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I'm planning a layout of approximately 120 feet in a big oval. I'm looking for advice on suitable power supplies (DC only, nothing special). I'm already running a couple tech II's on another layout, FWIW...
 

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If you wire a bus underneath the layout with periodic feeders (every 6-10 feet), up to your track, you could use pretty much any DC power pack. Conversely, if you rely on your rails to transmit power, good luck, no matter what power pack you chose.

A Tech IV is a good choice.
 

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I think a 14 gauge bus, or maybe 12 gauge, should serve you well, and then run a pair of feeders up about 6-8 feet, as suggested above. I don't know what your starting voltage is going to be, but if the maximum for DC is something like 12 volts in DC, then I would want 12 available to power all the way along the bus. If you go in two directions from the power supply, you could get away with maybe 14-16 gauge bus wires, but I'd still like a solid volt above the recommended high voltage output for the trains to run at their geared full speed and still have that left at the end of the line.
 

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I'm having trouble understanding the feeder wires - I solder the rail joiners when I use them, and they're thicker than the gauged wires cited... Can you provide more info?
 

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The rails of your track are very good electrical conductors but the rail joiners are the
electrical weak spots. Now if you solder every one of them, I agree you may not
need a bus and track drops. Even so, many, if not most, of us ensure good electrical
distribution by using a track drop every 6 feet or so. it is connected to an under table bus powered by DCC controller or
DC power pack. A little extra work but you won't find any low voltage spots in those hard to
reach areas.

Don
 

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It is true, the nickel-silver rails are very good conductors all by themselves. If they were monolithic and welded like modern steel rails, you would not have to worry about voltage losses over distance. But, when considering the paltry voltages we use in the hobby, and the low but necessary amperages the locomotive decoders must draw and mete out to the various internal components, it requires us to ensure robust voltage and minimal loss over our distances. As stated already, the joiners are flimsy metal sheaths that cover only a small portion of the rail surface. I mean REALLY small. Fractions of a couple of square mm. Yes, it's true. Look at one in profile, from the end, and see if you can tell how much of its inner surface area conforms to the surfaces of the typical brand of nickel silver rail cross-section. Splay that joiner a bit, or allow glues from setting the ballast to enter, and you have problems. So, prior to ballasting, you should drill small holes, drop feeder wire ends down them, and then solder smaller, bent, bared copper wire ends to the insides of the rails. The joiners immediately lose their status, and their 'obligation', to provide anything more than mere mechanical alignment at the joint. Where the joints are poor due to mismatched rail code heights, you can bend the joiners to align the rail head bearing surfaces, and THEN solder them. That way, the solder does two functions: improves electrical connectivity over the rail system and it aligns mismatched codes at the butted joints.

So, all that explained, the solders 'should' solve any problems, but they don't always. Solders can look okay but be incomplete, not sufficient to make a good connection, or they may be cold and have poor contact. The feeders, if done well, will neutralize any small breaks or defects at the many joints, even if every one of them is soldered*.

*You are not advised to solder every joint. If you have a finished layout room, inside a home, where the atmosphere is controlled and no wide changes in humidity are likely to occur, you could get away with it rather easily. In a basement, in a garage or an attic, or some other space that is essentially at the mercy of the outdoor ranges in temps and humidity, you must allow the track system to expand and to collapse at some non-soldered joints.
 

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An electrical bus moves power from one place to another. Use a good, thick wire (AWG12 may be overkill, but no harm in it). Solder smaller wires to this (you can also use suitcase connectors, terminal strips, etc), then feed them up and solder to your rails as mesenteria described .
 

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mesenteria made one small typo," and then solder smaller, bent, bared copper wire ends to the insides of the rails."

I do believe he meant to solder the wires to the outside of the rails.
Soldering to the inside will interfere with the wheel flanges.

Magic
 

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mesenteria made one small typo," and then solder smaller, bent, bared copper wire ends to the insides of the rails."

I do believe he meant to solder the wires to the outside of the rails.
Soldering to the inside will interfere with the wheel flanges.

Magic
Good catch. I missed that.
 

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I just finished reading/studying Larry Puckett's most excellent book from Kalmbach: "Wiring Your Model Railroad." This small book does an excellent job of explaining things like, "bus," "feeders," etc. Was a good read, even if it left me behind at places, and I am sure my first layout will be better and more successful for the read.
 

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Actually with care, there are reasons to solder the feeder to the inside of the rail. By soldering the rail closest to the viewer on the inside rail and the one furthest to out side rail, it hides the connections, you just have to particular careful - may help if you use a small gauge solid wire for the feeder. I like to use a PC tie for the connection, as then you can easily hide the entire connection to the the track.
 

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I find ballast hides the feeders rather effectively. Only a tiny little drop of solder betrays their location.
 

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I'm new hear and new to HO. What I do have is extensive electronics background. Nothing was said here about amperage and how much amperage one should have per say 100 feet of track. I fully understand the feeders and personally think 18ga solid core wire would be ample and of course here again that depends on how many amps are needed. I plan on building my own power supplies.
 

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Nothing was said about amperage because in DC, it isn't a limiting factor. You're not "powering" the rails, per se. They are a conductor, and a pretty good one. A typical power pack outs out 2-3 amps, which is enough to run a couple of locos. Since you can only control one at a time (or send the same control inputs to two or more), you run out of locos before you run out of amps.

In DCC, amperage becomes important because you can run multiple locos at a more or less fixed voltage. DCC operates at 14-ish volts all the time (constant power to the rails), each loco draws roughly 0.5 amps, so a 3 amp power supply lets you run about 6 locos simultaneously. Obviously, these are thumb rules; every loco is different. If you want to run more, you either get a more powerful DCC system or add boosters.
 

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Length of track is not in the amperage equation. Its the number of simultaneous locomotives running. new Locomotives are around 0.5 amps each while older one may be up in the 1 amp region. I use 22 gauge feeders, but keep them less than 2 feet and 16 gauge bus wire, but then my entire layout is 5x9.
 

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Got it, thanks for the response. So a 3 to 5 amp power supply at 14volts should power anything my grandson ran simultaneously, plus lighting, switches, and accessories
 
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