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Booster Network Wiring

Booster Network Wiring

INFORMATION #4-1: Function of Each Wire in Digitrax’ Loconet

Wire 3 and 4 is the LocoNet signal.  In Digitrax supplied cables, these wires are red & green.  However, in cables purchased from other sources, these may be different colors.

Digitrax literature and their website will lead you to believe that these are duplicated signals. They aren’t. From the command station end, the signal is only present on one of the wires. The signal gets to the other wire when a throttle or a radio receiver is plugged into the network. Unless you have a break before you reach a bridging throttle, this is rarely a problem; but have cost modelers many lost hours that this has happened to.

Wire 2 and 5 is LocoNet Ground. In Digitrax supplied cables, these wires are black & yellow. However, in cables purchased from other sources, these may be different colors.

Wire 1 and 6 is called the RailSync signal. This is fed to all the boosters in the system.  In Digitrax supplied cables, these wires are white & blue. However, in cables purchased from other sources, these may be different colors.

Contributed by Pekka Siiskonen: The RailSync signals are in opposite phase and should not be connected together. Digitrax Universal Panels will tie the wires together with diodes to supply the panel front (and side) connectors. There is no RailSync as such available there, so you cannot connect the booster to the Universal panel’s front or side connectors. If aux power is used with universal panels, there will be more power available to front (and side) connectors, but not at the back connectors, so adding the external power supply to one panel and chaining the panels from the back connectors will not get any more power to the panels further down the chain unless you also connect the power supply wire as shown in Digitrax documentation.

Another method is to connect the throttle UP chain to the side connector of the panel equipped with aux power. This means that the panels further along the chain will not have RailSync in any of the connectors, and thus no booster may be connected to such panels. If you have broken your network into separate networks for your throttles and boosters (described in 4-3 below), then powering other UP panels through the side connectors is a good way to go.

Which side of the connector do you start to determine which wire is number 1? If you think about it, it doesn’t matter. The middle two are always Loconet. The outer two are always RailSync. The two between these are always ground – no matter which way you hold the connector!  One of the pins is #1, but which one you don’t need to sweat. 

RECOMMENDATION #4-2: Put Your Booster Power Transformers in a Box!

I’ve only gotten zapped “bad” twice. It was twice too often! If you have been zapped mildly and don’t think it’s any big deal, ask someone who has died from electrocution. I’ve never been knocked across the room or worse. But I can assure you, it isn’t any fun and death is definitely possible.

Put your transformer in a metal or plastic box! If you use metal, be SURE it is grounded.

DO NOT settle for putting on a lot of electrical tape or heat shrink over the solder terminals of transformers. You may be shocked, literally, at how easy it is to accidentally have a screwdriver, or whatever, to find a way to contact the terminal where it meets the transformer. Also, the enamel insulation on the transformer is literally that — paint! It is extremely thin, intentionally for maximum transformer efficiency, and is easily scratched by a tool.

Make sure you use a ventilated box or drill a couple dozen 1/4″ holes. A dozen near the top and a dozen near the bottom. Put the holes on the sides. Things can be dropped through holes in the top. Of course, the more holes the better. Don’t make them any bigger than about 1/4″.

Digitrax sells a transformer for general DCC use that is already encased.  You have no excuse to risk your life or someone else’s!

RECOMMENDATION #4-3: Use a Separate Network for your Booster and Throttle Networks

This recommendation applies to any DCC system that has a network that both throttles and boosters share. The Digitrax Loconet is such a network. Please note the presence of such a network does not make that manufacturer’s product undesirable or bad. The Digitrax Loconet, for example, is a very good system.

Yes. Theoretically, the boosters can be on the same LocoNet network as the throttles. However, for best reliability, the boosters should have their own network. Should the boosters “fight” each other, they will corrupt the data being transferred on LocoNet. This will affect throttles trying to reach the command station or command station throttle.

If you are using a Chief, just connect one side of the Chief into your string of boosters and connect your throttle network into the other side of the Chief.  Or, if you want to keep a jack free on the Chief, buy a 2-way adapter or wall plate at your favorite home improvement store. The wall plate has a jack for a wall phone plus several other jacks.

RECOMMENDATION #4-4: Be Sure to Use a Transformer for Your Booster That Puts Out AT LEAST as Much Current as the Booster Can.

This is especially important if you have more than one booster. Having boosters with different capacity transformers can cause fighting when a locomotive crosses from one booster district to another.

Don’t use your old power pack to power a booster.

Many people who get into DCC want to use their old DC power pack to supply power to their new booster. While you can run a locomotive this way, I highly recommend that you do not use your old power pack. The reason is that boosters are typically designed to put out more power than your power pack is capable of supplying. Boosters are designed to shut down when they reach a preset limit. If your power pack isn’t able to supply all the power your booster is designed to, then the booster’s shutdown circuitry will never reach its trip point. What this means is that your booster will not shut down when there is a short. If your booster doesn’t shut down when there is a short, something on your model railroad will get very hot. Something will melt; maybe even catch fire. So I highly recommed that you avoid skimping on the $45 it costs to buy an adequate power source for your booster.

