I’ve seen a few references that suggest it is NOT necessary to run the bus-lines along the track route in a spiral helix, but rather just run the track feeders lines down one of the vertical legs (post) to the bus wires at the bottom. I thought this was a good idea.
My question is how many of these vertical connections should be made?
My helix is a double track affair with radii of 32.5” and 29.5”. I have plans to stagger the rail joints, and to solder all the rail joints,…code 100 Atlas rail.
Considering this sort of relatively small radius/circumference, I’m thinking I need only one feeder set of wires for each elevation/loop of the helix. And perhaps these feeders wires might be sized a bit larger than normal??
The circumfernce is 15 and 17 feet. 2Piradius Doesn’t sound so small, when people talk about feeders every 6 feet. I never built a helix, so it’s all theoretical to me.
My helix has the radius you have. I put 2 sets of drops on each track and level. Call it overkill or whatever, but it lets me sleep at night. I did not solder all the rails just in case there is a major track issue, the helix does not have to be ripped apart. Mine was custom made and would cost me a small fortune if I had to replace it.
In addition, I have all of my drops with 20 ga wire going to a track buss from the auto reverser. Works like a charm!
My helix is 22" radius and has 4 levels. The levels are supported by 4 posts (lets say they’re positioned at N-S-E-W. I ran the bus up the East and West posts and feeders to the rails. I used sections of flex track, which basically, ends up having a feeder every other joint.
I know lots of guys with large DCC layouts without all this “every 6-8 feet” feeder business and their layouts work fine. Why? Refer to my first question - their answer is yes.
But in a worst case, two bus locations 180 degrees apart, tapping each level should be more than enough.
I run DC, advanced cab control with base station radio throttles, detection and signaling. All my rail joints are soldered within each “block”, many of which are 20’ - 25’ long, each has only one feed which must run thru a current detector. No voltage drop issues.
32" radius amounts to 17’ of track per loop. The track length fed from one feeder/loop is 8.5’, reached from two separate points and ~0.15 ohm or 0.15 V drop at 1A.
If the feeder spacing is 8.5 feet, doesn’t that mean that the load (engine) is always less than 4.25 feet from the feeder? So, why isn’t the resistance of 0.00145 ohms per inch multiplied by 4.25 feet (51 inches)?
The postulated scenario states one set of feeders in 17’ feet of track. => Furthest distance a locomotive can be is 8.5 feet.
Sheldon,
Most locomotives now draw 1/3 amp or so. Is the OP running modern production equipment…
That 1/3 amp everyone throws around is the steady state draw of the locomotive measure current draw on a 30" curve with a 3% grade (or whatever this ends up being).
You are also assuming one locomotive will pull the train up this grade.
I think Greg’s comment of ‘reached from two seperate points’ clouded the issue. With one drop only, the 8.5 distance and voltage drop is correct. Robert’s conclusion,as well as mine, and maybe Sheldon’s, was that there were two seperate points where there is a drop. Rereading Greg’s post, he did say one drop.
Since we are on the topic of the helix, I would suggest making the helix its own power district, protected by a circuit breaker separate from other layout circuit breakers.
What I do know is it is easier to start both model train and real train on level ground than on a grade.
What I dont know is 1) if the OP has tested the ability of his locomotives to start a train on his planned grade and 2) will the locomotives will stay or slide backwards when power is secured.
With the small current draw of today’s locomotives, the issue in feeder size and spacing is no longer the voltage drop when running the locomotives. It is passing the “quarter test”. You want the circuit breaker to trip whenever there is a short on the track. With feeders too far apart a short will not trip the breaker.
i looked at The Great Feeder Experiment and have a hard time believing the results based on the description.
My understanding is he connected a 5A booster to a piece of 3ft flex track through
25’ of 14g
feeders of various gauge (18-26) and lengths (0.5 - 6ft)
am i correct?
based on wire resistance reported in the American Wire Gauge, i calculate the worst case wire resistance of 0.616 ohm for the 6 ft 26g case, total resistance for both paths.
if the booster supplies 15V, a short should result in 24A.
a more simplistic case is that 31ft of 26g wire has a resistance of 1.3 ohms or 2.6 ohms.
what am i missing?
i strung 54 ft of 30g wire, measured 5.8 ohm (5.6 according to the wire table) and 1+A bulb on my PowerCab lit up.