CSX RobertVail and Southwestern RRWait a minute! In your original post you said that was the signal on the rails! The signal to the motor is independent of the signal on the rails, at least as far as it's actual appearance... In his original post he had two photos labeled accordingly. The first was the signal on the rails: "Below is a typical DCC signal as applied to the track..."; the second was the signal to the motor: "Below is the signal going to the motor at half throttle..."
Vail and Southwestern RRWait a minute! In your original post you said that was the signal on the rails! The signal to the motor is independent of the signal on the rails, at least as far as it's actual appearance...
Rich....
My apologies for not being careful enough! I'd like to blame the small screen, but it was just a sloppy read on my part! You had done exactly the thing I wanted to see, and have seen.
Again, my apologies.
Jeff But it's a dry heat!
Ok, back to the original question. Click on the link below my name and search for dcc booster. The nice thing about this method is you can store the links in your Favourites folder for future reference. You will find a lot of info. It also eliminates a lot of the extra rhetoric involved in many discussions and keeps out opinions. You have the data from known DCC sources. Some discussions are known to morph. Ok, you may have to do a search for morph.
Ok, maybe you just want to talk. This is ok also.
I must have three hundred different links stored on different subjects while searching the 'Net. It is a huge library.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
Georgia Flash Before I travel the 110 miles to Savannah to pick up my new Digitrax Empire... system, I hope someone can answer a couple of questions regarding something called, "boosters". I want to be as informed as possible before I plunk down any more dineros$$$. And, this forum has been good for me, so far, during the construction of my HO guage layout. What are "boosters", exactly? Why, and how often would one need to install them? Are they simple to wire - in parallel; in series/or not? Thanks... "G. Flash"
Before I travel the 110 miles to Savannah to pick up my new Digitrax Empire... system, I hope someone can answer a couple of questions regarding something called, "boosters". I want to be as informed as possible before I plunk down any more dineros$$$. And, this forum has been good for me, so far, during the construction of my HO guage layout.
What are "boosters", exactly? Why, and how often would one need to install them? Are they simple to wire - in parallel; in series/or not? Thanks...
"G. Flash"
As fascinating as this discussion has been, I don't remember seeing the questions answered. So I'll take a stab at it.
1. What are "boosters", exactly?
The unit that puts the power and the digital commands together and sends it to the track.
2. Why, and how often would one need to install them?
You need at least one. Additional boosters are required for 2 reasons.
The first is that everything you are running using the power from the booster exceeds its capacity, usually 5 amps but some starter systems have less. Note that a 5 amp booster needs a 5 amp power supply in order to have the 5 amps at the track. In addition to powering the trains you can have accessories with their own decoders - if it all adds up to more amps than your booster handles, you need another booster. Note this is everything you are running at the same time off the booster - you may have 20 turnout motors but only throw one at a time, OTOH if you have indicator lights that are on all the time they all have to be counted. If your turnouts motors/lights are powered separately they don't count at all.
The second reason is that your wiring from the booster exceeds 30 ft. There are some recommendations for how to go longer and some that say you never should. The problem is degradation of the DCC signal. But for larger layouts multiple boosters may be needed. Note that you can run 30 feet in each direction from a booster so if it is in the middle of a 60 foot section, you are okay. Also note that this is the length of bus wires, feeder wires, and track.
3.Are they simple to wire - in parallel; in series/or not?
Yes, your brand should include instructions. Basically, each booster powers its own block of track that is insulated from the others. The boosters have to be connected with a cable from the manufacturer.
This site http://www.wiringfordcc.com/ has lots of info on DCC.
The booklets that came with my NCE system had everything I needed to get started.
Enjoy
Paul
One of the early posters pointed out that you don't need to know how it works to use it.
This food fight started as a discussion of whether a symmetrical bipolar signal that alternates between positive and negative is alternating current or direct current.
I sincerely doubt that either side is going to budge, so I am going to go have breakfast.
