Please make sure you have read this section: Booster Connections & Power BEFORE you read this section.
This section is ONLY about the special wiring required when working with multiple boosters. This typically applies to only large layouts (Club Size) or large scale layouts.
IN THIS SECTION:
1) WHY WOULD ONE NEED MULTIPLE BOOSTERS?
2) WHERE ON THE LAYOUR DO I INSTALL MULTIPLE BOOSTERS?
3) WHAT IS A BOOSTER COMMON?
4) WHAT OTHER NAMES ARE USED FOR BOOSTER COMMON?
5) WHY DO MULTIPLE BOOSTERS REQUIRE A BOOSTER COMMON?
6) WHAT CURRENT FLOWS IN A BOOSTER COMMON?
7) BOOSTER COMMON WIRE GAUGE CONSIDERATIONS.
8) DOES AND DON"T WITH BOOSTER COMMONS
9) BOOSTER COMMON CONNECTIONS BY MAKE AND MODEL.
1) WHY WOULD ONE NEED MULTIPLE BOOSTERS.
1) The primary reason for having multiple boosters is to maximize electrical performance of the DCC system while at the same time minimizing the cost of running long large gauge track bus wires.
2) A less common reason is to increase the available track power or isolated the track power in a given area of the layout due to relatively high constant power demands such as staging tracks full of trains with sound, lights or rolling stock with resistive wheel sets.
2) WHERE ON THE LAYOUT DO I INSTALL MULTIPLE BOOSTERS?
A lot of large layouts tend to concentrate all the DCC equipment in one single location. The belief is that it will allow better trouble shooting and/or simplify the wiring and/or make a impressive rack of DCC equipment to impress people with. Unfortunately electrically DCC wise this is the worse thing you can do.
DCC boosters are designed to be distributed around the layout so they are located near the area of track they are responsible for powering. Combined with DCC circuit breakers, the booster covers all the track levels within an geographical area of the layout.
Why?
1) Electrically you want to avoid running the track bus wires beyond 30ft or 10 meters. This eliminates any special wiring handling consideration such as twisting the track bus wires.
2) Keeps the voltage drop on the track bus wires to acceptable levels under the worse load conditions.
3) The booster control cable that runs between the command station and the booster is designed to be run over long distanced so you can distribute the boosters. In other words, a long control cable is not an electrical problem unlike long track bus wires.
For more information about the problems with long track bus wires go here: http://www.wiringfordcc.com/track_2.htm#c2
3) WHAT IS A BOOSTER COMMON?
With multiple boosters, DCC manufacture require a single wire that electrically connects all the power supplies of each booster together. It is typically implemented using a large gauge wire that is run between any and all boosters to connect each boosters power supplies negative terminals together.
Multiple boosters require the installation of a "Booster Common" The connection is made with a terminal labeled GROUND or to the metal case or screw. Consult your booster manual for more information. The booster common is the INTENDED PATH for track current to flow between boosters. Given most system only have one booster, this is normally never discussed.
Why a Booster Common?
4) WHAT NAMES DO DCC MANUFACTURE USE TO DESCRIBE THE BOOSTER COMMON?
The term "Booster Common" also goes by OTHER LESS technically accurate names depending on the author of the DCC manuals.
1) BOOSTER GROUND: Digitrax Name for booster common. However Digitrax by default uses the Loconet ground wires in the Loconet cable to electrically implement this function. Hence Loconet ground is ground for two different things.
2) DIRECT HOME WIRING: One of Lenz's name for a Booster Common. Not to be confused with Digitrax's name which has another purpose.
3) COMMON: Lenz and Bachmann name for Booster Common.
4) GROUND: NCE name for a Booster Common.
Hence potential confusion do to inconsistent terminology. Booster Common is the correct name both functionally and technically.
If you want to learn more about the meaning of all the various other type of "ground terms" that can be confusing to people people when they hear them spoken and what they truly mean, go here: Booster - Earth/Ground/Commons
5) WHY DO MULTIPLE BOOSTERS REQUIRE A BOOSTER COMMON?
There are two reasons.
