KB352: Powering your Digitrax Command Control Railroad

This article was last updated on Jan. 14, 2014, 6:33 p.m. | Print Article | Leave Feedback

Digital Command Control (DCC) has specific electrical requirements that must be provided for your layout control system to operate properly.

Input Power

All DCC systems require an external power supply.  Digitrax manufactures several power supplies for our command stations and boosters:

  • The 3 Amp PS415 (the Zephyr Xtra power supply)
  • The 5 Amp PS515 for all Digitrax 5 amp command stations and boosters
  • The powerful 20 Amp PS2012 can be used for multiple 5 and 8 amp command stations and boosters

 

Additionally, the PS14 is available to power various other devices for your railroad.  Digitrax strongly encourages you to use our power supplies to insure satisfactory operation.  You can, however, use another power supply which has the specified output rating for your command station and/or booster.  In countries outside of North America, your power supply must be rated at the proper input voltage for your country and have the proper output for the command station and or/booster which you are powering.  Digitrax systems are designed to work with either 60 cycle or 50 cycle power.
 
Digitrax recommends the use of inline fuses,  with the fuse being rated at the same Amperage as the rated value of the command station; either 5 Amps or 8 Amps, depending upon your system.  Zephyr Xtra users should use only the power supply sold with the set for proper operation.  DCS50 Zephyr does not need an inline fuse since its power supply is designed to prevent excess current consumption.  DCS50 users are reminded to be aware of and to stay within the Zephyr's 2.5 Amp rating and to add boosters / power supplies as your power consumption needs grow.

Output Power

The output power of the Digitrax command station and booster units is measured in Amps.  The 8 Amp Super Chief Series has more output power capacity than the 5 Amp Super Chief Series, meaning that more trains and devices can be run with the 8 Amp unit than the 5 Amp unit.  If less than 5 Amps of power is available to a 5 Amp unit,  it only provide the amperage available to the command station / booster.

Most Digitrax units offer the choice of output voltages, with the N-Scale setting producing a lower voltage than H0, which is, by turn, lower than Large Scale.  In the case of the PS2012, which produces 20 Amps, the output power can be divided amongst the power consuming devices by using the Y-Cable which is included with the unit.  The PS2012 is DC, so it is merely a matter of connecting the "Plus" output to any "+" connections and the "Minus" output to any "-" connection. issue.  We recommend using a YC-2 splitter cable with a 5A Polyfuse in each leg for secondary protection.

Powering Your Railroad

Power consumption is a major issue with command control and model railroads. Each locomotive has a decoder which consumes power, even when the locomotive is stationary. Likewise, illuminated passenger cars consume power, as do the command control components themselves. To address these power issues, a variety of electrical devices are used.  Most of the basic systems are a combination of command station and booster, connected to a power source and operated by an external throttle.  The command station and its related power supply components are connected to the tracks via a power bus.

When a DCC railroad reaches an electrical consumption limit, the system will begin "cutting out", which is a result of the circuit breakers having reached their limits.  To address this issue, the railroad is subdivided into power districts, and additional boosters are used; these devices have their own power sources and take the command control signal from the command station via LocoNet and repeat it to their particular power district.

Boosters

A typical model railroad is divided up into several power districts; these districts are electrically isolated from other areas of the model railroad by either insulated rail joiners or gaps cut in the rail. It is required that both rails be isolated at the points where they connect to other power districts. This is called Direct Home Wiring.

The boosters are connected together with the command station/booster by LocoNet, which is their communication connection to the command station. A throttle command made to LocoNet will be sent to all devices on the LocoNet data channel. A booster receives this signal from LocoNet and combines it with the electrical power supplied to it by its own power supply.

Since the power bus length for a particular booster is limited to about fifty feet, you may need several boosters to connect long segments of track. In this case, a large model railroad will have boosters located near the tracks which they serve rather than being centrally located together because of the power bus length  limitation. Fortunately, LocoNet is similar to Ethernet systems, with a physical limitation of about one thousand feet of length. In most cases, this limitation will never be reached by most model railroads, but the truly large model railroad will need to be designed with these two limitations in mind.
                
Power Management

Once your railroad is subdivided into power districts, you will also need to add a power manager for each district.  The PM42 is recommended for this function.  The PM42 adds short circuit management and/or auto-reversing for each sub-district.  Short circuit management increases layout reliability by preempting booster shutdown when a short circuit is detected by the PM42. This minimizes disruptions to operations by automatically restarting layout operation when the short circuit is cleared.  Typically, modelers use a PM42 to supply power to three sub-districts in the power district and then use the 4th node of the PM42 to operate the track switches.  By doing so, if a train derails in one location, other trains can continue to operate and track switches and such can still be operated while the short circuit is corrected.  
                
Autoreversing

Reversing sections have long been the bane of model railroads.  The AR1 automatic reversing unit will handle a single reversing section.  In addition to its power regulation function, the PM42 also offers automated operation of such return loops by monitoring the command control signal & power current in both the railroad and in the return loop.  It adjusts these two to be in phase with each other as a train passes over the railroad. 

