DCC and running locos from overhead traction wiring

Hi,
I've got a couple of loco models that have live overhead traction wiring support through their pantographs and one question which I've raised in
forums at my site in these two threads:
http://www.railzone.org/phpBB2/viewtopic.php?t 1
http://www.railzone.org/phpBB2/viewtopic.php?t0
is whether there is any standard for whether the left-hand or the right-hand rail is connected to the pantograph(s) for power collection using DCC.
I haven't come across a standard for this, but someone who's more savvy with the NMRA standards may well know what the answer is.
Failing that, I will ask the folks on the NMRA DCC working group list since I'm still a member of that list.
With the Modelling the Railways of NSW convention coming up, I'm hoping to fathom out what's going on with electric loco and passenger train models. I still have one of Ian Storrie's excellent 86 class kits (unfinished), but wouldn't it be fantastic to have high-quality brass models of the 85 and 86 class NSW electric locos, and perhaps even of the Victorian E-class locos, since that's an ideal medium for modelling electric locomotives in HO scale.
Thanks if you can provide a definitive answer to the question. Feel free to comment in the forums at my site too if you'd like to. I'll transfer any information from here to there otherwise.
Regards,
Craig.
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C. Dewick wrote:

Craig
http://www.nmra.org/standards/s-5.html
Section 4 provides the answer. In a nutshell appying positive voltage to the overhead should make the model go forward. The negative would be the left hand running rail, as per normal 2 rail practice. A switch (if fitted) would switch the positive connections between RH rail & overhead. Any DCC changes would have to reflect this.
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Thanks for the info. It doesn't really help much with DCC since there is no such thing as a 'positive voltage' and 'negative voltage' with DCC. It's a pulse-width modulated square wave with an amplitude of between 15 and 20 volts.
It could be something that's much more difficult to solve in reality because if the pantographs are connection to one specific power pickup side of the loco, changing direction would require either a shift in 'polarity' of the power feed to the overhead wiring or a device in the loco itself to change which side of the power pick-ups it is connected to. Does that make sense? I'm not sure if it does to me but maybe this is something that's been largely ignored in terms of DCC development.
Craig.
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C. Dewick wrote:

Not really, I can't see why DCC is any different WRT pantographs/pickups. Just liven the overhead so that it is equilavent to the RH rail. If you turn it around you might have an issue though, I haven't thought too much about that.
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no
What scale are you modeling? DCC on my HO club's layout is 14VAC at the booster (with the Digitrax Chief system) with a RMS meter, Tony's RRamp meter. And on my home HO layout, it's more like 12VAC (with my Digitrax Zephyr system).

because
To do that so the power pick up doesn't matter, the solution is simple... Wire both rails to the same polarity and use the catenary for the other polarity, just like the prototype. It's what my old club did for 45 years on our trolley trackage, and it worked very well, considering it was live overhead. It also meant that we never had to isolate diamonds and rail frogs.
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Pac Man skriver:

Yes, but the DCC system runs with square wave and not sine wave current.

Correct - until you want to run a diesel/steam loco...
Klaus
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According to Lenz (who developed DCC), several more European modelers, and myself, the reason not to run with live overhead is fairly simple and has been referred to indirectly in some of the answers. The small contact area of the pan/wiper as compared to the contact points of the wheels. Also, in our experience, more arcing takes place with pans and pantograph wipers which the highly sensitive control unit interprets as a short and then shuts down. Unless your layout will receive fairly heavy use to keep the overhead wire clean and arc free, I would suggest running normal rail to rail. It can be done, as I have done it (European prototype), however, it was found that the rail to rail solution was more reliable.
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Ok...but I have to tell you that our transformers powering our boosters are using the 14VAC taps. Are you saying that the voltage is higher than that after it goes through the booster?

the
You could simply use a toggle to switch between the two (live overhead vs. normal 2-rail)...unless you want to run diesels/steam with the electrics. Was that common in Austrailia?
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Pac Man skriver:

14 volts AC becomes 18VDC when it is rectified.
After that is is beeing chopped into squares.

