A Guide TO Dcc Page 11 A Guide to DCC

11 9 need that much power to be programmed, so see if your decoder needs it before making the purchase. Operational Considerations In general, there is very little that goes wrong within the DCC system components. Most of the challenges are in the wiring out of the system as well as how it is operated. As was discussed, if the system is not operating correctly, start working backwards from when and where it failed to what is known to work. Loose connections, cold solder joints, and broken wires can cause problems with reliable operation. Problems that can occur with a properly operating system can usually be traced back to a few areas. First and foremost is clean track and wheels. DCC requires a constant connection between the booster and decoder. The most critical element in these connections is between the rails and the wheels. Dirty tracks and dirty wheels are notorious for causing operational problems. Clean both tracks and wheels regularly to assure good electrical conductivity between the two. If your layout is in a dusty or humid environment, consider methods to keep dust off the layout and remove humidity from the layout room. There are varying opinions on whether or not to use track cleaning fluids and coatings. Each camp seems to have strong opinions of what works best for them. Do research and talk with fellow model railroaders on what works best in your environment. Regardless of the approach, all would agree that less is more and any kind of track treatment option should be used very sparingly. One final comment on this topic since DCC requires continuous and reliable communication of data via the tracks, any electrical noise will tend to cause problems. Besides dirty track and wheels, the next biggest culprit are occasional shorts and derailments. These tend to create electrical noise on the tracks that is occasionally picked up by locomotive decoders. The DCC data protocol is self-correcting, however you may find at some point the system is confused. A simple and effective remedy is to simply turn off all the power to the layout, including boosters and handheld controllers, wait 10-15 seconds to assure all the power capacitors are fully discharged, and then restart the DCC system. ADVANCED OPERATIONS Speed Curves - Getting Your Locomotives to Run Together Since decoders are basically on-board microprocessors, they can be programmed to adjust the motor control output to specific speed curves. A speed curve is a definition of how fast the motor should be running for each speed step. By default, most decoders are set up with a straight line speed control. That is, each speed step will increase the speed control to the motor by the proportional fraction of that speed step. In other words, each stop on a 28 speed step increases or decreases the speed to the motor 1/28th of the total. Similarly, a straight line speed curve on 128 speed steps will change the speed control 1/128th of the total speed control to the motor. Most decoders are provided with a variety of speed curves, including straight line and varying degrees of logarithmic and exponential. Logarithmic curves tend to have more gain in the first few speed steps, and are popular for situations where you might want to get the train rolling quickly. Exponential speed curves will tend to have a very flat response at first and then accelerate later. These are useful for programming into switchers which require a lot of slow speed control. In addition to preset speed curves, most decoders allow a user defined speed curve to be programmed into the decoder. The user defined speed curve allows you to create virtually any throttle response curve you can imagine. The most common use for these is to latten out the response at the ends of the curves so that the prime mover sound in sound decoders can be played before the loco starts moving or at full speed. User defined speed curves can be tedious to program into a decoder manually one point at a time, and most users will use some kind of PC interface to program them. Vmax/Speed Trim Similar to speed curved, Vmax and speed trim can be used to adjust the maximum speed of a loco. In general Vmax or Speed Trim functions will proportionally lower or raise the entire speed curve by some factor. These functions are very handy to speed match locomotives in preparation for MU consisting. Another common use for these functions is to limit the speed on locomotives, especially yard switchers. Some decoders offer speed trim for both the forward and reverse direction. This is very handy for locos that for some reason will run at different speeds depending on what direction they are going. Many decoders and systems allow you to adjust acceleration and speed characteristics. For example, switchers can be easily programmed for great performance at low switching speeds.

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