In the DC days, I thought I was pretty astute about the electronics involved but I'm finding out, often the hard way, that DCC is a whole new ballgame. Last night, my lack of knowledge came up and bit me........AGAIN!!!
At one time, my whole layout operated as one zone, but because I added so many locos to my roster, I broke it up into two zones. It used to be that if I had a short circuit, the system would instantly shutdown to prevent frying the decoders, obviously a very important design feature of DCC systems. What I have discovered is if the problem is in the primary zone, the whole system shuts down but if it happens in the secondary zone, only that zone shuts down and then only until the short is cleared.
Last night, I wanted to investigate a problem I was having with some locos derailing when entering a hidden staging yard which is on the other side of a wall from the layout. It is also in the secondary zone. Using my wireless throttle, I accelerated on a string of F-units to bring them through the wall into the staging area. Almost immediately, I got a shutdown. I did a quick check to see if I had placed a metal object on the track and if I had a derailed car or loco. Nothing. Did a quick check on the connections to the staging yard. Nothing. I went back around to the other side of the wall and I was greeted with the telltale smell of something overheating. I quickly discovered that the lead F-unit had derailed and created a short, shutting down the DCC in that zone. Apparently though it does not shut off the track power because juice was still flowing through the front truck, overheating it and causing the plastic truck to melt on one side. Complete toast. Fortunately, it seems the damage was limited to that one truck. No damage to the electrical components of any of the F-units or to the loco's shell. .
I seem to have read something about having circuit breakers installed to prevent this sort of thing. If that is so, what type of breaker do I need and should It be hooked to the bus line?
You may not have enough feeders or something less than solid connections.
What type of DCC system?
How big are the two boosters?
What type of circuit breakers.
What gauge are your bus wires and feeders?
Rich
Alton Junction
Some more questions:
What do you mean by two zones? Are the two zones electrically isolated by either gapping rails or using insulated rail joiners? If gapped, did you put an insulating barrier in the gap to prevent one or both rails from creeping until they touch?
How are the two zones powered? Is either (or both) zone powered through a separate external circuit breaker? If not, a short will probably trigger the command station circuit breaker, shutting everything down.
Does either zone contain a reverse loop or a reversing section?
If you have not already done so I highly recommend distributing power to the zones through external circuit breakers. Feed the command station power to the input side of each circuit breaker. You need a circuit breaker or, if appropriate, an auto reverser (which incorporates a circuit breaker) for each zone.
Power then goes from the output side of each CB/AR to one of the zones. Each zone must be fully isolated electrically from the other(s) with rail gaps or insulated rail joiners so that it will get power only through its CB/AR. Most of these units can be set to trip earlier than the command station CB thus protecting it while at the same time only shutting down one zone as a result of a short.
richhotrain You may not have enough feeders or something less than solid connections. What type of DCC system? How big are the two boosters? What type of circuit breakers. What gauge are your bus wires and feeders? Rich
Lenz system with CVP components.
Bus wires are 14 gauge. Feeders 22.
Boosters are both 5 amps if that's what you mean by how big
I have no circuit breakers except for the one in the Lenz system. That was my question. Should I add an additional circuit breaker to the second zone. What kind. Where do I attach it.
Hmm, that must be some wierd quirk in the Lenz boosters - if you have two of them, each feeding one of those two zones, and you have gapped both rails between zones, then only zone 1 should shut down if the short is there, or only zone 2 should shut down if there is a short there. You can certainly further divide each zone up into additiona 'sub zones' using circuit breakers, but that won't fix this problem, only mask it somewhat. You need to get the configuration working now as it is currently set up before adding more complexity.
The other thing is could be is a crossed feeder somewhere. You may have one or two feeders from zone 2 connected to zone 1's bus, or vice versa. In other words - the two zones aren't truly isolated from each other.
And - how do you have it all connected? Are both boosters connected to the command station through the control bus, or did you just feed the second one with the track power of the first? If set up the second way - that's why the short in one section kills the whole layout.
--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 And - how do you have it all connected? Are both boosters connected to the command station through the control bus, or did you just feed the second one with the track power of the first? If set up the second way - that's why the short in one section kills the whole layout.
I'll have to double check and get back to you. I thought when I divided the layout, I had isolated the two zones. I can tell you for certain the rails are gapped. Maybe I missed a feeder wire that's still connected to the wrong bus line. It's been a few years since I divided the layout and I don't want to rely on my memory as to how the boosters connect to the command station. Since the football games are about to begin, it will probably be later tonight that I get back to you.
Sometimes a circuit breaker will not trip if the current draw does not reach the trip current but is enough to create quite a bit of heat at the short circuit location. I have had several meltdowns and destroyed a tender.
Tonys train exchange has the PSX circuit breakers that can be adjusted much lower than the trip current of the command station. They also get their power from the command station so there is no need for an extra power supply.
retsignalmtr Sometimes a circuit breaker will not trip if the current draw does not reach the trip current but is enough to create quite a bit of heat at the short circuit location. I have had several meltdowns and destroyed a tender. Tonys train exchange has the PSX circuit breakers that can be adjusted much lower than the trip current of the command station. They also get their power from the command station so there is no need for an extra power supply.
