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Discussion Starter · #1 ·
I started this topic to find out what the standards are for DCC in G scale, in particular


1. What are the NMRA DCC voltages recommended for G? Output to track, decoder, motor?

2. Do they need to change? If so to what?
3. Is there a way to get feedback to NMRA?


I have difficulty trying to get this info from the NMRA.org site: NMRA DCC
 

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1) Digital Decoders intended for "N" and
70 smaller scales shall be designed to withstand a DC voltage of at least 24 volts as measured at the track.
Digital Decoders intended for scales larger than "N" shall be designed to withstand a DC voltage of at
least 27 volts as measured at the track.


The above was quoted out of the NMRA electrical standard .pdf.

2) I don't think they need to change, just more manufacturers need to actually comply with what is there. Massoth and Zimo are two (and maybe the only two) that are actually engineered properly to comply with the standards. So you get what you pay for.

3) Probably but you have to ask yourself how responsive they will be when the ones steering the bus are in a potential conflict of interest position.

Keith
 

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Hi Jim-
1. The standards (DCC Electrical Standard S-9.1) can be found here:

http://www.nmra.org/standards/DCC/standards_rps/S-91-2004-07.pdf

See the graph on page 3.

2. I really don't feel the standards need to change. At this point, increasing the maximum voltage to the rails would cause more problems than it would solve.

3. Here is a link to the DCC Working Group page on the NMRA website:
http://www.nmra.org/standards/DCC/organization.html

The DCC Working Group may be reached via email at [email protected].

Best regards,
Bob
 

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In my opinion, 24 volts to the rails in G scale is marginal, if you want to see top speeds comparable to normal operation on average DC power supplies.

Some locomotives will not run at a prototypical top speed with 24 volts on the rails. (These are passenger locos, and I'm talking about not being able to achieve 100 scale miles per hour)

I know a lot of people will say they never run that fast, but if this IS a MAXIMUM, then it should be chosen to not be a limit.

It's like a car. If you drive on a freeway, do you want a car with an absolute top speed of 65 miles per hour?

Anyway, all that said, the chances of we, the small group of DCC in G scale, being able to modify the NMRA standard has something to do with a snowcone in a really hot place.

Regards, Greg
 

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Again, in my opinion, it is the gearing on some locos.

I cannot see why it should be necessary to go over 18 volts DC to get a prototypical top speed on ANY locomotive.

You usually lose up to 3 volts in the decoder, so that would put it to 21 volts to the decoder to get the same speed as 18v on DC.

Thus the 24 volts on the rails DCC makes sense to me.

But, some manufacturers do not realize or notice or care what the speed is vs. voltage. Also, it seems that almost NO manufacturer appreciates that most of the top speed is in the last few volts, i.e. "losing" 4 volts of the "top" can reduce the top speed a great deal.

Case in point: I have an NCE system. Normally, the top voltage they output is between 20.1 and 20.3 volts DCC (I have measured a number of units). In several of my G scale passenger locos, notably a USAT F3, and an Aristo E8, the top speed attainable was between 62 and 65 miles per hour. After I had NCE modify my boosters to achieve 24 volts (NMRA max), I was putting 23 volts to the rails.

These two same locos can now achieve about 90 smph unloaded. Still under prototypical top speed, and of course less when loaded, but now acceptable.

Thus my opinions expressed.

Regards, Greg
 

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1) The maximum voltages from a DCC perspective are within S-9.1 which is on the standards page for the NMRA. The basic S9 voltages have yet to be modified for Large Scale or Z scale and currently remain at a mimumum max voltage of 12 volts to the motor. There is also no general agrement on this from a locomotive manufacturer standpoint as this can range from 16-35 volts DC.

2) S9 provides both a max voltage as well as a suggested voltage. In my opinion the suggested voltage levels for Large Scale are two low.

Note: Changing the max voltage above 24 volts DCC would likely be difficult because of the NationaL Electrical Code and EU voltage requirements. ALso the costs tend to go up for components as the voltages get larger. This is not an easy topic and requires cooperation between the manufacturters of the electronics and the manufacturers of the locomotives.

3) Several ways. The easiest would be to get folks that are part of the WG and frequent this list to paqss on this feedback. Greg for example is a member.

