Accessory bus help needed.

[AdeRail]

Hi,

 

 

sometimes i feel feel a bit thick..... but could someone clear this up for me please!

 

 

Ok, I'm about to set up my main track power bus with dropper wires and elink connected.

I wanted to have a separate accessory bus for things like LED lights in buildings and various other accessories, I would also like to run all of my point motors and maybe even some signals from this accessory bus too. But this raises a couple of questions that I just can't find in any of my books or the internet.

 

 

Firstly what power supply should I use, AC or DC? and where do I get one from?

 

Secondly all my books say to use an accessory bus but nowhere tells me how this would work with points and things that need to receive the DCC signal, if I powered my points and accessory decoders from this second accessory bus then how do they receive the DCC signals? How do they connect to my elink if they are not powered from the main elink track power bus?

 

I also have one hornby accessory decoder, and this I believe has to be run from the main power track bus? I'm confused

 

H E L P !

 

thanks

Ade

[96RAF]

OK let's start you off...

The accessory bus for your points if using accessory decoders is operated via a DCC controller. If you only have one controller then it shares with your track bus.

 

In RM you will have noticed you can have two controllers. A is for the locos via your track bus and B is for your points via a second controller on a separate accessory bus. This DCC points bus is powered by the second controller. Imagine it as a track bus without any track, just accessory decoders instead of locos.

 

Now the other bit . . layout lighting. This is usually also a by way of a separate bus but it's a DC bus and can be powered from any spare wall wart plugs you may have surplus to requirements, providing the voltage they output is made suitable for your lights, or they can be powered from the Aux output of a redundant analogue controller if you have one. Again you have to control the output voltage to suit your lights. We can get into more detail on that later.

Rob

[Chrissaf]

First of all you must not mix DCC connections with other NON DCC accessories. The wiring must be separate. Any accessory that is not natively DCC (i.e does not contain a decoder) must either be fed from a stand alone accessory decoder or wired to a different power supply as a completely separate overlay electrical system. OK yes you could put a bridge rectifier across the DCC BUS to create a DC supply of about 14 to 15 volts and use that to operate your non DCC accessories but that is wasting valuable DCC power best used to operate DCC locos etc.

.

DO NOT connect the output of your eLink to the same wires that have a DC power supply also connected to it.

.

Lighting (for example LED street light, platform and internal building lights) and general electrically operated model railway accessories tend to be 12 volt DC. Personally I would always recommend using a separate DC BUS for non DCC accessories with its own dedicated power supply.

.

OK as to power supply.

.

Yes you could use a general purpose 12 volt DC power pack of the wall brick type, but these tend to be relatively low current with higher current capability versions becoming increasingly expensive.

.

Personally I like to use an old recovered AT / ATX power supply from a PC. It can be easily modified (use of a soldering iron required) to provide both a 12 volt and 5 volt output. In general, ex PC power supplies are ridiculously cheap even if bought new (ebay) and provide very high currents and stable voltages.

.

This previous thread explains how to use a PC power supply for a model railway layout.

.

https://www.hornby.com/uk-en/forum/help-with-power-supplies/?p=1

.

I use the 5 volt output via an on/off switch to power the general layout lighting (the 5 volt output of a PC power supply unit usually provides the highest output current capacity). The 12 volt output of the PC power supply (without a separate on/off switch) I use to power accessories that will only operate on 12 volts, or need to be powered continuously. See drawings further below.

.

With regard to the single points decoder you have got. As a DCC device this must connect to same DCC BUS that your track connect to. Unless of course you are using a second DCC controller as supported by RailMaster.

.

I think this is where your confusion over "Accessory Bus" terminology is coming from.

.

RailMaster supports two controllers. Typically an Elite as the main track controller and an eLink as an accessory controller. The outputs of the two controllers are kept completely separate. The Elite output connects to the track (main layout Bus) whilst the eLink output connects to a completely separate "Accessory Bus" to control points and other DCC controlled devices via "Accessory Decoders". In this scenario the "Accessory Bus" is not the same thing as a general purpose 5 / 12 volt DC Bus to power NON DCC accessories.

