OK for those who don't know this a basic lesson and the differences between DCC and DC and what is really going on with your rails. First DC is analog which means the track voltage varies as well as the polarity depending on which way you want a loco to go. This effects the entire block or layout and all engines in this block will respond. DCC is Digital AC or square wave AC. It feeds the tracks an alternating positive and negative voltage instantly switching polarity. The tracks will ALWAYS be powered at the fullest potential of the system. This is why the DC only motors buzz or hum when they are set on DCC rails. The DC motor is being told to go one way and almost instantly being told to go the other way and rinse and repeat. Electric motors draw a high current due to the low resistance in the windings. This isn't that big of an issue when the motor spins as the coils that make up the armature are constantly being turned on, then off then on then off as the motor spins, plus the spinning will allow air to help cool the motor. On a DCC track the motor is being reversed before it can move, so the next set of coils do not get energized and the motor does not spin so no air cooling. It just keeps heating up one set of coils as if it were stalled. So now we come into 0 stretching. To allow a DC motor to run on DCC rails the track voltage must stay positive or negative for a long enough time to allow the motor to rotate to the next set of coils. The command station will keep the top of the digital signal high (or low) for an extended period of time depending on throttle settings. This will allow the DC motor to move. All the while the command station still needs to send AC down the tracks along with any signals to other trains. So while the track signal isn't perfectly spaced any more all the same signals are still transmitted as is the AC carrier. Some lag will be experienced in the DCC equipment but that isn't much of an issue, the real issue is since the DCC signals are still transmitted the DC motor also receives them. Even though the motor is running one direction the DCC track signal which are 1/2 the time the opposite polarity are still felt by the DC motor. This causes heat in the DC motor as it is being asked to reverse its direction while going along. This causes a current spike every time the signal is reversed and that can be hard on the command station electronics. This is one of the reasons why many command stations lack this feature. Now lets talk about how a DCC locomotive works. The decoder is always reading the signals on the track, receiving EVERY bit of information and ignoring all but the information that has it's address on it. A decoder will activate a motor by pulsing DC current at full track voltage to it in the polarity requested by the signal from the command station. It works with something called pulse width modulation. What that means is it changes the time of the "ON" pulse. At the slowest speeds the on pulse is short and the off pulse is long, and middle speed the on and off pulse are the same length and at full speed the on pulse is longer than the off pulse. THERE IS ALWAYS AN OFF PULSE! This is why some engines can run faster on DC than on DCC but that's not really why there is an off pulse. There is an off pulse for 1 main reason and there is a side effect that engineers (not the locomotive type but the electronic type) have used to make our lives a little better. First because of the way the MOSFET type transistors in the decoder work they need to be switched on and off really fast to function properly. If they are left on they will actually stop flowing current, so the off pulse resets them. This also applies to speed controls used in RC planes, boats and cars. The side effect of this off pulse has something to do with the nature of a DC electric motor. When pushed a DC motor will become a generator. During the off pulse the motor generates a slight DC current back on the circuit. Early decoders ignored this current but engineers have designed our more modern decoders to use this slight current to determine motor speed and load. Its called BEMF or Back Electro-Motive Force. BEMF can be used to feedback engine speed, or keep a steady speed if climbing a grade or descending down one without you needing to change the speed control knob. If you own a hybrid car or a Tesla this is commonly used to regen the batteries and on real 1:1 locomotives it's used for dynamic braking. AC motors can do this as well but they are way more complex and are not used in model railroading. Coreless motors are a unique little critter all on their own. A standard DC motor has fixed magnets on the outside of the shell, and the armature is an electro-magnet of 2 or more coils/poles. With our trains usually 3 to 7 polled motors are common. With a DC coreless motor there are 2 coils (more in larger motors) in the shell and a fixed magnet on the armature. There is usually a small transistor circuit built in on larger ones but really small coreless need supporting circuitry. This circuitry takes the DC analog signal and energizes the coils which will cause the motor to rotate, then reverses the signals again as the magnets align to keep the motor spinning. The more voltage the stronger the repulsive force applied to the magnet on the armature and thus the motor spins faster (just like any electric motor). The problem with using pulse width modulation on this type of motor, is it effects the supporting circuitry to the coreless motor. That circuitry needs to be designed for PWM signals which can get expensive. A second side effect is that coreless motors usually operate on a much lower voltage than standard motors. This is why even with 0 stretching you never want to put a coreless motored train on DCC rails. Yes some have supporting circuitry that can handle DCC and some even operate on DCC with the correct type of decoder but those need to be specially designed to operate together. Most DCC coreless motors are actually 3 phase brushless motors you will find on larger scale locomtives. N scale usually use 2 pole micro sized coreless that work on a max of 5v. If you are asking why? Well it's simple... they are small, simple and powerful for their size. If you are all still reading sorry it was so long (it could have longer, this is only a basic lesson and also thank you for still being here!
