WIMorrison Posted January 1, 2018 Share Posted January 1, 2018 I have been thinking how best to separate my single output from my Z21 into at least 2 circuits to allow for switching of points when a track short occurs as my last experience suggests the most common running fault is running over the point isolation causing a short circuit and the entire layout stopping. The splitting into different power districts map also help on diagnosis of where the fault lies. Given I want to use Railcom I want to ensure that this signal isn't lost and I have found this suggestion http://www.rr-cirkits.com/Notebook/short.html where car stop/tail bulbs provide the protection and running several in parallel would provide multiple track power districts and a separate bus for points and accessories. Has anyone used this idea, do you see any drawbacks or are there more cost effective solutions being used?? Link to post Share on other sites More sharing options...
Brian Posted January 1, 2018 Share Posted January 1, 2018 I use 12 volt 21 watt car bulbs for short circuits. What has to be remembered is they do not cut off the power but simply shunt away the power via the lamp when a short occurs. So they are not cut outs which an all electronic DCC device would give, they are simply current limiters. I find them simple and cheap to use and install. I've not had any problems either, but your DCC system needs to have a greater output than the current of the lamp, which is typically around 1.5 to 1.75 Amp otherwise if a low Amp system is used or you wish to have a lower threshold shunt level use a lower wattage lamp such as 12v 10watt festoon. You will find reference to them on my web sites DCC page 2. and also there is a good demo of them working... https://www.youtube.com/watch?v=giDZUCDIrKY Link to post Share on other sites More sharing options...
Junctionmad Posted January 1, 2018 Share Posted January 1, 2018 (edited) I have been thinking how best to separate my single output from my Z21 into at least 2 circuits to allow for switching of points when a track short occurs as my last experience suggests the most common running fault is running over the point isolation causing a short circuit and the entire layout stopping. The splitting into different power districts map also help on diagnosis of where the fault lies. Given I want to use Railcom I want to ensure that this signal isn't lost and I have found this suggestion http://www.rr-cirkits.com/Notebook/short.html where car stop/tail bulbs provide the protection and running several in parallel would provide multiple track power districts and a separate bus for points and accessories. Has anyone used this idea, do you see any drawbacks or are there more cost effective solutions being used?? The car lamp on its own is a very hit and miss affair , many boosters will trip far quicker then the time it's takes for the lamp to warm , the idea of using a PTTC fuse is clever , but these fuses are not designed for frequently occurring shorts and over time effectively develop higher and higher trip resistances or may fail to work. My view is an electronic circuit is best , MERG district cutoff is cheap , but you have to be a member and be able to assemble simple electronic kits. The lamp is also not a great solution as upwards of 2amps continued to flow under short circuit conditions , this means all the droppers must be " over-rated " to handle continuous currents of that magnitude , rather then a short time span short circuit current, until the booster trips. For example this precludes the common 7/0.2 wiring often used for " last mile" droppers in 00. Also if you get multiple ( 2 ) shorts the booster may trip anyway and the lamps provide no indication of the problem. Edited January 1, 2018 by Junctionmad Link to post Share on other sites More sharing options...
WIMorrison Posted January 1, 2018 Author Share Posted January 1, 2018 (edited) Thanks for the replies, I had thought about the MERG stuff but there are few details available and when I have written before to them I haven’t received any replies, not sure if writing again would generate any response My concern would be that their module (957 I think) would interfere with the railcom feedback - though it shouldn’t as it would be in the track/accessory feeds and not on the Loconet/expressnet feedback circuits - I would like confirmation that this is the case before I join to purchase Edit - the kit with all the parts seems to be Kit 57 @ £10. The other number is just the PCB. Would be good to hear of someone who is using this and what the experiences of it are Edited January 1, 2018 by WIMorrison Link to post Share on other sites More sharing options...
