Lets talk about wiring

Model Railroader Electronics and DCC
21

I used #20 for my track feeders - I used red and white #12 bus wire (#14 on the last one because it was a much shorter run and since I had to buy the wire, #14 was cheaper). The #20 was also red and white, came as a loosely twisted pair, it’s used for alarm switch wiring. The #12 and #14 was stranded - much easier to work with under the layout. The #20 was solid, better to make neat feeders. Soldering the small wire to the bus isn’t hard - you need somethign bigger than a 25 watt soldering iton though. This is where that big 100 or 150 watt soldering gun comes into play.

At voice frequencies, much of the twisting IS to keep it neat and bundled together. Crosstalk isn’t a huge problem except in the longest runs (like, miles along the poles or underground). For faster stuff like network, the twisting is critical, but still mainly for controlling capacitance. the impedence of a capacitor is dependent on the frequency - too much capacitive impendence will weaken the signal and/or distort it, reducing effective cable length.

Loconet gets away with flat phone wire because it actually tuns at a relatively slow speed - 16457 baud. The capacitance of flat wire is such that the signal can stay within the Loconet specifications for up to 1000 foot runs. I WISH I had the layout space where this would start to become a problem (they have Loconet repeaters if it is!).

–Randy

22

I was hoping for a comment. I was told that something in the signature was making my post go off page, so yesterday, I deleted them, which is whole nether story.

Back to wiring Rock Ridge!

Mike.

23
  1. Twisted is easier to bend. Solid is a little more robust and cheaper. But it also helps hold the wires together.

For your garage sized layout, you can get away with 16 gauge with #20 feeders every 3 feet or so easy. I use stranged 16 gauge on my son’s layout. Just google “Wire Voltage Drop calculator” to figure out what you need. Stay within 5% and you should be good to go.

  1. Twisting wires is a way to reduce signal interferrence. (Noise)

I use these to hold my power bus across the layout.

https://www.lowes.com/pd/Gardner-Bender-50-Count-3-4-in-Plastic-Insulated-Cable-Staples/4634631

BTW: I color code mine

Blue = DCC+

White = DCC -

Black = ground

Yellow = +12VDC

Red = +5VDC

Green = 18VAC +

Orange = 18VAC -

24

Some people suggest feeders on every piece of track. They say that one should not trust joiners for electrical connections. I suppose I could trust a joiner up to the point of failure…I do have a multi-meter. What about turnouts, do you wire every one?

25

For once that you can, like Atlas. I never had to hook up my frog power wires ebcause with power feeds on all 3 legs, every other part of the turnout had a reliable power connection and even a ittle 44 tonner could creep over the dead frog area. WHat I did on my last two layouts was make every rail joiner a power feed - basically stacks of terminal joiners. Even after painting the rails, including the joiners, there was never any loss of power.

–Randy

26

Okay, second set of questions:

  1. I plan on using 3V LEDs to light my structures. I have a multi-voltage transformer with a 3V setting.

1a) Should each LED have it’s own run or can I wire them in parallel?

1b) How can I tell when the transformer has reached capacity short of the white puff of death.

1c) How long a run can I make using 22 guage wire?

  1. I have an 800w power supply from a computer that delivers both 12V and 5V. Has anyone used one of these suckers to power layout accessories? The LEDs I’m looking at come with resistors for use with 12V. Seems it would be a well modulated power source.

2b) for Randy–would this work with your servos?

27

Mouse

White LEDs consume about 3.5V. But you need a current limiting resistor too. I recommend 5 Volts.

The math works like this:

5V (in) - 3.5V (LED) = 1.5V left over.

Let’s say you wanted to run 10ma per LED (Pretty bright)
1.5V = .010amps * R

R = 150 Ohms.

So a LED + one 150 Ohm Resistor will light a single LED.

1a) LEDs don’t work like incandecent lights. Every time you wire one into the circuit, there’s a voltage drop. If you hook two into series you would need 3.5V + 3.5V = 7 V + a resistor drop. I would recommend wiring them in parallel.

1b) using 10 ma for each 5V circuit you could literally run 100 @ 1 amp.