I don't have a clue. But I can tell you that here in Denmark a lot of diesels rund undeneath overhead wire.....
Klaus
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And regulated properly.

Sort of, but the duty cycle isn't fixed. It's a variable duty cycle signal. The timing of the voltage transitions is what conveys data to the decoders.

Same here. There are almost no electric locos now. Only about 4 are insured for live use but they're owned by a freight company (Silverton) which is partly-owned by the chairman of Pacific National and that company only runs diesel locos.
We've got many electric suburban and intercity passenger trains at CityRail running off the 1500 VDC overhead traction system system. The 46, 85 and 86 class electric locos ran off that as well. I was a trainee driver at Enfield in the early 1990's when all three classes of electric loco were still being used. I was rostered for the electric locomotive school the same week I had a call about transferring from freight over to CityRail in late 1994. 8-)
Craig.
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"C. Dewick" skriver:

Not allways. My Roco "lokmaus" just makes DC from the AC and chops is into squares.

It is a powerfull serial data transmission :-)

Only some lines i Denmark is electrified, so mainly all traffic is done by diesel. Except for transit trains between Swenden and Germany and a lot of local traffic on Sjlland (a large island, containing Copenhagen)
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boosters
than
I have to disagree with that. For starters, DCC is only rectified in the loco's decoder. After it comes from the transformer and goes through the booster, it's still AC. Digital square wave, but still AC. Secondly, I recently had to test exactly how much DC volatage was produced by a Digitrax DH123 decoder for a semaphore signal installation I was doing. Using our 14VAC booster and a Digitrax Chief for a "brain", my DH123 produced approx. 12.5VDC to the motor leads... So I don't know where you are getting 18VDC from.

It's also very common east of New Haven, CT today on the NEC. Connecticut runs diesel powered commuter trains called "Shore Line East" to Old Saybrook, and the MBTA runs diesel commuter trains between Providence, RI and Boston, MA...all under the wire. Historically, however, it was more the exception than the rule.
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Pac Man skriver:

You just vrote that you had a 14VAC transformer. If you rectify that voltage (and you do that inside the booster) you get 18 volts DC. This voltage is chopped into squares by the booster.
Have you ever seen a circuit diagram of a bosster, or even looked at the components inside a booster ?
(been there done that - got the t-shirt) Klaus
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Klaus D. Mikkelsen spake thus:

OK, OK: "chopped into squares" = converted to AC. The DCC signal is AC, just a square wave instead of a sine wave. Still AC.
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David Nebenzahl skriver:

You can call it AC. If you call datatransmission on a RS485 network for AC too.
Klaus
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I have no idea what RS485 is...but DCC is still Alternating Current...otherwise it wouldn't work. To quote from Digitrax.com: "Each bit is divided into two halves, which are "mirrored" around zero volts. The bottom half of the signal (below zero volts) is a mirror image of the top half, but shifted over half a bit width." Also: "The DCC signal is symmetric around 0 volts." If that doesn't describe AC, I don't know what does. Sure, it's not a sine wave AC, it's a square wave...but then DC has no wave at all. The booster does not rectify the AC to DC. Honest. At least, not for NMRA DCC.
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Pac Man skriver:

Serial communication.
Klaus
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Pac Man wrote:
> You could simply use a toggle to switch between the two (live > overhead vs. normal 2-rail)...unless you want to run diesels/steam > with the electrics. Was that common in Austrailia?
On the railway that Craig is modelling, yes - but mostly in an earlier period than he is probably interested in.
All the best,
Mark.
(Self-Confessed Rivet Counter)
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Pac Man wrote: <snip>

Paul, while I don't have any practical experience with this, I would think that a single point of pickup (the pantograph) would be somewhat unreliable. Even with both pantographs up, that is only 2 contact points. Most 4-axle locos have 4 contact points on each rail when used in the conventional way.
Peteski
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Your point is well taken with the older pantograph designs.... However, most modern pantographs have two or three contact points.
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