I know you guys have missed me, so here’s my next unbelievably Electronics 101 question. Yes, I could study wiring books, and I actually have been studying Atlas’ Wiring Your HO Layout by Paul Mallery Associates, which is thorough enough and has great illustrations but was written in 1958. I thought it would be a good place to start and it’s been useful. But a lot of water has gone over the dam since then, so I figured I’d see if I could rouse some of you guys from your Independence Day torpor.
Below is a crude drawing of my layout with (almost) all the turnouts lettered and each of the three joints for each lettered turnout given a unique identifier. (A1, A2 and A3 for turnout A, etc.) Some turnouts are back to back with others, or back to front, so some joints share a number (B1 and C1 are the same joint, for example, as are G3 and J3).
To see at max resolution, click open, then close, then click image open again. (I don’t know why.)
Things to note:
There are no reverse loops, but the yard lead (such as it is) connects to the main at both ends.
Currently the whole mainline runs on just two feeders from the DC pack or DCC power cab directly to the rails. Trains seem to be happy and do not lose power at the far end.
All frogs are dead, for the moment, although I may change this because I don’t like how some of my locos hiccup a little going over them.
I plan to run a bus line under the mainline, waggling it a little like a radio wave to enable shorter feeders from the branch, spur and yard tracks. I’ve got 14 gauge for the bus, and 22 for the feeders.
What I want to be able to do in DC is to isolate the yard and the branch from the mainline – I guess we call that creating blocks – so that I can run trains separately in all three at the same t
I’m old school and for a small layout like yours I would go with block wiring and forget buss wiring.
When I wired my layout I went with two conductor twisted pair #19 AWG Bell wire home runs back to my control panel. Each block has a DPDT center off reversing switch.
That will work with both DC and DCC. Each home run will handle 2 amps which is more than sufficient for two locomotives in each block.
My layout has a total of 28 blocks, the mainline has 10 blocks the rest are yard and sidings. My mainline is 121’ so about 12’ blocks.
It has worked fine for me for over 30 years both on DC or DCC.
EDIT:
I thought I should explain the switches on my control panel. They are mini toggles with colored slip on covers on the handle.
White is lighting – SPST, ON-OFF
Red is turnout control – SPDT, On-OFF-On momentary.
Blue is Block Control – DPDT, ON-OFF-ON (Reversing)
Green is turntable control - DPDT, ON-OFF-ON (Reversing) & OFF-ON momentary
Yellow is Special – DPDT, ON-ON (Track continuous 12 volts DC power for charging on board batteries)
Mel
Modeling the early to mid 1950s SP in HO scale since 1951
I use DCC and I would recommend feeders at each 36" of track - more if you have many joiners. So the simplest way to do this is to run a bus wire. But if you plan on having many DC blocks, then a common bus makes no sense. Looking at your layout I can see two locos running, one on the mainline and one on the yard. Three blocks should suffice. So 3 sets of bus wires maybe?
You only need to put isolating gaps in one rail to create a Block in DC. The other rail can be continuous (common rail if using more than one Cab as you indicate you will be). However, if you want to create Power Districts for later conversion to DCC you can put isolating gaps in both rails at each end of each Block. For convenience you can just wire one rail in common for now. You will want to convert to DCC from your description of desired operations. One DCC system will do what you’ll need three DC powerpacks to achieve. You’ll want sound. If it were my layout I’d double gap/isolate each Block and wire up a two wire bus for now. You only have the one DC locomotive. Don’t buy another unless you can’t resist it. Buy DCC with sound and convert to DCC as soon as you can.
For your immediate DC requirements you wire the other rail as the power control rail. Block power control requires at least a SPST power on/off switch to be included in the power feed for the one rail you select to be your power control rail. Atlas yellow button Connector switches are panels of three of these. This only works for you if you have only one powerpack (a single Cab layout). You can’t control more than one train concurrently with one DC powerpack. You can run one train and leave the others on powered off Blocks. You can use SPST power control for a DCC layout. Turning power off to only one rail is enough for DCC Block control. To achieve power on/off Block control means you can’t use a two wire bus anyway, the power control rail has to have separate power wires back to your bank of SPST on/off switches to allow Block power control.
