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Track Wiring
There are several sections in this website that you should read regarding track wiring. This section, Part II, covers track wiring. For general wiring information, testing, and troubleshooting, see Part I. The menu to the right will automatically take you to the right section. Connecting your track to your booster is covered in Booster Network Wiring. Wiring your turnouts also has its own section. Be sure to become familiar with all these sections. They have recently been expanded to cover topics that are frequently asked on the DCC Q&A forum. Finally, you may find the section on track and wire resistance interesting.
RECOMMENDATION: Do Not Have a Common Rail or Common Wire Between Booster Districts! In traditional layout wiring, modelers frequently had a wire that was common to all blocks. If you wired your DC layout this way, you may be tempted to use the same approach in wiring for DCC. Do not do this. Do not connect any of your booster outputs together. This, too, can be a cause of booster fighting in the form of "ground loops." Worse, shorts could result if either booster is set to auto reverse. Most manufacturers tell you not to have a common rail or a common wire between booster districts. I'm just mentioning it here to help them drive home the point. If you have an existing layout, you will need to cut your track and cut that common wire. Make sure you don't forget to cut the track when you cut that common wire. You will read in the section on booster network wiring that you should connect the grounds of your boosters together. This is different than connecting your booster outputs together. The grounds of your boosters should be connected together.
SUGGESTION: Don't Place Feeders Near the End of a Short Block.If you have a very short block and will only have one set of feeders, place it in the middle. Not at one end or the other. Don't sweat it if you can't get it right in the middle. There is the ideal and then there is the practical. Aim for the ideal.
SUGGESTION: What Size Wire to Use for Track Feeders?I find 20 AWG solid makes great feeders stripped from thermostat wire cables for HO. It tucks nicely along the outside of the rail. If you attach a wire to every 3' (1m) section of track, you can use wire as small as 24 AWG. Here are my suggestions. There are no hard and fast rules about the wire size you should use. Try to keep your feeders to about 6" in length or less - especially if you are using the smaller sizes of wires I suggest for your scale. When using the larger sizes suggested for your scale, try to keep your feeders to about 12" in length or less.
Of course, if you want to use even bigger wires for feeders than those suggested above, feel free to do so. I suggest that you use solid wire for your feeders. I like solid wire because it is easy to wrap around a bus wire, it is easy to shape and lay next to a rail, and it is smaller in size than the same wire gauge in stranded. Use large wire sizes for mechanical strength for outdoor railroads. I like to use 14 AWG wire for feeders on my garden railroad, not for electrical reasons, but mechanical ones. It will take a longer time before this wire corrodes through. A large wire is less likely to break off from a buried bus. Last, when you are digging around it, it will be more difficult to break it. You may want to check out my section on track and wire resistance.
SUGGESTION: What Size Wires You Should Use for Your Bus Wires Here are my suggestions. There are no hard and fast rules about the wire size you should use. Your wire does need to be big enough that you can shut down your booster by shorting the track at the farthest point away from your booster. See How to Know If Your Wiring is Adequate. You can always use wire larger than the largest shown in the table. I just provide a "largest" so that you know you don't have to go any bigger unless you want to. There are other reasons to use bus wires larger than what you really need to. For example, you may also find that larger wires are easier to strip. Also, you may find you can buy a 100' of #14 AWG romex cable at your favorite home improvement store than you can buy two rolls of #16 AWG from you favorite electronics store.
Personally, I use #10 AWG for my HO, not for any electrical reason, but because I use the fat wire size to indicate "main bus." Use #14 to indicate "sub bus." I like this system, but not everyone has worked with house wiring so much that they can tell the wire gauge by looking at. So this approach may not work for you. I use #10 AWG for my G, again not for any electrical reason, but for mechanical strength. It will take a buried #10 AWG to corrode through. If I hit it with a shove, I am not likely to break it. You may want to check out my section on track and wire resistance.
SUGGESTION: Place a feeder about every 3 Meters/ 10 Feetor so for Code 100. Every 2 Meters/6 Feet for Code 83 and Lower. For Weathered Rail, Solder a Wire to Every Section.After running my track and wire resistance tests, I have amended this section. How far apart can I place my feeders? A common question. But, how many of you can go even 10' before hitting a new block, usually caused by hitting a rail switch? Code 100 nickel-silver: 10' between feeders if you are using multiple feeders. A feeder should be 5' or less from the end of a block or insulated section. Code 83 and smaller nickel-silver: 2m between feeders if you are using multiple feeders. A feeder should be 1m or less from the end of a block or insulated section. The reason I give code 100 a longer distance is that it is oversize for its use. If you look at my track and wire resistance tests, you might ask why I don't recommend closer spacings for feeders to track like code 55. Good question! In considering these smaller sizes of track, I thought about their application. Narrow gauge track isn't likely to have 5 diesels in a lashup drawing 3 amps is a good example. Does this mean if you have a section 15' long, you need to make it 2 blocks? No, probably not. Again, aim for the ideal, but you probably don't need to knock yourself out. If you have weathered rail, why ruin the weathering soldering jumpers across the joiners? Solder a feeder wire to the bottom of every flex track section. Then don't solder any jumpers across your joiners at all. If you think about it, it is exactly the same number of solder joints as if you used jumpers. By the way, if you are trying to solder to weathered track, you are probably having trouble. It is not really a problem. You just need to know what to do. See the section on soldering for soldering to weathered rail.
