Lighting and other non-DCC devices.



It's DC.

It's still DC. How often did the current or voltage reverse?
All time varying signals have an AC component. Not all resulting dignals are AC.
MBQ
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The definition of an AC signal is that it has a time varying component, you seem to be regarding AC as some sub-set of that which is not correct.
Jeff
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No, the definition of AC is that the current or voltage alternates, i.e. reverses periodically.
MBQ
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wrote:

Lets see what Cambridge University have to say on the subject http://www.eng.cam.ac.uk/DesignOffice/mdp/electric_web/AC/AC_1.html
I'm struggling to find a definition that doesn't include reversal of current or voltage. Would you care to provide one, from an authoratative source?
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On 31/01/2012 13:38, snipped-for-privacy@hotmail.com wrote:

So you are trying to say that a pulsed signal is not AC, even though if it were a perfect square wave it would have components stretching up in frequency to infinity!!! You have to look more closely to understand where the periodic signals are, but they are there. A spectrum analyser would greatly assist you in seeing them.
Jeff
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If it has a large enough DC offset it is not AC.

I know where they are.
The resultant signal is also period.
Being periodic is a neccessary but not sufficient condition for a signal to be AC.
MBQ
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Another example. Take a DC power supply with a constant voltage regulator and a varying current load. Is the load current AC or DC?
Conversely take a constant current supply and connect a varying resistive load. Is the resulting voltage waveform AC or DC?
Think carefully before you answer.
MBQ
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On Tue, 31 Jan 2012 01:36:45 -0800 (PST), " snipped-for-privacy@hotmail.com"

And it's fairly common to use +x and -x rails in digital signals, this is still not described as AC for the simple reason that it's not, in any meaningful sense.
The question with DCC would be: what does the output waveform look like with no signal. I don't know the answer to that, I have no way of checking here at the moment. Guy
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On Feb 1, 7:52pm, "Just zis Guy, you know?"

Not sure what you mean by that. There's never really a situation with "no signal". If a booster has no input from a command station then good design would be to shut down the track output.
If there are locos being controlled then the control packets are sent repeatedly to those locos.
If the command station really is quescent then it outputs a continuous preamble which is a string of '1' bits which results in a square wave at 8.6KHz.
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Does any system actually do that? Digitrax certainly doesn't.

This is flat out wrong. Decoders assume that the previous instructions stand until they get an update. If dcc commands stop going out on the rails, the trains will happily keep running unless you kill power. You've never had any runaway trains? It definitely happens.

Not sure what point you're trying to make. This is kind of a dumb message thread anyway. *
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On Feb 2, 5:13pm, pv+ snipped-for-privacy@pobox.com (PV) wrote:

Fuck me, where do people get their DCC "knowledge" from? Try reading the specs. Specifically RP-9.2.4 section C. If you choose cheap decoders that don't implement the spec correctly, or disable the timeout then you deserve every run-away you get.

The point that there is always *something* even if it's just the preamble on the rails. It is neccessary to continue delivering power.

You didn't raise the level, so why did you bother replying?
MBQ
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Any time varying waveform has AC *components* as shown by a fourier analysis. That doesn't mean that the original waveform, complete with DC bias is alternating.
What do you think the word "alternating" means?
MBQ
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You said: "A pulse modulated signal is AC", which is simply false. You can have pulse modulated AC or DC.
And all waveforms can be described by a sum of sine waves, by that argument DC is AC. I have no opinion on what comes out of my Lenz DCC system because I still haven't got round to buying that second-hand oscilloscope I've been promising myself, and I don't care enough to look it up because it Just Works. Guy
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You can't have it both ways Guy!!! You say that "all waveforms can be described by a sum of sine waves" and then go on then say that you can have "pulse modulated DC"!! (DC cannot be described by sine waves unless you tale the case of zero frequency as a sine wave). If an FFT shows something other than *only* a DC component (zero frequency) the signal is AC!!!! All pulsed waveforms have a time varying component and are therefore AC.
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Please provide an authoratative reference for your definition of AC as anything that varies over time.
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Give the man a coconut, zero frequency is indeed a special case. Now find a railway power supply that puts out a perfectly smooth DC waveform.

Bullshit. If current only flows in one direction out of the supply then the current does not alternate.

Bullshit. See above. Guy
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On 02/02/2012 19:44, Just zis Guy, you know? wrote:

A car battery. Perfectly smooth 12v. DC.

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wrote:

I think you'll find it reduces over time, initially in a fairly linear way and later definitely non-linear. Guy
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On 03/02/2012 00:22, Just zis Guy, you know? wrote:

Depends if you recharge it between operating sessions or not.
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wrote:

Not really, no. It's a lot smoother than rectified DC but the voltage will still fluctuate, and will go down as the battery discharges. Guy
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