.

All some book references to "DCC Accessory Bus" mean, is that the Accessory Decoders connect to a common run of a pair of DCC wires that are termed the "Accessory Bus". This "Accessory Bus" may be connected to the output of a DCC Booster (very typical in the USA) or just connected in parallel to the main track DCC Bus at the output of the DCC controller. Although maybe termed the "DCC Track Bus" and the "DCC Accessory Bus" they are electrically one single Bus if wired directly in parallel.

.

The two drawings below represent my own personal layout wiring and give an indication of what I am trying to describe above. My DCC sub-system is completely separate from my non DCC electrical sub-systems. I have used colour coded wiring to make fault tracing, diagnostics and adding additional accessories over time easier.

.

/media/tinymce_upload/e9865b9392dcb6ddac2a336910d4d095.jpg

.

PS - In the drawing above. I am using the relay interface board and external CDU to operate my PL-10WE point motors. I found that the weak CDUs internally provided within the Hornby R8247s were just not powerful enough to robustly operate my PECO W version point motors to my satisfaction. I am also using Peco Electrofrog points with live frog power switching, hence the PL-13/15 point switches in the drawing. My layout isn't big enough to warrant a separate "DCC Accessory Bus", thus I use a single DCC Bus for all the DCC devices.

 

/media/tinymce_upload/0e1658320a22b1c929a9eb03f11d7cba.jpg

.

 

[AdeRail]

Well what can I say... Thankyou both for taking the time to help me out here  😎 

I had the pieces floating around in my head but couldn't fit them together, but now you have clarified this for me my head has stopped aching...

 

 

right so I currently use railmaster with an elink, and now I have to get another controller, but which combination do I choose, I could get a select for the track and trains and use the elink for the points and set up a dc bus for other lighting etc.. 

 

Or I could get an elite and link them both to the laptop, or maybe a dynamis ultima would be better... it's the price of these that's the problem though at about 200 smackers a piece!

 

Or maybe with my layout being about 3.5 metres by 3.5 metres, so not that big, I could do what you've done Chris and keep all my dcc Trains and points on one power bus, but would this bring up power problems when I am running say two trains and switching a few points? Could this be solved by simply upgrading the elink power supply to the 4 amp one?

 

[Chrissaf]

Ade,

For the layout you have described. Spending money on a second controller (Elite) and creating a separate DCC Accessory Bus would be complete overkill. When used to operate solenoid points, the R8247 draws very little current. When idle, the current is IIRC [if I Recall Correctly] about 20mA, rising to a brief internal CDU recharge pulse (200 milliseconds) of about 200mA when you fire a point. In the overall scheme of things this is miniscule.

.

Many people operate their layout running two or three locos simultaneously along with one or two R8247 Accessory Decoders without any issues whatsoever using the 1 amp power supply. You are worrying unnecessarily. Even if you did want to grow your layout, it would be far simpler and cheaper to just upgrade the eLink 1 amp power pack to the P9300 4 amp version.

.

Just keep a single combined "Track" and "Accessory Decoder" DCC Bus. If you want to future proof yourself, you could connect the track pieces to one Bus and the Accessory Decoder(s) to another Bus, but initially connect BOTH Bus' in parallel to the track output of the eLink. That way if you did in the future purchase an Elite, it would be easy to split the combined Bus' into two and have the track Bus connected to the Elite (using the 4 amp supply) with the Accessory Decoder(s) Bus connected to the eLink (using the 1 amp supply). But for a single R8247, particularly if you have no known plans at present to add any more, splitting the Bus' would be overkill.

.

Note that if you did decide to add a second controller, then use the Elite. The Elite works very well with RailMaster. The Elite control (speed) knobs feedback positional data into RailMaster to synchronise with the RailMaster throttle sliders (within certain control limitations). I'm not sure if using two eLinks in a "Controller A & B" RailMaster configuration is actually supported. Whereas Elite and eLink definitely is supported and documented as such.

