DCC Myths

DCCWiki, a community DCC encyclopedia.

With all new technology, a number of related myths and half truths will appear. Digital Command Control is not immune to mythology. They are spread by those who don't understand how this new control system works, or just need a reason not to embrace the technology.

If you are unsure of DCC, read on and explore the rest of the DCC Wiki as well.

Digital Command Control Myths

There are many myths surrounding DCC and how it works. These are just a few of the common myths you may have encountered. Some have been around for a long time and just will not die, despite evidence to the contrary. Don't let these myths deny you the enjoyment Digital Command Control can bring to your layout operations. You have highly detailed locomotives, why not have realistic operation to match?

Be sure to explore the DCC Wiki and you can click on the highlighted terms to learn more. The DCC Tutorials are also an excellent resource.

  1. DCC track signal is AC or DC: FALSE. In truth, it is neither. DCC is digital data sent in the form of Pulse Width Modulation on the rails.
  2. I can read DCC voltages correctly with a multi-meter: FALSE. Only a purpose built DCC meter such as the RRampmeter or an oscilloscope will give accurate readings. You can get an approximate voltage with a regular meter set to AC Volts.
  3. You can run Analog and DCC on the same layout: FALSE. When direct current and DCC meet, only bad things can happen. If you need to use analog power, wire the layout so you can connect only one source of power to the layout.
  4. Only two wires are needed for DCC: FALSE. DCC will eliminate a lot of wiring needed for analog operations. See the article on Wiring for more information.
  5. You have to use terminators if your Track Bus wire run is long: FALSE. Most DCC manufacturers do not recommend or insist on terminations. The track signals should be checked with an oscilloscope first to determine if there is a problem, which may require a different solution. Many signal integrity issues are directly related to inadequate wiring.
  6. DCC is much more expensive than Analog: FALSE. In the long run, the added complexity of analog wiring schemes will cost more in time and money than your DCC system. The big expense is the DCC Starter Set, which is a one time cost. How much you spend is up to you.
  7. Costly boosters are needed or it just won't work. FALSE. Additional boosters provide additional power, if required. A typical DCC system includes a booster.
  8. Larger layouts need additional boosters: FALSE. The number needed is based on the power consumption. Factors: How many locos are running at the SAME TIME. Do they have sound or lights? Do you run lighted passenger cars? Do you have stationary decoders on the track bus?
  9. The boosters with higher current ratings are better: FALSE. An oversized booster will have too much available inrush current for smaller scales. Unless you have correctly set circuit protection, locomotive damage is possible. If you employ a power management device and divide the layout into power districts, with a lower current (for example, 4A) setting, this may make sense. Remember, high current boosters can deliver a lot of current into a short circuit, as much as 60A for a brief period of time. Which results in damage before a circuit breaker can react to it.
  10. Sound Decoders need a lot more power: FALSE. High inrush current is only at cold start up. Otherwise, sound only needs about 20% more power than a silent decoder.
  11. BEMF never works in a consist: FALSE. It is sensitive to mismatches of decoder/loco/manufacturer and can be difficult to setup correctly. However, it can be done. Most users do not need BEMF, and it is ok to disable if causing issues. True, it can be an issue. But this is not an absolute TRUE/FALSE situation. Some multifunction decoders will disable BEMF when consisted.
  12. The command station will shut down when a booster is shorted: Maybe. If you only have one command station/booster and no circuit breaker at all, then yes. Remember that the protection in ANY booster or Command station is designed to protect the equipment it is part of. Other boosters will continue as if nothing is wrong.
  13. Programming on the main/OPS mode programming is dangerous: FALSE. Used for specific decoder address/specific CV. Programming On the Main (POM) means you instruct the command station to send instructions to change a specific CV to a specific decoder address. It is the same as sending a horn or light instruction. Blast Mode, often initiated by using address 0, causes instructions to to send to EVERY decoder in every locomotive on the rails. Both methods are not used with a dedicated programming track, which frequently leads to confusion. Remember you get NO read back of CV in POM/OPS modes. Unless you have Lenz’s Railcom or Digitrax’s Transponding technologies implemented on your layout.
  14. I have to convert all my locomotives to DCC: FALSE. You only need to convert those you wish to use on a regular basis. Some may not be easily converted to DCC. Others may not be worthwhile to convert. Unless you have real attachment to them, they can be sold off and newer motive power purchased.
  15. Stall Current is important: Maybe. Older locomotives, yes. Newer locomotives have improved drivetrains and motors which are more efficient and do not draw as much current. It does not hurt to check. Most decoders will shut down if they overheat, and many modern decoders have the ability to handle an amp of current to the motor.
  16. DCC Ready means the locomotive has a decoder: FALSE. The term DCC Ready can have many meanings. The DCC Ready locomotive lacks a decoder but can be converted easily.
  17. The selection of a multifunction decoder is determined by the scale: FALSE. Many N scale decoders will work in an H0 scale locomotive without problems. You may pay more and get fewer functions with an N or Z scale multifunction decoder.
  18. Digital Command Control decoders will reset to their default address when running on a continuous loop. This myth appeared in the United Kingdom and was promoted at train shows. Despite the fact that many of the exhibition layouts are loops and running DCC. Yet their decoders did not reset to "03". This myth is FALSE. A decoder can be corrupted, but running in a loop isn't a cause.
  19. Digital Command Control is only a benefit to a large layout. FALSE: DCC benefits any layout, large or small.
  20. I need a computer to be able to use DCC. FALSE. You do not need a computer. But they can be a very useful addition to your DCC system.
  21. You must purchase a decoder testing device. FALSE: While a Decoder Tester is a useful item, much like a computer it is not a requirement. Although they can be very useful.
  22. The track must be absolutely perfectly clean or DCC will not work. FALSE. Track must be kept reasonably clean for reliable operation, regardless of the control system used.
  23. Turnouts must be replaced with DCC Friendly ones. FALSE. There really is no such thing as a DCC Friendly turnout. If a turnout worked fine with analog operations, it will work fine with DCC as well. The issue is strictly electrical, and some turnouts may require adjustments or modifications to eliminate troublesome problems. Click on the link for more information of issues related to turnouts and DCC.
  24. CV29 is different among decoders: FALSE :The four mandatory NMRA CV’s are: CV1 Primary (short) address, CV7 Manufacturer version number, CV8 Manufacturer ID Number, CV29 Configuration Data.
  25. Automotive tail lights are necessary to protect against short circuits. FALSE. In fact, they may actually defeat the short circuit protection offered by the booster.
  26. To extend radio range you can use a pie pan. FALSE

See Also

Introduction to DCC