Feeders or soldered joints?

[lionelsoni]

I finally got my copy of the October CTT and found Phillip Hays's article about track very interesting. I believe his tests confirm my philosophy that feeders are usually useless when rail joints are soldered.

For example, consider a typical situation--a loop of track around a layout. Hays measured .004 ohm/foot for regular Lionel tubular O31 track, so the worst case resistance to the farthest point on the loop is .001 ohm per foot of loop. It is half Hays's value because it is halfway around the loop and half again because it is fed by the tracks in each direction, in parallel. This is coincidentally the resistance of two AWG10 feeder wires (one for center rail, one for outside rails) each half the length of the loop.

I have calculated the net resistance per foot of loop for various sizes of feeder wire, connected to O31 track:
AWG10 .00049
AWG12 .00060
AWG14 .00070
AWG16 .00079
No feeder .00100

Notice that AWG16, which is often recommended, reduces the resistance by only 21 percent. You have to go all the way to AWG10 just to cut the resistance in half.

But is it necessary to reduce the resistance at all? Suppose that the total length of the loop in question is 50 feet, with no feeders. The resistance, according to Hays, is .05 ohm. So even a very heavy train drawing 10 amperes of current drops the voltage by only half a volt!

The important inference from Hays's experiments, as I see it, is that most of the trouble with track resistance comes from the joints. Unless you feed every section (as Elliot does) or solder the joints (as I do), you can still have low voltage somewhere along the way: The track is only as good as its worst joint.

[Big_Boy_4005]

Thanks Bob. Just for those readers who may not have seen some of the other posts I made regarding why I use all the feeders, for me it is just a little easier. Because I use Gargraves, and lots of it, all I have to do is take a short piece of wire with a crimp on spade connector and wedge it up in the bottom of the rail, then tie that to the main feeder for that block of track. The splice is also a press on style, and I have a alrge supply of these leftover from the mall display 12 years ago.

One of the more interesitng results in that article, at least from my point of view, was that Gargraves has the highest resistance metal of any tested. It is more by luck that I have chosen the feeder method, so I have never had to find ot how bad it was. I'm guessing that if I was to solder 5 sections together, and place a feeder at one end, the drop at the other end would probably be noticable.

I'll admit feeders aren't the best choice for everyone, but they have worked well for me. I use 12 AWG for the main supplies to the rails. The short feeder branches are 16 AWG.

[lionelsoni]

Yes, that would be too much. Five 37-inch pieces have about .123 ohm resistance. AWG12 has only about .049 ohms for the same distance. However, if you were to feed every 5 sections, the Gargraves's resistance would be cut by a factor of 4 in the middle of the 5 sections, to .031 ohms, which would be quite tolerable.

With the size of layout that you apparently have, I think you would need feeders no matter what kind of track you used, although you could get away with feeding less often if there were any advantage to that. Actually, I wonder whether you wouldn't benefit from heavier feeder wire.

By the way, the electrical jargon for those "short feeder branches" is "taps".

[Big_Boy_4005]

That's right Bob, I do have a tendancy to do things on a rather grand scale, certainly larger than most. Most of my electrical blocks are actually going to be in the 12' -15' range, so if I was to place a single feeder near the center and solder a couple of joints that would easily do the job.

This past spring I had a chance to meet and talk with Jim Barrett from OGR when he visited one of the local hobby stores. I was explaining my monster project to him, including the plan to use TMCC.He informed of a number of issues associated it's implementation on complex layouts. Up until about a year ago, I was under the misconception that TMCC worked on a similar principle to that of DCC. In reality the TMCC signal is a radio signal, which has to be transmitted through the air from the ground rail, to the antenna in the locomotive. This allows for all sorts of strange things to happen.

The one particular to this discussion has to do with multiple taps on the ground rail. Jim was saying that it is helpful to place RF chokes in line with the ground feeds. When I explained my system of multiple taps, he seemed to think that I would need one choke per tap, at which point I cringed. Perhaps I need to go with the solder method on the ground rail, and the detection rails, but retain the tap method on the center rail, as that black anodization on Gargraves is so difficult to solder. Now would be the time to make changes.