.

Although it could be done, you would be loosing a heck of a lot of functionality and flexibility to run your trains from a completely different branded DCC controller (you mentioned Dynamis Ultima) and relegating your RailMaster / eLink combination to just operating points. After all, with just a single R8247, that is only four point ports. Hardly worth bothering with screen based PC control just for that alone. Note the Dynamis Ultima could not connect to RailMaster. RailMaster is propriety Hornby software and only supports Hornby Elite & eLink controller hardware.

.

Using a Select is in my view also a retrograde step as well. Firstly the Select is not compatible with RailMaster and secondly it has severely limited functionality compared to your current RailMaster / eLink setup.

.

Just keep your current RailMaster / eLink setup on a single DCC Bus (albeit maybe future proofed as described above).

[AdeRail]

Right thanks Chris,

 

Although I've only got one point controller at the moment I will have around 25ish points when I have all the track set up. So would this amount still be able to be run by the elink alone? Maybe with the upgraded 4 amp power supply?

[Chrissaf]

25ish points is about 6 or 7 x R8247's. The brief 200mA current draw is only when a point fires. You would be unlikely to be firing lots of points simultaneously. The idle background current would be about 100 to 150mA roughly equivalent to operating a modern loco at moderate speed. So on balance, I would tend to favour upgrading the power pack to the 4 amp one with that many R8247s fitted. Just to ensure that you can run as many locos as your layout design can support.

.

Even with 6 or 7 R8247s I still don't think that warrants a dual controller dual Bus set up, but that is just a personal opinion. However that said, read below for a possible caveat.

.

With the 4 amp power supply fitted, short circuit voltage spikes could potentially become a problem due to the higher short circuit currents that could be generated. The Hornby R8247s are prone to being corrupted / damaged by them. Again personal opinion but based upon my own personal experience of having a R8247 damaged by a short circuit spike, I would fit a 'Snubber' (Power Bus Suppressor) to the DDC Bus to protect the R8247s - see my first drawing above in my original reply for details.

.

Just to put a 'spanner in the works' so to speak.

.

One big advantage of having an Elite operating the locos on the track and an eLink operating the points separately in a dual Bus configuration, is that any shorts on the tracks will be completely isolated away from the R8247s. Thus the risk of R8247 corruption / damage is completely eliminated as it is usually locos and / or rolling stock issues on the track that generate the transient short circuits. And of course, the Elite comes with the 4 amp power supply as standard.

.

However that said, since fitting my 'Snubbers' to my DCC Bus I have had absolutely no further issues with my R8247s. The 'Snubbers' also protect the decoders in my locos.

.

Want to know more above 'Snubber' theory, then click here:

.

 

[AdeRail]

Ok I think I'm forming a plan now!

If the upgraded elink 4 amp power pack would be ok with 6 or 7 hornby R8247s, would it be ok if I had a mixture of accessory decoders, let's just say 'not hornby ones' as some of these run more accessories for a cheaper price. I suppose I may have to put a CDU in with some of them too?

[Chrissaf]

Yes you can pick and mix Accessory Decoders.

.

Nearly all Accessory Decoder brand / models (but not completely all) have CDUs built in. The ones that do not have an integral CDU are not normally designed to have a separate CDU externally unless they have relay contacts as their output circuit (hence my relay interface boards in my first drawing design). The non Hornby brands are, in the main, "Self Learning" Accessory Decoders, and as such, easier to set up and configure.

.

If funds permit, I think it is always a wise option to replace the eLink 1 amp supply with the 4 amp one. The P9300 is the Hornby documented 4 amp upgrade power pack.

[Fishmanoz]

Just on upgrading to 4 Amp, I'm not against it but suggest you see how the 1 Amp goes for a start then upgrade if you have overload problems like tripping out. HRMS have reported previously that they run their entire test layout with eLink and 1 Amp.

[96RAF]

Later on when you get your teeth into this...

