jwils1 wrote:
But here are my questions: Is there a difference in the number of recommended track feeders for DC compared to DCC? Which are you running? Technically, what happens over a period of time that causes a reduction in perfomance when too few feeders are used?
Good DC and DCC wiring practices are really the same, including turnouts. The difference is what happens when wiring is not up to the load. With DC, when wiring is insufficient, you get voltage drops and in worst case, some dead spots. At the dead spots, or places with too much voltage drop, the train simply stops or stalls. Current loads are generally lower with DC because of less consisting, and the home-run wiring required for block control, so the voltage drop is actually less.
With DCC, insufficient wiring can cause both voltage drops and control signal degradation/loss. Voltage drops are greater with DCC because the power bus carries the current load for the entire power district, not just one train. Once a certain point of signal degradation is reached, the controller can no longer communicate with the decoder. The margin for resistance in the electrical path from controller through the wiring, rails, wheels, etc., is just less than with DC.
Assuming secure electrical joints in the wiring - one of the issues in this thread - the most common places for degradation in the electrical path are:
- dirt in the wheel to track contact. Nearly everyone needs to clean their track and/or wheels periodically in some way. I'm not going to get into the track cleaning method arguments here! Just note that the nickel silver (or brass) oxidation of rail and wheels of the next point affects this contact, too. Also be aware that running trains frequently, especially heavier models with metal wheels would/will wear the oxide away.
- rail joiners loosening or oxidizing at their points of electrical contact. This used to be a real bear with brass rail and rail joiners. Brass oxide (tarnish) is a non-conductor, and brass is slightly softer than nickel silver. Over time, a brass rail joiner would loosen just enough so that the joiner edges would no longer pierce the oxide that occurred on the rail webs. The rail joiner would no longer conduct, and unless the next piece of track had a feeder, you would have a dead spot. Track cleaning and running the trains would not stop the oxide on the rail web or base, and actually helped the rail joiner soften its grip.
Nickel silver oxidizes as well, but the oxide forms much slower and the oxide is somewhat conductive. Therefore the oxide buildup and rail joiner loosening seldom creates an open circuit, but does increase the resistance in the electrical path.
- the third deterioration over time is wire-to-wire connections. Corrosion and vibration are the usual culprits here. For this reason, marine and aviation wiring have the most frequent problems, and why there have been countless attempts to develop wire connection schemes that are inexpensive (both in labor and materials), and resist long term deterioration. In model railroading, vibration is seldom an issue, so soldered, mechanically-solid joints using solid wire are the most reliable. They are also the most labor intensive. Airplanes, boats, cars often have to use stranded wire for it's flexibility and vibration resistance but it is far more susceptible to corrosion, especially anywhere the insulation is pierced or removed. In a corrosive and/or wet atomosphere, contact of dissimilar metals almost guarantees corrosion if exposed to the atmosphere. Hence, the long term problems with unsealed IDC's, depending on the environment your layout is in. There are more expensive IDCs that seal after installation, and that is the point of the Posi-Taps. To prevent corrosion, when I solder a joint on a car or boat, I seal the joint with electrical tape or shrink tubing.
I presently have approx. 130 lin. ft. of HO DCC track with just three sets of track feeders. I've been running it about 6 to 8 months. Everything runs smooth and slow. And, I'm using 9" long sections of Atlas snap track. Am I going to have problems down the road?
The rail joiners are going to be your key issue over the long term. How long? Depends on what the humidity and salt loading in your air is, how securely your track is mounted, whether you take it apart to make changes, how often you run your trains, etc. Since my previous layouts (except my 1st which was brass sectional track) used handlaid track, I just skipped the rail joiners completely, which mandated a feeder for every piece of rail. I used 26 gauge magnet wire soldered to the bottom of the rails.
An alternative to feeders that some use is to install wire jumpers around the rail joints.
my thoughts, your choices
Fred Wright