RECOMMENDATION: Electrical Connections & Soldering Track Joiners. This tip is for those who don't like to solder. Unfortunately, I'm not going to be able to tell you what you want to hear. I have a basic rule: Every piece of track should be soldered to something; either another piece of track or preferrable a feeder. Over time, joiners will fail to make good electrical contact. Should I solder my joiners? Apparently some people recommend that you solder every joiner for DCC. We are frequently asked about soldering all the joiners on a layout. I recommend that you don't. You should be aware that track laying experts will tell you that you shouldn't solder joiners as this will inhibit the track's ability to deal with temperature changes. Some people solder their joiners on curves so that flex track doesn't kink as a lesser of two evils. Soldering joiners to a turnout can be a real headache if you have to remove the turnout. If you solder your joiners between sections of track, expect it to be virtually impossible to get the track apart should you ever want to. Another way to look at it is, that if you solder your joiners, that is two solder connections per piece of rail - a solder connection at each end. If you drop feeders from each piece of rail, that is only one solder connection. Admittedly, it is a little easier to solder joiners together than drop feeders from each rail, but not by much. My recommendation is that you solder feeders to the track rather than soldering the joiners between track sections except when it is a short piece of track - like 15" or less. My rule above still applies, every piece of track should be soldered to something. This does not mean that you need to solder every joiner together. What if I am using Kato Unitrack or other sectional track instead of flex track? Things are a little different here. For one thing, rail is rigidly attached to the ties. Expansion will always be there, but I'm sure the rail doesn't walk as much as it does in flex track. I also presume that people who use sectional track are building smaller layouts - meaning that there won't be long stretches of track between turnouts. Some sectional track, like the Kato Unitrack or Atlas True-Track, uses a plastic subroadbed. This is something more to melt, but it also locks the track together. Sectional track also means a lot more joints. So what does all this mean for the sectional track user? The laws of physics don't change. And since you do have a lot more joints, the situation is potentially worse than when using flex track. So you really need to have a something soldered to every piece of track. However, if your usage of sectional track is temporary, then you may be able to get by without soldering every piece of track. Are you only using it at Christmas time for around the tree? Are you building a small layout for a child that you only expect to have for a few years? Is this layout sliding under their bed? I have had good experience with Unitrack used without soldering feeders to every piece of track or soldering all the joiners for a couple of years. In the case of a temporary or short term layout, you may get by attaching feeders every 3' (1m) to 6' (2m). But like I said, the laws of physics don't change. Oxidation of the joiners and rail is inevitable. If you try to go more than a few years, you are taking a chance. What chance are you taking? You can just solder the joiners later, right? Not quite. When the track is new, it will readily solder. Older track that has a layer of oxidation won't readily solder. Soldering joiners will be almost impossible. You will likely have to clean the rail with a small wirebrush to get it to take solder and attach a feeder. Worse, enough resistance can build up that you get erratic operation. Your booster may not shut down in a short. Damage could occur to your equipment. It may take quiet a bit of time before you realize your problems are due to poor electrical connections. You will wish that you had soldered feeders in the first place RECOMMENDATION: Insulate Both Rails Between Booster Districts.RECOMMENDATION: Insulate Both Rails Between Reverse Sections.Be sure to follow the booster manufacturer's instructions. For Digitrax boosters, the gaps should be directly across from each other. If you are controlling a reverse loop or wye with a relay, exactly where the gap is doesn't matter exactly where you put the gaps. For your own troubleshooting sanity, put them very close or across from each other.
Wiring Overview The drawing that follows has a lot of information in it. Don't let it scare you. It was intended to show you a variety of things. I'll point those out one at a time for you and explain the significance. 1. Connecting only one feeder when you solder your joiners: See the upper left of the drawing. Look at the fat, black line. Note that further to the right that it says, Rail 'A.' My basic rule of track power is that every rail should be soldered to something - either the next rail or to a feeder. 2. Soldering a wire to every piece of track: Moving a little to the right, you see shorter sections of Rail 'A.' This is for when you don't solder your joiners. This is how I build my railroad - a feeder to every section of track. 3. No common rail and no common wire: Right in the middle of the diagram under Rail 'A' you see that Rail 'A' is broken. If you look down the diagram, you will see that every horizontal line is broken. All the broken lines represent wiring under your layout. This part of the drawing was intended to drive home the point that you should not have any common rails or common wires. 4. Power routing your typical turnout: The circle with squigglies is the symbol for a light bulb. Visit the first part of this track wiring section to learn about light bulbs and how they can help an operating session go smoother. This particular light bulb refers to turnouts (rail switches). See the section on turnouts to learn more about using light bulbs with turnouts. 5. No bulb needed with DCC friendly turnouts: If you have a DCC friendly turnout, using a light bulb is optional. See the section on turnouts to learn more about DCC friendly turnouts. That is it for the top section of the drawing. Now lets move down to the row with all the light bulbs. 6. A light bulb is suggested for every electrical block: A 1156 car tail light bulb can help an operating session go smoother by limiting shorts to a single electrical block. Visit the first part of this track wiring section to learn about light bulbs and how they can help an operating session go smoother. 7. Use sub buses: Notice the line labeled "GRN or CLR." Notice that it is the same length as Rail 'A.' This is to show this this wire, called a sub bus, corresponds to the portion of Rail 'A' that it serves. A sub bus is a copper wire that provides power to the track above it. Every one of my sub buses has a light bulb to separate it from the main bus - which we will get to in a moment. 8. Optional disconnects to isolate problems: The next light bulb over shows a disconnect switch. This can be used in addition to a light bulb or instead of one. If you have a problem on your layout, a switch like this can help you isolate a problem section of track. You don't have to use a switch - which costs money. Trading a little inconvenience for saving money, you can connect your sub buses to your buses with a screw terminal. That is how I do it on my railroad. 9. Use a main bus: Look at Booster #1 and the wire above it labeled "MAIN BUS of Booster #1. Look above it and you will see the main bus wire has a break in it that corresponds to a break in Rail 'A' that we noticed earlier. What is the difference between a main bus and a sub bus? Two things. One, the main bus is attached directly to the booster. The sub bus is attached to the main bus through a light bulb. If you do not use light bulbs or a disconnect switch, you do not need sub buses. The second thing about a main bus is that it services the entire "district" whereas the sub bus only services a single electrical block.
