DC power-supply wiring question

[scott]

We've been having some problems with train sputtering out, hanging up in certain locations, etc. I just ordered a bunch of track-cleaning supplies and will work on that angle this weekend.

 

But I'm wondering if there could be power lost on portions of the track that are far from the power supply connection. Our main line, for example, has probably 30 feet of track (why does that sound so short?), and the power supply is an MRC Tech 4, either 220 or 260 (I can't recall at the moment).

 

Would it make sense to use a Kato 3-way extension cord to connect a couple more terminal unijoiners at points far from the main connection? Or would that make no difference electrically?

 

As you can probably tell, I'm a total electrical ignoramus, but any suggestions would be appreciated.

[David]

You can, and likely do, have voltage drop over longer stretches due to the higher resistence of the rails, and well as larger drops from loose joints (are you using Unitrack with Unijoiners, or track with conventional joiners - conventional joiners are known to wear out over time, becoming loose and thus harder for power to bridge. Many layouts solder the track joints for this reason).

 

Whether a voltage drop is the reason for trains stopping is a seperate question - do trains noticibly slow down? Dirty, uneven or misaligned track would seem the more likely reason for trains stopping entirely without slowing down first. With dirt or track geometry you can usually just nudge the train a little and it will start again, having been pushed past the minor obstruction.

[scott]

Thanks--yeah, we're using Unitrack with unijoiners, so that should be OK at least.

 

I'll check for misalignments while I'm cleaning the track. Over the weekend, we were trying out one of the new E127s while I was planting trees, and it would run at inconsistent speeds (slowing down, speeding back up) as well as consistently stopping at a couple of points. I couldn't find any misalignments at those spots with a quick check, but I can also go back over those spots with a brighter light.

 

So--dirty track or not, would it generally be a good idea to have multiple connections from a single power supply on a long track like this?

[David]

Yes, multiple feeders will help keep the voltage even, preventing trains from slowing down/speeding up for no reason. How many is up to you - there are people who supply feeders to every piece of track, others who do it every 3 feet, 6 feet, etc. If you plan on converting to DCC without having to rewire, every 6 feet would be a good starting point.

 

There are a number of ways to supply feeders:

 

• Use the Kato 62mm feeder track (or the doubletrack/viaduct equivalents) that connects with a plug.
  
• Use the Kato feeder cables, which are basically a pair of Unijoiners with wires soldered on, going to a standard Kato plug (these can't be used with Viaduct sections)
  
• Make your own Kato feeder cables using regular wire (cheaper then buying Kato's at $3 a pop). There are tutorials for doing this (ask), but it basically involves popping off the unijoiner, slipping the wire through in a certain way, and then reattaching it to make an invisible, tight connection)
  
• Soldering wires to the underside of the track. This takes some skill to avoid melting the plastic.
  

[scott]

Thanks, David. Sounds like 1 per 30 feet is pretty sub-standard. :-/

 

I found the tutorial on making your own connectors. I have a few extra terminal unijoiner sets, so I'll use those up first, but after that....

 

What I can't seem to figure out is how all these multiple connectors connect to the power supply. There's the 3-way extension cord that would allow you to do three feeders, but what if you need 5 or 10?

[David]

In a permanent layout wiring is often done using a bus (or more then one, when using multiple boosters/trip/block control). The bus is basically a line of higher gauge wire going from the power pack/boosters/block wiring panel along the bottom of the layout. Anywhere you want to add a feeder, you cut into the higher gauge wire and run some smaller gauge wire for the "last mile" connection.

 

For details of exactly how you go about it (so you don't get a short) consult the mighty google.

 

http://www.google.com/search?q=model+train+bus+wiring

 

The first link points out some differences between DC and DCC wiring restrictions

 

http://www.building-your-model-railroad.com/model-railroad-wiring-2.html

[scott]

Thanks for all the help with this--I'll do some reading on all that. Might have to learn a bit about wiring.

 

[bTW--for some reason, replies in this thread aren't showing up as "new", either in my "replies to your posts" page or in the DCC & Electrical forum.]

[KenS]

One thing to be aware of with Unitrack is that over time, the Unijoiners do become worn, and make poorer connections, and each poor connection effectively has higher resistance (less surface area in contact between the joiner and the rail) and higher resistance means higher voltage loss.  If you have a multimeter, you can check for resistance between two sections of rail.  A bag of new Unijoiners is cheap. Anything more than a couple of ohms is reason to toss the unijoiner, although a bad one is probably going to be 20+ ohms of resistance; I found about a dozen on a 30-foot loop of track after a couple of years of repeated connection/disconnections that failed my "more than 3 ohms" criteria and hit the trashcan, but only three or four were 20+ ohms.

