cromptonnut Posted October 14, 2014 Share Posted October 14, 2014 First question, does anyone know what is the maximum length Xpressbus run you can have, and how many devices can be attached? I'm using a Lenz system. Secondly, I understand that these can be "powered" to increase reliability particularly over long or large runs - how does one go about this? Many thanks. Link to post Share on other sites More sharing options...
Crosland Posted October 14, 2014 Share Posted October 14, 2014 If you mean XpressNet then that uses a standard called RS-485 at a fairly low bit rate so theoretically over a km for a point to point link. A lot will depend on the quality of the wiring and how many devices are connected. The A/B and C/D pairs should be twisted for best results with longer runs. The maximum number of devices is dependent upon the chips used to drive the bus but should be at least 32 if standard chips are used. If you can cope with the technical details www.ti.com/lit/an/slla272b/slla272b.pdf Andrew Link to post Share on other sites More sharing options...
cromptonnut Posted October 15, 2014 Author Share Posted October 15, 2014 Both of those sound well beyond the capacity of what I was envisaging. Presumably the "1km run" would be the same as end - 500m - base station - 500m - end? (not that I envisage it ever being more than 50m in total but hey) I know not to make it a ring. Link to post Share on other sites More sharing options...
Glorious NSE Posted October 15, 2014 Share Posted October 15, 2014 It's a lot less than a km in their documentation, I think due to the bus also powering the handsets, there is documentation on how to add additional power somewhere, I'll keep looking. Link to post Share on other sites More sharing options...
cromptonnut Posted October 15, 2014 Author Share Posted October 15, 2014 I'm "pre-thinking" for the modular meetups, if I'm providing the Lenz equipment for any that I may organise it might be useful to have that extra power to the bus. I have a set 90 although I don't know if that will make a lot of difference to powering the xpressnet bus. Link to post Share on other sites More sharing options...
Glorious NSE Posted October 15, 2014 Share Posted October 15, 2014 Okay, it does mention 1000m in the documentation! Doubt that would apply via the multiple connections you get on a modular layout though... http://www.lenzusa.com/manuals/xpressnet/xpressnet.pdf has the detail on which pins and polarity the power supply goes to (page 8 ). You've probably got an old 12v mobile phone (or similar) "wall wart" style charger sat in a cupboard, cut the plug off the (phone) end and wire the 12v outputs to the correct pins on an RJ or DIN plug, so you can plug it into an LA152. Lenz announced an "LY140" xpressnet repowering doodad this year, which is presumably an off-the-peg one of those (though presumably it comes with a German plug!?) - but I don't see it as in stock anywhere yet... Couple of "Gotcha's" that we've run across... 1. - Handsets - if they are all Lenz handsets then the installed power from the command station goes a long long way as they don't appear to need much, so for a 50m layout with all Lenz handsets you might not need to add any more power. But if you will have folk plugging in Roco Lokmaus (for example) then they seem to suck a lot more power out of the bus, so you're more likely to need an extra feed. 2. - Other systems (modular specific issue!) - whilst other DCC systems can use the same Xpressnet wiring and that's a big advantage for widespread adoption, and works really well, under another DCC system the bus may not be using the same wires for the same functions - and the connections between this bus and the command station are unprotected. For this reason never hardwire the extra power supply into the bus on a module, and if you make an adapter as above, check with whoever is planning the command gear before using it on any meet that you aren't organising yourself. We do know of damage occurring to DCC systems caused by getting this wrong and effectively putting 12v DC into a command station's data connection! The NMRA-BR version of our spec has put that in writing, demanding a "clean" throttle bus, with nothing hardwired to it. Link to post Share on other sites More sharing options...
cromptonnut Posted October 15, 2014 Author Share Posted October 15, 2014 Thanks for the explanation - until the official Lenz unit is out, and until we discover we actually need to have one, we're probably best to see how it works without one Link to post Share on other sites More sharing options...
RMweb Gold Tony_S Posted October 15, 2014 RMweb Gold Share Posted October 15, 2014 If you have people bringing their own Lenz throttles will you allocate them an Xpressnet ID to set their handsets to before the modular meeting? Link to post Share on other sites More sharing options...
cromptonnut Posted October 15, 2014 Author Share Posted October 15, 2014 I hadn't thought of that Tony but I'll add it to the list Link to post Share on other sites More sharing options...
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