You describe a three Cab DC system. If you wish to have more than one Cab powering your DC layout fitting a SPDT into the power feed to the control rail to each Block will allow connection of two DC powerpacks creating the ability to run two trains on the one layout. Atlas green button Selector switches are panels of four of these.
If you’re going to run DC locomotives, the best thing to do is to wire the layout as two-cab DC. You power each block with a DPDT center off switch. Two wires run from each block to its own switch. You can assign any block to either cab, or shut it off. True, you can’t run more than two trains at once. I don’t like to run more than ONE train at once, so I don’t see the point.
You’ve got a lot of what appear to be gapped rails–too many for me. For example, D, E, and F should be just one block. The pink “main” over on the left, should also include at least the two switches (G and A). C and B should be just one block. The two J switches should be a single block. That crossover setup in the lower left just might should be left alone. Some thought might resolve that.
One of the ways of figuring out block placement is to imagine running trains on it. Will it work?
Looks like you then have about 15 blocks. That’s 15 switches laid out on a track map.
I wouldn’t use the Atlas switches. They’re too big and too limited. Just use “regular” toggle switches.
You can use really teeny wire as a drop from the rail above to down below. 22 gauge, or even smaller. That’s because you will use a VERY short piece of it. Below, you will connect to the bigger wire, and run back to your DPDT’s. 14 gauge is not a bad choice, though you could likely go smaller. This all assumes you’re soldering the 22 gauge wire to the rail. You might also consider soldering SOME of the railjoiners. Every section of rail that ends in an unsoldered rail joint should hae the 22 gauge tap wire. You should never depend on slide-on rail joiners for electrical continuity.
When you want to run DCC, you replace one of the power packs with you command center. MOST people will also suggest y
Woops. Sorry, Ed. None of the joints are gapped. I just drew them that way so we could talk about the joints and see the locations we were talking about. The turnouts from the main into the yard/branch and all the turnouts (curved and straight) inside the yard are so far joined only with rail joiners. The west side of the mainline is pretty much all soldered both rails at each joint, except the west siding turnout. I wanted to get all this good info before I added gaps or plastic rail joiners or dropped any feeders.
All these responses are very helpful, and especially your assesment of what blocks make sense.
In reading back all the way to Mel’s response, I keep wondering if there’s a piece of this I’m not correctly imagining, and it’s about the location of the DPDT switches. If the switches are on a central panel, then how are they wired to the block’s rails? Because the feeders have to be very short. So when we talk about block wiring, are we saying that each block has its own bus that runs out from the DPDT switch on the panel to where that block’s feeders come down?
The RAIL feeders should be very short. That’s because they’re very small. And that’s because big wires soldered to your track look stupid.
Once those teeny wires get down below, you can connect them to the bigger wires that travel farther. In this case, to the center two terminals on your DPDT center off switches. Those wires feed power to each and every block you are creating.
You might find that a block has three track sections, each with two wires hanging down. You’ve got to “tag” each of those three with your fat wires.
So now you have two wires from each DPDT center off (center terminals) to each block. HOORAY!
What’s next?
I’m gonna be mean, and tell you to look in the books. NOT because I love being mean (which I do), but because they explain it much better, with pictures with circles and arrows…
Persevere, Horatio. Because when you’ve waded through this once, you look back and think: SO obvious.
Remember when getting a spoonful of Cheerios into your mouth was a challenge? Not anymore, I’ll wager. Same thing.
We’ll help you out! But not with the Cheerios; you’re on your own there, pal.
Yes, if you use a DPDT to control power to each block then you have a separate two wire bus to each block from the output side of each DPDT.
One input side of every DPDT is connected to one powerpack (Cab A) and the other input side of every DPDT is connected to Cab B.
This takes more wire then a simple two wire bus you would fit for a DCC only layout. But, it automatically means each Block will receive the full voltage direct from the powerpack through the gauge of wire you select for the Block wiring.
Two wire Block wiring is parallel wiring. Two wire bus wiring is series wiring for most of the length of wire. Voltage drop effects in parallel wiring are a lot less of a problem because you are powering only one locomotive per circuit.