You can also send an email to the NMRA Standards Chair or the DCC chair. If you like I can email you these offline.

Stan Ames
http://www.tttrains.com/largescale
 

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I don't know the EU specs, but if you look up article 720 of the National Electric Code, the low voltage definition, where you do not have to have GFCI, special wire, conduit, etc. is "under 50 volts". Most manufacturers stop at 48 volts.

So raising the voltage to 30 volts would not be a problem in the US.

Regards, Greg
 

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Greg

You are forgetting two elements.

1) in DC you have the potential for double voltages on reverse loops. To date this has meant you need to take 1/2 values for max voltages. While a properly wired DCC layout will not have double voltages it is still a consideration.

2) Wet environments tend to lower the max voltages recomendations.

In Europe model railroads are typically clasified as Toys with a max voltage of 24 volts. This is part of the reason the LGB DC 10 amp DC transformer costs so much because of the need to remove voltages greater then 24 volts. This is also why most EU approved DCC systems sut down at 24 volts DCC.

My information of EU requirements is a few years old but I do not believe these specifications have changed much.

If you believe these voltages should be raised you should propose this to the WG. I suspect that you may have difficulty getting concensus for anythig over 24 volts and even that may be difficult sonce several would perfer it lower.

Stan
 

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Hi Stan:

1. not forgetting, we were talking DCC and so assumed properly functioning autoreverser!

2. There is no part section 720 that says the limits are reduced for wet. That is taken into account for this part of the code. Wet condition provisions are applicable to 110v outdoors or inside, but we are talking the low voltage stuff.

Understand Europe is more restrictive, so it would probably be the limiting factor.

By the way, putting my hands on two wet rails gives quite a tingle at 23v DCC...

I agree with you, the likihood and really the practicality of the situation would leave this at 24v just to be an international standard. Unfortunately, with the current crop of locos, this is really just marginal in my opinion.

So, we are left with asking manufacturers to have "max performance" at 18 volts or so (again my opinion). I think this is doable, and could be a goal.

Regards, Greg
 

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The logical thing to look at is types of locos and at what speeds the locos ran. An E 8 and others made for pass service are meant to run at faster speeds. So If we could get the manufactures to just change gear ratio to match then we could for get boosting the volts to rails. Granted some manufactures locos do run faster than others. I think most folks think not only of speed but how many cars can they pull. Well remember pass units are not geared to pull long trains unless multiple units are used. Again another problem now you got to buy more than one unit to pull your 16 car passenger train. So i guess we are stuck on boostifng the volts to get our speed. Don't think the manufactures would go for having different gear ratios for different loco's. Later RJD
 

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Agreed, R.J. .... not likely we will get Aristo to change, although, looking at the construction of their gearbox, it would be simple to have a different worm and worm gear, plenty of room inside.

Oh well, will just have to keep running my "frog-zapping" voltage!!!

Regards, Greg
 

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Posted By Greg Elmassian on 10/17/2008 1:35 PM
Agreed, R.J. .... not likely we will get Aristo to change, although, looking at the construction of their gearbox, it would be simple to have a different worm and worm gear, plenty of room inside.

Oh well, will just have to keep running my "frog-zapping" voltage!!!

Regards, Greg


Why don't any of the manufacturers use a gearless motor with the axle basically running through the motor? This was done with some real life diesel trains and I don't believe you loss that much when doing it.

http://w1.siemens.com/press/pool/de/pressebilder/corporate_communication/media_summit_2008/soaxx200803-06_300dpi.jpg
 

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Basically you loose TE in that situation. Your need start power and it would be low using a 1to 1 drive. Later RJD
 

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All of the above highlights what happens when there are multiple interests at play. For example, LGB designed MTS to work well with 24V, 5A max. One reason they could get away with such a low amperage is that their own locomotives use efficient Buhler motors which draw low current, and well designed gearboxes. I can run three double motored LGB RhB trains on my layout at prototypical speeds and still not max out my MTSIII. So as an overall system it works fine. As soon as you introduce something like an Aristo or USA multi-engined loco you're toast. They (the 'non-system' loco mfg's) have no interest in keeping the electrical consumption down...it's not their worry how you're going to power your track or how many boat-anchor batteries you'll need. They just want to keep the cost down at the consumer's expense down the line. Same goes for the decoder manufacturers. I'm sure they would love to see the voltages drop because it makes their products cheaper to make and sell, but it doesn't help the consumer at the end of the day.
So in my opinion, the consumer pressure should not be on the NMRA to change the standards, the pressure should be on the loco and decoder manufacturers to comply with the standards and improve the design of their products to minimize electrical demand.

