General Q's on DCC and layout building

[Andymsa]

10 minutes ago, RobinofLoxley said:

Do any guidelines exist anywhere, or would it be a case of coming here with a specific equipment list. I am some way off the installation of accessory decoders anyway.

ask  a question but get 10 different opinions, your get good advice here but you will have to sort what’s right for you and what you want to achieve 

[melmerby]

2 minutes ago, Andymsa said:

in fairness I have never measured current for the trigger, but you can alter the ohm rating from 10k to 22k or vice versa.

 

i still have around another 100 detector sections to install but track to build first

I found the RS-8s would trigger with 14k 99% of the time (that's 1mA @14v track ) but not any higher, so I use 12k resistance for detection axles.

[WIMorrison]

1 minute ago, EsK said:

I am using Digikeijs DR4088LN-CS for block occupancy, which are very sensitive. So in my case should twisted wires be avoided all together?

for DCC you should be looking at around 12 twists per meter which is a very loose twist - especially compered to Cat5e which is very loose compared to Cat6e or Cat 7.

 

That said, I don't twist any of cables, but loosely bundle them together and I am using DR5088RC which are not as sensitive as DR4088xx. For most situations loosely bunding  the cables will work, where it doesn't then try the desensitising of the  feedback giving the false report. 

 

[Andymsa]

2 minutes ago, melmerby said:

I found the RS-8s would trigger with 14k 99% of the time (that's 1mA @14v track ) but not any higher, so I use 12k resistance for detection axles.

 

I been using 10k resistors so we are not far apart there, so I would say probably just a bit more the 1ma

[melmerby]

1 hour ago, WIMorrison said:

for DCC you should be looking at around 12 twists per meter which is a very loose twist - especially compered to Cat5e which is very loose compared to Cat6e or Cat 7.

 

Off topic but I have a Cat 7 cable which has totally flat parallel feeds, which when I bought it I thought was very odd for high frequencies.

EDIT

It claims to be U/FTP so I assume somehow the pairs are twisted, laid side by side and overall foiled.

Edited September 22, 2020 by melmerby

[Crewlisle]

Very interesting forum, except that anyone trying to decide whether to convert to DCC will be confused by all the jargon used & so called complications.  Someone once said that all you need to do to convert from DC to DCC is to change your controllers, fit decoders in your locos, allocate their address & open all your isolating switches!  Probably not that simple but I converted my 2.6M x 2.3M three level exhibition layout 'Crewlisle' back in 2008 using the Lenz LH90 with the LZV100 command centre control system.  Almost prehistoric by today's offerings!  However, with usual Lenz  DCC equipment quality, it has worked without any problems & has attended 7 exhibitions.  Since then I have added two DCC Supplies PSX-1 Circuit Breakers to split the layout into two districts one controlling the high level & the other controls the main baseboard & reversing loop.  So that if a short is detected on the high level & shuts down, the main baseboard is still operating normally. 

The layout itself is 47 years old & half of the 30 Peco Code 100 points are fitted with the old style primitive small cylindrical Peco solenoids which still work OK.  The remainder are controlled with a few of the newer Peco PL-10 solenoids & the remainder mechanically by use of 1.5mm wire from the inside of the operating well.  All solenoid operated points are operated from a CDU & by the simple but reliable Peco studs mounted on mini track diagrams on the inside of the operating well.  Some of the point solenoids also operate colour light signals via simple Peco PL-13 slide switches. 
 

Yes, I agree they just operate by 'slamming' over with no frog polarity changing switch but to upset the purists further, the only two polarity switches on the whole layout are to change the polarity of the live diamond on the double junction, converted from an Insulfrog diamond.  They are both simple Peco PL-13 slide switches operated by the junction point.
 

All of the old Insulfrog points & diamond have had their plastic frogs removed & fitted with hand crafted brass ones.  The rest of the points are normal Peco Electrofrogs (not the Unifrog versions).  None of the points have polarity switches for their frogs & all my points rely on good electrical contact between the stock rail & moveable rail.  The number of failures I have had I can count on one hand.  They were not important & only happened once at an exhibition.
 

DCC can be as simple or complex as you want to make it.  With DCC I can run upto 4 trains simultaneously which I have sometimes managed at exhibitions with 2 operators.  Anyone trying to decide whether to convert to DCC, I can send you a copy of my article 'To DCC or not to DCC?' which appeared in Model Rail in October 2008.

 

Peter

[RobinofLoxley]

Do you think your article is still as valid today as when written in 2008? Industrial electronics is supposed to bea rapidly moving environment.....

[Crewlisle]

Robin,

 

Yes, industrial electronics have moved on & will keep on doing so.  But how much & how often are you prepared to spend on & fit the latest 'gizmos' just because you can?  However, basic electric laws about size of wire & current carrying capacity do not change.  As I said in my comments, DCC can be as simple or as complex as you want.  The choice is yours but mine works with hardly any problems.

Yes the basic principles are the same.  Of course, there are more modern controllers with a lot more features available.  The point I wanted to make was that the basic principle of DCC has not

changed & my principle is 'If it ain't broke don't fix it'!  On the other hand, if I want to add or update any of the electronics it would not be a problem.

 

Peter

 

[Michael Hodgson]

Is there any formal (eg NMRA) or de facto (eg some manufacturer) standard for the resistance to be used on axles for reliable detection? 

