General DCC Wiring

DCC Wiring / Cable Bus Information :

•  Definition of a Bus

A group of wires that are used to distribute information or power.

• There are 3 DCC wire / cable buses to deal with.

Cab Bus :

The wires that go between the Cab in your hand and the Command Station

Control Bus :

The wires that go between the Command Station and the Booster Power Station.

Track Bus :

The wires that go between the Booster / Power Station and your Track.

Each type of bus has its own unique cabling system  -  Telephone , Coax ,Din , etc ...

There is also the AC /DC power bus wiring to consider.

·          Most DCC systems support some level of walk-around cab control.

Large systems / layouts typically are 100% walk-around.

 Wiring / Cable Bus Type :

All systems use individual wires for power and track buses.

·          Lenz Type :

5 pin DIN cable for Cab bus. Wires for control.

Track Bus: Adding up the DCC Layout Power :

·          Add up total maximum engine current.

Determine maximum number of simultaneous operating engines.

Determine motor current per engine.

·          If you are not sure ? - Use this as a rough scale guide : N = 1/2 Amp, OO = 3/4 Amp, S = 1.5 Amp, O = 4 Amps .

·          Calculate total current.

Max engine current  =  7 x  OO engines at 3/4 Amp per engine = 5.25 Amps

·          Add up total maximum rolling stock accessory current.

Lighted passenger coaches or caboose :

16 passenger coaches with five 25mA bulbs in each coach is 2 amps. (16 x 5x 0.025 = 2)

·          Add up total maximum Stationary accessory current.

Switch machine (points), signal power and general layout lighting :

Thirty 10mA turnout stall motors + 200 20mA street lights = 4.3 Amps

·          Total layout power is the combined sum of all the above.

5.25 Amps + 2 Amps + 4.3 Amps = 11.55 Amps.

Track Bus : How many power stations are required ?

·          Take layout current and divide by the individual power stations maximum current ratting.

Example : You will need three 4 amp power stations to run a 11.5Amp layout. (11.55 / 4 = 2.88 --> must round up --> 3 Stations)

·          To cut costs : Move street lighting to a separate 12V AC / DC power supply.

·          11.55A - 4A = 7.55 Amps. You now need :

·          Two 4 Amp power stations ---or--- One 8 Amp power station

·          Warning : Only buy >5 amps power stations for O scale.

To much current and small scale engines wires = burned wires.

·          More power stations = less layout power loss under short conditions.  . Think of frequency of derailment shorts.

Using a single power station means whole layout shut down.

Track Bus: Power Districts :

·          Problems may occur :

When running a layout from a single booster, all operations will stop when a short occurs.

·          Not a problem for single operator layouts.

No different than DC power pack short.

·          A bigger problem for multiple operator layouts.

Everyone stops running to an individual operators short.

·          Shorts may occur!

Frequently in areas with lots of switches such as Yards.

DCC systems tend to be less forgiving of shorts.

·          Some boosters shut down for a fixed period.

·          Recovery is not “instant” when cause of short is removed.

Some track switches are more short prown in normal use

Track Bus: Power Districts (Cont.) :

·          SOLUTION :  Divide layout up into Power Districts.

A Power District is a large section of track that is electrically isolated from other large sections of track for the purpose of minimize global power loss in the event of a short . Not the same as traditional power blocks.

Blocks tend to be to small.  -  Occupancy detection may keep it that way.

Example : Power Districts : Yard , Mainline , Branchline.

·          Three Ways to create a Power District.

             Use multiple boosters.

Expensive if there are many small districts.

            Use DCC Electronic Circuit Breakers :

Great for small districts or stubs. About ¼ of the cost of a booster.

             Use 12volt light bulbs.

Cheapest. Limited by motor current draw needs

 Distribute the power to allow more trains to operate.

Track Bus: Reverse Loop Wiring :

There are 3 ways to achieve this :

·          Keep using manual reverse loop switches :

Must set up loop voltage polarity before train enters loop  -     May force operator to stop train. Not prototypical.

Use reverse loop track switch to control loop voltage polarity  -   This partially automates the polarity issue.

·          Use a booster that supports reverse loop operation :

Full automatic operation.

Works with spring switches.

Most expensive solution. Not using the booster to its full capacity.

·          Buy a reversing Module :

Full automatic operation.

Works with spring switches.

Track Bus: Reverse Loop Modules :

·          Modules work by “Detecting Short”

 Short created by train entering loop and shorting gap.

 Module changes loop polarity to clear short across gap.

 Speed of module gives smooth operations into loop.

·          Two types exist.

Relay based :

Handles high current. A must for large scale layouts.

Slow mechanical response can cause problems.

Race to clear short. Relay Vs Booster “Short” protection delay.

Semiconductor based :

Best solution for smaller scales due to lower current ratings than relay.

Fast response. No booster shutdown first race issues.

Some only detect short on one rail. Problems with offset Loco pick-up.

Track Bus: Reverse Loop Modules :

·          Modules vary in how they “Detecting Short”

Most modules vary in how they "Detecting Shorts"

Some sense shorts in both rails independently  -    Best solution. No track gap installation issues.

Some devices require both gaps to short at same time   -  No offset gaps allowed. Gaps MUST be in line with each other.

Some use voltage drop Success sensitive to layout wiring.

Problems ?    Put 12 volt Automotive bulbs in series.

Lenz: After reverse (output side) before reverse loop.

·          Modules vary in how much current they can support.

Size reversing module with booster current rating :

Best value for hands off Operation.

Cost allows other options for usage

Turntable.

Simple Wye.

·          Some allow variable current trip thresholds.

Prevent false trips.

Tweak for scale current.

Track Bus: Recommended Wire Size :

·          Wire Gauge:

Lower AWG (American Wire Gauge) number = larger wire size

Higher the cable type ( UK Wire Gauge)number = larger wire size.

·          Track Bus

Wire runs over 50ft require larger size wire :

Actual wire length is 100Ft. Out and Back = Times 2!!

Recommended wire size for booster current ratings (I) of :

I < 4Amps = 16 to 14 AWG  -  (USA Wiring Spec)

7 / 0.2 mm Stranded copper .Max Current 1.4 Amps -  (UK Wiring Spec)

I ³ 4Amps = 14-12 AWG  -   (USA Wiring Spec)

16 / 0.2mm Stranded copper . Max Current 3 Amps  -  (UK Wiring Spec

I ³ 8Amps = 10 AWG  -  (USA Wiring Spec)

24 / 0.2mm Stranded copper . Max Current 6 Amps  -  (UK Wiring Spec)

32 / 0.2mm Stranded copper . Max Current 10 Amps  -  (UK Wiring Spec)

Recommend standard “Romex” 110V AC cable. 14-2 with ground  -  (USA Wiring Spec)

Recommend standard 1.0mm 3core 240 volt AC cable for mains wiring  -  (UK Wiring Spec)

·          Track Feeders

Use #20 to #24 AWG stranded or solid :

Use 32 / 0.2mm (UK Wiring Spec) stranded

Solder a minimum of one feeder per 3ft section of track. 6ft spacing.

Track Bus: Testing :

·          Check your track bus wiring

 DCC can make minor DC wiring problems become noticeable.

 Do the “Coin” test

Short coin on every sectional piece of track on layout   -  Booster shutdown   =  good wiring  /  Booster stay on = bad wiring.

Perform test on each section of track EVEN if you have solder joints.

DCC & DC Wiring Issues :

·          Need DCC short to DC power pack protection

DCC to DC power Circuit Breaker (recommend) Lenz LT100