Now that wasn't so bad, was it?
General Considerations for Running Buses Under Your Layout There are not really any rules on how you should run your buses under your layout. You can run them pretty much any way you want. For those that don’t know where to start, here are some guidelines you might want to follow. Don’t forget to review the discussions on blocks and feeder spacing covered in this webpage. 1. Even if your layout is a loop, don’t join the ends of your bus in a loop. If your loop is one big block, put one pair of insulated joiners in the track above where the ends of your bus are so that your layout doesn’t form an electrical loop with joined ends. See drawing below. 2. However you run your buses, do not have any bus length that is more than 30’(9.5m) from your booster. See the section below on long bus runs for more on that topic. 3. Your buses do not have to be one long piece of wire. You may run buses originating at a single point, called a star, or you can branch off any place you want – a siding, for example. See drawing below. 4. If a single-track main, run your buses directly underneath the track. This should allow you to keep your feeder lengths to about 4”(10cm). See drawing below. 5. If you have a two-track main or a main and a siding, run your buses underneath the layout between the two tracks above. This should allow you to keep your feeder lengths to under 5”(13cm). You can also use this approach if you have a stub siding that parallels the main line. See drawing below. 6. If you have a yard you have a couple of choices: 6a: For every three tracks, run the bus under the middle of the three tracks. This should allow you to keep the feeders to the outside of the group of three under 6”(15cm). See drawing below. 6b: You can “zig-zag” your bus under your yard to reach all your storage tracks. Put a set of feeders at every point that the bus crosses underneath the trackwork above. This will allow you to keep your feeders under 4”(10cm). See drawing below. Note: Either 6a or 6b will work fine. I personally prefer 6a. I like my buses under the layout to have some resemblance to the track work on top of the bench. This makes it a little easier to keep your sanity while trying to troubleshoot a problem. In addition, using 6a breaks your layout into zones of three tracks. This also helps make troubleshooting easier.
Example of some of the above guidelines. Track
is in black. For simplicity, only one bus wire (red) is shown. You
will need to run two bus
wires essentially in parallel with each other.
Example of wiring under yard with 3 tracks - 6a.
Example of wiring under yard with 3 tracks - 6a. For simplicity, only one bus wire (red) is shown. You will need to run both bus wires essentially in parallel. Track is in black.
Example of wiring under yard using "zig-zag" approach- 6b. Place a set of feeders at every point that your bus crosses beneath the track. For simplicity, only one bus wire (red) is shown. You will need to run both bus wires essentially in parallel. Track is in black. You will need to "zig" to correspond with your feeder spacings. See the section on feeder spacing.
