DCC Bus

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jon price
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DCC Bus

Postby jon price » Tue Mar 14, 2017 4:43 pm

I have a few queries which forum members may be able to answer. I've variously seen it suggested that DCC bus wire should be 15AWG. I read this as 1.45mm diameter. Since I will be raiding the stores (salvage) box is this correct as I can measure the wire I have but won't know what AWG number it is?

Is it allowable to have a T shaped (ie diverging) bus, or do I need to make one long single loop?

Will I need terminators on the ends of the T?

I'm connecting between boards with jumpers and banana plugs, and as far as I am aware placing sockets "upstream" closest to the power source is best practice, but when it comes to joining on the droppers is it OK to group them on screwed busbars and then make a single solder joint from there on to the bus wire (or even a screwed joint)?

I'm running a seperate bus for the turnout motors (which are likely to be Cobalt). Does this need to be the same spec as the main DCC bus, or can it be lighter? As far as I am aware my control bus (Lenz X-Bus) can be set up with 7 strand 0.2mm. Is this also suitable for the accessory bus?
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Re: DCC Bus

Postby grovenor-2685 » Tue Mar 14, 2017 6:13 pm

jon price wrote:I have a few queries which forum members may be able to answer. I've variously seen it suggested that DCC bus wire should be 15AWG. I read this as 1.45mm diameter. Since I will be raiding the stores (salvage) box is this correct as I can measure the wire I have but won't know what AWG number it is?

This is something of o piece of string question as it depends on two things, the length of the layout from the DCC power unit to the end of the bus and the current rating of the DCC power unit. Assuming a maximum length of say 6m and a rating of 5amps then cables around 1.5mm should be OK. To be sure connect the maximum length to your power unit and check that a short at the far end produces an immediate cut off.

Is it allowable to have a T shaped (ie diverging) bus, or do I need to make one long single loop?
Yes you can have a T

Will I need terminators on the ends of the T?
Most layouts don't need terminators at all, if you seem to have some interference issues then you can add them.

I'm connecting between boards with jumpers and banana plugs, and as far as I am aware placing sockets "upstream" closest to the power source is best practice, but when it comes to joining on the droppers is it OK to group them on screwed busbars and then make a single solder joint from there on to the bus wire (or even a screwed joint)?
That would be fine, but given droppers need to be in thin wire to connect unobtrusively to the rail, eg 0.5mm2 telephone wire keep the dropper short, around 6 inches.

I'm running a seperate bus for the turnout motors (which are likely to be Cobalt). Does this need to be the same spec as the main DCC bus, or can it be lighter? As far as I am aware my control bus (Lenz X-Bus) can be set up with 7 strand 0.2mm. Is this also suitable for the accessory bus?

Generally the accessory bus needs to withstand the same short circuit current as the main bus, so you have to take care if you reduce it.

Note that the benefit of a seperate accessory bus is only realised if you put a circuit breaker in the main bus. This allows a short on the track to be protected while keeping the accessory bus working so you can change the points and thus remove the short.
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jon price
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Re: DCC Bus

Postby jon price » Tue Mar 14, 2017 6:27 pm

thanks Keith. Exactly what I neded to know.
The accessory bus will be seperate because I don't need it to be run from the main controller. There will be an Alpha board and a Sniffer (whatever that is) running about twelve turnouts. There was no signalling on the prototype.

Main benefits: a mimic board with switches to easily see what is going on, and only two wires to the layout instead of having to have a couple of D plugs/sockets wired up and wiring running everywhere. Disadvantage: cost, but this outweighs the complexity of analog wiring, and the impenetrability I find of running turnouts from the main controller.

The control bus means I can use the controller from either end of the layout (or indeed have one at each end) I can use an obsolete Lenz Compact (cheap) as a slave controller as the railway only had engine numbers up to 18 so only being able to use two digits isn't a problem, and any of the "guest" engines I might run can easily fit into a two digit scheme.
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Re: DCC Bus

Postby grovenor-2685 » Tue Mar 14, 2017 7:14 pm

The accessory bus will be seperate because I don't need it to be run from the main controller. There will be an Alpha board and a Sniffer (whatever that is) running about twelve turnouts.
You don't need much power for Cobalts and 7/0.2 wire should be OK, but does depend on the possible short circuit current, wire that size would be Ok for 3 Amps or less with a fast trip.
Do you have any references for this Alpha board and sniffer?
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Re: DCC Bus

Postby nigelcliffe » Tue Mar 14, 2017 7:51 pm

"Alpha" is almost certainly DCC-Concepts turnout control board of that name. Its fairly expensive, the manuals a bit difficult, but seems to be meant as a general purpose way of using conventional switch inputs, and then generating DCC output to the accessories.
The "sniffer" is, I guess, sniffing the Lenz DCC signal and putting that into the Alpha system - I'd suggest that is optional !

It could be built for far less money using other hardware, but that requires increased technical skill and/or increased time to construct it all.


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Re: DCC Bus

Postby jon price » Tue Mar 14, 2017 8:06 pm

the alpha encoder is as you say the controller/emulator which transfers physical switch data into that required for DCC to control up to twelve point motors. The Sniffer appears to be a link which replicates a DCC control unit for accessories only so together they generate an accessory specific bus The controller is £60 and the sniffer £25 full price, but both appear to be available for slightly less from third party dealers like Hattons. To connect up to a Lenz X-Bus needs a much more expensive device, the alpha system is designed to work with NCE only.
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Re: DCC Bus

Postby grovenor-2685 » Tue Mar 14, 2017 9:39 pm

It could be built for far less money using other hardware, but that requires increased technical skill and/or increased time to construct it all.