The feeder wire gauge is less important because the feeders are short. Shorter the better to minimize voltage drop.
Another advantage of DC Block wiring even when running DCC is each Block is powered by its own bus which reduces voltage drop issues. Commonly you would actually be running each train in its own Block most of the time even when using DCC. You can only run one train per Block in DC mode.
That’s why I recommend you consider wiring your Blocks with one common rail powered by a heavier gauge bus wire and use single rail control to power the Blocks. SPDT switches controlling only the one rail will work for both DC and later DCC for your relatively small layout. The gauge of wire for the control rail Block sections can be smaller because typically only one train would be operating in each Block even in DCC mode.
Of course, I still recommend you consider wiring in a DCC power system right from the start. Stick a motor-only decoder into your one DC locomotive and forget about Block wiring. Wiring in one decoder and buying only DCC locomotives from now on (with sound!!!) will be a lot less work and deliver a lot more fun. All in less time.
The thing Mike is trying to talk about is “common rail” wiring. In this case, the block control switch only controls ONE wire to the block, instead of the TWO I described. Some people like common rail, some don’t. I don’t.
Get those books! Then you can read all about it yourself.
We have had discussions about which books are the best for learning the ins-and-outs of DC wiring.
Outcomes of these discussions are that there are a lot of books out there, and none of them describe wiring the way Sheldon or I do it, and Sheldon and I approach wiring differently from one another.
For my suggestion, I think “HO Primer” from Kalmbach has a good chapter on the basics of DC wiring, and is a good place to start.
Linn Wescott’s and Paul Mallory’s books are excellent, but are far more complicated than is needed today. If you were going to build a layout that complex, the clear choice today would be DCC for most people.
On books, I liked the Kalmbach “The DCC Guide”, which covers most subjects, including wiring. I have edition 1, which is fine. A couple of favorite websites were useful for more detail:
On power to track, I relied on (a) soldering nearly all rail joints, then (b) adding feeders at 6’ max spacing. (Occasional short (unsoldered) rail pieces and turnout parts got their own feeders so all rail was powered via a soldered connection.) That spacing means that the juice from a feeder to a loco has to travel no more than 3’ of rail, since the loco is always within 3’ of a feeder. I had seen that (for HO, nickle silver rail) as a guide in more than one place. After installing, do read about the DCC setup “quarter test” to ensure the setup is adequate for the booster (or subdistrict circuit breaker) to sense a short (and trip) on any piece of rail on the layout.
If thought experiments are difficult for you I suggest you draw a diagram.
Start at your power pack(s) and end with your locomotive motor(s) which connect the two rails. I’d use red for positive and blue for negative and assume your powerpack reversing switches don’t move. You can use just one ink colour or even a pencil, if you concentrate.
Common Rail and bus wires take power to all locomotives through just two wires: the current draw adds up in the bus wire(s). That’s in effect wiring your powerpack in series (until the very end of course, each pair of feeders and each locomotive is in parallel). All of the electrical load is carried by the bus wires all of the time.
Using single wire Block control each Block control wire runs from a common point powered by the powerpack. That’s equivalent to a very long feeder wire for each control rail connection. But, only one locomotive can draw from that feeder wire (assuming DC control which is technically only necessary for DC). That wire only carries the load for one motor (well several in a consist but you get the idea). Smaller gauge wire is adequate for the Block control wires for this reason. All locomotives are powered in parallel back to the bank of SPDT Block control switches (technically SPST are all that are necessary to control power to Blocks as has just been pointed out in an interesting post, SPDT are needed to convenie
Wiring in series is setting up multiples of the same two-wire electrical item (light bulb, resistor, capacitor) with the output of one connected to the input of the next.
Here is an example:
Note that ONE thing cannot be wired in series. So how is ONE powerpack wired in series, Mike?
It’s another word for “connected”. So Mike is saying that the power pack is in series with the layout wiring. Or something.
Note that, using your description, as soon as two block toggles are on at the same time, the system is no longer “in series”.
I had the impression that Mike was trying to explain the difference between regular two wire block wiring and common-return block wiring. And that he thought the difference was that the latter was somehow “in series”. I guess with that power pack he mentions.
