DCC Basics-Track Power, How Does It Work (305)
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- čas přidán 22. 02. 2023
- So many modelers assume that DCC is simply another form of AC power, however that is an incorrect assumption. In this video I'll show you how AC and DCC work on a model railroad. I'll also and show some things that can go wrong, and what you can do to counter them.
- Jak na to + styl
For those interested in digging deeper here is a link to a good description of DCC track power. Maybe their explanation will help too.
dccwiki.com/DCC_Tutorial_(Power)
Very cool..... it is confusing. If you measure the voltage between the dcc rails with a multimeter it will read 0 volts. But if you measure and observe the waveform with an oscilloscope, reference to common ground, you will see what is going on ( isolate your scope). On my layout Rail A is 0 to positive I2C. Rail B is 0 to positive I2C but with just enough phase offet to oppose rail A.... thus one must measure relative to a common reference....
The NMRA DCC Working Group description of the DCC signal is, and I quote, "The DCC signal is a bipolar square waveform, which contains digital information. Long pulses are zero and short pulses are ones." It can easily be demonstrated that the DCC current has both a direct current component and an alternating current component - simply measure the track current with a true RMS multimeter that has wideband current measurement capability or an oscilloscope with a good quality current probe. The dc current component is very small and due to variations in symmetry of the bipolar waveform caused by the DCC information encoding. The majority of the current alternates back and forth. The output stage of DCC boosters is generally an H bridge circuit using 4 power MOSFETs controlled to switch in pairs generating an alternating voltage on the rails. DCC loco decoders have a bridge rectifier, a microcontroller then a MOSFET H bridge circuit controlled to generate a unipolar dc pulse width modulated signal of either polarity to drive the motor at the required speed and direction.
Thanks for your explanation. Now I understand how it works with DCC.
Great information, and great job explaining the wave form of track power. I think I will look into a snubber for my home layout
Great info, Larry! I'm getting close to wiring my system and I'll be looking through your videos for tips.
DCC is technically AC power and the waveship is not relevant with regard to AC or DC. Also since there is no return or ground path, when a rail is positive the return path is to the opposite rail. So when one rail is positive you can say the the other rail is negative. The big advantage is that the DCC wave can be passes through a bridge rectifier to produce DC voltage for the electronics, lights and motors. At the same time the DCC signal can be sampled in order to decode the digital data.
paul
Much needed information, thanks!
Bonjour Larry, I think I'll install the DCC-Concept IP CB. Never had any problem in the past 4 years of building & operating my layout but it's good advice that I take onboard to protect the expensive decoders. Snubbers were installed from the beginning. Thanks for sharing this well documented video. Cheers, Filip
Thank you for your help with wiring my N gauge railroad between your multitude of CZcams videos & your book “Wiring Your Model Railroad.” Although I don’t always agree with everything I “hear” I find myself going back to your book as I have some learning issues so I don’t hear what you are actually saying. I’ve had your book awhile but I never saw the last page & took the time to read your bio today. Now I wonder if we should refer to you as the “DCC Doctor!” Thanks Doc!
Your diagram of DCC is a bit misleading as you show two different rails. Your description is spot on however. The diagram gives the illusion of + / - whereas, as you've stated, DCC is either on or off. The sine wave you showed earlier is the voltage relative to ground so it really shows only 1 rail.
I find it really takes some time to get your head around DCC, at a detailed level. Especially when you are trouble shooting and trying using a voltmeter! :)
Anyway, keep the videos coming, it all helps to piece it together.
Another clarification is that a typical decoder will sample the digital data in the middle of a data pulse (typically 25 us for the example given). This method tends to ignore the ringing and noise on the transition that was shown. The ringing must last longer than the 25 us to cause demodulation errors. Long tracks and multiple consumers can cause this to happen, in which case a damping network will help.
paul
As always Great information Larry. I use NCE equipment EB1 and Snubbers on each bus line all my EB1's use the push button reset too. This guy I know always says AC power for his DCC system I thought he was wrong for saying that but now I know he is thanks for the input
hello larry its is randy and i like u your video is cool thanks friends randy
Watching your playlist, learning so much and really understanding this material. I have your book & it is packed with info (great reference) but these videos help more for me as I have problems reading. In your DCC 101 video I loved the nod to “Radio Shack,” there was a store four blocks from our old house, loved the convenience. Thanks for sharing, do you perhaps remember the computers running on notched cards?
