How much track voltage for DCC?

[jwils1]

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?

Jerry

[NZRMac]

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.

 

Ken.

[Texas Zepher]

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.

[NZRMac]

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.

TZ I hadn't thought about lighted passenger cars I'm going to bring my voltage down too, thanks for the wake up!!

Ken.

[modelmaker51]

Tony's Train Exchange has special meter for getting real-time measurements of DCC track voltage. http://www.tonystrains.com/products/tteexclusive_measure.htm

Eventhough DCC track voltage is half-wave DC, you can get an approximate reading (about +- 1.5v) with an AC voltmeter.

[rrinker]

 The nearly 20 volts is definitely too high. 14.5-15 volts is good for HO, 12v is better for N scale, and my HO runs fine with 12v on the track.

                                            --Randy

[grayfox1119]

Tony's has a RampMeter that measures the DCC voltage ( pulsed DC ) very accurately, and the price is very reasonable.
Anything over 14.5 V is tempting fate. I like using a constant voltage supply. The current will drop if things get out of hand, but the voltage stays clamped at 14.5V

[Isambard]

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.

[jwils1]

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.

Jerry

[modelmaker51]

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.

[train18393]

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

 

[Paul3]

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.

Paul A. Cutler III
*************
Weather Or No Go New Haven

*************

[grayfox1119]

Paul3 DCC is "bipolar" DC, which is a "form"of AC, it is NOT a true sine wave as AC is. The DC power is modulated which allows for data to be encoded in the form of "1's and "0's".

[larak]

AC means "alternating current". It has nothing to do with a particular waveshape such as a sine wave. The type of AC that we are used to in our homes IS a sinusoid (or a reasonable approximation depending on reactive loads) alternating at a rate of 60 cycles per second ... but it is certainly not the only form of AC.

AC can also be a square wave, a triangle wave, a stair step and many others. It simply means that polarity regularly and symmetrically (well, not always either) alternates.

If DCC has equal amplitude positive and negative components then it is AC. If it is symmetrical from zero to some peak then it is AC with a DC component added to it to shift the average level.

If there is no repetition, then we have a pulse of series of pulses. (Which may or may not be a digital signal).

This is excerpted from one of my Cisco CCNA lectures. If it makes no sense let me know. If it does make sense then those four years at RPI paid off again. :-)

By the way, many companies make "True RMS" digital multimeters. Fluke is one of the best and most expensive but all brands work well enough. These should be able to measure the RMS voltage of DCC accurately for well under a hundred bucks. A 'scope is cool too if you can afford it.

[modelmaker51]

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]

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.

Paul A. Cutler III
*************
Weather Or No Go New Haven

*************

[rrinker]

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?!)

 If it were half-wave DC it would not alternate around the common reference, but merely go from common to some positive potential. Since there is a negative component in reference to the common, it's not DC.

As for not being able to accurately read the voltage, I would have to go into calculus to explain the concept of RMS voltage and the area under the curve. Suffice to say the area under the curve (ok a square wave is not exactly a curve) for a square wave signal is not the same as for a sinusoidal signal. Therein lies the difference in readings when using the common method of measuring. A more expensive true RMS meter will calculate properly for either waveform (and many others - like triangular). These meters are more expensive because they must process the input more to obtain the accurate reading.

                                                           --Randy

[Anonymous]

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.

 

 

[jfugate]

POOR MAN'S METHOD FOR READING DCC TRACK VOLTAGE



1. Take the hood off one of your locomotives and install a decoder.
2. Put the locomotive on the track and turn on your DCC system.
3. Get a VOM meter and set it to read DC voltage circa 20-25 volts.
4. Connect one meter lead to the blue function common on the decoder.
5. Connect the other meter lead to the green function lead on the decoder.
6. Select the decoder address (usually 03 on newly installed decoders) on your throttle.
7. Press F1.

Watch the meter reading -- you may need to reverse the leads if the meter reading goes below zero.

The volt reading is the DC voltage output of your DCC system (what decoders see), and that's what you want to know.

When I use this method, I get a perfect 14 volts on my system.

[Anonymous]

Thanks Joe Yes I did that before I got my RRampMeter. It is just that I find a cheapo digital meter seems to read the track voltage just as accurately as the RRampMeter and/or my Fluke.

[grayfox1119]

Absolutely correct Joe. I think that people get confused about half wave DC thinking that because it is a square wave with varying pulse widths within the packet of info, that they think it is an AC signal.
What may help them understand is, if a pulse a DC voltage ( modulate ) between 0 volts and some positive level, say 12volts, I can use this as a digital signal "0" at zero volts and a digital signal signal "1" at 12Volys. This is varying, but it is NOT AC as in house VA.

We will get through this, it just takes some understanding.

[Paul3]

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

*************

[grayfox1119]

Paul, the pulsed DC does not go negative that is the difference. If you had an oscilloscope and checked the AC sine wave on house current, you would see that it goes 120V positive and then swings through 0 volts and goes negative 120V. If you had a 220V ac outlet, one leg would be 120V positive while the other leg was 120V negative given you the difference of 220V
Now for DC, it is normally a straight line on the O scope at whatever voltage level you are measuring. If you pulse the DC between say 12V and 0 volts, you would see a square wave 12v positive to 0 volts at some given pulse width. But just because the voltage drops to 0 volts doesn't mean that it is an AC voltage.

[Paul3]

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 equal
voltage levels that have opposite polarity.

Now, doesn't that sound just like AC?

Paul A. Cutler III
*************
Weather Or No Go New Haven
*************

[jwils1]

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

[selector]

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 equal
voltage levels that have opposite polarity.

Now, doesn't that sound just like AC?

Paul A. Cutler III
*************
Weather Or No Go New Haven
*************

 

I'm going to get smacked for this, but...Paul, it sounds to me like DC!!  DC is polarity sensitive.

[Paul3]

Hey, selector!  "SMACK!"  There, feel better?  LOL

While DC is "polarity sensitive", so is AC.  While DC current can vary from 0v to +12v (or whatever) or from 0v to -12v, it doesn't flip back and forth between -12v and +12 many times per second...like AC does. 

According to the NMRA, DCC is an AC signal.

According to internet rumor, DCC is half wave DC.

Now, who are you going to believe?

Paul A. Cutler III
*************
Weather Or No Go New Haven
*************

[selector]

Well, just when we thought we were figuring this out....

 

http://www.yodermfg.com/Tube_Mills/Main_TM_SqWave.htm

[grayfox1119]

Yes, DC can indeed be a negative voltage, or a more common positive voltage. But referring to DC as AC because you swing a voltage bipolar through 0V does not make it an AC current.
AC is continuously changing and instantaneously changing.

[rrinker]

Not to mention the inductive load of the transformer in said welder would actually phase shift the current with respec to voltage (in the AC wave form) so the little picture there isn't 100% accurate. But hey, it helps sell DC welders....

 I think the reason they call it a DC welder is the INPUT is DC, which is then chopped by that mechanical system into a reversing DC - those contacts basically work like a reversing switch that is flip-flopped rapidly back and forth. The INPUT to the chopper is DC - I would not call the output DC.

                           --Randy