Obviously the optimal value will be dependent on the sensitivity of the detection equipment chosen, so one might expect to see some sort of standard evolving.

 

I have occasionally seen such axles advertised on ebay and there are plenty of metal wheelsets available to replace older plastic ones, but the DIY approach seems to be the norm when it comes to resistors.  10k seems to be a popular value, but higher values are also used. 

 

Surely this must be a gap in the market or is it so difficult for RTR manufacturers to automate that it would push the price up too much for those who don't need it?

[WIMorrison]

@Michael Hodgson the resistance is dependent upon the detection units that you are using and the track voltage.

 

a dr4088 will show indication at 2-3mA therefore with a track voltage of 15v a resistance of 5k will work and many people will advocate 10k for these units whereas a DR5088RC needs around 10mA therefore you need a 1k5 resistor for them with a 15v track voltage Other detectors will fire with different current draw and your track voltage also need to be considered. 

[Michael Hodgson]

Thanks for that Iain,  It used to be simple - we all used 12v DC.

I think that tends to reinforce the argument for somebody like the NMRA putting forward more detailed standards.

 

As you say voltage affects current draw, and I don't really see a need for that to vary from command station to command station either, although I can see that larger scales might justify higher voltages.  If you need to draw as much as 10mA to get get detection, you wouldn't want every axle detected if you run very long trains as our transatlantic friends often do.  In steam days my local station saw trains telegraphed as "HW" (hundred wagons) - with 200 axles that would be 2A!   Not that I will be equipping every axle of course.  It will be every brake van (and some of those will have working tail lights anyway), and end vehicles on coaching stock in fixed rakes, plus any odd vehicles that get used as tail traffic - horse boxes, parcels etc.  Fitting SMD resistors is going to be a tedious job, but at least it can be done in batches.

 

I have not yet finalised my choice of detector, but your comment steers me away from DR 5088RC as I would prefer something that can see a vehicle at less current.  Don't think I will be using Railcom anyway as iTrain can keep track of what's what but it would be nice to keep that option open so that it can self-correct if things are crane shunted. 

 

The Z21 has multiple interfaces and should be able to handle a mixture of different detectors, and I suppose it 't doesn't really matter if only one or two sections are Railcom detecting and they fail to notice all the wagons.

[Andymsa]

37 minutes ago, Michael Hodgson said:

Thanks for that Iain,  It used to be simple - we all used 12v DC.

I think that tends to reinforce the argument for somebody like the NMRA putting forward more detailed standards.

 

As you say voltage affects current draw, and I don't really see a need for that to vary from command station to command station either, although I can see that larger scales might justify higher voltages.  If you need to draw as much as 10mA to get get detection, you wouldn't want every axle detected if you run very long trains as our transatlantic friends often do.  In steam days my local station saw trains telegraphed as "HW" (hundred wagons) - with 200 axles that would be 2A!   Not that I will be equipping every axle of course.  It will be every brake van (and some of those will have working tail lights anyway), and end vehicles on coaching stock in fixed rakes, plus any odd vehicles that get used as tail traffic - horse boxes, parcels etc.  Fitting SMD resistors is going to be a tedious job, but at least it can be done in batches.

 

I have not yet finalised my choice of detector, but your comment steers me away from DR 5088RC as I would prefer something that can see a vehicle at less current.  Don't think I will be using Railcom anyway as iTrain can keep track of what's what but it would be nice to keep that option open so that it can self-correct if things are crane shunted. 

 

The Z21 has multiple interfaces and should be able to handle a mixture of different detectors, and I suppose it 't doesn't really matter if only one or two sections are Railcom detecting and they fail to notice all the wagons.

I wouldn’t get too hung up on vehicle current draw, every wagon on my layout has a resistor per bogie and there are no big issues on current draw. Off the top of my head with 15 trains and around 30 wagons plus passenger coaches I get around 1 amp with trains at rest. 

[WIMorrison]

@Michael Hodgson even at 10mA that is less than most coaches will draw for lighting and as @Andymsasays don’t get hung up on it.

 

track voltage is what you want to make it, much like the 12v days when it varied from 10v to 16v DCC varies in a range. Personally I use 17v and that works extremely well for me and is well within the NMRA standard of specification for decoder operation.

 

100 wagons would be 100 axles for detection (unless you are planning in cutting wagons in half) which is 1A and most people don’t place a resistor on every wagon, just the at the ends. You may even find that higher resistances work for you, I use 1k5 on my axles which with the wheel, paint and contact resistance gives me around 2k5 which works for my DR5088RC.
 

Plus if you are getting to the stage where the wagons are going to be too heavy a load then you will have a lot of locos to pull them and they will force you into having boosters, not the wagons behind detectable.

 

sometimes it is better not to over think things and just go with the flow :)

 

 

 

 

 

[peach james]

On 22/09/2020 at 09:47, melmerby said:

Is the BDL 168 particularly sensitive? The RS-8s trigger on about 1mA (resistive)

 

I'm using 10k Ohm on single axles and get reliable detection with both BDL 168's and BD4/DS 64's.   That works out at about 1.5mA unless my math skills have gone wonky.

I have a couple which will set the wrong way on startup occasionally- the trick I find is to have a brake van with the resistor that I can pick up, plop on the track section that is marked as "hot", then remove, and that clears them.  I know which sections are likely to do that, and they usually result in trains moving then stopping after a couple of feet on first start up.  

James