1c) depends on how much current you pull through it. Run the numbers through the voltage drop calculator to find out. Stay within 5% voltage loss. (.25Volts drop @ 5 Volts out)

  1. There are tons of videos on youtube showing up to turn a computer power supply into a regular power supply. It’s easy. But you’ll need a sandbar resistor to keep the power supply from shutting off. (It’s looking for a power good pin to be high on voltage) But for Safeties sake, divide it into blocks and put a 3 amp fuse on each block. Also if you are only using a little power <15% rated capacity, the efficiency of said power supplies drops off a cliff. That means you’ll pay more for the same juice over a dedicated low power supply.

For my layout, I use a 400 Watt computer power supply. But for my sons, I home built a small power converter that uses 3 L7812 chips to supply 3 amps of 12 V power and 3 L7805 chips to supply 3 amps to the 5V. I run it off a left over 19 Volt laptop power supply.

28

The MFR says that the LED is rated 3-3.1V. Should I still go with the 3.5V?

So let me see if I have this straight. My Rockipeutians would have been using candles, fireplaces, and lanterns for light, so 10ma would proably be too much. I’m guessing I’ll have to experiment to taste, but lets say I go with half that 5 ma.

5v-3.5v=1.5v left over

plugging into Olm’s

1.5v=.005a * R

R=300 ohms

Now, can I use one resister for the entire circiut or do I need one for each LED?

So you think 800w to power 25 LEDs is a tad overkill?

I have 2 DC power supplies. I have a Bachmann unit that came with my EZ track Hogwarts set which I plan to use to power my turntable. I also have a Mech II I was hoping to sell to help fund my layout project. I also have the adjustable transformer that I could set to 5 (or 6) volts. I guess any of these make more sense than using my power supply.

Will the LEDs work on AC?

If not, do I stick my multimeter on the terminals of the rheostat and duct tape it when it hits 5V?

29

If your spec sheet says 3.1V then trust the spec. 3.5V is a rough average for white LEDs

Resistor for each LED. Each circuit is wired in parallel.

800 watts its a tad bit on the heavy side unless you want 8000 LEDs

Be careful of those cheap bachmann supplies. Mine is rated for 16VDC, and it was outputting 25V! I had two fail right in a row.

LEDs will work with AC most of the time. However you may notice a 60Hz flicker as it turns on and off quick. Most LED christmas tree lights work this way and you’ll never notice it unless you try to film it.

30

I planned to use the DC output for the turntable. The motor is rated at 7V, so I thought I would find a good speed for the TT on the Bachman and leave it there, then use a DPDT switch to run it. Do you think that would be an unreliable method?

Those Rockipeutians do love their strobe parties. I hear the red spotted muchrooms grow in that part of the country.

31

One LED, one resistor. Use the specs of the LEDs you are using.

A computer power suppyl works, but many don;t regulate wellw ithotu a decent load on them. A handful of LEDs will not put much of a load on it.

How many LEDs before you smoke a power supply? Well, you did the calculations - you just don’t know you have answer. If you put resistors on each LED to limit the current to 5ma, then 10 LEDs will be 50ma, and so forth. Each LED/resistor combo gets wired in parallel with all the others. So you jsut add the currents. Don;t load the power supply to more than 75% of its rated output. So for a 1 amp wall wart, 750ma. That’s 150 LEDs if they are all configured for 5ma.

–Randy

32

Wow man!!! far out!

Mike.

33

Chip, sorry to resurrect this part of the conversation, but I would recommend only soldering every second set of joiners, and using the soldering process to affix a feeder to the same joiners. That way, you get positive electrical transmission from that soldered joiner pair outward in both directions for the distance until you encounter the next set of joiners.

In graphic form:

======X=======0========X========0====

You solder only the X’s and leave the opens to slide and to let your track system adjust to changing temps and humidity as needed. If you use DAP Alex Plus with silicon for the adhesive, it will be rubbery and let your tracks squirm just enough to prevent the wows and kinks. (Please only use the stuff that dries ‘clear’. I was not the least bit happy with whatever the ‘white’ stuff is, but the 'clear variety held well and didn’t show up as much. Note that it is white in the tube, but will dry slightly clear/yellow).

But the point really is to only have to solder every second length of flex, not every length, and that applies to feeding each with robust power as well.

-Crandell

34
  1. I think you mean solid versus stranded.

https://dccwiki.com/Wire_Types

  1. Data cables use twisted pairs, and
35

Love this.

Makes sense o me.

