# Flash of insight on DCC



## ftauss (Sep 18, 2012)

I've been staring at my EZ Track #6 crossovers trying to figure out what made them DCC friendly. with the rails gapped where they are. I was skimmimg through old posts to try and reboot myself on the N as I get back to it. The smoke and sound of O gauge stuff is nice but layouts are boring due to size limits.

Anyway, I thought I read that DCC is AC not DC and I suddenly had a brain fart. Runnng them as AC is how you can drive the trains everywhere including reverse loops without complex wiring. (The crossovers make "hidden" reverse loops and I've been wondering how to deal with it) Perhaps more impetus to go DCC. Hah! Conventional O gauge AC helped me make the mental stretch to "get" DCC. Conventional AC laughs at DC for ease of setup.

Need to inventory the engines to see what is and isn't upgradeable.

Frank

And Gunrunner, you are a patient man. I read a few exchanges with posters that were somewhat less than civil. To much attitude in some of those boys.


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## rzw0wr (Aug 28, 2013)

DCC is not AC.

AC has a sine wave. DCC does not.


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## fcwilt (Sep 27, 2013)

Not sure what you were running in O scale but typically its not being powered by AC but having the center rail that makes it simple.

DC and DCC both need special handling of reverse loops. DCC makes it easier in that it has been possible to design electronic devices that automatically adjust the polarity of the power applied to the reverse loop as required.


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## ftauss (Sep 18, 2012)

rzw0wr said:


> DCC is not AC.
> 
> AC has a sine wave. DCC does not.



Um, no.

http://www.dccwiki.com/DCC_Power

Digital Command Control uses a high frequency alternating current waveform to provide power and transmit data. DCC can also be described as a special form of alternating current (AC). One of the main differences between Command Control systems is that DCC, unlike previous Command Control systems, puts a 100% digital signal on the rails and derives both power and information from the same digital signal. The digital data is not superimposed on a DC or AC waveform, nor does it use high frequency signals in addition to the power applied to the track. 

Since the signal is AC, the DCC waveform is a complex sine wave. The voltage quickly switches from +12 volts to -12 volts. Since the signal changes at a very high frequency, a Digital MultiMeter (DMM) cannot read electrical values accurately. They do not sample at a high enough frequency to be able to calculate the value accurately, as they are typically designed to measure AC in the 50-60 Hertz range. Also, digital multimeters are designed to calculate and display the RMS value of a pure sine wave. 
Using a DC function on a digital multimeter will not give accurate readings either, due to the changing nature of the signal. There are meters available that will accurately measure DCC signal, such as the RRampMeter, which was designed specifically for measuring DCC voltages and currents. 

A booster takes DC power from the power supply, and the DCC command information from the Command station, and creates a digital waveform, which is applied as track power. The length of time that the voltage changes provides a method for encoding data. DCC uses a binary encoding system. To represent a one, the time is short (nominally 58µs for a half cycle). A zero is represented by a longer period (nominally 100µs for a half cycle). 

The succession of zeros and ones (binary code) contained in the track power signal are the commands being sent to the layout. DCC decoders mounted in model locomotives and accessories then receive this digital information, interpret it, and perform commands such as moving, turning on lights, throwing switches, or making sounds. 

A stationary decoder can also be attached to the rails at a fixed spot, to allow control of switches and lights. If you are considering connecting a stationary decoder to the rails, please read: Avoid connecting stationary decoders to rails.


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## rzw0wr (Aug 28, 2013)

DCC is NOT Alternating Current! period.


alternating current
noun
an electric current that reverses direction at regular intervals, having a *magnitude that varies continuously in sinusoidal manner*. Abbreviation: ac

From NMRA site:
The DCC signal is an *alternating DC* waveform, which contains the digital information.

http://www.nmra.org/beginner/dccbasic.html

DCC may or may not alternate, BUT, it is a square wave form.
So a DCC signal does not conform to the AC definition.


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## NIMT (Jan 6, 2011)

Wow talk about a blow up!
DCC is both DC and Square wave AC.
The current does alternate, so it is alternating current (AC), but it's not sinusoidal its Square.
It also has a DC carrier signal imbedded in it.
NO it does not work like Lionel (O gauge), just as a note: The reverse loop thing has nothing to do with it being AC it has to do with it being 3 rail.
DCC does require circuits to keep the Phase (not polarity of DC) of the rails from conflicting on a reverse loop.
A DCC friendly turnout refers too 3 major points , the frog is isolated or controlled , the points are isolated from each other, and it's not power routed.


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## Ray Haddad (Feb 19, 2014)

rzw0wr said:


> DCC is NOT Alternating Current! period.
> 
> 
> alternating current
> ...


That is a definition that would not stand up to engineering scrutiny. I am an electronics engineer. DCC is an AC waveform with a zero crossing. Without that, you'd not have a proper signal and you'd never be able to run forward and reverse on one track without switching polarity. As far as the NMRA is concerned, they are defining their OWN standard and not conforming to ISO. The NMRA is wrong but within their bounds to describe the waveform as they see fit. They cannot, however, redefine AC. That stands alone.


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## fcwilt (Sep 27, 2013)

You don't have to have an AC waveform of any shape to achieve bi-directional travel. There are systems that simply have DC on the rails and control the engines via RF. To change direction you only have to "swap the leads" to the motor. You could also have a DCC type system with a uni-polar waveform of some sort. It happens that a bi-polar waveform has some advantages but it is not a requirement.

And since the most common use of term AC in the world of the model railroaders refers to the sinusoidal waveform coming from their home's power outlets I think it's fair to NOT use AC to describe the DCC signal just to avoid any false assumptions.


