I appreciate this on-going discussion. The Technical Section of the Digitrax Big Book of DCC was a total mystery to me, but now it's starting to make just a little sense. Some of this stuff is starting to sink in. So thanks to you all.
Jerry
Rio Grande vs. Santa Fe.....the battle is over but the glory remains!
grayfox1119,Have you ever looked at a DCC wave pattern? How do you know that it doesn't go below 0 volts? In fact, it really does, but for whatever reason, you won't take my word for it.
But would you take the NMRA's word?
Click on the following link (you need a .pdf reader):http://www.nmra.org/standards/DCC/standards_rps/S-91-2004-07.pdf
Note that this is NMRA Standard S-9.1, approved in 1994, 2002, and 2004, latest rev. adopted in July 2004. Just in case you don't have Adobe, here's the important part:
A: Technique For Encoding Bits
The NMRA baseline digital command control signal consists of a stream of transitions between two equalvoltage levels that have opposite polarity.
Now, doesn't that sound just like AC?
Paul A. Cutler III*************Weather Or No Go New Haven*************
From www.britannica.com (Encyclopedia Britannica):
Alternating Current -
"Flow of electric charge that reverses periodically, unlike direct current.
It starts from zero, grows to a maximum, decreases to zero, reverses, reaches a maximum in the opposite direction, returns again to zero, and repeats the cycle indefinitely."
Direct Current -
"Flow of electric charge that does not change direction."
Now, which of these sounds like DCC, and which one doesn't?
Paul A. Cutler III*************Weather Or No Go New Haven
*************
Joe Fugate Modeling the 1980s SP Siskiyou Line in southern Oregon
Randy,
I have an expensive Fluke RMS digital that gives just about the same reading as my Tony's meter.
But here is my question. I also get the same reading using a $4.00 digital meter that I bought from Harbor Freight. In fact I bought 4 of them and monitor the voltage on each of my district's. I operate them from a common wall wart. Are we/I missing something here?
Just hard to justify the cost of the RRampMeter. And since I own 3 different types of meters and get the same, + or - about 1/10 ,volt readings I am speaking with experience.
modelmaker51 wrote: Paul3 wrote: modelmaker51 & grayfox1119, Both of you are claiming that DCC is actually a DC output, not AC. The only problem is that DCC is AC. It is square wave AC, but it is AC all the same. If you graph the DCC signal, it oscillates equally from positive to negative volts, which makes it an AC signal. I am no expert here, but do rely on them. I have been told by the technical folks at Digitrax, NCE, and Tony's Train Exchange that DCC is NOT AC, but is what they call "half-wave" DC. Ask them. (and if it is AC why can't you read the voltage with an AC voltmeter?!)
Paul3 wrote: modelmaker51 & grayfox1119, Both of you are claiming that DCC is actually a DC output, not AC. The only problem is that DCC is AC. It is square wave AC, but it is AC all the same. If you graph the DCC signal, it oscillates equally from positive to negative volts, which makes it an AC signal.
modelmaker51 & grayfox1119,
Both of you are claiming that DCC is actually a DC output, not AC. The only problem is that DCC is AC. It is square wave AC, but it is AC all the same. If you graph the DCC signal, it oscillates equally from positive to negative volts, which makes it an AC signal.
I am no expert here, but do rely on them. I have been told by the technical folks at Digitrax, NCE, and Tony's Train Exchange that DCC is NOT AC, but is what they call "half-wave" DC. Ask them.
(and if it is AC why can't you read the voltage with an AC voltmeter?!)
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Well, I'll ask them, but according to what my college professors taught me back at Wentworth Inst. of Tech., DCC sure looks like AC to me (but then, I was in for Mechanical Engineering, not Electrical).
As for why you can't read an accurate voltage with an ordinary multimeter on DCC track power, look above my first post, the one by train18393, where he states that normal meters are based on sine waves at 60 Hertz, and DCC is not either.
BTW, take a look at a real DCC "packet". Note that the square wave has an equal positive and negative voltage...and that's AC.
Jay
C-415 Build: https://imageshack.com/a/tShC/1
Other builds: https://imageshack.com/my/albums
The mind is like a parachute. It works better when it's open. www.stremy.net
The voltage that you get on an AC voltmeter is (usually)only accurate at 60Hz, especially your garden varity of voltmeter. The DCC waveform is in no way close to 60HZ, is it not 60CPS and it is not a nice sine wave. It is a pulsed square wave. When using a normal voltmeter your readings may vary depending on the number of messages being sent and some DCC sets can use an extended pulse to run a DC (not DCC) equipped device. The best thing a normal voltmeter can be used for is to check for comparative voltage drop or if there is a voltage there. The voltmeters specifically made for measuring DCC voltage is the way to go, or use an modern digital oscilloscope with a built in voltmeter, that will tell you peek-to-peek voltage, RMS, Average or what ever way you want to measure the voltage.
Paul
Dayton and Mad River RR
You might want to bring the 16v setting down a bit. Your lightbulbs (in those trains that don't have LEDs) will last longer.
I just measured my track (NCE Pro) which is supposed to be 14.5 v and got 14.96vac on my AC meter. In my case the accuracy tolerance seems to be a little closer. The Ramp Meter would be the only way to actually confirm any of this.
Maybe someone out there that has one would do a test with the Ramp Meter vs. an AC volt meter and see how close they are.
modelmaker51 wrote: Eventhough DCC track voltage is half-wave DC, you can get an approximate reading (about +- 1.5v) with an AC voltmeter.
Eventhough DCC track voltage is half-wave DC, you can get an approximate reading (about +- 1.5v) with an AC voltmeter.
Just got back to the train room. Thanks for all the input. I've set it at 16V and get a reading of 17.3V. Looks like that's within the tolerance you mention.
At WIMRC we operate five to six HO locos at a time, some sound equipped, with "N" voltage setting on the DCS200 (8A), having found that "HO" setting produced "hiccuping in some loco's.
Isambard
Grizzly Northern history, Tales from the Grizzly and news on line at isambard5935.blogspot.com
Tony's Train Exchange has special meter for getting real-time measurements of DCC track voltage. http://www.tonystrains.com/products/tteexclusive_measure.htm
Texas Zepher wrote: jwils1 wrote:I'm using a Lenz Set-100 and according to the manual I can adjust the track voltage. Should I reduce the voltage? To what value?Only you can answer that question. Our club reduced ours from the default of 17.5V to 15.5V just to be more friendly to stock lightbulbs in RTR locomotives and we were melting down lighted cabooses. At home I went even further and set mine to 14V, mainly because I have a bunch of lighted passenger cars.You also realize you can set the voltage in the Lenz in two ways. It can be done with software or with a jumper inside the unit. I chose the jumper just so an accidental reset doesn't jump it back up and fry my lightbulbs.
jwils1 wrote:I'm using a Lenz Set-100 and according to the manual I can adjust the track voltage. Should I reduce the voltage? To what value?
TZ I hadn't thought about lighted passenger cars I'm going to bring my voltage down too, thanks for the wake up!!
Ken.
Most muilti meters will give you a false reading on DCC. The factory setting on my Set 100 is 16 volts at the track, which is fine for all BLI etc locos.
With a Radio Shack meter I'm measuring 19.9V on my HO DCC track. Some decoders, like Soundtraxx say not to exceed 18V. I'm using a Lenz Set-100 and according to the manual I can adjust the track voltage. Should I reduce the voltage? To what value?