RECOMMENDATION #4-7: Do Not Run More Than One Booster Off a Single Power Supply

If you read the documentation that came with your booster, it may tell you to run each booster from its own power supply. This is generally the rule. Some may say something different or nothing at all on the topic. More specifically, do not run multiple boosters off a single power supply that is not fully capable of sourcing all the power that all the boosters attached to it may draw. Example: If you have two boosters that may draw 5 amps each, if you are using a common power supply, it must be capable of supplying at least 10 amps.

Always heed your booster manufacturer’s instructions. Some manufacturer’s manuals may say do not run multiple boosters off of a single power supply. Then follow those instructions.

RECOMMENDATION #4-5: 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.

Please note that the recommendation below refers to connecting a ground wire between your boosters. In the recommendation below, you are connecting the grounds of your boosters together. This is different than connecting your booster outputs together. The grounds of your boosters should be connected together. 

RECOMMENDATION #4-6: Run a Heavy Ground Wire Between Your Boosters:

You should run a heavy wire between the ground (lower gray spring terminal), or case, of each booster to the other boosters. It is also extremely important when doing this, that you disconnect wires #2 & #5 (for Digitrax supplied cables, the black and yellow wires) in your booster network. 

Adding the heavy ground wire makes a better common reference connection between boosters than the second and fifth wire do. Eliminating the second and fifth wire from the booster network prevents “ground loops.” Ground loops can also be a cause of booster fighting or otherwise corrupting the data on the network.  Note that I said remove the ground wires (Digitrax #2 & #5) from your booster network. Do not remove these wires from your throttle network.

Remember: Do not use a common rail between booster districts. This, too, would cause ground loops. See 4-5 above.

Diagram contributed by Bob Milhaupt

You only need to disconnect #2 & #5 in your booster network at one end as shown by Bob’s diagram.


I admit, cutting the ground connections in your booster network cables is a little of a pain. I don’t know that any of the manufacturers advocate cutting the booster network ground wire(s). However, if you have erratic operation or runaway trains, these could be signs of a ground loop meaning that cutting the booster network ground wire(s) may be a way for you to solve your problem. 

SUGGESTION #4-8: Put Your Boosters Electrically Central to Their Operating District

Actually, calling this a recommendation is almost an understatement. It is now almost mandatory that your mount your boosters central to their power district.

Be sure to read about terminating your bus wires in the section on track wiring. Modelers have found that when their wiring from their booster is more than 30′ feet long, they have encountered problems. The worst of which is blowing locomotive decoders.

Therefore, the conventional wisdom is now to locate your boosters in the middle of the track bus that they serve. Doing this will allow you to make a track bus that is 60′ long. Just attach your booster to the middle of your track bus.

SUGGESTION #4-9: How Many Boosters Do I Need?

You are buying your first DCC system. It isn’t clear to you how many boosters you will need. Do I need one? Or two? If you are worrying about this, you don’t need to. Just plan your wiring for 2, but buy only one. You can always buy the second one later if you run into problems. Nothing is going to blow up if you really need two.  In the mean time, run a pair of #10 wires between your booster #1 and wiring that will ultimately go to booster #2.

If you are building a club-sized layout, buy about half as many boosters as you think you will need. Wire as above. If you need more, buy the ones you need.

SUGGESTION: Resetting Your Booster

What to do if your sound-equipped locomotives are making it difficult to reset your booster.

Contributed by Don Vollrath,

Problem: New locos with sound decoders have large DC energy storage capacitors for operating the sound system. (soundtraxx, QSI and practically all others) These large microfarad caps are necessary to isolate minor disturbances in track pick-up from interfering with operation of the sound control computer in the loco decoder. The problem is that when several sound equipped locos are present on the track, the booster and electronic circuit breakers have difficulty starting up and/or restoring track power after a short circuit because the large inrush of current necessary to charge up all the large capacitors simultaneously causes them to re-trip.

Solution: Place a current limiting light bulb in series with each lead from the booster to track. (the 1156 or modern equivalent automotive tail-light bulb again). Provide a DPST normally closed switch in parallel with bulbs so that under normal conditions track current flows through the switch, not the bulb. Use a momentary push-button or spring loaded toggle switch with normally closed contacts. (rated for booster/track current amps).

Now when/if the booster cannot recover, momentarily open the switch so that:
1) Booster output current is limited by the light bulb, allowing the booster to recover.
2) If the track short still exists, the light bulbs will illuminate to indicate that there is a hard track short that needs to be fixed.
3) If the track short has been removed, the booster will recover but track current will be limited by the light bulbs, allowing….
4) The large energy storage caps in each loco decoder will charge up under limited current conditions. The booster will not re-trip on over current. Then….
5) When the booster is seen to recover (usually after a few seconds after the short is removed, plus a fraction of a second to charge up all the capacitors) release the switch to re-close around the light bulbs. This will fully restore track voltage and current capacity.