SUGGESTION: Using Blocks with DCC While you don’t need as many blocks as you would need with traditional DC-powered wiring, you will need a few on all but the most basic of layouts. Primarily, you will need blocks for polarity reversing sections. This would be for wyes, balloon tracks, and turntables, to name a few. A reversing section needs to be at least as long as your longest train – especially if your train contains a lighted caboose or passenger cars. Obviously regarding a turntable, your “train” consists of nothing more than a locomotive. You will need blocks if you are planning block detection. Primarily you will use block detection to determine occupancy on your mainline for signaling and occupancy in hidden yards. How you do that depends on what information you want to gain. If you just want to know if the mainline is occupied between two passing sidings, you only need one block between signals. If you want to have a train stop in front of a signal, you may need as many as three block detected sections between signals. Other than block detection and reversing sections, there are a few more reasons to consider blocks – short isolation and troubleshooting. If a train shorts out the track due to a derailment or picking the points on a frog, all trains operating on the booster that power that section of track will shut down. With some systems, the entire DCC system will shut down. By breaking a layout up into blocks, you will localize the problem – maybe only one or two trains will be adversely affected. Furthermore, if you have to troubleshoot a problem, you know your problem is localized to a much smaller area than what is served by the booster. How should you break a layout up into blocks? This is up to you. Creating a block for each town is always a good choice. If you have a large yard, especially one that is double-ended and worked by two operators simultaneously, you may want to break it into two to four zones. Breaking a layout into blocks for problem isolation doesn’t do you any good unless you provide some form of isolation. This can be achieved by either using an electronic circuit breaker or a light bulb. Either approach will isolate any problem to that particular block. See section regarding use of using light bulbs. If you are using circuit breakers instead of light bulbs, just substitute a circuit breaker for a light bulb. Circuit breakers cost a lot more than light bulbs, so this fact may weigh into your decision as to how many blocks you create. Especially if you opt for the more expensive circuit breaker, here is another way to further isolate your problem without significant cost. Suppose you have a town served by one circuit breaker. Instead of feeding the town by a single sub bus, break the town into two or more sub sections each fed by its own sub bus. Then connect all the sub sections to a terminal strip. Then connect the terminal strip to a bulb or circuit breaker. Now if you have a problem and your bulb lights or circuit breaker trips, you can start isolating your problem by disconnecting sub sections from the terminal strip. This beats having to cutting a large sub bus into pieces. You may not want a very long run of mainline on a single block. Again, this is to avoid adversely affecting too many trains. Your mainline could be part of the same block belonging to the town that it passes through. I chose to put my mainline into it’s own blocks and gave each block its own bulb. This immediately localizes the problem during an operating session. This approach is economical because bulbs are cheap. If you are using circuit breakers, you probably wouldn’t want to do this. How long are my blocks? They are 15-21 feet long. I did this because I am using block detection and allows the dispatcher to know the location of a train on the layout. If you are breaking your mainline into blocks and are not using block detection like I am, you might want to consider how many turnouts you might have in a given mainline block. This is because turnouts are likely to be your source of trouble. The more turnouts you have to deal with, the longer it will take you to find your problem. There is no hard and fast rule about how many turnouts should be in a mainline block. If you are using bulbs, I suggest no more than four turnouts. If you are using circuit breakers you have to decide what works for you and your budget.
Planning a large layout? Do you have slow spots? Are you blowing decoders? Considerations for Layouts with Long Bus Wires Introduction: There are problems with long bus wire runs. The problems are difficult to describe without a background in radio or an electrical engineering degree. It would take a lot of explaining and you would have a bad headache. You don't want a headache and I don't want to give it to you. Furthermore, to really see the problems requires an oscilloscope - a tool few model railroads have. Not everyone sees the problems. Even on my relatively large Digitrax layout with a few long bus runs, I don't seem to have the problems. Note: I am told that Digitrax equipment does not seem to experience the problem like NCE equipment does. The problems are out there and one of them is blowing decoders. So for that very reason, it is wise to be aware of the problems and consider doing something about them before you loose one or more decoders. A partial reason why everyone isn't seeing these problems is that I suspect that the equipment of some manufacturers is more sensitive to the problems than others. I didn't discover these problems. But since this is a website dedicated to DCC wiring, I felt that the topic needed to be included here. I am going to try to cover the topic by showing you a few pictures, giving you one simple tool you can make, and describe a few symptoms. I will avoid the deep technical discussion. One of the solutions is difficult to implement on an existing railroad. So look for instructions for owners of existing layouts. Here is what we are going to cover: I. Interference Some modelers who have long bus are experiencing interference being caused by their DCC systems. This interference may be interfering with the operation of throttles. The interference isn't too hard to understand. The relatively sharp rise and fall times of the DCC squarewave generates radio waves. Your booster is in effect, a radio transmitter. Your bus wiring is an antenna. What to do about interference: Keep your throttle and booster network wiring as far as possible from your bus wires. I don't mean they have to be on the opposite side of the room. But if you can separate them by just 6" (154mm), will make a huge difference. If you can separate them 12" (308mm), that will be four times better. Why is twice as far, four times better? I could tell you, but I promised not to give you a headache. Just take my word for it that for every little bit further you can reasonably separate them will be very significant. Another way to cut interference is a lot harder to do. See the discussion below on twisting your bus wires. The problem - blown decoders (unterminated bus end): The second problem is due to the lack of termination at the end of a long bus run - in essence, an unterminated transmission line. As you might guess, the solution is to terminate your long bus runs. DCC wasn't intended to need terminations or cause radio interference. Still, it is hard to get around the laws of physics. Before I get into how to fix the problems, let me try to show you what is happening to your DCC signal. Take a look at these pictures. This is a picture of a DCC signal on my garden railroad. This is actually a nearly perfect DCC signal. Notice that some of the squarewaves have sharp corners. This is good. Notice that some have spikes on the corners. This is not good. Neither are the rounded corners you see on the other squarewaves. While spikes and rounded corners are not good, the world is not a perfect place. So these spikes and rounded corners are not too bad and are acceptable.
Now take a look at this picture from my HO railroad. Notice the spikes are much taller. The wavy tops to the squarewaves is called ringing. Notice also that the previously flat tops to the squarewaves are now slanted. As you might suspect, this waveform is not as good as the one above. Believe or not, my trains run on this.