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## ftauss (Sep 18, 2012)

I realized a bit after I'd posted that it was the 3 rails that make setting up O gauge easy and not the AC. Felt kinda stupid for posting that in the first place.


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## fcwilt (Sep 27, 2013)

ftauss said:


> I realized a bit after I'd posted that it was the 3 rails that make setting up O gauge easy and not the AC. Felt kinda stupid for posting that in the first place.


No need to feel stupid - we've all been there and realized AFTER we posted something that it was wrong.

I've posted my share of bogus stuff - sometimes I catch it before it's read, sometimes somebody has to point out my mistake.

It's all part of being human - and that's a good thing.


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## wsboyette (Jan 25, 2014)

As an old electronics tech, it would appear to me that the RF control signal that DCC puts on the track has to be pulsating DC (one polarity), as there would otherwise be a conflict with the DC track power voltage.


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## NIMT (Jan 6, 2011)

wsboyette said:


> As an old electronics tech, it would appear to me that the RF control signal that DCC puts on the track has to be pulsating DC (one polarity), as there would otherwise be a conflict with the DC track power voltage.


There is no DC track power in DCC, it's a square wave AC signal.
The DCC decoder takes that square wave AC signal and converts it back to DC for the motor and lights.


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## wsboyette (Jan 25, 2014)

NIMT said:


> There is no DC track power in DCC, it's a square wave AC signal.
> The DCC decoder takes that square wave AC signal and converts it back to DC for the motor and lights.


Oh, I thought the trains used pulsating DC in HO and N scales. I do at least know they use AC in O gauge (3-rail).


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## NIMT (Jan 6, 2011)

wsboyette said:


> Oh, I thought the trains used pulsating DC in HO and N scales. I do at least know they use AC in O gauge (3-rail).


It certainly does get confusing...or at least it does me! :retard:


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## fcwilt (Sep 27, 2013)

wsboyette said:


> Oh, I thought the trains used pulsating DC in HO and N scales. I do at least know they use AC in O gauge (3-rail).


Many (most?) HO and N locos (those that are not equipped with DCC decoders) do run on DC.

Power pack makers found that locos would often run better if the DC was not steady DC but "pulsed" in some way.

Lots of difference "pulsing" schemes have been used but the goal was the same.

There are HO scale locos that run on AC, Marklin being one well known brand.

There may well be N scale locos as well that run on AC.


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## wsboyette (Jan 25, 2014)

The MRC RailPower 1200 power pack I use for N scale does put out pulsating DC. It has fancy circuitry that senses load and helps control the final output for better slow operation, and there is a big improvement over the old-school power packs. Even my old Atlas steam loco will creep along ever so slowly on its output. The old-school power pack I used way back in the day was nothing but a variable output transformer with a diode to chop off the negative-going half of the AC voltage.


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## rzw0wr (Aug 28, 2013)

I was not going to respond to this post again.
I can see I started and argument more than a discussion.
My apologizes to all.

As a newbie to DCC when I first heard that DCC was AC I thought that it meant that it was the same as household current.
This confused me some.
As I learned more I found that it IS an alternating current because the voltage does drop below referenced zero.
So, I agree that DCC is an alternating current.

My main disagreement is in the fact that most laypeople and model railroaders think of household current (120 volts) when the term AC is used.
When I was going to school to become an Electrons engineer, the signal like the one produced from DCC was referred to an Alternating DC signal, an alternating digital signal or a alternating DC signal.
The term AC or alternating current by itself was intended to mean an alternating analog current with a sinusoidal wave form or household current.

My intentions are not to argue about what DCC is but, to help the newbies to the hobby better understand correctly what DCC is and how it works.

I hope this helps all to understand what I was trying to say in my earlier posts.


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## Ray Haddad (Feb 19, 2014)

Dale, congrats on becoming an electronics engineer, a career that served me well and sitll does. Discussion and disagreement are the only way we learn. Politeness, as happened here, is how we learn best.

Onward!

Ray


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## rzw0wr (Aug 28, 2013)

Thank you Ray.
I should have mentioned, I never completed my schooling.
Kids, life and my chosen career got in the way.


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## Ray Haddad (Feb 19, 2014)

Dale,

I went to UCONN for 3 years and then got drafted. Off to Vietnam for two back to back tours. Volunteered, for those of you who are right - you don't get back to back unless you do volunteer. Then I stayed in for 22 years and completed studies over that time. Formalized it near to my retirement and opened my own firm. Nobody was hiring 40 year old engineers with no experience.

After several years I sold the firm and moved to Australia. Now, in Connecticut, I do only design work for one client. Me. I have several DCC projects on the table. You should consider joining MERG. You'd love it.

http://www.merg.co.uk for info. You'll see me there.


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## rzw0wr (Aug 28, 2013)

Ray, When I started my schooling I was just starting out as a Die Maker.
I just wanted to know how electricity worked.
I had just started MRR also.
I had some ideas that I wanted to put into my layout.
However, my 7 day work schedule and my family came first.
I did learn what I wanted to know, But I never put it to any use and I have forgotten 95% of what I knew.


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## Ray Haddad (Feb 19, 2014)

Dale, if you can solder, you can build a MERG kit. You'll save truckloads of money, too.


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## wsboyette (Jan 25, 2014)

rzw0wr said:


> I was not going to respond to this post again.
> I can see I started and argument more than a discussion.


Oh, I wouldn't call it an argument, it is actually a rather informative discussion. I am not familiar with the workings of DCC and would like to know more about it.


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