Installing Digitrax on an Existing Layout

A common problem occurs with installations that connect new Digitrax electronics to existing layouts.  In many cases, these layouts were wired to operate in the conventional DC environment, and many use common rail wiring.  In other cases, the railroads have existing wiring problems which cannot be solved by new electronics.  The easiest way to approach such a conversion is to add the electronics and test the system's performance without any rolling stock (locomotives, freight & passenger cars) on the track.  If the command station will not work in this situation, it is not going to work with locomotives and cars present.  In most cases, there is a wiring problem which must be remedied before you can enjoy the benefits of Digitrax command control.  Although it may seem quaint in this day and time, if you have brass or steel rail on your railroad, you are not going to have successful operations.  The only exception is with large scale, where the trains are heavy enough to allow for proper electrical contact.  Likewise, dirty track will prevent you from successful operation.

Powering the Decoders

Mobile Decoders

Every locomotive on your railroad will be equipped with a mobile decoder.  (You can also run one analog locomotive without a decoder on your Digitrax layout.)  Each mobile decoder is assigned a unique address which allows you to individually control each locomotive independently of all others.  In operation, these decoders will draw a certain amount of current.  Even when the locomotive is sitting idle, the decoder's circuitry will still draw a small amount of current.  In practice, you can generally estimate how much power areas of your railroad will need, but there are a variety of variables that make it difficult to exactly predict.  To a degree, getting your power distribution will be a matter of some trial and error.  The addition of sound units to locomotives adds an additional power load to your railroad and may require further adjustment.  As mentioned earlier, adding boosters will help distribute electrical power and the DCC signal to your railroad.  

Stationary Decoders

Stationary decoders are added to your railroad to control turnouts (track switches), signals and other track related devices.  The DS64 and DS44 are used to control up to four solenoid devices such as turnouts.   While they can be powered from the track, you may find it better to power them independently so as to avoid drawing power away from the trains.  The DS52 is used to control two solenoid devices, and is powered & programmed via either a track connection or directly to a power bus.  The DS51K1 is designed for Kato Unitrack turnouts, and can be powered from the track or direct connection to a power bus.  Other devices like the SE8C signal decoder and the BDL168 occupancy detector both require  a power source such as the PS315 or other power supply.  The smaller  BD4 can use track power or it can be independently powered.

Stationary Decoder Power Requirements

  • DS64-The maximum input power for your DS64 is 300ma at 12V DC.  DS64 requires either a PS14 power supply (or 14V DC, 300ma equivalent power supply) plugged into the modular socket provided on the back of the DS64.

 

  • DS44-DS44 is powered by directly connecting the unit to the track power of your railroad.

 

  • DS52-DS52 is powered by directly connecting the unit to the track power of your railroad.

 

  • DS51K1-The DS51K1 is powered by directly connecting the unit to the track power of your railroad.

 

  • SE8C-SE8C is powered by 12V AC or 15V DC power supply to Pin 3 and Pin C on the 44-Pin edge connector. This powers the SE8C. Multiple SE8Cs can be powered by a single shared power supply as long as you provide at least 100mA for each SE8C. This power supply should not power any devices other than SE8C and BDL168.

 

  • BDL168-The BDL168 requires a 12V-16V AC or DC power supply which is sold separately.  Multiple BDL16 series detectors can be powered from the same power supply as long as 100mA is provided for each BDL16 series detector. One Digitrax PS14 power supply can run up to three BDL16 series detectors.



While it is possible to power many of these stationary decoders from the track (such as DS44, DS52 and DS51K1), keep in mind that doing so will draw power resources away from the locomotives.  You may find it better to supply power to those stationary decoders via a power bus, using one node of the PM42 for short circuit protection.  

Likewise, while it is possible to use a single power source such as PS12 for several devices, you are advised that care and caution is required in doing so to insure sufficient power for proper operation and to prevent out of phase connections.  If you are unsure, ask your dealer or other Digitrax customers.


Powering Other LocoNet Devices

  • LNRP-The LocoNet Repeater uses the PS14 power supply.
  • UP5-Universal Panel-The UP5 can be powered with the PS14 power supply as a "battery saver" for throttles which are plugged into LocoNet.
  • UR90-Infrared Receiver-The UR90 requires a PS14 power supply for proper operation.
  • UR91- Simplex Radio/IR Receiver'The UR91 requires a PS14 power supply for proper operation.
  • UR92- Duplex Radio/IR Transceceiver'The UR92 is sold with the PS14 power supply necessary for proper operation.


    Please note: The PS12 power supply has been discontinued and is replaced by the PS14 power supply.  The PS14 is a plug compatible replacement for the PS12 (Any Digitrax product that used a PS12 can safely use the PS14.)

    Ground

    We recommend safety grounding (earthing) of the Command Station/Booster in at least one place in the system, primarily for safety.  Without the safety ground return it is possible that a breaker or fuse will not trip.  With the safety ground connection at the booster, any stray current is most likely to be diverted safely through the booster electronics to ground.  Even though the safety hazard may be a low-probability event,  grounding is simply a good practice in most power distribution schemes.

    Most of the command stations and boosters have a terminal marked Ground.  You should also be aware that several Digitrax accessories also have a terminal marked Ground, which is used as a common connection for the device to its sensors; these should be considered as a Common + connection and not connected to the ground connection of the command stations and/or boosters.  Consult your Digitrax documentation for further details.

    The LocoNet has typically two 1-amp rated common ground conductors, but it is good safety practice to have solid grounds at each booster, since this is the likely return for stray currents on the tracks.  Lightning strikes near a house can also induce stray voltages in the layout wiring that can be bypassed with a safety earth/ground connection.

Was this article helpful? Send us feedback!

Please let us know if this article was helpful to you.

Please leave a detailed message below.