A boy named dumb

[Anonymous]

I know this sounds really dumb[#wstupid] but I'm a beginner, so can anyone be nice and tell me: what exactly is the difference between DC and DCC? And please tell me I'm not the first person to ask this; it would make me feel better [:I].

[Anonymous]

Not a dumb question at all! DC uses a varied voltage of 0-12V DC on the rails to control and power the train, DCC puts around 14-16V AC on the track constantly and uses coded instructions passed to decoders fitted in each loco to control the trains. DCC also allows you to have headlights that are constantly illuminated even when the train is stopped (as there's always power on the rails) and neat stuff like sound units and remote couplers. Hope this helps!

[Anonymous]

DC is direct current (the opposite is AC, alternating current). It is the electricity found in batteries, for example. A DC control system uses switches to connect a DC power source to various track segments (called blocks) and then you vary the voltage of the DC to make the eninge speed up or slow down.

DCC is digital command control. It uses an AC current with a superimposed digital signal on it. Each engine or accessory has a "decoder" in it which recieves the digital signal, decodes it, decides if the signal is for it and then then does what the signal tells it to do. A typical decoder in an engine acts like a little remote control "power pack" in the engine that controls just that engine.

With DC every engine on the track in the same block will move in the same direction when the voltage is raised. In DCC only the engine or engines selected will move and different engine can be selected independently and moved in different directions and speeds.

Dave H.

[simon1966]

You are far from the first person to ask the question!!

take a look at some of the web sites
http://www.tonystrains.com/tonystips/dccprimer/index.htm

http://www.litchfieldstation.com/university/


http://www.gatewaynmra.org/dcc.htm
There are some good intros there

[chateauricher]

QUOTE: Originally posted by nhs792
DCC is digital command control. It uses an AC current ...

I was under the impression that DCC used DC current as well; just at a constant voltage and an imbedded coded signal to tell the (decoder equiped) locomotive what to do.

If DCC uses AC current, then how is it possible to use a non-decoder equiped locomotive on a DCC layout ?

[ereimer]

QUOTE: Originally posted by chateauricher


If DCC uses AC current, then how is it possible to use a non-decoder equiped locomotive on a DCC layout ?

my understanding is that DCC uses a very high frequency AC , 8 thousand cycles per second (regular house current is 60 cps in north america) which to a DC motor seems the same as DC . the motor actually does try to reverse direction 8000 times per second which is what causes the buzzing sound of a DC loco on DCC track


edit : the only dumb question is the one you don't ask !

hopefully someone who really understands DCC will come along and correct any mistakes i just made

[earlfrye]

DCC is a DC signal with a digital code superimposed on the signal. The digital signal looks like noise to a DC engine. The DCC signal is interpreted by the DCC board into highly distinct instructions. Like Loco address, Mars light, speed , direction. This is how you are able to run more than one train on the same track.

[ereimer]

sorry earl , i have to disagree

quote from Allan Gartner's great site , wiringfordcc.com

QUOTE: Another complication is that the DCC voltage on the rails is AC rather than DC. However, this is not quite the same as the smooth cycle constant low frequency 50/60 Hz AC available at the local utility wall outlet. The command station to loco communication scheme relies on relatively fast reversals of track voltage to be detected at the loco decoder. It is the timing of these transitions that form the serial bit stream of computer to computer communications.

[Anonymous]

Thanks guys, this has cleared up my understanding... at least sort of. If only DCC weren't so expensive; it would make my life so much easier. [:D]

[Anonymous]

I disagree about DCC being expensive. It does have a high startup cost but with DC to acheave the nearly the same results you need extra switchs, control pannels, complicated wiring. All these have to be considered even though they are expendetures that are spread out in time as the layout is built and they involve your time as well as your cash.

Personally I chose to start with a cheap DC power pack to use while I build the basic layout. I am wiring for DCC so for now I am limited to 1 train at a time. That will change after the layout has matured to the point it will benefit from the advantages of DCC.

[simon1966]

Cutter, the cost of entry kept me out of DCC for quite a while. However, as Bukwrm notes, you can plan for DCC and have quite a lot of fun in the mean time without actually having to invest in DCC. For example, you can wire your layout for DCC. You can make sure you install DCC friendly trackwork. You can purchase locomotives that are DCC ready, or already have DCC that can run on a DC layout. Then as funds permit, you can make the switch. In my case, I divided my layout into 4 distinct blocks. One each for 2 different yards and then the main split into 2. I initially ran these 4 blocks with cheap DC controllers that either came with my original train set or cheap off e-bay. A year later, I got into DCC. I just joined the power bus for these 4 blocks and hooked up my DCC system and away I went. I got a Zephyr and spent about $180 getting the system and installing a couple of decoders. So, plan for DCC and have fun while you are saving for the system.

[rrinker]

DCC is a square wave signal and carrier in one, there is no superimposing like older command control systems (CTC16 for example - fixed DC level with a command signal superimposed on top of that). Because DCC is a square wave, the nominal DC voltage is zero - there is equal area above the 0 line as there is below it. A DC motor placed on DCC tracks will see a net 0 volts and not turn, although it wil hum or buzz at the DCC frequency. To run a DC loco on DCC, those systems that support it use a technique called "zero stretching". When no other commands are being sent, the DCC command station sends a constant string of 0 bits. Because the DCC standard defines anything with a cycle time greater than a set amoutn as a 0 bit, this can be made as long as required and still be a 0. To move forward, the zero stretching extends the top half of the 0 bit waveform, makign a net positive DC voltage. A regular DCC decoder still sees this non-symmetrical wave as a 0 bit. To move reverse, the lower half (negative-going) half of the 0 bit wave is stretched, creating a net negative DC voltages.

Somewhat simplified, but that's basically how it works.

--Randy