Heck, I can remember sitting at a key punch machine tapping out those cards to run my statistics programs when I was doing my masters work in college. Do you remember the Xmas wreaths people used to make out of those old IBM cards?
@@TheDCCGuy I do not. When I was a freshman in High School I visited my brother taking a computer class with the long notched index card.
Basically you would roll one end over to make a cone and staple it, do that about 50-100 times. Then just create a ring of those with the pointed end of the cones facing out and staple or glue them all together. Finally spray paint gold or whatever and glue on pine cones, glitter, etc. They were the thing in the late 1960s. Google search will show what I mean.
@@TheDCCGuy I remember starting work in an ER and Win 3.1 was released
Time stamp 5.25 is not how computers send data. The wide pulse would be more than one high, and the low would be your zero or low pulse. It's timed, and the timing is synchronized with a start pulse. This is how serial transmission works, like RS 232 and USB, which came out of RS232. The reference line is in the wrong place as well. It should be on one of the rails, because what you are showing is an AC signal. For this to be a DC (DCC) the reference has to be high or low, not in the middle.
It's also sent as packets, which means that more than one character / command, can be sent back to back without a timing pulse for each character, or in this case command sent. The computer samples the high or low in the middle of the high or low to see what it is. If the timing is off, then the signal message is corrupted.
You need to know the start and how big the data message is to tell the binary message sent. It looks like the one you have as an example is 10101011 00101100 1100... This is assuming these are bytes, and we know the start of the massage is on the left.
As usual, everyone has their own 'can of worms' (have taken a couple of physics courses + am a USN trained Electronics Technician of 50+ yrs) ... People R gonna' always disagree (once the teeth get set in the bone, they can't seem to accept any other explanation/viewpoint) ... I do have a question on one of the scope pictures ... The picture shows the 100us label over the right rail with the explanation being a "0" ... I think the label should B one pulse to the right over the left rail ... Very good explanation/examples of DCC basics !!
Larry , I enjoy your videos on DCC. I’m new to the hobby. I have bought all four volumes of DCC. I like what you did for your SW1 switcher. My switcher are all in O scale 3 rail. I live in a real small town and there are no hobby shops within 80 miles or so. If you have any suggestions I would greatly appreciate it. I would like to add the following: sound, ditch lights and whatever else would go with these switchers. Any cues where to find the decoders and speakers would be greatly appreciated. Thanks for all your assistance in this matter. Ed.
Are these AC or DC locos? As for sources check out www.sbs4dcc.com. Bryan is a great seller who provides good quality at fair prices and he knows his stuff.
@@TheDCCGuy all AC
Fascinating, Larry. DCC is, at its essence, really very clever, isn't it? To a non-physicist, non-electrical engineer like me, embedding the signal in the "waveform" is like some kind of hi-tech cold war spy stuff! Or the start of the movie Independence Day.🤣
I was intrigued that the DCC Concepts appears to have a third component in addition to the capacitor and resistor, and wondered what that contributes and whether it would be worth adding to to your homemade filter? (I rewatched the other video on RC filters, but you didn't have the DCC concepts one then, it seems.)
I need to ask them what it is and what it does.
I gotmout my magnifiers and looked at the third device and it appears to be a TVS diode which I discussed i a video recently on protecting locos and decoders. They act to limit the maximum voltage while the RC components actually will kill certain voltage surges. So it appears to cover both bases. I hope to hear back from DCC Concepts this week.
How do the circuit breakers you discussed compare to the built-in circuit breaking action of, say a DCS210+?
Great video Larry. I have wires going from my power cab to terminal strips and then feeder wires out from the strips to the track. If I install a filter where should that go. Thanks for the videos
The RC filters go at the ends of your bus wires.