If my trains run on the above, what does it take to not make a train run? It can get worse. I just don't have an example to show you. What blows the decoders are the spikes. The spikes in this picture are about 24V. Many decoders can't take over 25V. I have heard of people measuring 38V on their HO layouts! For more scope traces of a DCC layout showing high voltages, click here. How to tell if you have the unterminated bus problem: The above pictures were taken with an instrument called an oscilloscope. If you have a friend who is an electronics technician or an electrical engineer, they may work for a company that has one and will let them borrow it. Oscilloscopes can be a lot of fun. If you have a friend who can borrow one and knows how to work it, you should try to get it. Ask them to borrow a portable 'scope. If they can only get one that plugs in, tell them they will need to isolate the ground before hooking it up to your booster. You will damage your booster if you don't isolate the ground. What do you do if you don't have a 'scope? You can buy yourself a DCC voltmeter from Tony's Train Exchange or you can build a simple little circuit you can use with a digital voltmeter you may already have. Just click here for more on the circuit or Tony's meter. If building the circuit, build the peak reading circuit. If you are running HO and are reading greater than 20V, you should be concerned that you have the unterminated bus end problem. I'm going to hold off covering what to do about this problem for moment. Let's talk about one more problem you may have first. P.S. If you can capture a 'scope trace of situations worse that what I have shown above, write me. I am looking for one or two more. The problem - slow spots (excessive inductance): The last problem related to long wiring is excessive inductance. This can make your trains run slow. Yes, small wire size or poor electrical connections are a likely culprit. Read the rest of this section on wiring and make sure your wiring and connections are adequate. If you have great wiring and are still having problems, and you have long bus wire runs, then you might have an inductance problem. How to tell if you have the excessive inductance problem: For starters, you should only be considering the excessive inductance problem if you have a long run between your booster and where your train is running slow. If you train is running slow and you only have 10-20' (3m-7m) to the problem spot, your probably have a basic wiring problem - wire too small or bad electrical connections - and not the excessive inductance problem. After you are sure you have good wiring, do the following: 1. Disconnect your booster and hook up your old DC power pack. 2. Run a locomotive that does not have a decoder in it. If it runs equally well in the problem spot as it does on a spot close to your booster connection, you may have the inductance problem. Solution for both unterminated bus end & excessive inductance: As mentioned earlier, DCC was designed with the intention that you shouldn't have to do anything special. That is true for bus runs under about 30' (10m) from the booster. So the simplest, if not the cheapest, thing to do is make sure your bus runs don't exceed 30' (10m) from your booster. If you can keep your runs down to under 30' (10m), you won't have to do anything special to your wiring! You will not suffer from untermined-bus-end-itis or excessive-inductance-itis. If you don't try to run your whole layout on one 8A booster, you will probably find that this 30' maximum is not really a problem. To prevent meltdowns, I have always recommended not using more than a 5A booster for HO. If you do chose to use something like a PM42 power management device, don't forget that you will need to count all wiring going to it as well. If 30 feet (10m) sounds really short, don't panic. There are things you can do to maximize the amount of layout each booster covers. Let's look at a few example situations. The "basic" situation: Here the booster is located in the middle of its booster district. You can run your bus wires 30' (10m) in opposite directions. Your booster can now cover almost 60' (20m) of track. Note that I said almost. The amount of wire going from your booster to your bus must be counted. If that wire is 3' (1m) long, you can only go 27' (9m) in each direction. So keep your booster close to your bus. Also, I am assuming that your bus ends about where the track it serves ends. If not, you will need to count to the end of the piece of track.
Note: I am showing a single black line that represents your bus - which consists of two wires. I have shown a single line to keep the drawing clean and simple. The "helix" or "wye" situation: You may be able to get creative and cover more track. If you have a helix, place the booster close to the base of the helix. Split off from your booster in three directions. 1. One 30' run goes to the track leading to the helix. 2. One 30' run goes to the track leaving the helix. 3. The last one goes for the helix itself. You just covered 90' of track! If you have a really big helix, you can take this idea one step further. You can make a four-way split where the fourth segment starts in the middle of the helix. Likewise, if you have a wye, you can go 30' in each direction. Of course, if you have a wye, you will need to worry about reversing which is a topic covered below.
The "yard" or "double-deck" situation: Here is what you can do if you have a yard. Also, this could be used on double deck layouts. Just suppose that some of these black lines could be on different levels. Make sure that from the end of any wire back to the booster is not longer than 30'.
Those are just some ideas of how you can get more track covered and stay within a 30' limit. In light of the above, block detectors now should be located as close to a block as possible. If you use a device such as the BDL-162 (16 block detectors on one board), you may need to use the RD2 remote sensing diodes to avoid long bus lengths. Failure to locate detector close to block as possible or putting more than the recommended number of twists per foot (1 recommended), will cause the capacitance to go up and will cause false indications of occupied blocks. Solution for unterminated bus ends: The name of this problem suggests the solution - terminate your bus ends. This is simple and inexpensive to do. Just put this "RC network " at each end of your long buses. Yes, you will need two of these circuits for each bus - one at each end.
Values are not critical. R1 may range from 100-150 ohms.