That's good information. It might be coincidence, but this is the third meltdown I've had and all have happened about the same location of the layout, right before the entrance to the reverse loop where both rails are gapped. This is about as far from the power source as it could be. Would it be a good idea to put the circuit breaker at this end of the layout or does it matter?
I got a lot of good information about the placement of boosters and circuit breakers on this thread.
http://cs.trains.com/mrr/f/744/t/225721.aspx?page=1
I used 3 circuit breaker boards on my NCE 5A system downstream of the main device. My HO layout is only about 5' x 10' and has 2 reversing loops, a teeny mainline between them and 3 yards. I used the OG-ARs ($32) on the reversing loops and the OG-CB ($25) on the main, and included the yards in the section where they reside. Tony at Tony's Train Exchange can advise whether more sophisticated (and higher priced) boards are needed and how to choose.
http://www.tonystrains.com/products/type_powerprotect.htm
So the main buss from the NCE to the 3 boards is about 1' long. Then three busses (mine are 16 gauge stranded wire, different colors) for the sub-districts lead from the appropriate circuit boards. I branched a buss if needed to lead into yards. I used 22AWG solid feeder wire from buss to the rails. Feeders are no more than 6' apart, with soldered rail joiners connecting track.
Paul
Modeling HO with a transition era UP bent
What you probably need are heavier bus wires and/or more feeders. Try the quarter test, set a quarter on the rails and see if the breaker trips. If not - you have too much resistance in the circuit, either through inadequate bus or feeders.
What sort of distance are we talking about here? Logical placement of the boosters is also important - keep the wire lengths as short as possible on the track power side - the low current command bus can run quite far. If your current arrangment is something liek this:
==============<booster1>=|=<booster2>==============
The following would make more sense:
======<booster1>========|=======<booster2>=======
The second version minimizes the run length of each bus. Say the overall length end to end of the bus was 100 feet. If the two boosters are smack in the middle, you have a 50 foot bus out of each one. Instead put the boosters at the 1/4 points, and you have 25 feet of bus, the booster, another 25 feet of bus, the gaps, 25 feet of bus, the second booster, and the final 25 feet. No point is more than 25 feet from a booster, instead of 50 with the centralized model.
jecorbett Last night, I wanted to investigate a problem I was having with some locos derailing when entering a hidden staging yard which is on the other side of a wall from the layout. It is also in the secondary zone. Using my wireless throttle, I accelerated on a string of F-units to bring them through the wall into the staging area. Almost immediately, I got a shutdown. I did a quick check to see if I had placed a metal object on the track and if I had a derailed car or loco. Nothing. Did a quick check on the connections to the staging yard. Nothing. I went back around to the other side of the wall and I was greeted with the telltale smell of something overheating. I quickly discovered that the lead F-unit had derailed and created a short, shutting down the DCC in that zone. Apparently though it does not shut off the track power because juice was still flowing through the front truck, overheating it and causing the plastic truck to melt on one side. Complete toast. Fortunately, it seems the damage was limited to that one truck. No damage to the electrical components of any of the F-units or to the loco's shell.
Last night, I wanted to investigate a problem I was having with some locos derailing when entering a hidden staging yard which is on the other side of a wall from the layout. It is also in the secondary zone. Using my wireless throttle, I accelerated on a string of F-units to bring them through the wall into the staging area. Almost immediately, I got a shutdown. I did a quick check to see if I had placed a metal object on the track and if I had a derailed car or loco. Nothing. Did a quick check on the connections to the staging yard. Nothing. I went back around to the other side of the wall and I was greeted with the telltale smell of something overheating. I quickly discovered that the lead F-unit had derailed and created a short, shutting down the DCC in that zone. Apparently though it does not shut off the track power because juice was still flowing through the front truck, overheating it and causing the plastic truck to melt on one side. Complete toast. Fortunately, it seems the damage was limited to that one truck. No damage to the electrical components of any of the F-units or to the loco's shell.
There is a current thread running on the Wiring for DCC forum that discusses the possibility of a short and subsequent fire if a 10 amp booster doesn't trip in the event of a short.
The point was made that, by applying Ohms Law to a 10 amp booster and 16 volt track power, the maximum resistance value that can be tolerated from one track terminal on the booster is 1.6 ohms.
However, in practice, the 10 amp booster puts out 12 amps (production design margin to guarantee 10 amps) which means that the actual real resistance value is closer to 1.3 ohms.
This is the maximum resistance value that can be tolerated from one track terminal on the booster out and around the layout all the back to the other terminal of the same booster. In that case, the layout wiring should be less than this value. The quarter test can be used to determine if the resulting short will shut down the booster. If a short circuit between the rails does not shutdown the booster, there is a wiring problem with too much resistance, meaning that there is more than 1.3 Ohms resistance value.
I'll check the wiring. This derailment happened just before the locos went over a double crossover which itself is just outside of the reversing loops. I have Peco switch machines with accessory switches attached to change the polarity of the powered frogs. All feeder wires are 22 gauge and the bus lines are 14 gauge. When I first began in DCC these were the recommendations in the DCC primer I was reading.
Initially, I thought there was just cosmetic damage to the side of the truck on the lead A unit of a 3 loco F-unit lash up. It turns out the whole truck melted and one wheel fell completely off. It will have to be replaced. In addition, the Peco accessory switch for the nearest turnout also overheated and melted and must be replaced. On the upside, none of the three loco decoders was damaged.