Everyone, If you cruise the Information Superhighway as much as I do, you already know about this site. For those who prefer to let the world come to them, Take a ride over to this little gem and read all about DCC. You will find DCC described in plane english mixed with a little EEE lingo that will actually tell you how this stuff works. Just click on the bar labeled DCC on the left when the site loads. Link to: N Scale Org. Have fun GM [ March 16, 2006, 10:34 PM: Message edited by: GM ]
Thanks, great site! DCC is about to take off her in the UK and I want to get ahead of the game. James
James, Owen, Sheldon: It was slow yesterday also! It was slow this morning too. Whoever wrote that thing is showing off all of the tricks he knows, but forgot about his customers. Oh well. What fascinated me, was: This bipolar waveform is similar to the common Alternating-Current (AC) waveform found at the duplex outlets in your home, or to the AC waveform used to operate AC locomotives; similar, but definitely NOT the same thing: The wave shape is different sinusoidal for AC square wave for DCC The voltage is different ±165 volts peak (115 volts RMS) for AC (USA) ±14-16 volts peak (14-16 volts RMS) for DCC The frequency is different 60Hz for AC (USA) Approx. 8000Hz (8KHz) for DCC So...don't confuse the DCC signal with any AC signal. The bipolar DCC signal is a hefty, high-current signal, which allows the on-board Decoder to </font> (1) extract the data packets from the Command Station and</font> (2) rectify and filter the bipolar signal to provide clean Direct Current (DC) for application to the locomotive motor (actually, the Decoder provides a Pulse-Width Modulated [PWM] DC signal to the motor, but we'll cover that later).</font> Next I need to turn my attention to the function of the decoders. When a train enters or leaves a reversing loop, the Phase is changed 180° to match the track ahead. I think I know why the train continues in the same direction, but have not been able to find anything written about how it works. I will keep looking. Owen, Thanks for the Link. Unfortunately I didn’t find what I was looking for there. James, That site had some good basic information. There is a lot more to it than what was written. Most of the additional things you will need to know relate to the specific model and manufacture of the equipment. Things like programming the mobile decoders etc. are fully covered in the manufacturers owner’s manuals. Download those that you might be considering for future purchase and study them. I have to run into town for a while. See you all when I get back. GM [ March 17, 2006, 04:35 PM: Message edited by: GM ]
GM Here is another site I found very usefull http://www.wiringfordcc.com/ and http://www.siliconvalleylines.org/downloads/dccwirin.pdf
Here is the best DCC site for info about DCC in plain English. It's all outlined into different chapters: Tony's Trains DCC Primer Tony's Trains is one of the leading experts in the field of DCC. Have fun.... Stay cool and run steam......
Hi Bob, Maybe you can help answer a question. What is it that makes a locomotive continue on its journey in the same direction when exiting a reversing loop? When the loco enters the loop, the reversing loop controller will only change the phase of the AC wave 180° if necessary. That action by the controller eliminates the potential for a short circuit at the entrance to the loop. I suspect that the same logic is applied when the loco is in the process of exiting the loop. Is it the rectifier that makes it possible to see the DC current in the same manner regardless of the phase? I cannot find this type of information in anyplace on the net where I have searched. Do you know how it works? GM
GM: You're correct. The same logic is applied when the loco exits the reverse loop. Stay cool and run steam....
Bob, Did I just get lucky on one of those 50% probability things? I'm still looking for the source for this change in phase reversal of polarity thing. Us older folks could use some research guidence by the younger ones like yourself. Thanks for your help. I will keep looking. GM
GM: "Us older folks could use some research guidence by the younger ones like yourself. " I think you have that reversed. Stay cool and run steam....
"Did I just get lucky on one of those 50% probability things? I'm still looking for the source for this change in phase reversal of polarity thing. Us older folks could use some research guidence by the younger ones like yourself. Thanks for your help. I will keep looking." GM: Here is the answer you need directly from Tony's Train's DCC Primer in the Reverse loop section: You can operate reverse loops manually or automatically using DCC. You must double gap (completely isolate) both ends of the reversing section. If you choose manual operation you will power the reverse section separately and use a switch or relay to handle the polarity change as the locomotive enters and leaves the reversing section. If you use an auto reversing strategy you will power the reverse section separately and use an auto reversing booster or other auto reversing device to handle the polarity change. Note that when the polarity change occurs DCC equipped locomotives will continue at the speed and in the direction commanded but any analog engines running will reverse direction because they "see" the polarity change and respond to it. If you choose the auto reversing booster strategy, you will need at least two boosters. One will be the system reference booster and the second will be the auto reverser. The good news is that you can run more than one reversing section on a single auto-reversing booster. Note that some auto reversing devices require that you make changes to locomotive wiring where the pickups are not "side by side" on the locomotive. This is an issue in many steam locomotives where one power pickup is on the locomotive and the other is on the tender. Stay cool and run steam......
Bob, Well with this little tad bit of knowledge we are really getting somewhere. I just did a cut and paste of the following from your previous post. "Note that when the polarity change occurs DCC equipped locomotives will continue at the speed and in the direction commanded but any analog engines running will reverse direction because they "see" the polarity change and respond to it. That text incorrectly uses the word polarity (alternating current has no polarity) when in fact the author probably meant to use phase. Like most of the articles I have found to date on the Internet, everyone try’s to tell us what happens when the locomotive leaves the reversing loop, but nowhere do they tell you how it actually works in plane English. As I understand the technology at this moment, there is no DC current whatsoever on the rails. It is all square wave Alternating Current. Once that AC passes through the bridge in the decoder, it is in the form of Direct Current. Now comes the magic of this stuff. The decoder sends some of that DC at full amplitude to the motor in the form of timed pulses, which control the velocity of the locomotive. The longer the duration of the pulse, the faster the train goes. It is only when the decoder receives a 10 or 11 command packet from the controller will the velocity or direction change If you or anyone else needs to know all the gory details about how this stuff actually works, they can be found at: http://www.nmra.org/standards/DCC/standards_rps/rp921.html#Speed%20and%20Direction%20Instructions . As usual I really do appreciate your help in these matters. GM [ March 17, 2006, 09:19 PM: Message edited by: GM ]
GM: I'm just the messenger. I didn't write the article. Glad I could help out. Stay cool and run steam.....
I know. I just received a response to a message I sent earlier today to the author of the DCC article I quoted in the initial post. I posed the identical question to him. For your edification, the following is his response. ”You've got the answer to your question exactly. The loco doesn't care about the relative polarity (phase) on the track, as the AC signal is indeed rectified to drive the decoder and the DC motor; the decoder remembers which way it's supposed to be going, and drives the motor forward; the DC polarity would have to be reversed to cause the loco to reverse, and only the decoder can do that. The only issue with a reversing loop is the phase of the AC signal itself; unless you have insulating rail joiners on both rails somewhere inside the loop, you get a dead short (to see this, simply follow the "outside" rail around the loop; once it gets back to the main, it's the "inside" rail).” That rectified current (Now in the form of DC)never reaches the tracks. I sure do appreciate the responses I receive from you young folks. GM