A) It eliminates any chance of a "voltage doubling" problem when using a dedicated booster is dedicated to implementing the automatic reversing section within a reverse loop. If your booster does not do autoreversing, your OK. To learn more, go here: Boosters without a common
B) Address the electrical problems of a locomotive stalling when crossing between two Booster Districts. The degree of the problem observed is very dependent on how the locomotives electrical power pickup is implemented. There are two types of engine power pickup.
B1) Offset wheel power pickup. Steam Engine Example: Tender picks up Rail A while the engine picks up Rail B. It is not limited to Steam Engines but found on Diesels between the front and rear trucks. Many older engines including many older brass engine NEVER HAD "all wheel pickup" which most of us take for granted today with modern production. PROBLEM: The offset wheel pickup locomotive completely stalls at the booster district boundary when it is attempting to cross into the next booster district. You have to drag the engine across the double insulated rail joiners (Double Gaps) to get it running again.
B2) All wheel power pickup. Most modern engines made today, steam and diesel, have all wheel electrical pickup. This gives the most reliable and smoothest operating locomotives possible for the given wheel arrangement. PROBLEM: Generally they make it across just fine. But sometimes the Locomotive may stutter a bit and/or the headlight might blink. It only works because the internal wiring of the locomotive between the front and rear trucks of the engine is being called upon to connect or electrically bridge the the two boosters together during the transition. This dynamic bridging establishes a momentary booster common using the locomotive internal wiring running between the two trucks. However the success of the booster common depends on the electrical pickup reliability of the locomotive wheels front truck versus the pickup of the rear truck. The two truck are not electrically working together anymore for a common cause. Stated another way, the number of wheels picking up power have been cut in half. Hence the herky jerky crossing. The SOLE purpose of the locomotive electrical system is to just reliably pick up power from the track and feed it to the motor. It is the installation of a booster common in the booster wiring whos joob is to prevent the dynamic bridging from taking place and restore the all wheel pickup function keeping the locomotive itself running smoothly.
6) WHAT CURRENT FLOWS IN A BOOSTER COMMON?
DC Current. Each Booster has a DC power source (internal or external) to Feed the circuit's that create DCC's AC Signal (Inverter).
The only way you can have a complete circuit between two booster to exchange Locomotive power requires a booster common.
There are TWO levels of DC current that can flow in a booster common depending on what is happening at the track level..
NORMAL CONDITIONS: The current passing down the Booster common will the same as that of a single locomotive that is crossing the Booster District. Hence at first glance, it looks like small gauge wire is OK to use. Potentially something as small as the wire gauge found inside the locomotive itself.
ABNORMAL CONDITIONS: The common wire can see the FULL RATED BOOSTER CURRENT. This typically can happen if there is a short circuit that "bridges" the booster district boundary such that two booster are sharing full current with each other.
In my professional opinion, some DCC manufactures seemed to be only aware of the first condition and have not considered the second condition and/or re-reviewed the condition when high current boosters are involved..
7) BOOSTER COMMON WIRE GAUGE CONSIDERATIONS.
A booster common wire can carry the same current as the booster current rating of the highest current booster involved. The selection of the wire gauge should follow the same recommendation one used in choosing the wire gauge for the track wiring. This assume the track wiring gauge itself passes the track short circuit test as a minimum (not the best) standard.
If no wire gauge is offered or recommended. Use 18AWG for under 10ft runs of Booster Common. Use 14 or 12AWG wire for longer booster runs.
8) DO AND DON'Ts WITH BOOSTER COMMON.
1) Unless you has a ESD (Static Electricity) problem, do not connect the booster common directly to Earth Ground. There is no safety requirement at play here. It may seem to be a good idea at face value but in large or complex layouts, it creates more problems than is solves. "Ground Loops" involving your house earth ground wiring. Bad.
2) If you have a ESD situation, connect the booster common through a 100K or 1 Megaohm resistor (any watt rating will do) to Earth Ground.
9) BOOSTER COMMON CONNECTIONS BY MAKE AND MODEL.
User Connection Method: The type of connection used by the booster to make a Booster Common.
Connection Label Name: The specific "Name" or "Label" of the electrical connector or the pin/screw terminal used on the booster.
5/23/17
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