Phil S Posted January 2, 2018 Share Posted January 2, 2018 "My concern would be that their module (957 I think) would interfere with the railcom feedback - though it shouldn’t as it would be in the track/accessory feeds and not on the Loconet/expressnet feedback circuits - I would like confirmation that this is the case before I join to purchase" Railcom ( cutout) compatibility is a separate issue to be checked, but do not confuse the Expressnet or Loconet busses between handsets ( and PCs and feedback detectors ). With any DCC track or accessory busses ...... It is the TRACK DCC bus which wants protection FAST and preferably with auto- Resetting every 2 seconds. .... I usually suggest the psx but am uncertain about railcom with it as us makers are behind in these matters. The accessory us is not usually exposed to short circuits ... And so the direct output of the controller is normal. Link to post Share on other sites More sharing options...
WIMorrison Posted January 2, 2018 Author Share Posted January 2, 2018 Phil It is this ‘protection’ that I am trying to create and my hope was that this MERG Kit 57 would provide the protection by ‘tripping out’ when an excess current is drawn. This tripping would also protect the occupancy detector as that would be in the circuit - however I need to use a device that is railcom compatible and as MERG claim to meet NMRA standards I was hoping that this included the bi-directional transmission of the railcom information on the track bus. Link to post Share on other sites More sharing options...
WIMorrison Posted January 2, 2018 Author Share Posted January 2, 2018 So it appears that the MERG unit has some limitations none the least of which is that it doesn’t work with Railcom which presently leaves me without a solution or way to create a track bus that has overload protection and railcom - unless one of you clever chaps can point me at something that will fit the bill? Link to post Share on other sites More sharing options...
Nigelcliffe Posted January 2, 2018 Share Posted January 2, 2018 So it appears that the MERG unit has some limitations none the least of which is that it doesn’t work with Railcom which presently leaves me without a solution or way to create a track bus that has overload protection and railcom - unless one of you clever chaps can point me at something that will fit the bill? A railcom compatible booster for the main track, and use the Z21's main output for the accessories. Thus, a short will shut down the booster, but leave the Z21 running for the accessory bus. Link to post Share on other sites More sharing options...
RMweb Gold RFS Posted January 2, 2018 RMweb Gold Share Posted January 2, 2018 (edited) What about the PSX from DCC Specialities? You could always ask them first whether it supports Railcom. Email contact details here - http://www.dccspecialties.com/ I used to use a PSX with my Lenz system, with the track bus passing through it but the accessory bus bypassing it. In that way a track short (usually caused by forgetting to switch points) left the command station and accessory bus running. But I can't say whether it affected Railcom. However, I now use a separate booster (LV102) for the accessory bus, with the main command station+booster (LZV100) providing track power. The CS is set to not shut down other boosters when a short occurs. Hence I've stopped using the PSX. Edited January 2, 2018 by RFS Link to post Share on other sites More sharing options...
richard brown Posted January 2, 2018 Share Posted January 2, 2018 (edited) I use it on my layout which have a ECoS as the DCC system and I have Railcom on and it has not had any problems with it Richard Edited January 2, 2018 by richard brown Link to post Share on other sites More sharing options...
Junctionmad Posted January 2, 2018 Share Posted January 2, 2018 So it appears that the MERG unit has some limitations none the least of which is that it doesn’t work with Railcom which presently leaves me without a solution or way to create a track bus that has overload protection and railcom - unless one of you clever chaps can point me at something that will fit the bill? Hi, Im a MERG member and a professional electronics engineer. I also use Railcom , I do not understand the perceived issues with railcom, Once the district cutoff is triggered , that section controlled by that cutoff is deprived off power, hence railcom doesnt work Outside of that the cutoff is not aware of any railcom signalling and is not affected by it. The Merg booster is " railcom capable " in that it can be used to generate a railcom cutoff, but thats a different matter. Im not aware of any other limitations of the MERG unit, what do you understand are its limitations , its has a programmable trip speed and many other clever features Link to post Share on other sites More sharing options...
