In recent months our mr club finally made the complete transition from DC to DCC. We completely rewired the layout dividing it into three power districts. For the bus we used 10 gauge stranded wire. Each district is approximately 100' to 120' in length of mainline with the booster located in the middle of each district. All feeders are 18 gauge and less than 12" in length and are 6' apart. We are using Digitrax.
Here is our problem, in one district at one end of the district we can not get the system to shut down when shorting across the rails. While troubleshooting this problem we found that if we crelated a short circuit by joinin the two ends of the bus wires it still would not shut down the booster. We then worked our way back along the bus wires directly shorting across the bus wires until we got the system to shut down instantly, we therefore figured that our problem was a broken or damaged bus wire after the point where we got it to short out properly, although nothing obvious was found.
It gets better. I cut off the bus wires at the point where we got it to shut down ok, this was about 10' from the end of the district. I then soldered in place new bus wires to the end of the district. Without attaching the new bus wires to any feeders We figured that touching the two ends of the new bus together should get an instant short, but no. The system would not shut down.
We found that we could get the system to shut down instantly approximately 54' from the booster ( shorting directly across the bus wires) but at 60' the system would not shut down. We ruled out the booster by swapping it out with another booster.
We would appreciate any suggestions on what to do next. Sorry for being so long winded.
Thanks Martin.
Try swapping the boosters. I suspect you've got one that is not sensitive enough, or has a defective circuit breaker.
Since you've got multiple boosters, you have the luxury of being able to do this easily.
It takes an iron man to play with a toy iron horse.
My suggestion is the addition of a PM42 power manager in each booster district. Dividing the booster district into shorter sections, each with it's own breaker.
Dave
Lackawanna Route of the Phoebe Snow
It's not sensing the short. This tells me the bus wire is too thin for the length of the run. What size wire is this, and how long does it run from the booster? It appears that it is at least 10 feet too long (20 feet of wire) for the size of wire being used. If it's enough of a voltage drop that the system won;t shut down when shorted, it may even be measureable. Check the voltage near the booster, and then at the far end of this problem bus run. Don;t worry about the actual numbers - unless you have a meter made for the square wave output of DCC, it won;t be completely accurate, what you are looking for is the DIFFERENCE between the two numbers. Anything over .5-1V will definitely be noticeable in reduced speed of locos and likely is enough to precent the full current from flowing through a short at the far end, which is why the breaker doesn't trip. The breaker should trip just by laying a quarter on the rails - NOT pressing it down, not touching the two bus wires together. If it does not, the bus and/or feeders are insufficient.
Not sure what's up with all the suggestions for additional breakers. While it's a good idea to divide things up so a derailment in one location doesn;t shut down the whole layout, adding a PM42 and connecting the very same bus wires will return the very same result - it won't shut down when shorted at the far end.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
rrinker It's not sensing the short. This tells me the bus wire is too thin for the length of the run. What size wire is this, and how long does it run from the booster?
It's not sensing the short. This tells me the bus wire is too thin for the length of the run. What size wire is this, and how long does it run from the booster?
Wouldn't this be large enough?
Rich
Alton Junction
Thank you for the replies. The bus is 10 gauge you would certainly think it is heavy enough. I also agree that it simply apears that the bus is simply too long, but we have other districts that are longer which operate just fine.
We tried switching out the boosters and that made no difference.
Thanks again.
#10 at 50 feet (100 feet total wire) is right at .5 volt drop. Assuming it's copper wire - #10 is getting big enough where it comes in aluminum as well, and that's a much worse conductor.
How is the bus attached to the booster? #10 wire won't fit in the screw terminals, so there has to be a jumper of somethign smaller to connect - it should be as big as fits in the terminals AND as short as possible - and also a good solid soldered connection.
At some point, using heavier wire to make the bus longer becomes more expensive than just adding anothe rbooster closer to the destination.
Somethign else that might be a problem - there may be leakage dependign on the type of track and ballast used. The only way you could really prove this out would be to disconnect every feeder and then try shorting the end of the bus - if the breake rtrips, it's not the bus, it's somethign in the track. Or even somethign as silly a 1 feeder in 100 connected backwards. It might not be enough to make a permanent short, alhough it SHOULD, unless there is poor conenction between that section and the sections on either side of it (loose or missing rail joiners sort of thing)
Good points Randy. The 10 Gauge is stranded copper, there is a very short jumper to the booster, we used the largest that would fit. I think the next thing we try is to remove all the feeders like you suggest and then test just the bus wires. Go from there.
I agree with Randy. It is likely a voltage drop problem.
You might try this: move your booster closer to the buss and feed your buss run from the center instead of from the end.
At our club we run 640 feet of mainline off of the command center and 2 boosters. No track is over 50 feet from its booster.
I've had districts up to 85 feet one way from our booster with 12 ga bus and powerpole connections every 6 feet. quarter test tripped the Booster immediately at that distance. I suspect the extra resistance may be somewhere in the wire and not the extra ten feet. Adding ten feet of new wire would not change high resitancesomewhere in the initial bus wire. Check the resistance of that bus run and compare it to the resistance of one of the other similar bus cables. Are there any joints in the bus run? Continuous is better if possible.
Martin Myers
Remember, the rail itself is serving as a secondary bus -- in effect doubling the gauge of your bus wire.