Another Possible Cause for Sound Dropouts: Too Few Track Feeders?

[tehachapifan]

I'll be sure to pick up a multi-meter soon.

Something that's always sort of confused me regarding the run-a-bus-wire-under-the-track concept is, doesn't that just sort of mimic what the track itself is basically functioning as? I mean, how often does this bus wire itself need to be fed by a power feeder? Why is running what, in my mind, basically amounts to another set of rails under the track any different than the track being its own bus, if you know what I mean (aside from maybe overcoming a poor connection at a rail joiner, but wouldn't that depend on the number of track feeders regardless)? Am I way off track here? Remember, this is a table layout and not a module setup, where I can understand you don't want a ton of individual feeders running to each module and this under-the-track bus is probably the only way to really go.

Let me ask this another way....

If you wanted to power an oval track in, say, 3 spots on a 4x8' sheet of plywood, would you run a matching oval bus underneath the track with feeders coming up or would you just run some wire basically straight out from the power unit, maybe via a terminal connection of some sort, to each point? Is there a clear advantage with one over the other?

At any rate, I'm now looking for some good terminal connectors, T connectors, etc., to try to make this go a little better. I've seen some recommendations after doing a search here but the ones that come up as the clear favorite seem a bit pricey and perhaps a bit of an overkill for this purpose. Anyone know of any other good connectors? I had been using 22 gauge stranded wire, which seems to be working OK so far.

PS- It sure is nice being able to ask dumb questions here again without fear of being down voted off the island!

[MK]

Good question!  I can see where the confusion can be by running another "set of tracks" underneath the real tracks.  Yes, your tracks above can be a bus.  The difference between it and the real bus underneath is that it has connections and where there is a connection, things can go wrong and transmission can drop a little.  So if you have a bunch of connections, add up the flaws and you can get some serious drops the further away you are from the power source.

But, the bus underneath is a) a continuous run and b) much thicker gauge so there's much much less resistance than your tracks.  And like Peteski said, once you have a solid bus, you only need 24 gauge wires as feeders if you keep then short (under a foot).  But if you don't have a bus, and you start running feeders from the command station or power supply, then you really can't use 24 gauge wires as they will be too thin for the longer runs.  End result is that you'll be running a bunch (many) of thicker wires, all originating from one spot.  Much simpler if you have a big bus underneath and use short, thinner wire for feeders.

[peteski]

To get a bit more technical (yeah, you going to love that  ), every electrical conductor (in your case metal tracks, metal wire) has a certain amount of resistance.  Per Ohm's Law, the larger the resistance is and larger the current passing through it is, the larger the voltage drop across the resistor (in your case piece of metal track or wire).  Also, every joint of the conductors (track, wire) also has resistance, so it all starts to add up.

Why double bus?  Nickel silver metal used for N scale track has much higher resistance than copper wire.  So while you could use just the track as your bus (feeding power directly to your trains), the resistance from the point you are feeding the power to the track to where your locomotive is, would quickly add up, causing (per Ohm's Law) voltage drop.  If you have unsoldered rail joints, those are also points of higher resistance, causing more voltage drop.

If you have the track as one (higher resistance) bus, and a paralleling  heavy gauge copper wire (lower resistance bus), and you connect them both with copper wire feeders, the electricity will travel through the path of least resistance (mostly through the copper wire bus, then through the shortest path over the track), and will get to your locomotive that way.   That will give you low voltage drop.

This double bus with feeders is actually a complex resistor network (since ever piece of metal in that circuit is a resistor), but you really don't need to think of it that way. Just think of it as the current feeding the model traveling over a path of least resistance (mostly over the copper wire and feeders, then over the track to the model, using the shortest path between the feeders and the loco).

Even if you do not have a heavy copper wire bus but only bunch of feeders all tied together at some location under the layout (like MK mentioned), the feeder resistance would likely be less than the track resistance, so even that method would be better than just using track to feed the power to your models.

As far as terminals go, if you do not want to go the bus route, I would recommend standard crimp terminals and screw-type barrier blocks.  Cheap and reliable.

[tehachapifan]

Thanks for the additional info, MK and Peteski! All makes perfect sense. I'm not opposed to running the bus under the track in principle, it would just be pretty difficult to do so in a few areas on the layout due to areas of finished scenery, etc. The best I might be able to do is sort of a hybrid setup with a bus running in the general area and, in some cases, longer than 6" or 12" sections of track feeders running from the bus to the track (maybe up to 18" or 24" in some spots). Now, for my next and I think final stupid question. In my oval track example with a bus wire running under the track, is it recommended to connect the bus wire ends back to each other with DCC? My assumption would be that this is fine, but... I could probably look this up somewhere but might as well close it out here.