Dave
Lackawanna Route of the Phoebe Snow
I really hope the OPs questions were answered and not scared into another hobby like basket weaving? Maybe we can all go to the White house and sit and have a beer? I did not mean to start an argument about what DCC really is. I will leave that to engineers and scholars and other people that make way more money than I.
Pete
I pray every day I break even, Cause I can really use the money!
I started with nothing and still have most of it left!
I guess for simple explanation, the transition from positive to negative is constant and you can say a type of AC, equal positive/negative transition of the waveform with digital information riding the waveform. Remember, AC is equal positive/negative transition of the waveform. The NMRA will explain it in much better detail but can get very technical and confuses some people. Rivet counters will want to use the real terms which lay people do not understand sometimes. To keep it simple, I call it a type of AC.
The diode bridge takes the positive/negative transitions and changes that to pulsating DC which is filtered to pure DC by a couple filter capacitors. The data information is picked off just before the diode bridge according to a couple diagrams I have seen for decoders. The NMRA explanation will tell you how power (amps) is inserted into the data stream and the power taken from the data stream by the decoder. It does get quite complex for those are technically challenged.
richg1998 Quote:It is very important to note that this example is running a DC locomotive using "Zero stretching". It is NOT what a DCC signal does to command a DCC locomotive to operate. Many systems no longer support this mode. It is an interesting feature, but not an example of typical DCC operation.------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- You are quite wrong. I knew this was going to happen. The DCC signal is from a NCE Power Cab that does NOT have zero bit capability. The decoder is right next to the 'Scope in the photo. The 'Scope leads are attached to the motor terminals which areout of sight. The signal to the motor is from a SoundTraxx Micro-Tsunami decoder. Standard signals for DCC systems. The decoder sends pulse power, PWM, to the motor even if the decoder was being run be a DC power pack. The micro processor develops the pulse power for the motor and controls the DC on/off functions. I have worked with the same type of power in industrial applications for many years. This is a much lower power version. Pure DC in the decoder is only to power the chips in the decoder and providing pure DC for lighting. I have done the measurements. The Micro is a dual-mode decoder. ALL decoders send pulse power to the motor. If you do not believe me, get a 'Scope and do the measurements. You can also find these same DCC signals on the 'Net if you do a search. I have a couple bookmarks showing essentially the same thing and also a site showing stretch zero bit DCC track waveforms which are directly applied to the motor from the track. I use to use a MRC2000 that had zero bit capability and have observed the waveforms with a loco with no decoder. Very noisy motor. Rich
Quote:
It is very important to note that this example is running a DC locomotive using "Zero stretching". It is NOT what a DCC signal does to command a DCC locomotive to operate. Many systems no longer support this mode. It is an interesting feature, but not an example of typical DCC operation.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
You are quite wrong. I knew this was going to happen. The DCC signal is from a NCE Power Cab that does NOT have zero bit capability. The decoder is right next to the 'Scope in the photo. The 'Scope leads are attached to the motor terminals which areout of sight. The signal to the motor is from a SoundTraxx Micro-Tsunami decoder. Standard signals for DCC systems. The decoder sends pulse power, PWM, to the motor even if the decoder was being run be a DC power pack. The micro processor develops the pulse power for the motor and controls the DC on/off functions. I have worked with the same type of power in industrial applications for many years. This is a much lower power version. Pure DC in the decoder is only to power the chips in the decoder and providing pure DC for lighting. I have done the measurements. The Micro is a dual-mode decoder. ALL decoders send pulse power to the motor.
If you do not believe me, get a 'Scope and do the measurements. You can also find these same DCC signals on the 'Net if you do a search. I have a couple bookmarks showing essentially the same thing and also a site showing stretch zero bit DCC track waveforms which are directly applied to the motor from the track. I use to use a MRC2000 that had zero bit capability and have observed the waveforms with a loco with no decoder. Very noisy motor.