 

If you want to use a CDU to give a bit more oomph to your points AND still use DCC to control them you can as Chris says use a relay panel as the middle man. 

 

Here is just one way of doing it which also also allows you to switch them manually as well as by DCC. You can use any switching method in lieu of my rotary and push button method.

Rob

 

/media/tinymce_upload/8cca26659c6ecaad7f757dd8e63b0aa6.GIF

[Flashbang]

I have to say some serious suggestions for the OPs question.

I'll jump in...

Never use an AX or ATX ex computer power supply on its own directly feeding any items. These beasts deliver up to 25 Amps of power at 12 volts. This is 300 watts.  It will, under fault conditions, melt and burn your wiring inside seconds and long before any internal overload trip operates, if it ever operates!  They should IMO be left solely inside PC cases!   Your home insurance is very unlikely to cover you either should anything untoward occur.   If you need 12v DC power see text below.

 

If you want DCC operation of points whether from the DCC console or a PC programme, then upgrade your power supply to the recommended 4.0Amp version. Then tap off the DCC bus pair of wires to feed the accessory decoders or DCC Ready point motors of choice.   They can be any make when uses with the Elite or elink.  The Select will not operate DCC Concepts Digital Cobalt as you cannot remove the self centring feature or change direction of normal operation which require you to set CVs 197, 198 and 199.   I recommend if you want to install a separate DCC bus pair for point accessory decoders then add an electronic circuit breaker into the track DCC bus pair as soon as it leaves the consoles terminals.  This then when set to below the current rating of the main DCC system, trip the track power in the event of a loco running into an unset set of points and still leaves the accessory DCC bus pair operating, allowing the incorrect points to be moved over and thereby removing the short.  Such unit is the PSX-1 

 

If you want layout lighting and LEDs are the best options as they draw low current and dont get hot. Then consider running is a second DC lighhting bus pair of wires. Ideally use red and black for these and of course use the red as positive.  Feed this totally separate bus pair of lighting wires from a 12 volt DC Regulated power source. Rated at 1.0Amp to 1.5Amp.  Ideally take the output directly to an in line fuse or self resetting circuit breaker rated at 1.0Amp.  This is wired into the positive feed only.    Tap off the 12v DC bus pair to feed lights as reqired ensuring suitable series resistors are in any standard LEDs feed.

'Regulated' means the output voltage remains virtually constant regardless of the load.  These plug in power supplies are often sold under the heading of 'CCTV power supplies' and come in various current output ratings.  Alternatively look for ones that offer user selectable output voltages often 3v, 4.5v 6v, 9v & 12v etc. Just ensure the current output is suitable.

[Chrissaf]

Flashbang makes a fair point about the current output of an ex PC power supply. I use a fairly small power supply rated at 120W, but this is still potentially 10 amps at 12 volts. I use inline fuses rated at 4 amps on my 12 v & 5 v outputs so that I am not reliant just upon the internal power supply shut off routines (which of course will be configured to handle the maximum output power). As Flashbang says, a 300W (typical) PC power supply could have an output current of 25 amps before it shuts down. So, if used, do include additional lower current fuses on the outputs. Particularly as some PC power supplies can be rated at 400W or more.

[Rog RJ]

I agree with you, Flashbang, ex-computer power supplies should be avoided completely for model railway use unless you really know what you are doing.  Far too much power for the majority of users and too easy to cause damage or have an accident in the hands of the unwary.  I won't use them unless they're in a PC.

[AdeRail]

Flashbang makes a fair point about the current output of an ex PC power supply. I use a fairly small power supply rated at 120W, but this is still potentially 10 amps at 12 volts. I use inline fuses rated at 4 amps on my 12 v & 5 v outputs so that I am not reliant just upon the internal power supply shut off routines (which of course will be configured to handle the maximum output power). As Flashbang says, a 300W (typical) PC power supply could have an output current of 25 amps before it shuts down. So, if used, do include additional lower current fuses on the outputs. Particularly as some PC power supplies can be rated at 400W or more.

