power fed and would have block detectors etc fitted. For my DC layout, now rapidly disappearing I followed the convention of positive wire to the right hand rail, loco direction of travel. Is DCC the same?

[grriff]

DCC is effectively a 'square AC signal' and so both sides of the track are 'power fed'. Thus either side of the DCC command station can be fed to either side of the track. However, you must then be consistent if you have more than one track feed, which is probable. So it's best to set up a convention of your own, using wires of different colours for each of two the track feeds. For example red for the 'outside' rail and black for the 'inside' rail for the first connection you make, with every other connection made as you would for DC. Hence, there is usually no need to rewire a layout for DCC. There is no 'loco direction of travel' with DCC as this is set by the controller and DCC decoder. The voltage to the track is always constant and doesn't change polarity, all control results from DCC signals sent to the loco decoder. Hope this helps and I haven't caused confusion!

For more information on DCC try the free book 'Electronics for model railways' by Davy Dick available from MERG (http://www.merg.org.uk)

[BernieL]

4 hours ago, RobinofLoxley said:

Is DCC the same?

As grriff says, Yes, in that you must maintain consistent polarity and No, the wires are not direction dependent.   Also unlike DC, I don't think you can use a common return path with other circuits on your layout. There are a lot of discussions about interference with the control signals in the circuit and the extra current involved needing equal resistance on both sides.

[Sol]

You can use common return on the track  with other power supplies as long as all power supplies are separate units - it happens in the real world with Mother Earth as the common. My layout works well with common return that share 5 different supplies & track power. Of course the common return wire has to be substantial like a mains power earth wire.

[grriff]

12 hours ago, Sol said:

You can use common return on the track  with other power supplies as long as all power supplies are separate units - it happens in the real world with Mother Earth as the common. My layout works well with common return that share 5 different supplies & track power. Of course the common return wire has to be substantial like a mains power earth wire.

Ron, not quite sure what you mean. If you are referring to the DC power supply TO the Command station, I suppose a common return (the 0v terminal) would be OK. I presume you are not referring to the DCC signal FROM the command station to the track as DCC isn't a simple 'power supply' but a message bus (i.e two wires carrying commands) for the decoder (which converts the DCC supply to a DC supply for the motor). As far as I am aware, it should not have a common return connected to other power supplies and you cannot use a 'common return on the track'.

There does seem to be the occasional assumption that DCC and DC can have a 'common return' and therefore the wires which go to the decoder (from the track) can have a common return with the wires from the decoder to the motor. This is definitely NOT the case and any connection will result in a blown decoder.

Edited October 24, 2020 by grriff

[Sol]

I do use a common return for one of the DCC track power bus wires & the common for other supplies & my signalling circuit uses DC for the relay to work at the same time on of the bus wires is connected.

Power supplies can be AC ( regular sine wave_ or DCC ( square wave )  or DC ;

telephone exchanges 30 odd years ago used 50v -, 24v+ & 130v- all using a common return/earth  as does SWER  https://en.wikipedia.org/wiki/Single-wire_earth_return

 

Wires from decoder to motor have to be isolated from wires to track.

 

http://www.rail.felgall.com/crw.htm

[Andymsa]

On 23/10/2020 at 16:58, RobinofLoxley said:

I may have missed this, but I can't find through searching, if there is a convention for which side of the track is power fed and would have block detectors etc fitted. For my DC layout, now rapidly disappearing I followed the convention of positive wire to the right hand rail, loco direction of travel. Is DCC the same?

 

as others have said keep the track feeds consistent. When I do initial wiring I use Red/ white Coloured pins temporarily to indicate polarity. With all other aspects mentioned the premis of KISS applies.

Edited October 25, 2020 by Andymsa

[Crosland]

21 hours ago, Sol said:

Power supplies can be AC ( regular sine wave_ or DCC ( square wave )  or DC ;

 

The essential bit of information missing from Ron's post is that, to use common return, all of the power supplies must be isolated. E.g. transformer based with individual windings or switch mode PSUs that have no earth connection.

