DCC is the future

Agreed.

Reply to
John Sullivan
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The advice I had from ZTC was that whilst their decoders can be set to DC compatability mode, they shouldn't be unless your DC controller is outputting a pure - ripple free - DC. Otherwise the Decoder attempts to interpret the ripple as DCC code. As the number of DC controllers that output a pure DC are exceedingly few I was advised not to even bother enabling the option

Reply to
Ian Birchenough

The "preventing higher speeds" sounds odd - what happens to locomotives that operate at reasonable speeds as analogue locos when you fit a decoder? eg most Roco locomotives run at about 1.3 time prototype speed on 12 volts DC.

It works with NCE decoders.

OK, but what effect does that have?

Sure, everything is relative. 4.5-9kHz is still audible frequency so not usually called "high frequency".

A square wave produces harmonics way up the frequency range - I think to about 9 times the actual frequency or 81kHz.

Regards, Greg.P.

Reply to
Gregory Procter

In article , Gregory Procter wrote: snipped\

Phil: This is the transmitted data frequency, and independant of drive frequencies - see below)

(Phil: In theory to infinity! 1/3 1/5th 17th 1/9th etc on each successive harmonic..3rd,5th,9th etc)

Phil: this is one reason why the dcc waveform is 'shaped' and NOT a perfect square wave - ie the higher frequencies have been filtered off by rise-time limiting/slew rate limiting or other technique the output waveform from the controller.

Also to note, that whereas the Zero-1 system had to have different modules for the USA (60Hz) and Europe (50Hz) countries, because it was based around the mains frequency of its country - the triacs used to pulse-width drive the motor were (usually/hopefully) turned off by the next reversal of the waveform, in the DCC system, there is COMPLETE FREEDOM of choice in the final drive method to the motor: by default the incoming data/power is full wave rectified to dc for the decoder power supply and any function.

The control processor on board detects the edges of the incoming waveform and therefore extracts the control info.

Different decoder designs then either pulse width modulate the motor drive or one type does quote variable dc: perhaps it is a high frequency pulse drive with its own smoothing cpacitor on board???).

Whereas earlier decoders used low pulse rate frequencies similar to zero-1, (not suited to some motors) several current designs use 'silent; or 'whisper' or similar phrase drives at above-audio frequencies (>16kHz)

- which will also be perceived by the motors as simply dc (easier to smooth the rapid series of smaller pulses -- the same idea as 256x oversampling 1 bit DtoA converters for CDs etc)

As with power supply inverters and aircraft power supplies, the advantages of going to higher switching frequencies are smaller quantities of energy in each cycle: in a transformer this means smaller, lighter laminations/iron core, and in the decoders this probably means smaller capacitors. (The down side is that 'a greater proportion of time might be spent in the linear region during switching, and this is when heat is dissipated / energy wasted - but newer components are probably faster than a few years ago.) (( In a transformer, the energy each half cycle is converted from electrical to magnetic-field and then back to electrical wnrgy in the secondary - therefore a higher frequency (Aircraft at 400Hz, or sine-wave inverters at higher frequencies) stores less PER half CYCLE and needs less material before saturation is reached - and this in turn leads to more efficient, smaller designs. At higher frequencies, laminations are replaced by dust etc))

Reply to
Phil

=>The "preventing higher speeds" sounds odd - what happens to locomotives that =>operate at reasonable speeds as analogue locos when you fit a decoder? =>eg most Roco locomotives run at about 1.3 time prototype speed on 12 volts DC.

I think you mean "maximum prototype speed."

Well, if you want, you can use the programming facilities of DCC to program a speed vs voltage curve for each loco so that all locos will run at protoypical maximum speeds. Or all will run at the same speeds at the same speed controller setting. Or whatever you like. This facilitry was originally designed into DCC so that locos from different manufacturers could be used in multiple - recall that NMRA DCC standards were developed for N. American conditions, where multiple units are the rule, not the exception

Then there's the question of what is a "prototypical maximum speed"? Is it the maximum speed used for timetabling, which will allow occasional higher speeds to make up lost time? Or is it the technically maximum speed attainable (which will always be higher than the design speed in the case of steam locomotives)? Most electric locos have a sustained maximum power output, one which brings the operating temperature to a sustainable maximum, and a short term maximum which would turn the motors into molten metal if run for more than about 15-30 minutes at this setting. AFAIK, the maximum speeds as specified are well below whta a loco could actually reach if you wanted to test to near destruction.