WIMorrison Posted January 3, 2018 Author Share Posted January 3, 2018 I have been conversing with the MERG TSM on the suitability of the MERG Kit 57 DCO for use as we discuss here and his advice is that it isn't compatible (or he will not say it is compatible, or will work, with Railcom). He has also provided me with 20 pages of a MERG Forum thread discussing this issue where some people find it does work with Railcom, though not 100% of the time, and other say that it doesn't - the consensus seems to be that the issue is with the DCO timing method and the Railcom cutoff timing, but as I am not an expert in this field I can only paraphrase what I have read. Can I ask which DCC system you are using to control the layout using Railcom with this DCO and how many you are using? As you say it should work and that was the start of my questioning with MERG and I fully expected to get a positive answer, regrettably I didn't - hopefully you will be able to convince me otherwise, as presently the cost wouldn't be as cheap as the headline price when you consider membership, joining fee and then the module (plus the time to build it) Link to post Share on other sites More sharing options...
DCB Posted January 3, 2018 Share Posted January 3, 2018 Combining point operation with DCC track power sounds like a bad idea. Separating the two systems with isolator switches would be a good start, but for any but the tiniest layout division of track supply into manageable chunks of say 9 points , and up/ down lines has to be a good idea. Link to post Share on other sites More sharing options...
WIMorrison Posted January 3, 2018 Author Share Posted January 3, 2018 That is why I am trying to create different busses - at least one for the track and at least one for the accessories Link to post Share on other sites More sharing options...
WIMorrison Posted January 4, 2018 Author Share Posted January 4, 2018 Some good news - despite having been told by two resellers that the PSX-1 doesn’t work with Railcom, in one case an emphatic NO, I decided to email dccspecialties to get their comment as the makers of the unit and Larry came back to tell me that it does work and that it is best to wire it using J1-1 and J2-1 for best practice. I will therefore order one in the next few weeks and create my track bus using the PSX-1 and connect the accessories directly to the Z21 thus giving control even if there is a short on the track. I hope this is useful for others. Iain Link to post Share on other sites More sharing options...
RMweb Gold RFS Posted January 4, 2018 RMweb Gold Share Posted January 4, 2018 (edited) There's only one way to wire - see below J1 Input Power Connector J1-1 Connections for Daisy J1-2 Chaining to next PSX J1-3 DCC Input 2 J1-4 DCC Input 1 J2 Output Power Connector J2-1 DCC Output 2 J2-2 DCC Output 1 Input from your booster goes to J1-3/4, output to track to J2-1/2. The most convenient way to connect the accessory bus that bypasses the PSX is to connect it to J1-1/2 (daisy chain connection). I don't know where you intend to mount the PSX but you need to be able to see if there's a short, since that is indicated by an LED on the circuit board. I found it useful to wire a 12v red LED to the J5-1/2 connectors, with the remote LED being located where I could see it easily. Edited January 4, 2018 by RFS Link to post Share on other sites More sharing options...
WIMorrison Posted January 5, 2018 Author Share Posted January 5, 2018 some expansion and clarification from me might help Larry said to put the Railcom detector into the J1-1 to j2-1 circuit as this is just a copper trace on the circuit board. The path that is actually switched off during a fault is J1-2 to J2-2. As he designed the unit I will go with his advice Link to post Share on other sites More sharing options...
RMweb Gold RFS Posted January 5, 2018 RMweb Gold Share Posted January 5, 2018 some expansion and clarification from me might help Larry said to put the Railcom detector into the J1-1 to j2-1 circuit as this is just a copper trace on the circuit board. The path that is actually switched off during a fault is J1-2 to J2-2. As he designed the unit I will go with his advice OK - understand that now thanks. I had assumed your Railcom detection, as in my Lenz LZV100, was built into the command station and not a separate unit. Link to post Share on other sites More sharing options...
WIMorrison Posted January 5, 2018 Author Share Posted January 5, 2018 The Z21 also has Railcom in the command station, the issue is ensuring that the Railcom coming from the track through the DR5088RC block detector isn't impacted by the cutout and that the cutout isn't affected by the Railcom - hence saying that the detector is placed on the lune which is J1-1 and J2-1 as the detector will then not be impacted in any way Link to post Share on other sites More sharing options...
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