Simond Posted March 10, 2015 Share Posted March 10, 2015 I experienced a minor disaster some time back, when due to carelessness, I placed my Ixion Fowler on my layout in such a way that the two wheels on one side were on different track polarities - please see post #35 of my Porth Dinllaen thread (link below). Chaz, of Dock Green fame has had a similar experience, link to the relevant posts here http://www.rmweb.co.uk/community/index.php?/topic/58132-dock-green/?p=1811521 Would be interested to know if anyone else has experienced the same issue, and any suggestions for avoiding the damage (apart from the obvious...) Thanks Simon Link to post Share on other sites More sharing options...
Phil S Posted March 10, 2015 Share Posted March 10, 2015 'The Coin Test' in which a conductive metal object (eg a Coin) is placed across the rails, at ANY part of the dcc system, should cause enough current flow to ensure the Central Controller (or Booster, if in a boosted District) protective cutout works - and promptly. This failure is highly suggestive that the loop-resistance of your dcc wiring bus is too high .... as this should have caused the protective cutout to operate. The higher the current capabaility of a Central Unit/Booster, the higher the 'normal' (acceptable maximum) current,and therefore the higher the 'trip' current... meaning that the wiring must be with heavier gauge wire to ensure lower overall resistance. If a 'starter dcc controller with maybe 1A-1.5A output is used, then 'ex-analogue' wiring may still be acceptable. However, if a 5A unit is used, then the trip current is probably about 7A, and from V=IR ... 14V = 7A x 2 ohms shows the loop resistance needs to be LESS than 2 ohms. (And a lower track voltage means even lower resistance!) Note that by using sub-districts, with individual protection from devices like PSX's, with each sub district limited to (say) 2A, then it is only the LOCAL protection (the PSX) that the coin test needs to trip ... Link to post Share on other sites More sharing options...
Nigelcliffe Posted March 10, 2015 Share Posted March 10, 2015 Suggestions: a - don't drive into short circuits :-) b - check the wiring of the layout. Does it really pass the coin short circuit test, every time, really quickly ? If not, sort the wiring. And, the coin test is only an approximation, what's actually needed is a coin over a pair of pickups onto some typical wheels, which is what your locos provided and failed to trip the overload, which suggests the wiring isn't adequate, or the system's power is too high. c - use a lower current system - as a general rule, those with a "one engine running" layout don't need 5A, something nearer 2A is probably enough. With lower current system, the demands on the wiring are less severe - what fails a 5A coin test may well pass at 2A. Or fit current limiting devices such as power district breakers, or even wiring a car bulb in series with the track feed to limit the current. (edit, or what Phil S said above). Link to post Share on other sites More sharing options...
Adrian Wintle Posted March 10, 2015 Share Posted March 10, 2015 Part of the problem would be that the relatively light wiring of the pickups is acting as a resistor (and then fuse ) at the current levels involved, so the command station is not seeing a dead short. A lower-current system or current limiting is probably the best defense. Adrian Link to post Share on other sites More sharing options...
Simond Posted March 10, 2015 Author Share Posted March 10, 2015 Thanks all The Greater Windowledge Railway is coming to the end of its useful life, and will soon be dismantled. I am currently building track panels for its successor. The wiring was a little unconventional as you can read in the thread. I had already come to the conclusion that there was some voltage drop over the very limited length of the layout (clue in the name... ) and this is at least in part due to the use of self-adhesive copper tape as the busbars. It was nearly a good idea! Convenient, but won't be repeated. Similarly, the wiring itself is actually quite light, and whilst this is ok for droppers, it ain't up to the job of the main feeds. Rather concerningly, applying a needle file handle to one part of the layout failed entirely to cause the loco running elsewhere to even slow down, although the coach lights on the same bit of track obligingly went out! Not how it's supposed to be! PD Loco will be more conventionally wired and equipped with more weighty busbars, and feeds. Chaz has identified a similar root cause in his case, and has identified a simple cure Thanks again for the replies. Simon Link to post Share on other sites More sharing options...
Crosland Posted March 11, 2015 Share Posted March 11, 2015 Part of the problem would be that the relatively light wiring of the pickups is acting as a resistor (and then fuse ) at the current levels involved, so the command station is not seeing a dead short. A lower-current system or current limiting is probably the best defense. Adrian Or dirt or oxidization on the wheels/pickups causing a high resistance path. Andrew Link to post Share on other sites More sharing options...
Simond Posted March 11, 2015 Author Share Posted March 11, 2015 Not, sadly, in the case of my Fowler, which was only a few months old, but had been unused, awaiting a chip, for most of that time. The chip was in for a matter of days when incompetence struck! I'm pretty sure we are looking at high resistance wiring on the GWR, will be remedied in due course. Thanks again Simon Link to post Share on other sites More sharing options...
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