Lighting and other non-DCC devices.

As a newbie to DCC, is the voltage used on this generally AC? And is it about 18v? Or have I been living on another planet? Anyway my point or question is, that with a normal train controller (Select, Elite, GaugeMaster etc), there are certain things that need still 12v DC supply, signals, maybe some lighting etc, what is the general way that other model railway users power these auxiliary items, I know that most controllers have an extra output for AUX or maybe even 12v dc, however if  you are building a fairly big layout or even one with a lot of 12v DC demands, what is the best way to power these without putting extra demands on your controller/controllers? Is there or can you get a dedicated 12v DC controller/power supply over the counter/bought that is designed or meant to be used as a separate power unit for these sort of devices and loads? If so what make, what is the best, and how have you address/resolved this on your layouts? 

DCC is AC voltage with digital info. Those who do not understand DCC will say it is not AC voltage.
http://www.loystoys.com/info/how-dcc-works.html
Many are around 12 to 14 VAC. Some higher for large than HO scale which many run.
You can power many items on a layout if you prefer with DCC. There are different amperage systems. Many prefer to use DC to power accessories. Some use AC, some DC.
Running a DC loco on a DCC system. Two or three ddifferent systems can do this.
http://members.shaw.ca/sask.rail/dcc/DCC-waveforms/DCC_waveforms.html
Lots of DCC info.
http://www.mrdccu.com/
A free eZine with a good set of forums.
http://model-railroad-hobbyist.com/
All kinds of DCC info.
http://www.wiringfordcc.com/wirefordcc_toc.htm
Do a lot of reading. Store the links in Favorites.
R

There is no best, only what you like best. NCE, Digitrax, MRC, Lenz are a few of the DCC systems. There are about six or more decoder companies. There are also two or three companies that have a form of DCC and can run on DC layouts and DCC layouts. You will have to do a lot of searching for different companies on the Internet. The digital control of trains is rapidly evolving. Many DCC on board, sound and none sound can run on a DC power pack. Just do not use a DC power pack that has pulse power option. From you first request, you will have to do a lot of reading to catch up with the latest in model railroading or you may go down a path you will not care for. Stuff in other countries I am not familiar with. Only the USA stuff.
R

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It can get quite heated at times :-)
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Some systems can be adjusted, some you can adjust by using a different voltage power supply.
If converting locos with filament bulbs designed for 12V it's worth considering changing to LED as the higher voltage of some DCC systems will reduce the bulb lifetime.
I would arrange seperate supply(ies) for accessories such as lineside lighting and point motors. Keep the DCC for loco control.
MBQ

On 29/01/2012 16:35, snipped-for-privacy@hotmail.com wrote:
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I suppose it depends on what you call an 'AC voltage'. It is not an AC voltage in the sense of being like the mains or the auxiliary AC output of a conventional controller ie a sine wave. Also is is not a control signal superimposed upon another voltage. It is purely square-wave like digital data sent with a high enough voltage and with sufficient current capability so as when rectified it will run motors etc.. So it is an AC signal in as much as it is a pulsed signal with varying mark space ratio, but it is not a continuous sine wave like the mains.
The contentious bit is calling a pulsed signal AC, when does a pulsed signal become AC rather than DC that is switched on and off, at what pulse rate does that change occur. Is turning DC on and off once a second AC? To some it is, depending on the application and over what period you are observing the signal!!
Jeff

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The definition of AC has nothing to do with frequency, waveshape or having control superimposed on it.
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DCC is not a "pulsed signal" it is AC.
A decoder sees two connections to the track, lets call them A and B. During one half of the cycle, A is more positive than B and current flows from A to B. During the other half of the cycle, B is more positive than A and current flows from B to A. The current flow reverses twice every cycle. The current alternates. It is an alternating current.
DCC is AC. It is not a "pulsed signal", nor is it "bipolar DC" as some would have it.
Contrast this with a real pulsed DC controller where the pulses simply turn the track on and off. The current only ever flows in one direction (unless you flip the reversing switch!). That *is* a pulsed DC signal and not AC [1].
I think the confusion arises due to people looking at the output of a command station with reference to the local ground. If you measure the two outputs A and B independently then they do look like pulsed outputs. The point is that DCC is defined by the two track signals alone, there is no ground reference. It is the differential signal between the rails that is DCC and that is AC.
MBQ
Being really pedantic you could show that it is a combination of an AC signal and a DC offset but that is taking things to a ridiculous extreme.

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It is most certainly is a pulsed signal, with pulse width modulation that carries the data. The fact that it is applied to the track in a differential manner is not really relevant to that fact.
The fact that it is a pulsed signal is what causes the confusion. Towards the limit if the pulse rate was low enough it would tend to being called DC (if for example the state changed say only once a minute), but because the pulse rate is high it would normally be refereed to as AC.
If you viewed the spectrum of the DCC signal you would observe a classic pulse envelope, but there again so would you if you observed a DC signal being reversed every minute, if you viewed it over a long enough sample time!!
Jeff

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DCC is *frequency* modulated.
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The fact that it is applied differentially means it is AC as seen by the decoder.
Are you sure you are not getting confused with the motor drive output of the decoder, which is PWM and is DC, only reversing when the direction of the loco changes.
MBQ