Wait a minute! In your original post you said that was the signal on the rails! The signal to the motor is independent of the signal on the rails, at least as far as it's actual appearance. That's one area where decoders can actually perform differently. They can use different frequencies (hence "silent" decoders"), they could even use DC, though I don't think any would! But the output of the decoder to the motor is not part of the standard, and isn't related to this discussion. The signal to the motor is decoder dependent, and not control system dependent. The whole "debate" here is about what it on the rails, not what goes to the motor.
An interesting exercise would be to put the input to the decoder on one trace, and the output to the motor on the other.
Crazy discussion. If the current in the track were not AC, then why is a bridge rectifier circuit in every decoder?
C&NW, CA&E, MILW, CGW and IC fan
richg1998 A picture is worht a thousand words. AC/DCC http://www.newrailwaymodellers.co.uk/electrics-ac-dc-dcc-pwd-controllers.htm Rich
A picture is worht a thousand words. AC/DCC
http://www.newrailwaymodellers.co.uk/electrics-ac-dc-dcc-pwd-controllers.htm
Yes and with AC, t should be constant. In the case of DCC t is not a constant. Interestingly, if you go to the NMRA website at: http://www.nmra.com/standards/DCC/index.html
They describe DCC as:
DCC is short for DIGITAL COMMAND CONTROL. It is not just another method of control, it is a standard for manufacturers to use to make their products compatible with other products on the market that meet this standard. In this respect, the playing field has been leveled and we can begin to reap the benefits of controlling things that we have never been able to control before.
The DCC signal is an alternating DC waveform, which contains the digital information, This coded signal controls a specific decoder placed in a specific locomotive causing it to use as much of the track voltage as it needs to move forward or backward, turn its headlight on or off or even dim it for meets with other trains on another track. Decoders can be set so that locomotives that could never have run together with a conventional power pack can doublehead or even operate in pusher service without one of the locos working too hard or not hard enough. Many of the newest locomotives have light boards that can be removed, and a decoder added in the same space.
Engineer Jeff NS Nut Visit my layout at: http://www.thebinks.com/trains/
You didn't quote the paragraph about powering your own device from the DCC signal:
If you are new to command control you may not have realised power supplies for mobile equipment are easily built for DCC controlled equipment. As full power is present on the track at all times a bridge rectifier converts the AC signal to a steady DC voltage and a cheap three terminal regulator reduces the voltage to the whatever your circuit requires. All manner of light, sound and animation effects can emerge from stationary loco.
Zero bit.
With the DCC signal on the track which is applied directly to the loco motor, The positive zero bit is stretched for forward and the negative zero bit stretched for reverse considering the positive motor terminal is to the right rail. This was not always true with older locos or reworked locos.
http://www.geocities.com/OzDCC/dcctut01.htm
Store the links in your Favorites folder.
While that sounds cute, it is an invalid comparison. Changing polarity in response to operator input is not the same. If you turn the DCC command station on, connected to the track and nothing else with no operator input of any kind, the polarity of the rails will continue to oscillate between plus and minus. That is why your DC engine sits there and buzzes. Because the power to it is alternating between plus and minus.
CSX RobertRex Beistle Look up "Alternating Current" in as many dictionaries as you care to. What you will find is "Alternating current n : an electric current that reverses its direction at regularly recurring intervals" or some text of identical meaning. Did you notice? "... at regularly recurring intervals" 50 Hz, 60 Hz or 400 Hz, the single distinguishing feature is a sine wave of constant ampitude and frequency. There is a type of drive system for controlling motors that use variable frequency AC to control the speed of the motor. Is that power still considered AC as you adjust the frequency up and down? I think most people would say yes. I have looked up the definition of AC in many places, and have found many different definitions. Many of them specify a sine wave, yet it is well known in electronics that AC can be a sine, square , triangle , or sawtooth wave as well as others. An audio signal is also often referred to as being an alternating current, yet an audio signal has a constantly varying frequency and amplitude. I can also find "regularly recurring" used to mean consistent time intervals as well as "somewhat" consistent time intervals. I guess it really depends on what you consider the correct definition of alternating current because there are many definitions out there. DCC is not what you consider AC and it is not what Jeff considers AC, but it is what Phoebe Vet considers AC and it is what I consider AC, so I will just agree to disagree on this point.