Hi Larry, on the NCE Snubber board there is marked provision for Extra C and Extra R at each end res[ectively. Does this mean that the RC filter can be altered by adding more resistance and capacitance. I have constructed and installed two RC filters on my layout at the wiring stage and with the tolerance in the components they are both providing different effects by approx 45nF which I would not think is going to make a great difference . Thank you for your insights and info into DCC ...... Helps and older DC modeller change to the new technology,. Cheers Greg
Yes, Jim provided those tabs for folks who want to experiment.
can I add a transorb or snubbing networks along the track
As a physicist, I'm not sure I agree with you Larry. DCC is alternating current power. Think about it this way. DCC is a very, very poor attempt at producing an AC sinusoidal waveform. A standard diode bridge ... followed with a filtering capacitor ... will yield DC power when each the two rails of a DCC system are connected to the diode bridge. Swapping the rails when connecting to the bridge yields the same result. Of course, there will be a small voltage drop across the diodes of the bridge.
A sinusoidal wave of alternating current is timed and constantly cyclic above and below 0. A DCC wave is clipped and not constantly timed. It is the variety of time that carries the digital signal. Take away the digital signal and you will have DC.
@@peteengard9966 No ... technically the DCC waveform is not made of "waves" ... it's made of "wavelets". The DCC signal is constant "zeros" until a "1" comes along when needed.
@@peteengard9966 Alternating current has nothing to do with the shape of the waves.
It's DC PWM, not AC.
@@BriansModelTrains Could be wrong, but as far as I know, all DCC encoders have diode bridges in them. One function to convert the AC between the rails into DC to power the engines DC motors and things like LED lighting., etc. It doesn't matter how the signals are put unto the rails .. or what the waveforms look like measured from either rail to the ground of the command station (or booster). What matters is what the decoders see between the rails.
Great video, also went back to the earlier video of yours that you suggested. I've been trying to solve a problem, maybe a snubber would help, what do you think? My problem is with using the newest Walthers switch machines and that system's dedicated controllers, I get a lot of ghost commands making the switch machines change route. Sometimes when going across (powered) frogs, but sometimes with no apparent track hiccup. It is a small 4'-6" x 6'-6" layout with 27 (eventual, 17 installed so far) switches so a lot of wiring congestion below the layout. I've been trying to keep separation between the wires (suggested by the Walthers tech folks) but as you can imagine that is difficult to do in the yard. It is frustrating and I'm getting close to changing out to either toggle switches or going all the way to Tortoises, but that entails a lot of work and expense I've already put in. Any suggestions on things I might try?
I suppose it is possible and a snubber is a quick and cheap bandaid to apply. I have a set of these but have never had time or inclination to try them out. I guess I need to find a spot on the layout for a test installation. You seem to be doing what I would have suggested-document what was happening each time a phantom operation occurred. Also go,over your wiring a d look for anything that does not follow DCC wiring protocols.
Dave, a question popped into my mind. How many turnouts throw when this happens? Is there any consistency to the number that throw or does it vary at random? At any rate following Walthers suggestion with the wiring, try tracing the wires on switches that do this and see if they pass near other sections of wires. You might try using twisted pair wires for the machines as this will help with electronic noise if that is the cause. You could try pulling them from Cat5 cables.
Have ever done the subject of code 308/306 on decoder pro and arduino? Almost all my locos work using decider pro /except/ an atlas with lok sound. It has all the lighting, and sounds , but, will not move at all.....
I have mentioned it somewhere and basically when I get it I shut the program down and restart it and the DCC system, which usually clears the conflict. However I have heard from several viewers lately having issues like this with the recent DecoderPro versions and some decoders so I suspect a bug. They even told one guy to fix the program himself! I steer clear of Arduinos so you’re on your own there.
@@TheDCCGuy Thank you for your response....
Very cool video, also first comment/like
/view
Interesting, thanks!
So it's a dual channel DC PWM signal being decoded as a digital signal? I think that's what people are confused about, the right and left rails are two separate signals form a pair of parallel PWM signals. Would explain why shorting is so destructive
The signals on the two rails are exact mirror images just slightly out of phase. Even though there is no true polarity in terms of positive and negative it still behaves that way since a short between a high and low is still a short.
