DCC Track Buss Length

[Anonymous]

Does anyone have experience with a track buss in excess of 30'?

I have a large room (36'x20') in which I am building a walk around layout in. I expect to have over 300' of mainline track when completed. I have completed the first phase benchwork and track laying (yard and mainline only) that is approximately 100' (linear) of mainline track with a temporary loop (not a reversing loop, but end to end connected) for contiuous running for now (mainly for the kids to run while I build).

I am using a Digitrax Zephyr 3.5amp system with one DC jump throttle for control. I ran my "A" and "B" rail buss wires last week (12 gauge stranded wire) and added feeders ((20 gauge) every 6'. I ran the track buss "east" and "west" from the throttle location around the layout approximately 45' run each way. The buss is not a complete loop. I ended the buss' approx 10' before the temporary loop section connecting the main's together. I constructed the loop to connect with the correct polarity on "A" and "B" rails so there are not problems with shorts.

I believe I may have "toasted" a DH123P decoder after just a few days operation. This didn't seem normal so I started searching for answers. I was reading on a DCC website to limit each buss run to 30' or less to avoid voltage spikes. It also suggested terminating the ends of the buss with a resistor and capacitor connected between the "A" and "B" rail wires.

I am curious if anyone else has experience with long track buss lengths. I was not aware of this limitation with DCC. I was under the impression if you ran a large enough buss, length was not a problem (Eventually, I expect to get another booster so I can spilt the layout into power districts).

If is best to limit the buss length and terminate the buss ends as described, I will be truely dissappointed with the Digitrax marketing folks because this is not mentioned in any of their product info including the Zephyr manual. They claim you can just hook it up and go on a small layout and to run a buss on a large layout. The only limitation I saw was on the loconet length (2000' I think).

Any help or advice is appreciated.

Thank you,

MR in Tulsa

[mcouvillion]

Mike,

I haven't heard of a bus length limit in DCC other than that imposed by potential voltage drop. Your 12 gauge stranded wire should be good for at least 100 feet. As far as worrying about "voltage spikes" in bus lengths over 30 feet, where did you find that? I've wired one modular layout that has DCC buses over 30', running Digitrax, and never had a problem. I have not heard of "terminating" the bus wires, although the Digitrax Loconet apparently has a plug-in termination of some sort for the end of it's run. Where are you getting your information?

Mark C.

[rrinker]

You shouldn;t get any spikes on the bus, at least not somethign to fry the decoders, unless you have the bus lines passing in close proximity to 120v AC lines for some reason. 45' in each direction should be fine with #12 wire (good choice). Good idea put the booster in the middle, too. 50' thout is about the practical limit even for #12 wire, at that point you have 100 total feet of wire and the voltage drop starts to get noticeable. So you're ok with 45'.
The only time you should need termination on the ends of the bus are if you have wierd problems like engines taking off all by themselves or not responding to commands. If you plan to install block detection you'll want to avoid doing things like twisting the bus wires or adding terminators. Yes it can clean up the signal and reduce electrical noise, but it also changes the inductance of the wire which leads to false detection.

--Randy

[Anonymous]

Thank you Randy for your input. I thought I was doing the right thing with the guage of the buss and the location of the booster.

Is it normal practice to run a linear buss that is not terminated at the ends, i.e. cut with dikes, or can you run the buss as a continuous loop back to the booser?

Here is a link to the website I was referring to: http://www.wiringfordcc.com/track_2.htm

Mike in Tulsa

[rrinker]

Depends on how your layout is set up, I suppose. If it's convenient to loop back, it won't hurt anything, as long as you keep the polarity straight. The section of layout I have up now is an 8x12 oval (2' wide sections - so the middle is a big opening). I ran my bus wires out equally from the booster which is in the middle of the rear 12' section. In the middle of the front - they are cut, not a continuous loop. I ended up with about 15-20' of wire in each direction from the booster. I don't know that connecting them at the front would actually buy me anything. The rest of my layout will be linear along the walls, there's no practical way I could have the bus loop back on itself.

--Randy

[Anonymous]

I know its not recommended to loop the loconet cable on itself. I don't see why you would want or need to loop the power buss. You may want to look at dividing your track and buss up into a few sections or districts. Right now if you have a short (caused by derailment) your whole layout is going to shut down. If you operate by yourself this may not be a problem, but with multiple operators it is a pain. Power districts will help troubleshooting the system also. This is what I think Digitrax and others meant when they set limits on power buss length.
Jeff "tweet" Kerr

[howmus]

Mike, check out this page. It should answer your questions.

http://www.wiringfordcc.com/track_2.htm#problem_interference

[Isambard]

QUOTE: Originally posted by Mike Rehling


I believe I may have "toasted" a DH123P decoder after just a few days operation. This didn't seem normal so I started searching for answers. I was reading on a DCC website to limit each buss run to 30' or less to avoid voltage spikes. It also suggested terminating the ends of the buss with a resistor and capacitor connected between the "A" and "B" rail wires.
Any help or advice is appreciated.

Thank you,

MR in Tulsa

[Isambard]

QUOTE: Originally posted by Isambard

QUOTE: Originally posted by Mike Rehling


I believe I may have "toasted" a DH123P decoder after just a few days operation. This didn't seem normal so I started searching for answers. I was reading on a DCC website to limit each buss run to 30' or less to avoid voltage spikes. It also suggested terminating the ends of the buss with a resistor and capacitor connected between the "A" and "B" rail wires.
Any help or advice is appreciated.

Thank you,

MR in Tulsa

Let's try again. See if re-programming your decoder's address brings it back to life. I had a decoder near death experience last Saturday and thought I had fried my 2-8-0's DH121 decoder due to intermittent power surges, the loco going "dead". Reprogramming brought it back to life.

[Anonymous]

I swapped decoders in the problem loco with a decoder from a loco that is running fine. Turns out that it appears to be an engine problem and not the decoder at all.

Not all is lost from posting this subject. I believe I am now more educated on proper buss techniques and have benifited greatly from everyone's help. Thanks so much and I have confirmed why this is such a great hobby...........it the people!

To think yesterday I was considering buying another booster............I know I will eventually need one, but for now, the Zephyr is all I need.

Now to figure out what is wrong with the engine. The drive train feels very stiff.........time for a visit to the shop.

Mike in Tulsa

[grayfox1119]

Stranded wire has more capacitance that solid wire, but I seriously doubt if that is causing your problem, that tends to be an issue with AC, not DC. I believe Isambard may have your answer. If you had access to an Oscilloscope, you could check your main power buss to see if it has an spikes.