C1 may range from 0.1-0.47uF
Solution for excessive inductance: If you have long bus runs, you will need to twist your bus wires. This will also greatly reduce interference. Twisting your bus wires together is easy. Once twisted, however, it is hard to attach feeders. Worse, if your railroad is already built, twisting your bus wires together is not really an option. While the more twists the better, more twists will make it much harder to attach feeders. Therefore, I only suggest about 1 twist per foot (or 3 twists per meter). In case you have never used a drill to twist wire, here is how it is done. 1. Put an "eyebolt" in a variable speed drill or a cordless screw driver. Do not use a drill that you cannot run slowly. You can buy an eyebolt at your favorite home improvement store.
An eyebolt 2. Put the wires to be twisted through the eye and twist them around on themselves. Run the drill slowly and make sure the wire does not knot up while you are doing this. 3. Your wire will untwist a bit when you are done. So put a little more than the recommended twists of 1 per foot or 3 per meter. 4. Be careful when you remove the wire from the eyebolt. It is going to unwind some. Keep it under control so that you don't get hit with it and it doesn't knot up as it unwinds. What to do if you have excessive inductance on an existing layout: You don't have much choice. You either twist the bus wires or limit the length of your bus feeders from the booster to 30' (10m) or less. I don't like this any better than you do - I'm an existing layout owner, too! There is a little relief. If you have a long bus run from your booster to the first feeder, you can twist only this long run. This will help. It may help enough for you not to have to do anything more drastic. Just be very careful if you twists your wires with a drill. I'm having nightmares of you going too fast, twisting and breaking your feeder wires! Thanks to Don Vollrath for his input in writing this
section. Also, Mark Gurries has an extensive discussion on this topic
on the NCE-Yahoo chat group. Mark does a great job of giving you the
technical explanation of what is happening if you are interested. Some
of the information presented here is based on his coverage of this
topic on the NCE chat group.
Wiring Reversing Sections There are three basic things you must do when you wire a reversing section. 1. Make sure the reversing section is at least as long as your longest train. If you are not using any lighted cars, the reversing section only needs to be longer than the locomotive. 2. Double gap the track at both ends of the reversing section. 3. Do not connect your main bus to your reversing section in any way. Your reversing section must only be connected to your reverse section controller, reversing relay, or reversing switch. Be sure to follow the diagrams in this webpage or the instructions for your reverse section controller carefully.
In this example, a relay is used to reverse the loop. If you are using an electronic reverse section controller, just substitute it for the relay in the above diagram. Note that the blue and magenta main bus are not connected to the red and green loop.
SUGGESTION: Have a Simple Reverse Loop or Wye? You Might Not Need to Buy Another Booster! If you have a simple reverse loop or wye, you can simply use a relay with an existing booster. The relay is controlled by a set of contacts on the throat turnout. A simple reverse loop is one that connects to your main trackage through only 1 track. If you don't have a simple reverse loop or wye, but you do have a track arrangement where a reverse polarity will take place, you may have to buy another booster or an automatic reverse section controller which is made by most of the DCC manufacturers. If you have a loop or a wye where trains can enter it from more than one track, you may not be able to take advantage of this idea. If the train is moving when the throat turnout is flipped, it will probably jerk a bit. You probably won't be throwing the throat turnout while the train is moving if you are going through a wye. But you might be moving when going through the reverse loop. Think about it, you may not use your railroad that way. I intend to use reverse loops for off layout connections. My train leaves the layout and onto the reverse loop. There it stops. Sometime later it returns. So the problem of a jerky movement never takes place or would be seen if it did. Since my storage loops will not be visible, I will cut the power to the track just before the train reaches the throat after it has fully entered the loop.
Balloon track using a turnout that has power routed frog rails.
Balloon track using a turnout that does not have power routed frog rails. SW#1 is attached to your turnout or switch machine. You may have to experiment with swapping the wires on SW#1 to make sure the locomotive runs fine through the turnout without shorting your booster. The wire on SW#1 that also goes to the relay may have to be moved to the other contact on SW#1 to get the train to run properly through the reverse loop without shorting your booster. The reason I can't say for certain which way to wire these up is because it depends on how they are oriented with respect to your turnout. However, if you build your turnouts and their switch machines all the same way, once you figure out how it goes, it it will be the same for all your turnouts. If you are looking at this drawing to learn how to hook up a turnouts, you don't need the relay! The relay is shown for those considering using a relay to avoid buying a booster. You only need SW#1 attached to your turnout. A simple wye is one where the tail does not reconnect with the rest of the layout. It is okay if the tail track feeds a stub-end yard. As long as none of the stub tracks reattach to the rest of the layout, you have a simple wye that can use a relay to handle the reversing. See the two examples below.
I use the configuration as in "F" on my garden railway and its yard. Reversing a Balloon Track with a Tortoise This is the lowest cost way to reverse the polarity of a balloon track. If you have a wye with a tail track, you can use this approach on a wye as well. Just follow these easy steps. 1. Determine which diagram below applies you. Under each diagram, I have listed some popular turnout types. Find yours.