[Anonymous]

Elliot:

Wow, I didn't know that Jim had said any of that to you. I've never heard any of it, but that doesn't mean he's wrong. He's more likely to be right than I am, that's for sure.

Tony

[Anonymous]

Lionelsoni---Your post was interesting. It is good to see how the experts do it...on paper. I have no training in electronics but I have quite a bit of practical experience from the College Of Hard Knocks. Without ever having studied voltage drop over distance I did have a noticeable drop in the speed of my train half way around a loop approximately 50 feet in circumference. Even running thick wire feeders only helped in spots (using sectional track). The thing you haven't figured into your equation is corrosion at rail joints around the pins. I have a policy of soldering jumper wires across each section of track thus not having to worry about poor connections between the sections of track. Also corrosion and collection of gunk from using fluid track cleaners are prevented from causing dead sections and even open flames at joints. Fire??!!? Yes fire. Over the years I have had one third rail joint flare up like a match lighting and I have inadvertantly burned my fingers at hot spots on my tracks. This has stopped now that the track is hard wired in place. Voltage drop is alleviated by the use of thick wire feeders. Hope this helps us poor undereducated hobbyists out here in the hinterlands. Odd-d

[Anonymous]

BTW I forgot to mention my bad experience with soldered railjoints. I strongly recommend that you don't do it. Back when I was doing HO I soldered my flextrack together and was forever cursed with expansion and contraction of the benchwork due to the hot steamy Georgia climate causing my track to buckle. Also I soldered pieces of O gauge sectional track together for reasons of conductivity only to find that it was a real beast to change the layout without removing all the sections soldered together and unsolder them. I used under the table jumpers from section to section. If I want to remove some track I simply pull it apart and snip the jumpers. Good luck. Odd-d

[lionelsoni]

Actually, I started soldering my joints just to solve the problem of getting one piece (like a switch) out without tearing up the whole neighborhood. The trick is to leave out the track pins! I flow solder into the rail heads and also put a lump over the rail flanges. It takes a little practice; but I can make a pretty clean and smooth joint. To get a section out, I just suck out the solder from each joint and unscrew it from the table. I have never had trouble with expansion and contraction. That may have something to do with having the layout inside the house.

The reason I didn't consider track joints in my analysis is that their resistance can be virtually anything, from almost zero to infinity, as you have so dramatically experienced. So, to get predictable performance, it's either soldered joints or a feeder tap to each section, as Elliot does.

[cnw1995]

This is a very helpful discussion for me. Thanks for all your insights.

[Big_Boy_4005]

QUOTE: Originally posted by vitabile

Elliot:

Wow, I didn't know that Jim had said any of that to you. I've never heard any of it, but that doesn't mean he's wrong. He's more likely to be right than I am, that's for sure.

Tony

The other suggestions had to do with shielding of layered tracks, and signal confinement for multiple tracks. The other forum is much more of a techno haven, and some of the guys over there have learned a lot about some of this stuff.

[Anonymous]

QUOTE: Originally posted by Big_Boy_4005

QUOTE: Originally posted by vitabile

Elliot:

Wow, I didn't know that Jim had said any of that to you. I've never heard any of it, but that doesn't mean he's wrong. He's more likely to be right than I am, that's for sure.

Tony

The other suggestions had to do with shielding of layered tracks, and signal confinement for multiple tracks. The other forum is much more of a techno haven, and some of the guys over there have learned a lot about some of this stuff.

I know about the sheilding for tracks that are on multiple levels. There's also a need to ground any metal bridges that your track might cross in order to preserve the signal. The stuff about the chokes is news to me, though. Though, given the nature of the signal, I suppose it's to be expected when you're building an empire in a basement.

Tony

[3railguy]

My practice with tubular track has been to solder a small bead (blob) of solder to the side of the adjoining rails after the track is assembled. Just enough solder to make an electrical bond. When removing track, the bead can be easily cut or ground apart making the track reuseable..

[lionelsoni]

John, are you familiar with solder suckers? They are cheap and a lot easier than grinding. (I'm still using the one I got about 35 years ago.)