Which inline fuses and inline housings do you use Chris? Have you got a rapid catalogue number? As I have an old pc psu I can use.

thanks

[Chrissaf]

I used two of these and one pack of these .

.

I liked this particular holder style because they can be screwed to the underside of my baseboard. Although Rapid / Farnell / RS Components and others do something similar, these were the only ones I found in this price range that were screw mounted and also equipped with input / output spade terminals for ease of installation and connection.

[AdeRail]

Thanks again Chris, you've been amazingly helpful  😎

[Chrissaf]

I try to be.

[AdeRail]

Right ok, I've finished installing the main bulk of my bus wires, thanks to all the amazing help I've been given here...

 

 

I've put one twisted pair of t&e 2.5mm around my layout as the DCC bus, lightly twisting about 3 turns per foot...

Also I've put another pair of t&e 2.5mm but this time untwisted and separate about an inch apart from each other as the 12v DC bus for all the layout basic dc things like lights and other things.

 

 

Now I'm left with the dangling ends of the wires, which on the DCC twisted pair will have a resistor capacitor snubber terminator on..

 

 

This raises two more questions... Firstly I know it's best not to join the DCC wiring in a loop, hence the snubber, but is it ok to join the DC bus in a loop or should I leave these ends with a break in too?

 

Secondly, do I need to install a third 5v DC bus, or is the 12v one enough?

 

Thanks

[Chrissaf]

The DC Buses can be looped without the slightest issue. In fact it is desirable to loop them as the current can take two paths to the attached accessory, current distribution is then more balanced and evened out in the wires. Consider a straight open ended run, the current along the length of the run builds up as accessories are attached. The result is that the total current drawn has to go through the wires at the end connected to the supply, with a loop, for any individual connected accessory the current in the wire is halved as it goes both ways round the loop. OK, not a big issue if the overall currents are low and the wire is thick. But as the Tesco advert says "Every little bit helps".

.

No, you don't have to implement the 5 volt DC supply, but as you have previously indicated that you are going to use the ex PC power pack supply with additional low current fuses for extra protection, just note that these supplies provide higher current output capacity on the 5v rail. Using 5v for the LED lighting, means that the current drawn through the 1,000 ohm LED protection resistor will be reduced, increasing LED lifespan even more than it already is. In the main, you could just use the 12v power rail for accessories that just won't work on 5volts and use the 5v rail for everything else.

[AdeRail]

well thanks again Chris!

 

 

Ill be back under the baseboards installing my 5v rail today and joining me ends together  😎

 

Then I'll be tackling my psu!

 

 

Ive only installed one DCC twisted pair as I think this will be enough for my needs in conjunction with the Hornby 4 amp psu for my elink.. maybe followed with the Elite in the future which comes with a 4 amp..

[AdeRail]

A quick question.

 

 

With all these bus rails running under my layout, does it matter if a DC bus crosses a DCC bus? If so then what to insulate with? 

 

No no matter how hard I try I just inevitably have to cross wires sometimes!

[Chrissaf]

Electromagnetic wave radiation is created when a current / voltage transitions from one level (state) to another. DC accessory current / voltages are predominantly stable. They might vary slowly over time, but unlikely to experience rapid fluctual changes (say like firing a solenoid point motor for example). If varying Electromagnetic wave radiation is not produced, then induction into nearby adjacent wires is unlikely. In other words, and in English, your DC (lighting) distribution wires crossing over the path of your DCC Bus wires is unlikely to have any effect.

.

The above statement is true for constant current devices such as LEDs. If your DC accessory contains electric motors, then the motors can (if not suppressed) generate noise spikes in the DC supply wires. Therefore, to be 'belt n braces' it is prudent to not let a DC Bus and a DCC Bus share the same route over an extended length of run. In other words, maximise their separation where you can. Twisting the DCC Bus (as you have indicated you are doing) also helps to reject any induced interference from adjacent wiring. In general, it is wires containing different signals running in parallel that is more of a potential issue than wires crossing a right angles.