 

Unitrack seems to work pretty well even when it's been in use for a long time without cleaning.  That said, a bag of cotton pads and a bottle of isopropyl alchohol (rubbing alcohol) will clean the rail quite nicely.  I haven't found any need for fancy cleaners.  Note that full-strength isopropyl alcohol may remove some of the paint from the ties, so you do need to exercise a bit of care to only clean the railtops, and not the whole track.

 

And, as others have said, loss in rail is higher than loss in a reasonably sized feeder or bus wiring, so multiple feeders are a good thing on any moderate-sized layout.  On my 30-foot loop I saw a visible speed reduction about 3/4 of the way around the loop (I had an insulator in one end, so power was going 20+ feet to reach the train at that point).  Once I got my bus wiring and "every six foot" feeders wired up, that problem went away.  See this page for a nice summary of voltage loss in wire and track at typical amperages.

[scott]

Thanks for the helpful info, Ken--I doubt our unijoiners are that worn yet, but that's a good thing to remember.

 

I've ordered some terminal blocks for connecting bus wires to feeder wires, and I'll check the hardware store for spools of wire. Looks like I have some hole drilling to do....I'm glad I learned about this now rather than after the track-side vegetation etc was done.

[KenS]

For bus wiring, wire sold as "primary wire" (used for electrical wiring in cars and other non-AC-power applications) is a good choice.  You can get it in 14 Ga. and 16 Ga stranded forms, and unlike power-wire (THHN and similar) it uses a lightweight, flexible insulation that makes it easy to work with.  I found some in my local Home Depot.

 

Crimp-on connectors (spade lugs) are useful for connecting wires to terminal strips, but if you go that route, it's worth investing in a good crimping tool.  The typical ones made from stamped (flat) metal are painful to use if you're doing dozens or hundreds of connectors.  A good one (found in better hardware stores or electrical specialty stores) have longer and rounded handles. Like this one.

[scott]

Thanks again, Ken--we have some primary wire on the way; 14 ga for the bus and 22 ga for the feeders. Let's hope I get some time to catch up on all this soon. It'd be nice to have things running better.

[keitaro]

didn`t want to tart a new thread this may be a stupid question.

 

currently have a 2 amp controller want to set 3 wires to keep power up through the whole track.

 

was wondering if it`s as simple as wiring to one of these http://www.hoscalemodeltrains.com.au/p397-Model-Train-Selector-Switch-Rail-Layout.html

 

and then switching them to on and plugging in to required area.

 

i have no idea about this so decided id`d ask or willi need to seperate the areas if i do this

[KenS]

If you mean to operate blocks using one of two DC power packs with a "common rail" wiring system, then yes it really is that simple, although it will use more than three wires.  One wire from each power pack is tied to the common rail, which doesn't need to be gapped.  Then you divide the other rail into blocks with insulators, and connect each gapped rail block through an A/B switch (to which you wire the other outputs of the two power packs).

 

You'll end up with lots of wires running from your central switch to the gapped rails (one per block) and you'll likely need a wire that connects to the gapped rail in several places since rail is a poor conductor compared to wire.

 

All those block wires is one reason people like DCC, since you can do that with only two wires (one per rail).

[keitaro]

ahh ok no i mean just one dc power supply connected to 1 line but connect the power up at multiple spots on the track to keep the power running smoothly across whole track.

 

i will be having 2 supplies 1 per line on the board.

[KenS]

Ah, in that case you don't need switches or insulators.  I'd use four wires and keep the two powerpacks completely separate, but you could make one rail on each "common" and connect one wire from both power packs to its bus wire and it should work (I've never done that though). Having multiple feeders from the bus wires to the rails without any gaps isn't a problem, as the current will prefer whichever path (rail or bus wire) has the lowest resistance at any given point.

[keitaro]

ahh ok awesome so i just need to get a branch wire for the tomix then?

[Martijn Meerts]

If you want 1 power supply per line, you'll need to completely isolate the 2 lines from each other using for example the plastic rail joiners. You can hook up as many wires to each line as you want though, as long as they're all from the same power supply.