Clan McCormick Posted October 13, 2009 Share Posted October 13, 2009 Hi Every now and then questions pop up about volt drop on a layout. I do not see it as a big issue unless you have a large layout. What I am asking is anyone actually interested in how to work out volt drop? If so I can post some simple examples and forumla's that you can apply to your layout. Cheers Martin Link to post Share on other sites More sharing options...
bertiedog Posted October 13, 2009 Share Posted October 13, 2009 Good Afternoon Martin, To start with it's an un-important issue on most smaller layouts, unless the layouts are very large indeed. Second, it is easy to cure afterwards if it is found to affect the operation of both DC and DCC layouts. The indication is quite obvious as far as the general running of the locos, if they slow or control is jittery on the farthest extreme of the track system, then jumpers, or a full bus bar system may be needed to be added. But the issue is complicated by how many Locos and Coaches, and accessories are drawing power at any one point, and a layout may well run normally till the final straw is one extra items drawing power. It is very difficult to measure the drain as it is a dynamic system altering as the commands are followed and the items draw power, so a meter reading is only a snapshot of the system at that moment and may be little or no help. So the usual advice is to design in some extra capacity, in the form of a bus bar system, a duplicated pair of delivery wires or tapes etc, that are in parallel with the track. The idea originated with the commercial developers of DCC to help with RTR track sections, where the joints all risk poor contact to the next track section, so keep in mind that if it is say all Peco track and soldered together, then the bus bar may have little effect on all but the deepest of drains on the power supply. But the best approach is belt and braces, and be it a RTR set rack, O gauge, or hand made P4, the usual best practice advice is to put in extra bus wires and or copper tapes etc, simply in parallel with all the track, even sidings etc. Next, total what you expect to be actually running, and as a precaution, total all the possible drains, including coach lighting, and all extras like points under DCC control, if you can check each item the current drain of each can be checked with a meter and a total arrived at, sometimes it frightens people who then realise the power pack could not handle the total, and they then fit the bus, when it should also be an increase in the power supply that is really needed. But the pragmatic approach is to realise that in practice the actual drain will be a lot lower, and difficult to quantify in useful terms. It's a horses for courses situation, no formulae will exactly fit, it just needs a bit of forward planning, and to make sure the basic DCC power supply can handle want you want to be running. A small freight line with draw little power, but a suburban layout, even a small one, with EMU's trundling about with lights on and several in motion, will draw an awful lot more amps. Likewise with the difference between a round n' round, and and end to end layout, where the requirements of an end to end on a timetable will be minute, compared to a layout with lots of items in motion. Hope this all helps to sort it out, all is adjustable later on if needed, so plan a bit and then test to check out, nothing is wasted, only additions would have to be made down the line so to speak. Stephen. Link to post Share on other sites More sharing options...
Edwin_m Posted October 13, 2009 Share Posted October 13, 2009 The other issue with volt drop is that it (or rather the resistance that causes it) can defeat the short circuit protection - make sure you do the coin test on even remote parts of the layout. This can be a problem even (particularly) if the layout is wired on the assumption that it has few trains and therefore low current. A couple of ohms in each of the feed and return means a short will only draw about 4 amps, if you have a 5A command station it will not cut out but it will be generating as much heat somewhere on your layout as a 60-watt light bulb. I agree with Stephen there are so many uncertainties that precise calculations don't help much, and if it is done when the layout is built good wiring is not much more time or money than bad wiring! Link to post Share on other sites More sharing options...
Rick White Posted October 13, 2009 Share Posted October 13, 2009 Good Afternoon Martin, To start with it's an un-important issue on most smaller layouts, unless the layouts are very large indeed. ...... With all due respect to your detailed advice Stephen, i think that Martin was suggesting in his original post above that he would be happy to give answers to people having any voltage drop problems with their layout wiring, rather than hime asking for such advice. Best regards, Link to post Share on other sites More sharing options...
bertiedog Posted October 13, 2009 Share Posted October 13, 2009 With all due respect to your detailed advice Stephen, i think that Martin was suggesting in his original post above that he would be happy to give answers to people having any voltage drop problems with their layout wiring, rather than hime asking for such advice. Best regards, Yes, the phrasing looked like request, so back to the poster for his advice, but of course replies are as usual not just to poster but to the general readers as well. Stephen. Link to post Share on other sites More sharing options...
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