Rex Beistle Look up "Alternating Current" in as many dictionaries as you care to. What you will find is "Alternating current n : an electric current that reverses its direction at regularly recurring intervals" or some text of identical meaning. Did you notice? "... at regularly recurring intervals" 50 Hz, 60 Hz or 400 Hz, the single distinguishing feature is a sine wave of constant ampitude and frequency.
Look up "Alternating Current" in as many dictionaries as you care to. What you will find is "Alternating current n : an electric current that reverses its direction at regularly recurring intervals" or some text of identical meaning.
Did you notice? "... at regularly recurring intervals" 50 Hz, 60 Hz or 400 Hz, the single distinguishing feature is a sine wave of constant ampitude and frequency.
I have looked up the definition of AC in many places, and have found many different definitions. Many of them specify a sine wave, yet it is well known in electronics that AC can be a sine, square , triangle , or sawtooth wave as well as others. An audio signal is also often referred to as being an alternating current, yet an audio signal has a constantly varying frequency and amplitude. I can also find "regularly recurring" used to mean consistent time intervals as well as "somewhat" consistent time intervals.
I guess it really depends on what you consider the correct definition of alternating current because there are many definitions out there. DCC is not what you consider AC and it is not what Jeff considers AC, but it is what Phoebe Vet considers AC and it is what I consider AC, so I will just agree to disagree on this point.
One of the main reasons I can't consider DCC on the rails as AC is because there is not a regular duty cycle for the waveform. There is a standard pulse width but that's it. True AC should be able to be defined by an alternating or infinite series differential equation that describes the waveform through all 360 degrees of the waveform cycle. DCC cannot be expressd by this method. If we were talking about a continuous frqeuency square wave with a bipolar encoded output, I would be more inclined to agree with you and Phoebe Vet. In this case we are taking a digital stream of pulses, encoding with a bipolar output and shifting the outputs by 180 degrees in order to transmit power on the rails. I consider that an encoded digital pulse stream and not AC, even if we do agree that the output changes polarity. I can't make the leap that just because an output changes polarity that we are talking about AC., A stretch of that thought would be to say that your DC power pack output is AC because you throw the direction switch every few minutes. Thus it would be AC with an extra long duty cycle
richg1998Below is a typical DCC signal as applied to the track. Zero volts is the center of the 'Scope. This is also measured with a AC voltmeter, not a DC meter. Even with the throttle at zero speed, the pulses are still on the track.Below is the signal going to the motor at half throttle. The wider the pulses, the faster loco. Zero is in the center. Can be measured with a DC meter, not an AC meter. Negative going pulses for reverse. Rich
Below is a typical DCC signal as applied to the track. Zero volts is the center of the 'Scope. This is also measured with a AC voltmeter, not a DC meter. Even with the throttle at zero speed, the pulses are still on the track.
Below is the signal going to the motor at half throttle. The wider the pulses, the faster loco. Zero is in the center. Can be measured with a DC meter, not an AC meter. Negative going pulses for reverse.
As far as something a previous poster wrote, I've found the the dictionary is not the place to go do determine the meaning of a technical term. The DC/AC debate has gone on 'til the horse is dead, and through the glue factory. In my mind, the problem with calling it either is that AC and DC are terms generally used to describe power distribution, rather than a data signal. The DCC waveform is interesting in that it is used for both signal and power distribution. Rather than calling it either, I would call it a differential data signal, and leave it at that.
Rex BeistleLook up "Alternating Current" in as many dictionaries as you care to. What you will find is "Alternating current n : an electric current that reverses its direction at regularly recurring intervals" or some text of identical meaning. Did you notice? "... at regularly recurring intervals" 50 Hz, 60 Hz or 400 Hz, the single distinguishing feature is a sine wave of constant ampitude and frequency.
Rex BeistleDCC track power, as implimented by all major makers, is a unipolar differential data stream. It is unipolar because the two output terminals of the booster have, in relation to the booster circuit common point, only one polarity.