[john new]

On 23/10/2020 at 17:17, grriff said:

Snip....... There is no 'loco direction of travel' with DCC as this is set by the controller and DCC decoder. The voltage to the track is always constant and doesn't change polarity, all control results from DCC signals sent to the loco decoder. Hope this helps and I haven't caused confusion!

... snip

You haven’t, but as a relative newbie to DCC after years of DC operation that lack of directionality set by the track I find a big annoyance with DCC. 

[Andymsa]

10 hours ago, john new said:

You haven’t, but as a relative newbie to DCC after years of DC operation that lack of directionality set by the track I find a big annoyance with DCC. 

if I am understanding correctly, your trying to apply DC principles to DCC. The same conventions in DC if applied to DCC would defeat the operation of a DCC system.

[norman]

10 hours ago, john new said:

You haven’t, but as a relative newbie to DCC after years of DC operation that lack of directionality set by the track I find a big annoyance with DCC. 

Yes I do understand but the ability to control the direction of the loco is the correct concept, left and right have no meaning, it just depends upon your relative position.  So grasping the correctness of DCC, forward means forward and reverse the reverse is really quite simple.

[john new]

35 minutes ago, Andymsa said:

if I am understanding correctly, you are trying to apply DC principles to DCC. The same conventions in DC if applied to DCC would defeat the operation of a DCC system.

Yes I am and I wish there was a way to preserve that universal directionality whilst adding in the extras. (The missing DCC function perhaps)

 

DCC has advantages of sound, independent control of locos, smoother control steps, etc., and is why I started experimenting with it. The significant advantage of DC is that setting the slider switch to the left means the loco always goes left (as I am looking at the layout), right it always goes to the right. In practice that is very simple, slider left train goes towards the station - slider right it goes into the fiddle yard.

 

Everyone is different but personally my experience has indicated that DCC has the fundamental flaw that you are constantly having to faff about with remembering forwards and backwards as, obviously, that setting differs whenever you select another locomotive. With a double ended diesel or DMU is not always obvious and it is annoying when you find you have put the locomotives on the track for a session the wrong way round. (My layout has to be put away after each running session) Equally to drive a loco out of the hidden bit of my fiddle yard, it is not just a simple slider setting. Even with a steam engine, obvious when you can see it, but forget it went in chimney first and it attacks the buffers rather than emerges into the open.

 

Each to their own but I have found DCC to be less of the advantage I anticipated when I began my trial of it; about 50:50 when comparing the gains and losses against DC.

 

 

Edited October 27, 2020 by john new
Rewritten in places to add clarity.

[Andymsa]

28 minutes ago, john new said:

Yes I am and I wish there was a way to preserve that universal directionality whilst adding in the extras. (The missing DCC function perhaps)

 

DCC has advantages of sound, independent control of locos, smoother control steps, etc., and is why I started experimenting with it. The significant advantage of DC is that setting the slider switch to the left means the loco always goes left (as I am looking at the layout), right it always goes to the right. In practice that is very simple, slider left train goes towards the station - slider right it goes into the fiddle yard.

 

Everyone is different but personally my experience has indicated that DCC has the fundamental flaw that you are constantly having to faff about with remembering forwards and backwards as, obviously, that setting differs whenever you select another locomotive. With a double ended diesel or DMU is not always obvious and it is annoying when you find you have put the locomotives on the track for a session the wrong way round. (My layout has to be put away after each running session) Equally to drive a loco out of the hidden bit of my fiddle yard, it is not just a simple slider setting. Even with a steam engine, obvious when you can see it, but forget it went in chimney first and it attacks the buffers rather than emerges into the open.

 

Each to their own but I have found DCC to be less of the advantage I anticipated when I began my trial of it; about 50:50 when comparing the gains and losses against DC.

 

 

that’s one of the advantages of using computer software that you can see what way is forwards or backwards. But computer control is not everyone’s cup of tea. But I do get the point of if the direction issue.

[Crosland]

25 minutes ago, john new said:

Everyone is different but personally my experience has indicated that DCC has the fundamental flaw that you are constantly having to faff about with remembering forwards and backwards as, obviously, that setting differs whenever you select another locomotive.

 

You are doing something wrong

 

Forget about "left" and "right" and think about forwards and backwords.

