Hi everybody. I am doing the wiring on my 4’ x 8’ HO layout that will be attached to my Digitrax Zephyr and I have a question that I think will generate pros and cons but I still need some expert help. The 14 gauge buss wires follows the track plan and are a total of 20 to 22 feet long. I am planning on about 4 or 5 feeders of 20 gauge wire. With the exception of turn-outs I have soldered the joiners. I was planning on wrapping the ends of each buss wire with electrical tape until I read Allan Gartner’s “Wiring for DCC” and he suggested using a “R” and a “C” at the end and I am assuming he meant resistor and capacitor. Is wrapping each end in electrical tape ok?? Please keep your responses simple; I have trouble keeping my watts,volts and amps straight!!!
I just left mine dead-ended with electrical tape on them. I haven’t observed any problems.
Frisco Kid,
I used a 2 pole terminal strip and attached the end of the buss to the terminal strip so it wouldn’t be hanging loose nor would I have to worry about the ends accidently coming in contact with something and causing a short.
Don Z.
I’m capping my bus terminal ends with wire nuts. That seems to be acceptable. Probably a better idea than just electrical tape. Looking forward to other replies from DCC experts.
One of the things I’m finding on my new journey into DCC, is that some info sources - especially web sites dedicated to the subject - seem to make it more complicated than it needs to be. While you don’t need more wiring, it seems to generate more words. Just an observation from a DCC newbie.
You can leave the bus elements open-ended (tidy is always smart) or loop them back to their originating posts…your choice. Just don’t let the two elements/wires come in contact electrically. In that regard, an appropriate covering is wise.
Simple.
I looped mine back and connected them back to where they started !!! I’ve read over and over to not do this, but in six years of operation, I’ve witnessed no adverse problems (?)
I guess it works, because at the time I didn’t know it shouldn’t !!! [;)]
Mark.
Mine terminate at two terminal strips per Don Z.
Electrical tape is fine. That’s what I used, and no problems here.
Impedance matching terminations (your resistor and capacitor) are generally not needed until your power bus run from the command station exceeds 50ft. The DCC pulse widths are enough that reflections from unterminated ends have no effect until getting above 50ft or more (100ft to pulse return).
These distances are seldom seen in real life because on layouts that large, multiple power districts with separate power buss are employed.
hope this helps
Fred W
You do not need Buss termination until you have Buss lines longer than 50 to 75 feet.
You will know when you may need the Buss terminated as the engines will run away for no apparent reason or you can not seem to slow them down once you have started them moving. (At least this was my problem and once I put the R/C filter on the Buss ends everything went back to normal).
All the R/C filter (Resistor/Capacitor filter) does is cut off the high frequency spikes or noise that seems to be generated in real long Buss runs (Remember that the Buss run has two conductors and both lengths of wire need to be figured into the 50 to 75 feet)!
The longer the Buss run gets the higher the noise (high frequency spikes) is generated and this noise finally is greater than the digital signal and the decoders then begin missing the commands. This is why it seems that they are running away when in fact they just keep missing the commands due to the noise.
And, Yes the R/C filter makes a very high pitched squeal (that us older modelers can’t hear) but my younger members are always complaining about when they stand near the terminator at the end of my one Buss line!
Also Digitrax does not recommend connecting the Buss wires back on themselves. Just leave the ends not attached to anything.
Any method of insulating the Buss wire ends will be fine (tape - terminal strips - wire nuts).
I have used all three on my home layout!
BOB H - Clarion, PA
A majority of the time, the BUSS only has to carry current to the furtest ‘jumper’.
Terminating the buss with a 2 contact terminal strip is wise: It affords easy contacts for adding on to your layout, plus prevents shorting.
I’ve never heard of ‘impedence matching’ for 60 cycle electricity. TV antenas, YES. That’s up in the no-current high-loss megacycle range. Extreme cases maybe.
The idea of a ‘BUSS’ , is to reduce voltage drop from more resistive track IE: provide better power distribution over long track lengths - and for those using nickel silver or steel rail with DCC.
It’s also good idea for those using sectional track with lots of rail joiners (they get ‘arthritic’) with age.
HOW MUCH is too much? $10 volt meter will show drops in your rail as it gets further away from the power entry point. If I’m going to use sectional track and rail joiners with DCC, I’d solder every 3-4 sections together and run Buss & feeders to every 3 ft. for long term consistancy.
REASON: DCC signals are square wave signals super-imposed on the DC and are WEAK to start with.
What if, instead of having a 50’ buss run, you placed the power supply in the middle of the run and had a 25’ run leaving each side of the power supply? Would this eliminate the need for R/Cs at the end of each buss wire? Would you be able to have a 50’ buss on each side of the power supply (thus powering 100 linear feet) before R/Cs were needed?
Yes, but at 50 feet you almost certainly don’t need termination on the bus anyway. (This is just for info, the more accepted spelling is only one ‘s’, I think the two ‘s’ spelling is propagated by the spelling of the company that makes fuses.)
That is the general idea behind power districts. But simply using 2 lengths of wire (4 wires one set going left one going right) you still maintain the same load even tho you are not traveling the same distance in one direction. Power managers like the PM42 take the booster power, splits it then amplifies it so that there is no additional load on the booster but full power comming out of each channel. the R/C filter as mentioned above must be “tuned” so that it does not remove the wanted signals. I am not sure what the proper cap and resistor would be you should check with your DCC manufacturer for that info. Tuning the filter usually involves changing the cap (just like a tuner on a radio) the resistor is there to provide a load so your booster does not think that the signal passing through the cap is a short.
An added FYI:
Buss (disambiguation)
Buss may relate of any of these:
- Buss is an alternate spelling of bus, used mainly in the case of an electrical bus, also rarely for a computer bus.
Don Z.
I don’t suppose anyone has the spec.'s for the resistor/capacitor filter? As in, what kind? How it’s attached to the buss, etc.? I’d like to try it on my home DCC layout…
Paul A. Cutler III
Weather Or No Go New Haven
Here’s NCE’s recommendation:
Don, are you sure that DCC is a 60Hz signal? The NMRA spec (http://www.nmra.org/standards/DCC/standards_rps/S-91-2004-07.pdf) shows minimum bit durations on the order of 100 microseconds. That is far from 60Hz. Also the signal is shown as a series of pulses of varying duration, not an offset square wave except when it is a string of 1’s or 0’s.
Am I out in left field? I am still learning about DCC and I don’t (yet) have a system that I can throw a 'scope onto.
Karl
You’ve got it right Karl. It is not 60 Hz. On the other hand, in electrical terms it is not real fast, which is why, until you get into pretty long runs, you don’t need the termination.
Vail and Southwestern RR,
Thanks for the link. If I read it right, I need a 1/4 watt resistor that is 47 to 100 ohms and a .1 uF capacitor. Correct me if I’m wrong, but don’t caps come in different voltages? Does it matter for this application? And if so, what should it be?
Thanks again.
Paul A. Cutler III
Weather Or No Go New Haven