CSX Robertlocoi1saSquare wave DC is not the same as AC. AC has a consistent frequency (spaces between high and low.). Square wave DC signals are not spaced consistently. You're right that square wave DC is not the same as AC, but the DCC signal is not square wave DC. There is no DC component to the DCC signal. It IS square wave AC. Having a consistent frequency is not a requirement for being AC.
locoi1saSquare wave DC is not the same as AC. AC has a consistent frequency (spaces between high and low.). Square wave DC signals are not spaced consistently.
Certainly other things also reverse polarity from time to time. Any signal at any frequency you care to discuss, from one cycle per century to light might reverse polarity from time to time. AC, to the preponderance of working technical people I have dealt with for more than 50 years, is a sine wave of constant amplitude and frequency. To that group of technical folks, AC is typically thought of as power such as comes from power lines or transformers.
Telling the DCC neophyte that DCC track power is AC is doing them a disservice. Tell them that DCC booster power is DC that changes polarity thousands of time per second in accord with the electronic 'code' being broadcast by the command station.
DCC track power, as implimented by all major makers, is a unipolar differential data stream. It is unipolar because the two output terminals of the booster have, in relation to the booster circuit common point, only one polarity. The signal varies from near zero volts to some positive voltage. For HO scale the voltage is about 14.25 volts. It is differential because the two output terminals of the booster are, with some exceptions, exact opposites. When one terminal (rail) is positive the other terminal (rail) is near zero and, as determined by the data being broadcast by the command station, they will trade states from time to time.
Knowing that the rails are carrying this "unipolar differential data stream" it is obvious that, from rail-to-rail, the voltage will change polarity in accord with the data being broadcast.
I generally don't care for physical or hydraulic comparisons, but the DCC track power might be compared to a playground teeter-totter. Watch two children from a perspective of standing on the earth (our universal common reference) and you will see that the two seats go from near the earth to some point above it. Now join the fun with a child and you will see that some of the time you (rail 1) are higher (more positive) than the child (rail 2) and other times the child is higher (more positive) than you. The relative positiions of the two seats on the teeter-totter (the two rails) reverse from time to time.
The potential difference (voltage) between rails is rectified and filtered to make DC in the decoder. The data in the data stream is detected by the micro-processor in the decoder and used to control the motor, lights and etc by way of the power amplifying parts of the decoder.
There is often a difference of opinion regarding whether or not the DCC track power is AC. When Webster's, Funk & Wagnalls, McGraw Hill and others change all the dictionaries, the unipolar differential data stream known as DCC track power will be AC.
Until that happens, DCC track power is not, by definition, Alternating Current because it does not reverse its polarity "at regularly recurring intervals."
seacoast I am curious do you use the PM42's if so are they effective?
I am curious do you use the PM42's if so are they effective?
No, I do not use PM 42s. But the way I have it wired they can be easily added if I ever feel the need for them.
CSX Robertjbinkley60 The NMRA spec says: bipolar signal must appear differentially on a two-wire cable with a signal amplitude of no less +-8V and no greater than +-22V. The Command Station output must be capable of supplying +- 8 volts into a 1K-ohm resistive load, so that multiple Power Stations may be connected to this output. A unipolar signal must appear on a two-wire cable, one signal, one ground, with a signal amplitude of no less +8V and no greater than +22V. The Command Station output must be capable of supplying +8 volts into a 1K-ohm resistive load, so that multiple Power Stations may be connected to this output. This is refering to the low current DCC signal produced by the command station and it can be bipolar or unipolar. The booster output to the track, however, is always bipolar.
jbinkley60 The NMRA spec says: bipolar signal must appear differentially on a two-wire cable with a signal amplitude of no less +-8V and no greater than +-22V. The Command Station output must be capable of supplying +- 8 volts into a 1K-ohm resistive load, so that multiple Power Stations may be connected to this output. A unipolar signal must appear on a two-wire cable, one signal, one ground, with a signal amplitude of no less +8V and no greater than +22V. The Command Station output must be capable of supplying +8 volts into a 1K-ohm resistive load, so that multiple Power Stations may be connected to this output.