Design Improvement Twists:
1) If one uses electronic circuit breakers for track current distribution (Digitraxx, NCE, On-Guard, etc.) wire the light bulbs in parallel across the CB. That is, each bulb has one wire to the input side of the CB and the other wire to the corresponding track output connection of the same polarity. The electronic CB takes the place of the manual switch in the above scenario, but recovery is now automatic (if the electronic CB is set to do so). [Some multi-channel distributions CBs designed for this purpose have one power lead as a through-wire and will need only one bulb per channel.]
2) One cannot do the above if the electronic CB is also meant to auto-reverse.
3) A lower cost method would be to substitute a conventional DPST or DPDT, 12Vdc operated relay to do the above auto-recovery switching. Use normally open contacts of the relay (rated for booster current) to bypass the light bulbs. Power the 12Vdc coil from the DC output of a small full wave bridge rectifier (maybe with a slow-to-operate R-C delay). Wire the AC input side of the rectifier bridge to the track power side of the lamps. Now when track power is shorted or the booster trips or is shut off, the relay will drop out, placing the bulbs in the track circuit. When the booster is first powered up or resets, track current will be limited by the bulbs. When all the caps are re-charged, track voltage will build up to near normal levels allowing the relay to pick up and jumper out the light bulbs.

Any 12VDC relay may be used. Use a relay rated for 10A to ensure long life.

Radio Shack P/N
Z1 Bridge rectifier, 50V, 1A or higher
Bulbs 1156 Automotive tail light bulb
Relay 12VDC, 10A
275-218 relay
275-220 socket

See the section on parts for a relay that doesn’t require a socket and has built-in mounting tabs, Digikey P/N PB159-ND.


SUGGESTION #4-10:  Divide and Conquer a Short in Your Booster Bus

Track Wiring #5-21 has a good discussion on localizing a short.  If you used phone connectors to make your booster bus, you can just disconnect them rather than cut the wires. 

If you ran a separate ground between your boosters, just try to localize the problem with leaving this ground connected to all boosters first.

SUGGESTION: How to Test Your Booster

If you tried shorting your track to verify that your booster will shut down and it did not, try the test again. This time, directly short out your booster. If your booster does not shut down, you may not have it set up right or it may be defective. But more likely, you are using a power source that cannot adequately supply all the power your booster needs to trigger its overload detection circuitry. See the section above, Be Sure to Use a Transformer for Your Booster That Puts Out AT LEAST as Much Current as the Booster Can.


SUGGESTION #4-11: Buy a Spare Command Station/Booster

It is always a great idea to have spare equipment on hand. You only have one command station. If it goes down, you whole layout is down. Also, if you have two, when it is time to upgrade them, you can send one back at a time.

Yes, these cost money. So this is only a suggestion. However, if you have a system like Digitrax Chief, the cost of doing this is only about $50. The Chief is both a command station and a booster. Furthermore, the Chief can be placed in a booster only mode. The cost difference between buying a Chief set versus a booster, a throttle, and a decoder is only about $50. Keep one of the Chiefs in booster only mode and use it as you would a booster. Should one of the Chiefs fail, you can use the second one after you restore it to Command Station/Booster mode.

Note: You can only have one command station per system! If you are using a spare command station as a booster, you must set that command station to booster only mode. See Suggestion #4-12 below on how to do this.

SUGGESTION #4-12: Use Spare Command Station as a Booster

Here is how to turn a spare Chief (DCS 100) into a booster.

1. Set Op switch 2 to C.
2. Set Op switch 5 to T.

You will then need to set it to auto reversing mode or non-reversing mode.

Auto reverse mode: Set Op switch 3 to C.
Non-reversing mode: Set Op swtich 3 to T.

See Chief manual on page 117 on how to set Op switches .

Mysterious Operation

My radio throttles seemed to become unresponsive. When I plugged into Loconet, the throttle would seem to freeze. What was my problem? It turned out that the command station (Digitrax Chief) was overheating. The manual says that the Chief command station will keep working even if the booster section overheats. This turns out not to be true. I put a muffin fan on it and the problem went away!

I had a booster that would trip but it didn’t always reset. So I put a small muffin fan on it. So far, so good.

Does this means you need to put a fan on your command station or boosters? Not necessarily. But if you have erratic operation, especially operation that seems to get worse as the day goes on, it might be something to consider. Make sure you have fresh batteries in your throttles. Reset the variables, slots, and such in your command station. If all this fails to get your erratic operation to go away, try a fan.

Definitely make sure your booster and command station can get some air. If you have encased them, you may be causing heat failure.

Crossing Between Booster Districts