Indeed the MERG kit for that runs to £10.50 and a pretty simple build.
Regards
PS. had a look at the Cobalt Alpha instructions, not all that clear but so far as I can see there is no need for a sniffer if you are keeping the track bus and accessory bus separate and as it needs only a 1 amp power supply your 7/0.2 wire is going to be enough for a few Cobalt motors. (The sniffer is to put the point commands onto the track bus).
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Re: DCC Bus

Postby jon price » Tue Mar 14, 2017 10:48 pm

To be honest with myself, given that I am learning everything starting from a zero knowledge base my time is going to be fully taken up building rolling stock, locos, automatic couplings, track, buildings, wet and dry scenery, ships, wiring and flat baseboards all of which will be slightly dodgy but I hope will just about work, so the additional simple electronics required to build my own DCC equipment would be a (wheatstone?) bridge too far. If I had started earlier and younger I might have taken up the challenge, but realistically I have enough to learn (which will nevertheless keep my brain active). I have made two chassis that seem to run properly, and one that only goes in one direction. I have also already apparently disabled my Lenz system simply by connecting it to a test track and frying a loco decoder, so after discussion with the importers it will have to be sent off for repair. My basic level small analog gaugemaster Combi controller is working however so testing can continue. It is interesting to note that despite best practice suggesting that the upstream power should be fed through a socket this is not the case with the guagemaster whose plug in transformer (like all these things) appears to have a plug on it, whilst the socket is on the device.

Thanks for the input on the redundant Sniffer Keith. I havn't read (or found) the manuals for the alpha encoder and the sniffer yet but obviously I can set up everything else, and if it works I will have saved £30, and if it doesn't I can just buy one as DCC concepts seem really keen that I should have one.

If this all sounds a bit negative it isn't. The support and input from people in the Society, the Crags, a Missenden course, and several suppliers, have been of inestimable value, and my gradual progress is (to me) really interesting, and satisfying. Maybe eventually I will have the photos to prove it!
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Re: DCC Bus

Postby nigelcliffe » Wed Mar 15, 2017 8:03 am

jon price wrote:the alpha encoder is as you say the controller/emulator which transfers physical switch data into that required for DCC to control up to twelve point motors. The Sniffer appears to be a link which replicates a DCC control unit for accessories only so together they generate an accessory specific bus The controller is £60 and the sniffer £25 full price, but both appear to be available for slightly less from third party dealers like Hattons. To connect up to a Lenz X-Bus needs a much more expensive device, the alpha system is designed to work with NCE only.


My reading of the (very confusing) DCC-Concepts documentation is that you need two things to make a "switch panel to a DCC-Accessory Bus" work; namely an "Alpha" (board, for twelve inputs, £60 list price) and an "Alpha Box" (to generate the DCC signal on the bus, £90 list price). Not sure if you need to add power supplies to that lot as well.
There is an alternative wiring shown in one document which only has the Alpha board, but that's a complete waste - need as much wire as if doing things with analogue turnout wiring, and offers no advantages over analogue.


I'd suggest that you check whether the Lenz LW150 input panel (Lenz part 25150 according to the UK Lenz Importer, £70 and in-stock at the one UK retailer whose prices I checked) plus a circuit breaker (to separate the main DCC bus into two, one for accessory bus, one for track bus) works out as a better option.
The LW150 takes inputs from pairs of push buttons for 16 turnouts, and provides LED output indicators for those 16 turnouts, so simple and neat control panel can be done with one module. According to A&H's instructional video (UK Importers) you can add a track-power button which gives an emergency stop button on the control panel, and unlikely to need its own power supply either, thus keeping wiring simple.
It appears to be cheaper, and keeps everything "Lenz" which should help with warranty/compatibility issues if any arise.


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Re: DCC Bus

Postby jon price » Wed Mar 15, 2017 5:24 pm

Thanks for the info on the Lenz LW150. I wasn't aware of this device and this should resolve all my issues.

DCC concepts told me by email: "The other option is to make the accessory system "stand alone" by using encoder to sniffer to create a separate DCC accessory only bus. (The sniffer unit is also a 1.2A DCC accessory driver) . If you wanted to upgrade to connect to the Lenz later, then the sniffer would be replaced with a Alpha box and Lenz adapter." but the only reason for going down the sepoerate accessory bus route would be to avoid the expense of buying the Alpha encoder AND the Alpha Box AND the Lenz adapter.

The Lenz LW150 would work fine for a similar price, deals with 16 accessories which allows me a bit of expansion, and so is better than the Alpha encoder route which only deals with 12.
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Re: DCC Bus

Postby Winander » Wed Mar 15, 2017 8:00 pm

grovenor-2685 wrote:Indeed the MERG kit for that runs to £10.50 and a pretty simple build.


Hi Keith,

Out of interest, which MERG kit is it?

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Re: DCC Bus

Postby grovenor-2685 » Wed Mar 15, 2017 8:57 pm

Its DCC Kit 54, "Accessory encoder"
It can handle 128 switches, not just 12 or 16 like the commercial ones, so the cost difference is much bigger if you have a largish panel.

If you just have 12 or so points, then my opinion would be to stick with a simple traditional wired panel and save the need for DCC auxiliary decoders as well, even built into Cobalts they are an extra cost

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Keith
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