The NMRA spec says:
bipolar signal must appear differentially on a two-wire cable with a signal amplitude of no less +-8V and no greater than +-22V. The Command Station output must be capable of supplying +- 8 volts into a 1K-ohm resistive load, so that multiple Power Stations may be connected to this output.
A unipolar signal must appear on a two-wire cable, one signal, one ground, with a signal amplitude of no less +8V and no greater than +22V. The Command Station output must be capable of supplying +8 volts into a 1K-ohm resistive load, so that multiple Power Stations may be connected to this output.
I have an 18'x18' HO layout, one level unless you count the subway as a level. On it I have 13 powered locomotives. 4 of them with sound, 6 lighted passenger cars, and 8 DS-64s that are temporarily powered by the track. My single Digitrax Super Chief isn't even breaking a sweat. No boosters required.
Phoebe Vet's idea of using pm42 seems like a great idea, especially if you have just an averaged sized home layout and dont need the added expense of adding boosters...
Hi!
You have lots of good advice already, so I'll just pass along my experience......
I went to DCC last January after a lot of investigation. My new layout is HO, 11x15, two level, and I like to run 4 unit F locos all powered. Anyway, I initially thought, and it was confirmed by several knowledgable folks that two boosters would easily provide all the power I could want.
I ended up with a Digitrax Super Chief 5 amp system and bought a Digitrax Empire Builder to add the extra controller & booster (cheaper as a set than individually). I also got two 5 amp power supplies and two DCS4 circuit breakers.
While the layout is not yet up and running, my tests show that what I bought should do anything I could ask of it and power or signal strength will never be a problem.
Oh, the success of the above is highly dependent on good DCC wiring, with plenty of feeders, etc.
Mobilman44
ENJOY !
Living in southeast Texas, formerly modeling the "postwar" Santa Fe and Illinois Central
You see, the rule is: They're not launched until they have everything out of the attic and basement. Until that time, moving back in is considered SOP and adding to the stuff left behind when they go is permitted.
Moral of the story? Have them get the stuff out and change the locks. A former boss actually moved to a house that was too small for the kids to return, in another state no less. But he issued keys, they found a place to perch and he had to put on an addition so he and his wife could have a little privacy in their own new house!
Phoebe Vet The only reference available to the decoder is the two rails. If it was not AC at the rails then zero stretching to run a DC engine would only work in one direction. If you put a scope on the two rails you will see AC because first it flows from rail A to rail B then it flows from rail B to rail A. Except when you are using zero stretching, it is symmetrical.
The only reference available to the decoder is the two rails. If it was not AC at the rails then zero stretching to run a DC engine would only work in one direction. If you put a scope on the two rails you will see AC because first it flows from rail A to rail B then it flows from rail B to rail A. Except when you are using zero stretching, it is symmetrical.
Technically it is differntial DC pulses. Yes, the rails alternate polarity with regards to each other. Zero stretching works because the duty of the DC pulse is altered.
I'll end the discussion here. I am never going to agree that DCC is AC but we can certainly agree on how it operates, even if we want to disagree on what we want to call it.
jbinkley60Your statement about alternating polarity is partially correct and limited to whether the manufacturer chooses to use bipolar vs. unipolar encoding. You can't tell the difference unless you know the refence point and place a scope on the rails. If they choose to use unipolar encoding then the signal never crosses the zero reference point and thus never changes polairty with respect to the reference point.
Once you get to the rails, you don't know or care whether it's bipolar or unipolar, since you don't know, or care what the reference point is. At the rails, with respece to each other, it looks the same. By writing the spec the way they did, the NMRA specified a signal with no "ground" or reference at the rails, allowing for a differential signal with no reference other than itself.
Thinking about it that way, I guess one could say that it has characteristics or DC, AC, neither, or both. It's a differential signal that can supply enough current to be used for power.
Another Engineer Jeff.....