 

Forwards is always forwards with DCC no matter which loco, nor which way the loco is pointing, unless you have wired the decoder incorrectly. 

[john new]

3 minutes ago, Crosland said:

 

You are doing something wrong

 

Forget about "left" and "right" and think about forwards and backwords.

 

Forwards is always forwards with DCC no matter which loco, nor which way the loco is pointing, unless you have wired the decoder incorrectly. 

Will recheck next time I get the layout out but memory is that it works as I described. Nothing fancy and most chips I have had factory fitted.

 

However, on a single line branch how does it know which way is forwards?

 

Edited October 27, 2020 by john new
Added extra observations

[Andymsa]

8 minutes ago, Crosland said:

 

You are doing something wrong

 

Forget about "left" and "right" and think about forwards and backwords.

 

Forwards is always forwards with DCC no matter which loco, nor which way the loco is pointing, unless you have wired the decoder incorrectly. 

I think the point being made is that direction response is not as expected with DCC as opposed to  DC where direction is always constant.

[Crosland]

12 minutes ago, john new said:

However, on a single line branch how does it know which way is forwards?

 

I don't understand the question. The track configuration is irrelevant. Forwards is ALWAYS forwards. Turn the cab/throttle forward and the loco will move forward. For a steam loco it means smoke box first. For a diesel it means "front" first, whateber that is

 

1 minute ago, Andymsa said:

I think the point being made is that direction response is not as expected with DCC as opposed to  DC where direction is always constant.

 

In that case the DCC expectations are flawed. You command and expect a loco to move forwards, it will move forwards.

 

DC is not without issues. You have to think about where the loco is. E.g. at the back of a loop the loco will move the opposite direction (relative to you) than if it were at the front of a loop. Left doesn't always mean left, etc.

[Nigelcliffe]

3 minutes ago, john new said:

Will recheck next time I get the layout out but memory is that it works as I described. Nothing fancy and most chips I have had factory fitted.

 

However, on a single line branch how does it know which way is forwards?

 

 

Part of the "problem" with Left/Right is that some DCC handsets/controls have keys which indicate a left/right arrangement, rather than a forwards/backwards.   Typically on physical buttons, keys either side will be seen as left/right, those arranged above/below will be forwards/backwards.  Similarly arrows on screens will be left/right (poor) or up/down (clearer).    
For example the Hornby Elite tends to encourage "left/right" from the LCD screen which can be downright confusing  (and its far from alone in doing this !).  

So, part of the confusion comes from DCC handset/system designers.   Some get it more "right" than others.  

 

 

For any track, including the branchline,  "Forwards" comes from the wiring inside the loco.  Very roughly...  the track power is alternating (square wave), so doesn't have an orientation/direction.  Inside the decoder, it is rectified to DC (which does have an orientation).  That is connected to the motor.    If the decoder receives an instruction for "forwards" it applies DC in one direction and makes the motor spin one way.  If it receives "reverse" the DC to the motor is reversed, and the motor spins the other way.  

 

 

In terms of identifying loco direction.   

Steam locos obvious if you can see them.  Diesels can be learned (there are conventions around grills etc..).    Cameras or mirrors are one way to see locos which are not in direct sight.   
Or, there are technology add-ons which can report locos and their orientation, but those depend on DCC system and decoders used in locos (ie. not everything can do it).  

 

 

[Andymsa]

10 minutes ago, Crosland said:

 

I don't understand the question. The track configuration is irrelevant. Forwards is ALWAYS forwards. Turn the cab/throttle forward and the loco will move forward. For a steam loco it means smoke box first. For a diesel it means "front" first, whateber that is

 

 

In that case the DCC expectations are flawed. You command and expect a loco to move forwards, it will move forwards.

 

DC is not without issues. You have to think about where the loco is. E.g. at the back of a loop the loco will move the opposite direction (relative to you) than if it were at the front of a loop. Left doesn't always mean left, etc.

I would say that it is the expectation of the user is flawed and not DCC per-say. 