Ok. That solves my question. I think. Since that guy ran a dcc ready locomotive on a dcc layout. He probably wrecked the motor. Which is what my problem is to begin with. A burned out motor. I really need to find a new motor for mine and skip on the one on evil bay. Thanks. If anyone knows anything of that motor in the Fox Valley Hiawatha. I hope you can share some info with me. Sent from my SM-G975U using Tapatalk
Now to throw a wrench into the gears, according to what I've read on DCC: "The DCC signal is not an Alternating Current sine wave, nor is it a special form of AC. The DCC signal switches quickly between states, and varies the time period (the modulation) it is High or Low to convey information to trains on the track. Contrary to popular belief, there is no negative voltage present on the rails. The average Direct Current Voltage is Zero Volts." My interpretation of the above statement is, the motors hum because you are turning the voltage on and off at a very high rate and the motor does not move because the on time is not long enough for the armature coils to build up enough magnetism to advance to the next field. "The reason the oscilloscope trace appears to have a positive and negative component is the reference point changes with respect to the signal. What the scope displays is a signal that is either more positive or more negative than the 0V reference. With the ground clip is attached to Rail B, and the probe to Rail A, when Rail A is ON or HIGH it shows a positive going trace. When Rail A becomes the zero reference, the ground clip's potential appears to be less positive and a negative going trace is drawn. Despite what the scope displays, the signal on either rail is of the same potential, just reversed when the phase changes." Myths about the DCC Power There are a number of myths circulating about Digital Command Control that refuse to fade away. Most are the result of applying analog concepts to a digital technology.. DCC is Alternating Current. DCC is a form of Alternating Current DCC has Polarity. Correct Answer: None of the Above. Digital Command Control is based around Digital Technology. Unlike Analog electronics, digital electronics have no concept of polarity. They have two states: On and Off. This is called Binary, as there are only two defined values. The binary nature of DCC means no negative voltages present on the rails. The signal on one rail is always the inverse of the signal on the other rail. Thus, when Rail A is ON, Rail B is in the inverse state, or OFF. From reading through the information found at the DCC Wiki, (https://dccwiki.com/DCC_Tutorial_(Power) ) it appears time also plays a role in the DCC signal and that is where bit stretching comes in. It appears an OFF bit has a value of 100 microsecond and a ON bit has a value of 58 microseconds. One of the illustrations on the web page shows an example of ZERO or Bit Stretching. DCC can be a hard subject to get your head around until you stop worrying about polarity and think more in terms of computer bytes, the states are either on or off. I'm no expert on DCC, but this is my understand on how the systems work via reading the information on the DCC Wiki page.
WARNING: Unless you have an isolated or battery powered oscilloscope, DO NOT PUT THE SCOPE's GROUND CLIP ON EITHER RAIL SIGNAL. The ground clip on standard oscilloscopes/probes is tied to the scope's AC power ground. Different DCC systems, with different power supplies, may or may not isolate the rail signals from ground. Both rails may be periodically driven to non-ground voltages as part of the DCC waveform. Thus, depending on the power supply, the ground clip could short out the rail to which it is attached. Even if the DCC power supply is isolated, shorting a rail to ground through the scope could cause rapid changes in the local "ground" potential for the command station, inducing electrical and RF noise which may interfere with correct operation of the DCC system or other nearby electronics. If you have more than one scope channel, put one probe's tip on each rail, and either view both signals simultaneously, or if your scope allows, display the difference between the channels (e.g. "A-B") as one scope trace. The DCC signal is a differential signal, comprised of a relatively positive and negative component relative to each other. The data encoded on the differential signal is based on relative time periods with one signal greater than the other. Thus, as far at the data is concerned, the polarity of the two differential complements is meaningless. HOWEVER, to prevent shorts in the track/wiring, polarity STILL MATTERS. The problem with AC is most people co-equate that nomenclature with household power wires and/or sinewaves. Technically, AC just specifies that voltage and current flow in the circuit switches directions frequently. This is true of DCC track signals, and therefore it is correct to refer to DCC as an AC waveform. In fact, the AC DCC signal is also rectified, filtered and regulated by the decoder to provide the DC power necessary to operate the remainder of the decoder and the locomotive's motor, very similarly to most electronic appliances that plug into your 120/240 VAC power. Thus DCC is a type of AC power signal for the rails (and locomotives riding on them), that also conveys commands and data by the timing with which it alternates. When a DC motor is given pure AC voltage (which DCC is, without zero-stretching) for an indefinite period of time, the motor can overheat, some types more than others.
I should have worded what I was saying a bit more like you did here, but I was trying to make it a simple concept that beginners could use and understand while also letting them know that it's not the same AC as your wall socket.