Keith
 

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Posted By aceinspp on 10/17/2008 3:00 PM
Basically you loose TE in that situation. Your need start power and it would be low using a 1t0 1 drive. Later RJD

Seems to work on the Siemens train I pictured. I can't imagine with a little engineering they couldn't do this. It would probably solve a number of issues I've read about with G Scale.
 

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Steve, it's not that they couldn't do it, it's just that they choose not to do it because of the cost. There are beautifully designed drive systems out there for G scale, but it all comes down to $$ at the end of the day. People aren't willing to spend a little extra for long term value it seems...and hence we get this race to the bottom for most of the current flock of big-volume manufacturers.

Keith
 

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To me this seems rather simple and straight forward.

The maximum DC voltage for G-scale is 24 volts. Every power pack that is in the current (2206) LGB catalogue specifies 0-24 VDC. On the AC side, the power specified is 18 VAC.
LGB started the current G-scale product in 1968 and to me therefore establish a de facto standard.

Aristocraft's new power units are becoming 24 Volt units as well - finally; Bridgewerks never had a problem with voltage - theirs was typically too high.

So if 24 volts DC is the maximum DC voltage for G-Scale, that would make 26 volts the maximum standard voltage for DCC in G-Scale. Two volt drop through the decoder (same as for H0) and you get 24 volts to the moter as in DC operation.
This makes the currently specified 27 volt spec for the decoders a bit marginal, but if they can REALLY handle 27 volts, they can probably also handle up to 30 volts.
27 volts is not a recognized standard breakdown voltage spec for any electronic components I'm aware of.

A 24 volt max. DC spec and other specs derived from that should make all existing equipment compatible - I can't see anyone agreeing to a lower voltage like 16 or 18 volts that have been proposed simply because of backwards compatibility.

As to locos that don't reach their "prototype" speed at 24 volts (at the motor) - I don't know of any but if they do exist, then the gearing of those should be changed.

It's rather ironic - in the smaller scales and I'm thinking mostly H0, the top speed of most engines at 12 VDC is way more than the prototype speed. In fact, the European standard allows the top speed of the model to exceed the prototype speed by 40% - NEM 661.

Not something we need to worry about in G-Scale it seems.

BTW Stan - if you are still reading this thread - what was the NMRA rationale to specify the maximum DCC track voltage for Large Scale at 22 volts?
 

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Discussion Starter · #19 ·
From the spec (link provided by Bob above) I see volts for the decoder listed, which this is actually volts to the rail, correct, since that is where the decoder gets it's power? I see the maximum of non-N scale decoders at 27v input. This seems reasonable for G as most motors are set to 24v max. This would also allow for 3v drop in a decoder and still give the motor 24v.

So is the problem with the manufacturers of DCC power stations? If I set my NCE to the max I get about 21v to the rails which is the input to the decoders, another 2v drop for a decoder and I'm only getting 19v to the motor. I'd prefer to be able to get closer to 24v for the motor.

Is NCE the only manufacturer that restricts the power to the rails be so low or do all DCC manufacturers do this?
 

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Knut,

The 24 volts that LGB used was to get the lights & sound going before the loco moved.. This took up about 5 volts & left 19 volts for the motor.. I would guess that the NMRA looked @ the 19 volts to the motor & said lets limit the voltage to 22 volts so most of the boosters can get 19 volts to the motors.. So 22 volts became the standard.. They had to go with 27 volts for the decoders because of the LGB systems that put out 24 volts.. Today the manufacturers use 22 volts as the max..

jimtyp,

The Digitrax puts out 20 volts, CVP puts out 22 volts, NCE puts out 20 volts, LGB puts out 24 volts..

BulletBob
 
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