 

[john new]

17 minutes ago, Crosland said:

 

I don't understand the question. The track configuration is irrelevant. Forwards is ALWAYS forwards. Turn the cab/throttle forward and the loco will move forward. For a steam loco it means smoke box first. For a diesel it means "front" first, whateber that is

 

 

In that case the DCC expectations are flawed. You command and expect a loco to move forwards, it will move forwards.

 

DC is not without issues. You have to think about where the loco is. E.g. at the back of a loop the loco will move the opposite direction (relative to you) than if it were at the front of a loop. Left doesn't always mean left, etc.

 

Therefore it does matter, as I said, which way round the traction unit is placed on the track as to which direction it moves in, relative to the layout, when you apply power. That is the fundamental flaw of DCC, as I see it, compared with the simplicity of this aspect of DC control, others have other views I appreciate. We shall just have to agree to differ on this as it is drifting the topic away from the OP.

 

Edited October 27, 2020 by john new

[Butler Henderson]

Struggling to understand the issue here unless it is down to confusiom resulting from the DCC system being used, you control the individual loco so forwards is the loco going forwards (etc). No problem on a single track layout therefore and my DCC system (Multimaus) has a nice clear graphic of which direction the loco is moving. As for diesels rightly or wrongly I go for the "front" being that with the fan nearest

 I can see problems could arise with hidden sidings if some are running backwards.

 

Edited October 27, 2020 by Butler Henderson

[meil]

28 minutes ago, john new said:

 

Therefore it does matter, as I said, which way round the traction unit is placed on the track as to which direction it moves in, relative to the layout, when you apply power. That is the fundamental flaw of DCC, as I see it, compared with the simplicity of this aspect of DC control, others have other views I appreciate. We shall just have to agree to differ on this as it is drifting the topic away from the OP.

 

No it doesn't. As has been said a number of times now the loco will always, irrespective of its placement on the track, always move forward if forward is selected and reverse if reverse is selected. Blindingly obvious with a steam loco perhaps not so obvious with a diesel/electric if you don't know which end you've chosen as the front.

[john new]

58 minutes ago, meil said:

No it doesn't. As has been said a number of times now the loco will always, irrespective of its placement on the track, always move forward if forward is selected and reverse if reverse is selected. Blindingly obvious with a steam loco perhaps not so obvious with a diesel/electric if you don't know which end you've chosen as the front.

This is getting silly. On my layout from the usual viewing point if I add a DC loco chimney first pointing at the station it will go forwards/left+, with DCC turn it around and as you state it therefore goes right/for forwards and away from the station. How is that not relating the direction it goes to the way you put the loco onto the track? 

 

All I was saying is that of the two systems I prefer the way DC does it. DCC has many undoubted advantages but lacks an option to turn on some form of fixed directionality relative to the layout* not the loco' [for want of a better phrase DC cloning] somewhere in the system.

 

Is there perhaps a way to design a circuit module that sits between the handset and the layout that forces forwards to be a set direction of travel relative to the layout, perhaps if you set a relevant CV setting, so that all the benefits of DCC are added to the fundamental basics of DC. At present, and this is only a personal view, DCC adds lots to my simple layout** but at the same time also deducts the biggest advantage I have when I am running it under DC. 

 

+ left slider (or tender/bunker first into the fiddle yard with slider set to the right)

 

* if there is I haven't read about it anywhere.

 

** As not all my locos are DCC fitted it can be run in either mode but obviously not concurrently!

 

Edited October 27, 2020 by john new
Clarity

[Nigelcliffe]

John, 

I think its possible to do what you want around direction, but its going to get into serious complexity and techie stuff.  Do-able, but bonkers difficult.      
Simpler might be to investigate other handset designs, and look at whether any of those give clearer indication of direction.  

 

You've not said what system you are currently using;  I think different people's experience of different handset arrangements will alter their views of how things work.

 

 

- Nigel

[john new]

17 minutes ago, Nigelcliffe said:

John, 

I think its possible to do what you want around direction, but its going to get into serious complexity and techie stuff.  Do-able, but bonkers difficult.      
Simpler might be to investigate other handset designs, and look at whether any of those give clearer indication of direction.  

 

You've not said what system you are currently using;  I think different people's experience of different handset arrangements will alter their views of how things work.

 

 

- Nigel

 

NCE Powercab