So Roco's 1.3 time prototypical speed at 12V is about right- that means that normal maximum operating speed will occur around 9v, and the loco can be run above normal max if necessary - just as the protype occasionally does.

There's also the visual illusion generated by the usual unprototypical high angle viewpoint. Trains run at prototypically slow speeds generally seem to run too slow; it takes a deliberate effort to learn to recognises prototypical speeds as correct. This illusion also happens in real life. I used to live to rather nice little hill whose peak was about 600 feet above the valley floor. Excellent views of both the CNR and the CPR from up there - and they sure seemed to crawl, even though I _knew_ they ran at 40-60 mph! Anyhow, the illusion is the reason most people run their toy, er, pardon me, model trains too fast.

HTH

Wolf Kirchmeir ................................. If you didn't want to go to Chicago, why did you get on this train? (Garrison Keillor)

Reply to
Wolf Kirchmeir

I think you're right! :-)

That's a major reason why I would like some form of decoder for my DC locos operating on analogue.

OK.

I recall that the NMRA took the Lenz standards and has worked in conjunction with Lenz etc to extend them.

You can't know that figure because it differs over time and railroad.

I work with design speed. Ditto the NEM.

I do that all the time ;-)

It can also reach "maximum speed" with a realistic load.

I work from the rotational speed of the side rods - if they become a blur then the loco is running too fast.

not me!

Regards, Greg.P. Takaka, NZ.

Reply to
Gregory Procter

=>I work from the rotational speed of the side rods - if they become a blur then the =>loco is running too fast.

Ah, well, your cute little NZ trains never did run very fast... Big Boys have been clocked at over 90mph. At that speed, all four sets of rods are a blur. :-)

And I recall GWR/early BR steamers running fast enough that even my then much younger eyes saw only a blur where the siderods should be.

Wolf Kirchmeir ................................. If you didn't want to go to Chicago, why did you get on this train? (Garrison Keillor)

Reply to
Wolf Kirchmeir

Kb's frequently topped 100 mph. (4-8-4 Springfield - Rolleston) Ja's could manage 90mph on the flat with 7-8 coaches (around Levin) The last chase (1988) I did with a J class with 12 coaches on the Canterbury plains, my little Renault 8 peaked at around 85mph and the train walked steadily away from me. Against a K (4-8-4 without booster) between Rolleston and Springfield (a constant uphill grade around 1:60-75) the train ran at 75mph constantly. I had three other enthusiasts in the car on the parallel shingle road as witnesses! They actually seemed more interested in the speedo than the train at the time! ;-) The modern Diseasels that replaced them are all limited to 60mph :-(

Sure, but I was meaning common operating speeds - a 4F at 120mph is pushing your luck a little.

Regards, Greg.P. Takaka, NZ.

Reply to
Gregory Procter

=>Kb's frequently topped 100 mph. (4-8-4 Springfield - Rolleston) =>Ja's could manage 90mph on the flat with 7-8 coaches (around Levin) =>The last chase (1988) I did with a J class with 12 coaches on the Canterbury plains, my =>little Renault 8 peaked at around 85mph and the train walked steadily away from me. =>Against a K (4-8-4 without booster) between Rolleston and Springfield (a constant uphill =>grade around 1:60-75) the train ran at 75mph constantly. I had three other enthusiasts =>in the car on the parallel shingle road as witnesses! They actually seemed more =>interested in the speedo than the train at the time! ;-) =>The modern Diseasels that replaced them are all limited to 60mph :-(

Cool.

That must have been some ride behind those 4-8-4s - handsome brutes by any standard!

Wolf Kirchmeir ................................. If you didn't want to go to Chicago, why did you get on this train? (Garrison Keillor)

Reply to
Wolf Kirchmeir

plains, my

constant uphill

They were very well balanced, 4'6" drivers and rode very smoothly for steam locos.

The J's/Ja's (4-8-2) were lighter and the cabs moved side to side at higher speeds. They pulled the expresses across the Canterbury plains. My old BSA could go to

70-71mph with me flat on the tank and it was never quite enough to match the "Limited's" running speed when it was on time.

Greg.P.

Reply to
Gregory Procter

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