@@TheDCCGuy if there's no polarity swing, it's DC PWM.
Hi Larry, excellent information. I am new to HO scale and DCC. I am coming from the O scale world where Lionel and MTH control systems are proprietary (yes MTH DCS can control Lionel TMCC but not Legacy). Are DCC control systems and locomotive decoders proprietary also? I am searching for confirmation that DCC control systems are compatible with any DCC decoder regardless of manufacturer. If I have the NCE DCC Power Cab system, do I have to have NCE decoders in the locomotives? Thank you.
DCC is an NMRA standard so yes, most things are compatible among the different systems. A Digitrax decoder will work with an NCE system and vice versa. The differences come when you get to extended functions and sounds as these can be implemented differently among manufacturers but they will still operate on the various systems. Also, some pieces of equipment are not interchangeable among manufacturers such as throttles and some other hardware. I have about a half dozen different systems and all my decoders will work on each and I have them from at lest 6 different manufacturers.
@@TheDCCGuy thank you so much, I appreciate your time. I am switching from O scale to HO due to space limitations. HO models have really nice detail. Thanks again.
I'm not Elec. genius..But it's like this: How would say, Bachmann put a decoder in their loco knowing many customers would be hitting the ceiling because their Bmann loco won't take commands from say an NCE throttle, or, say a Digitrax made throttle ?!
No. 99.99% of the time any and all makes of DCC throttles can correctly control any and all makes of decoders...
It's universal..Nothing to be concerned with there.
A few years ago I was going to build a railroad in nscale but never got started, rummaging around i came across the dcc set I bought it is the digi traks empire builder . My question is, would that be good to use or maybe get a newer one?
The Empire Builder set was built around the DB150 command station/booster and is rated at 5 amps. The only major limitation is the programming output and track power are a single output so you can do one or the other but not both at the same time. However it does support programming on the main as a work around. I suggest you start with it and as you find put more about DCC and what the newer systems offer you could upgrade then. You cans still use the DB150 as a booster for more power on the layout.
@@TheDCCGuy would this also work for HO
Yes
It doesn’t quite work like that. Each rail is grounded whilst the 14 odd volts goes through the other BUS. Then B is grounded whilst the 14 volts goes through A. The phasing continuously grounds the rail between each phase. It could be long or short for 0 or 1. You never get 28 volts between both rails.
is your book on electricity and wyring up to date?
Ask the guy who commented just before you, Stephen Dougherty, he has a copy.
It would have been easier to say yes or no
I will buy it the same with his brothers
I always feel it is a stronger recommendation coming from someone who has a copy than for me to try to sell you one since I have a financial incentive on each copy. However, yes I think it is up to date. There may be a few pieces of equipment that have come out since then but not a lot has changed in DCC in the last few years-Covid kind of got in the way of a lot of new developments and slowed others down.
how does railcom work in all that
Good question. I assume the Railcom data are just part of the DCC waveform transmitted bidirectionally. At this point there are so few decoders using the NMRA Railcom standard there is little to base it on other than digging through their literature on the NMRA website. This is further complicated by the fact that the European version developed by ESU apparently has its own approaches in some areas so that adds another level of uncertainty that will have to be ironed out.
DCC is indeed AC.
High frequency AC yes, more like a low frequency radio signal or high frequency Audio. with a 58 micro second on and off timing that works out to about 9 Khz i believe.
It is not. It is digitized DC. It alternates to distinguish the ones and zeros of the digits of the digital signal. Take away the digits and you will have DC.
The difference is in current flow. In AC the voltage varies above and below the reference and the current is either flowing in or out, but it is flowing (*except at the exact instance where it crosses the reference, or 0 v). In DCC it is either flowing or it is not. Therefore, DCC is more of a pulsed DC than it is an AC waveform. At any rate, since the current flow does not reverse, it is not AC.
@@pathvalleyrailroad9277 It's PWM, or pulse width modulation.
@@pathvalleyrailroad9277 Consult your local electrical engineer.The current reverses once the zero voltage line is crossed. DCC is indeed AC.
Why isn't the sites recommend not showing up. I wanted watch a couple more videos.
Which? It just worked for me