Peco Electrofrog, Pilz/Elite/Tillig, Orr (after modification)
Atlas, Kato, Micro Engineering, BK Enterprise, Roco, Walthers DCC Compatiable turnout The diode shown in black should be a 1N4001 or better diode. The relay can be any 12V, DPDT relay. See section on Parts for relays. 2. Install your Tortoise and get it working. I have shown a red/green LED pair. You can either use a single LED that has them both built-in known as a dual-color LED. Or you may use two separate LEDs if you want. You can even use two of the same color. Before soldering wires to your LEDs, first hook them up with alligator clips. If the indication is backwards from what you want, swap the wires going to the LEDs. Then solder your connections to the LEDs. Note: No dropping resistor is needed. That function is performed by the Tortoise. 3. If you are using turnouts with powered frogs (such as the Atlas, Kato, etc. above), connect your frog wire temporarily as shown to the green wire on the output of the relay. Run a locomotive with all wheel pick-up, like a diesel across the frog. If it shorts, move the frog wire to the red output of the relay. (If you are using the turnout that doesn't have the isolated frog, you need not perform this step. Go to step 4.) 4. Hook the red and green wires to the track. If a locomotive shorts when it goes across the track into the balloon, swap the red and green wires going to the track. You're all done! Other Wye Configurations: Here are some sample wye configurations. There is nothing magic about them. I am providing these to give you some ideas. A reason to use a particular one is to minimize the need to trigger the reversing circuit. Some systems hesitate briefly while the switching takes place.
I have shown these wyes drawn with a straight side. I only did that because it was easy to draw. Please realize the orientation of the wye can be any way you need it to be. In fact, look at "B" and "D" carefully. Turn "D" on its side. "D" and "B" are essentially the same! Remember the basic rule of reversing sections: the reversing section must be at least as long as your longest powered train. Configuration "C" appears that it may be hard to implement if you have a lighted passenger train. It could also be a problem if you have a lighted caboose. If the only powered unit is your locomotives, than the reversing section in "C" may be able to be short. If you are lashing up locomotives, be sure it is at least as long as your longest lashup.
Reversing Through Wyes For Lighted Passenger Trains and Long Lash-Ups
The configurations shown below will handle the reversing needs of a wye where long, lighted passenger trains or long lash-ups are involved. I show a spur and a siding to illustrate that you may have a reversing section that contains these track work features without a problem. I have also shown black/red tracks leaving the far end of the reversing section. If you just read the section above about simple reversing sections, these two examples do not qualify as simple. Therefore, you will need a automatic reverse section controller - which is available from most DCC manufacturers. The final thing to notice is the somewhat subtle difference between the two diagrams below. The diagram on the left only involves the turnout in the reversing section. This is how the wye in my garden railway is wired. The diagram on the right shows that most of the two legs of the wye are also involved in the reversing section. The differences between these two diagrams is not profound. I just wanted to illustrate to you that either way works. The diagram on the right simply allows you lengthen your reversing section or "pull in" the far end of the reversing section as is shown.
Using Double Crossovers with Balloon Tracks The track shown in black is connected to your non-reversing booster. The track shown in green is connected to your reversing booster. In Fig. 2, the green area must be at least as long as your longest powered train. Maybe that is 5 lashed up diesels. If you have a lighted passenger train, then the green section must be as long as all the lighted cars. If you fail to heed this rule, you will short out your booster. In Fig. 1, measure from the center of the "X" to the end of the green zone in each direction. The green zone from the top of Fig. 1 to the "X" must be at least as long as your longest powered train as described in the paragraph above. Also, the green zone from the "X" to the bottom must be at least as long as your longest powered train. The reason for this is that by having the crossover in the middle, you have effectively created three entry/exit points into your reversing zone. At all times, when a train is entering and exiting a reversing zone, that reversing zone needs to be at least as long as the powered portion of that train.
Using a Common Passing Siding in a Dogbone If you want to use a dogbone with a common pasing siding, just make the entire passing siding a reversing section. You will need to use a reversing section controller. Make sure your reversing section controller is set to trip at a lower current setting than your booster can put out.
Reverse Section Indicator Do you want an indicator that indicates when a reverse section is at the opposite polarity of your main track? Go to the section on Signaling for a circuit.
SUGGESTION: Automatic Balloon Track Control Use a DCC autoreverser to control the turnout leading to a balloon track. See the circuit in the section on turnout control.
Wiring a Turntable Below are two drawings of turntables. Perhaps being full circle they are a bit unrealistic, but they serve a purpose of being somewhat universal as there are a large number of configurations that can be used with a turntable. Besides, admit it, you would really love a full circle turntable, wouldn't you? The Split Ring Turntables require some form of reversing. The first drawing depicts a turntable that uses a split ring to effect the reversing function. The split ring could a split ring rail around the pit. Or it could be split rings located under the turntable. Note the yellow zones shown on the split ring. This is the disadvantage of the split ring approach. You need a dead zone represented by the yellow sections. No working stall tracks can be placed across from the yellow zones. The width of your dead zone is determined by the width of your split ring pick-up. Your dead zone may be one to perhaps three tracks wide. If you are planning a roundhouse that is a semi circle or larger, you can not use the split ring approach.