36

You have now hit upon the way I tried to tell a club I belonged to, but they insisted on wiring each 3’ section. Also, they insisted on soldering the feeder to the side of the rail. I laid some (and they didn’t know this) with the feeder wire soldered to the bottom of the rail. This was done prior to actual installation. i.e. do this soldering at the table/workbench. Then, as I put the track in place, carefully marked where to drill the hole and placed the track down and that wire was hardly noticable at all. Hidden by ballast. So if you were to solder the feeder to a rail joiner, could be done the same way. And soldering a rail joiner at the “X” to make a totally solid connection. And excellent way to lay track. Leaving that expansion joint every 6’ is also good/great. Needless to say, I don’t belong to that club anymore. One other thing they did I didn’t agree with, was the use of those plastic connectors/suitcase connectors?. I soldered/PERIOD. But I only laid a siding and they got angry with me because I didn’t follow their “standards”. I know some don’t like soldering, but talk to any electrician worth his salt and he’ll agree about soldering.

37

Comments about breakers and house wiring really don’t add any pertinant info to a discussion about layout wiring. The Natural Electrical Code tables used for such impose limitations because of things not normally present under a layout and the type of insulation on the wire

For example, #14 NM-B (Romex) is limited to a 15 AMP breaker in most applications, but is rated at 25 AMPs in the code book. Those same wires not in a cable, but in free air (under layout wiring) are rated at 35 AMPs.

The meat of the thing is that a #12 buss wire on a 12 volt supply will supply about 11.2 volts at 5 AMPs at 50 feet, about a 6% drop, or 11.77 volts at 25 feet, a 3+% drop. At a 2.5 AMP load, the drops are about 3% and 1.5% respectively. Also keep in mind that if you use rail joiners (I don’t) and feed each or every other piece of rail, the voltage drop will be even less as the rail will act as a parallel conductor.

A #24 wire will give roughly these same results in 2 feet, a bit of a caution in trying to use too much small wire in hooking up loads, like a foot long piece from rail to feeder.

Communications cables are twisted to BASICALLY eliminate two things. Crosstalk between pairs and 60Hz noise. Quite a science involved to reject all this stuff and is why different pairs are twisted more or less times per meter than others.

38

What Selector said is exactly what I did. I soldered two pieces of flex together, then connected it to another 2 pieces soldered together, but did not solder that joint between the two. However, I did have feeder wires to the joiners between the two sections as well - other than where I needed an insulated joiner, EVERY joiner on my layout had power feeds. Overkill? perhaps, but I never had stalling issues and I never cleaned my track. I barely dented a spool of the #20 wire I used for the feeders - even with a 12x15 or so around the room layout, there aren;t as many track joints as you might think, at least when using flex track.

–Randy

39

LION did NOT read the whole thread, but there are some considerations that you want to take into account…

HO scale amps are different from 110 volt amps.

Our place has 40 amp breakers out on the utility pole, but that is at 4600 volts. We have dozens of 400 amp fuses (breakers) inside our building at 110 volts. On the layout Amps are measured at perhaps 12 volts.

So if you have so many lamps on your layout and they draw say 3 amps at 12 volts (a reasonible number and fused as such) the transformer will draw a small fraction of an amp on the 110 volt side.

Ergo you do not size your 110 volt fuses for what your layout is drawing on the 12 volt side, but rather how much amps are the transformers drawing on 110 volt side of the layout.

Layout of LION draws perhaps 25 amps on the HO side of the layout, but only 2 or 3 amps on the 110 side of the system.

WHEN installing bus wires under the layout, I use either 12 or 14 ga wire, not because my power supply puts out 15 amps, but because electricity tries to travel on the outside of the wire not on the inside. 12 ga wire has more outside than a 22 ga wire, and thus it can carry the required power for longer distances with less resistance losses in the wire.

Some people tell me I am full of LION POO, but it is the SLOWER speeds that you loose with the smaller wires. This is because you must increase the voltage to move the power through a small wire than you would require with a larger wire.

Look at the power pole outside of our buildings, they are pushing power at 4600 volts through relativly small wires, once they pass the transformers (ostside of the building) the same power requires much heavyer wires, mutiple wires in fact for each leg of the transformer.

I do not need the big bus wire for 15 amps at 12 volts, but the trains sure know the difference. But again smaller drop wires from the tracks to the buys are fine, they travel only a short distanc

40

Thanks for the info, Lion.

LOL

Mice are pretty cheap, too. But you left something out. It’s even cheaper if you have half a 500 ft roll left over from when you wired home networks.