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I think it is you that is confused with the definitions of AC and DC. A pulse modulated signal is AC, whether that be pulse width modulated or otherwise modulated. DC is an unchanging constant voltage. Perhaps Pulse width modulation is not quite the clearest term for the DCC signal as it is really a pulse train that caries data, however, the pulses are of different fixed widths for a one and a zero and so it is the width of the pulse that encodes the information. There may only be 2 allowable widths but that does not alter the fact that it is PWM. It is not frequency modulated as such, although the spectral content for a string of zeros would be half of that for a series of ones.
Any signal that varies with time is considered to be AC; mathematically DC is nothing more than a special case where the time component is zero. Even the PWM motor signal is AC as it is a pulse train and it is not constant with time.
If you are being really pedantic even the output of a conventional DC controller is really AC as soon as you make any change to the voltage!!
Jeff

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PWM implies a fixed frequency variable mark/space ratio.
DCC is fixed mark/space ratio (discounting stretched zeroes for driving analogue locos) with variable frequency. A '1' is sent as a single cycle of approx 8.6KHz nominal, a '0' as a single cycle of 5KHz nominal.
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The width of the pulse *and* the width of the idle period are critical in decoding a DCC bit stream. Both are significant and it is the overall period that matters. Hence DCC is frequency modulated, not PWM.
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This is getting into the real of AC with DC offset, which I did mention in an earlier post.
MBQ

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No, there is no such constraint on PWM, DCC is PWM with 2 discrete positions. PWM is AC.
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It is merely sent as RTZ with a fixed width for 1 and a different fixed width for a '0'; that may equate to 5kHz (sic) for a '1' but it is not frequency modulation. It would be FM if the data stream were used to modulate a carrier.(Actually '1' is nearer 8.3kHz, 60us per bit 120us total period).
Any data stream of this type will have frequency components that are related to the bit widths, that actual spectral components of the DCC waveform will not just contain 8.33kHz, and its harmonics, due to the unequal bit periods there will be other components in there as well depending on the data sent (particularly if there are long highs for non DCC powering.
Jeff

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No, the period changes since both the mark and space are changed.
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I don't know where you are getting you information, but I *was* correct, the nominal bit time, for a '1' is 58us per *half-bit*, 116us total per bit, or approx 8.6KHz. See http://www.nmra.org/standards/DCC/standards_rps/S-91-2004-07.pdf
Send a stream of 1 bits and you get a square wave at approx 8.6KHz, send a stream of zeroes and you get 5KHz. That *is* frequency modulation.
MBQ

On 30/01/2012 18:43, snipped-for-privacy@hotmail.com wrote:
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Ok, so from memory I rounded '55 to 61us' to 60us rather than 58us. '0' bits do not have a fixed duration, they must be in the range 95us to 9.9 seconds (start & stop bits >0us), the duration is set by the need to keep the average of 1's an 0's at zero. So there is no nominal frequency for '0' bits.
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NO. See above: 0's can lie anywhere in the range 95 to 9900us
No it is not FM, it would be frequency modulation if the baseband data had 1 & 0 of equal width, i.e. a constant data rate, and that data then caused the modulated data to shift between 2 different frequencies at the data rate. In the case of DCC the data rate is different between a 1 and a 0 due to the fact that the encoding is contained in the pulse width, i.e. PWM. If you also add to the mix the stretched 'bits' which can be up to 12 seconds and form form the start bit of a valid '0' in arbitrary positions, and the fact that 0 bits are variable length as well, it is NOT FM.
Jeff

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I did say in an earlier post that I was discounting stretched zeroes. These are only used for driving a single unchipped loco and are not even supported by all command stations. Use of an unchipped loco on DCC is deprecated by those who value their locos, due to the risk of destroying some types of motor.
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PWM implies a fixed frequency with variable mark space ratio. Perhaps we'll just have to agree that it's neither.
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Where do you get 12 seconds from?
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As I said, stretched zeroes can be ignored.
MBQ

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It implies nothing of the sort. That may be the case for controlling a motor, but *not* when encoding data.
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My apologies, on consulting the spec it should be 10 seconds with a total of 12s for the complete reversal.
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No they cannot, as the period of the 0 bits is dependant on the length of any stretched bits, so as to keep the average at zero.
Jeff

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Every definition of PWM I have seen assumes fixed frequency. I would be inetrested to see a description of your version of PWM.
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Oh FFS. Its 12000 us, or 12 milliseconds.
I am beginning to wonder how much practical, or even theoretical, knowledge of DCC you actually have.
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Again, you clearly do not understand DCC!!!
Stretched zeroes are ONLY used to give a DC bias to allow unchipped locos to be driven. This feature should be disabled, and is not included in some system, due to the potential to damage some motors. When stretched zeroes are disabled EACH AND EVERY ZERO on the DCC bus is nominall 200us total (100us each half cycle).
MBQ

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Sorry my brain was working in ms not us.
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Please read the spec again, there is no requirement for the 0 bit to be a nominal 200us it may be anything to 12000us. So a nice 100/200us period fits your view of FM, but the spec allows 100/anything>200<1200us, which does not fit (anything is allowed to change on a bit to bit basis). In practice this does not usually happen unless there are stretched bits but it can and a nice 100/200us is just a sub-set, so you cannot say DCC is FM based on one case when the spec and stretched bits allow something different.
Jeff

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Which is my point.
MBQ

On 01/02/2012 14:08, snipped-for-privacy@hotmail.com wrote:
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But you point only works for one specific case where there happens to be a fixed 100/200us. If there are stretched bits, or for some other reason the bits periods are not constant, which is allowed by the spec, then you description fails. You cannot characterise DCC based on a restricted sub-set of what is allowed.
Jeff

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I am basing it on what happens in practice. I was quite clear early in tne thread about ruling out the use of stretched zeros, as they are deprecated. I challenge you to find any DCC command station that does not use fixed duration equal timing when not using stretched zeros to drive an unchipped loco.
MBQ