[peteski]

With DCC I don't see any problems electrically looping both tthe track and the bus under the track.  But DCC complicates things slightly. DCC is actually a type of a square wave (more AC than DC) and that complicates things a bit.  The bus, and the track (which is the other bus) have other electrical properties like capacitance and inductance, which can affect or degrade AC or pulse type of signals. The DCC signal is pretty robust, but it can be affected by the inductance and capacitance of the buses and the overall wiring.

The bottom line (to keep this simple), if the loop is small (like on a HCD or a 4x8 plywood), then it really shouldn't make a difference whether the track and the bus are connected as a continuous loop. But on a larger loop, I would leave the loops open (both the track and the wire bus under the track) at the same location).  Then I would feed the power on one of the open ends.  If you want to be on a safe side, you could also leave the bus and the track loop open on your layout.

[tehachapifan]

OK, thanks! I'll leave it open. I once knew how many feet the mainline run is, but it takes about 7 minutes to return to the same spot at a realistic (mountainous mainline) speed. That's definitely bigger than an 4X8' oval!

...I just went out and measured the double-track mainline run and it comes out to approx. 167' before it returns back to the same point which, if I did the math correctly, is almost exactly 5 scale miles. This is on a 6X 17' table layout where the mainline winds up basically 4 levels and then back down a helix. When I went out to envision trying to run the under-track bus, I just can't see doing it now. Seems like running straight shots between the power source and various points on the track would be easier and would be shorter runs of wire. If I did do the bus, how big would the bus wires need to be to run along and power 167' of double track? Or, would it have to be another set for the second track? Seems like I would still get a power drop at at least the fartherst end if I don't connect the ends back to each other....but that's a complete guess.

[MK]

Yeah, what Peteski said.  . As for what type of wire for running the bus, that leads to philosophical debates all day long.  Some people say12 gauge, some say 14 gauge.  I personally use 14 gauge solid only because when you get to 12 gauge it's hard to work with, especially around tight corners and bendd to go through holes, etc.  Sme people say use 12 gauge stranded but I don't know if that's easy to get.  I know you can get 14 or 12 gauge solid wires at Home Depot all day long.

[Jbub]

And then we can talk about twisting the bus wires together, boosters and all that jazz...I can see why some avoid DCC, out can be a lot to take in.

[tehachapifan]

Thanks, guys!

And then we can talk about twisting the bus wires together, boosters and all that jazz...I can see why some avoid DCC, out can be a lot to take in.

To be fair, my wiring was pretty substandard when my layout was still all DC too. All thing considered, things are actually working surprisingly well given the circumstances.

[peteski]

And then we can talk about twisting the bus wires together, boosters and all that jazz...I can see why some avoid DCC, out can be a lot to take in.

It really  isn't *THAT* bad.  For most home-size layouts, none of that jazz applies. Russ' layout is a perfect example: He didn't apply any of the DCC wiring best practices and his trains still run just fine (with just few slowdowns). But he doesn't loose control due to severely degraded DCC signal. So in most instances DCC really *IS* very simple to wire.

Only on huge club-size layouts problems can occur which will degrade the DCC signal quality bad enough to really require to apply best practices (and sometimes even snubbers too).

Russ,  A single bus can feed both tracks on a double track line. 12 or 14 AWG wire would be ideal.  It sounds like your entire layout is a single power district (one huge "block").  You are probably a lone-wolf operator (no multi-person operating sessions).  If you conducted operating sessions you would want to divide the layout into multiple power districts (blocks) with a circuit breaker for each. That way someone running against a switch in a yard while switching cars (and shorting out) would not affect running of the entire layout).

But still, with the length of main line that you have I would recommend breaking it down into few smaller blocks. Both the track  (gapped), and the wiring under it.  That makes troubleshooting of shorts much easier (if and when something goes wrong - and it will - trust me). Even if they are still powered from a single booster, you can quickly disconnect blocks and narrow down where the problem is.  Each block can have its own short-bus and all those would then connect to a barrier strip terminal which feeds them all from a booster.  If you don't think you can really implement a full bus method, you can wire the feeders from each block together (in a "star" arrangements, so all the feeders are tied together at a central point which the is hooked up to the power distribution terminal).  Or you can run sub-buses where a short heavy-gauge wire bus distributes power to the block's feeders, then that goes to the central power distribution terminal.  Just like your electric company's power grid.

[tehachapifan]

Thanks, peteski! I think your star arrangement suggestion may be far more doable with my layout. If I was to start a layout over from scratch, I would do the under-track bus thing for sure, but at this point the star setup is probably the best. I'll also consider separating blocks as you suggest.