If you desire to have two tracks directly aligned from each other where a locomotive can pass across the turntable without turning it, you must wire the stall tracks as shown above. That is, all the blue tracks are wired together and all the red tracks are wired together. Notice that the wiring is reversed on the bottom half of the above drawing. I have highlighted two blue and two red rails so that it would be obvious to you where the wiring needs to be reversed. If you mentally rotate the turntable bridge, you will see that a locomotive can pass across it while maintaining proper track polarity. I show the split rail as being red and blue as well. However, I need to make clear that what I show as blue and red on the split ring may need to be reversed on your layout. It depends on which rail of the turntable bridge is wired to which split ring pick-up. If a locomotive tries to move from a stall track and shorts out as it makes its way onto or off of the bridge, you need to reverse the two wires supplying track power to your split ring. Make sure you make your split ring so that your pick-ups don't hang up on your split ring. The Auto Reverser The autor reverser controlled turntable bridge has a few advantages over the split ring. One, it is mechanically simpler. Two, there is no dead zone. You can have a semi-circle roundhouse or larger if you like.
If you desire to have two tracks directly aligned from each other where a locomotive can pass across the turntable without turning it, you must wire the stall tracks as shown above. That is, all the blue tracks are wired together and all the red tracks are wired together. Notice that the wiring is reversed on the bottom half of the above drawing. I have highlighted two blue and two red rails so that it would be obvious to you where the wiring needs to be reversed. If you mentally rotate the turntable bridge, you will see that a locomotive can pass across it while maintaining proper track polarity. Your auto reverse unit is wired to the turntable bridge. Stall Tracks Some people like to kill the power to the stall tracks to avoid locomotives accidentally taking off. You can do this two ways. One, is to put individual SPST switches cutting power to one leg of each stall track. This is your best insurance against accidental launches into the pit, but it is a lot of work. Two, you can use a single SPST switch to cut the power to all the stall tracks simultaneously. This is a lot less work if you are worried about accidental launches into the pit. If a locomotive starts to move when you flip the switch, you can quickly flip it off.
SUGGESTION: Wiring Three-Rail and Catenary Systems This applies to all three-rail systems and systems with some form of third-rail or wire power pick-up such as Lionel, Marklin, MTH, and catenary systems. Good news! In at least one respect, wiring a three-rail model railroad is easier than wiring a typical two-rail system. In all two-rail systems, something must be done to switch the polarity of the reversing track, balloon track, or wye. In a three-rail system, you don't have to do anything special! See the drawing below for a balloon track. Red matches to red, and blue matches to blue. Compare to the balloon track shown above for two-rail systems above. While I have not shown a three-rail wye here, the same thing happens; red matches to red, and blue matches to blue.
So how do you wire a three-rail system? How do you utilize the two rail diagrams in this website? It's simple. Just wire to one of the outside rails; either the inside or outside rail. It doesn't matter. Wiring to the outside rail of your choice corresponds to one of the rails in a two-rail diagram. The third, center, pick-up rail or catenary corresponds to the other rail in a two rail diagram. You can wire both outside rails if you want to. You might get better electrical pick-up if you do. Many three-rail systems already have the two outside rails connected together. I am not familar with all three rail systems so I cannot advise you as to which ones are. Lionel definitely is. How often do you place your feeders? For the smaller scales like HO, about every 3'(1m) to 6'(2m). For the larger scales like O, about every 6'(2m) to 9'(3m). There is one thing different about most three rail systems. Most use short sectional pieces. This website normally recommends that "every section of track be soldered to something else - either another piece of track or a feeder. Obviously that is somewhat impractical for short sectional track. Hence the reason why greater feeder distances are not recommended here. Instead of soldering all your sectional track together, apply some anti-oxidant gel to the joiners between each section. Anti-oxidant gel doesn't improve conductivity. It just inhibits the build-up of oxidation. You can get anti-oxidant gel in the electrical department of your local home improvement store or an electrical supply store. You can also use the gel you would put on your car's battery terminals. Three-rail systems, such as Lionel or MTH, are only used at Christmas time. For a temporary display such as this, you can probably get by with only one feeder as long as you make sure your connections are clean and tight when you set up your trains. You also don't need the anti-oxidant gel unless you want to use it. Your trains will not be set up long enough for oxidation to build up. I do not have first hand knowledge of many of the three-rail systems. If you have something to add to this section, please write me.
SUGGESTION: Wiring Dual Gauge Track and Turnouts Please note that I am not a dual gauge modeler. What is written here is based on examining a friend's layout that is and is wired for DCC. If you have anything that you think I should add, please write me. There is not much to wiring dual gauge track. There is not much to wiring, dual gauge turnouts either. For the most part, this section serves to comfort you that what you suspect is correct. The section on dual gauge turnouts does include information on how to control the polarity of a frog of a gauge separation turnout. Dual gauge track generally consists of a rail shared by both gauges on one side of the track and two rails, one each for each gauge, on the other side of the track. You will see that it is rather straight forward as shown in the drawings below.
As you can see, there is no need for a separate bus for the narrow gauge track. Both the narrow gauge and standard gauge are powered from the same bus. If you are using light bulbs as discussed elsewhere in this website or electronic circuit breakers, I still see no reason to put the narrow gauge and standard gauge on separate buses of any kind. For information on handling dual gauge turnouts, see the section on turnouts.
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