# Anyone have Links to DCC info for G?



## jimtyp (Jan 2, 2008)

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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## Cougar Rock Rail (Jan 2, 2008)

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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## rwbrashear (Jan 5, 2008)

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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## Greg Elmassian (Jan 3, 2008)

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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## rwbrashear (Jan 5, 2008)

Hi Greg-

Is the problem the track voltage or the loco's motor/gearbox?









Best regards,
Bob


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## Greg Elmassian (Jan 3, 2008)

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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## StanleyAmes (Jan 3, 2008)

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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## Greg Elmassian (Jan 3, 2008)

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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## StanleyAmes (Jan 3, 2008)

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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## Greg Elmassian (Jan 3, 2008)

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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## aceinspp (Jan 2, 2008)

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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## Greg Elmassian (Jan 3, 2008)

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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## Steeeeve (Sep 10, 2008)

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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## aceinspp (Jan 2, 2008)

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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## Cougar Rock Rail (Jan 2, 2008)

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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## Steeeeve (Sep 10, 2008)

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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## Cougar Rock Rail (Jan 2, 2008)

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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## krs (Feb 29, 2008)

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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## jimtyp (Jan 2, 2008)

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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## Road Foreman (Jan 2, 2008)

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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## Cougar Rock Rail (Jan 2, 2008)

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. 


Then you should look at other manufacturers...Zimo and Massoth both have adjustable voltage up to 24V and their hardware is designed around it. I think the others use lower voltage so they can get away with cheaper decoders. It seems to me the NMRA decision on voltage was based more on lobby pressure from non-complying manufacturers, not common sense. 

As Knut says, it shouldn't be this difficult. 24V DC max and adjust gearing to suit. 

Keith


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## Road Foreman (Jan 2, 2008)

Keith, 

It is not difficult, why should I have to pay more than twice the price of the most expensive system here for one of Zimo's.. Also why does Massoth have a system for over there & a system for over here?? & I do not want to here any thing about the difference in AC power!! We are a global society are we not.. 

BulletBob


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## Cougar Rock Rail (Jan 2, 2008)

Hi Bob, 

Are you sure Zimo is double the price? I'm not sure what you are comparing them to, but their sound decoders are very reasonably priced and if you compare the built-in features of their decoders or Massoth's then the value looks even better to me. The one thing Zimo is missing is a reasonably priced wireless handheld--theirs is very powerful but it would be nice if they would bring out a simple loco throttle. As far as why Massoth makes the different systems...well is there more to it than just the AC power issue? I don't know. They do make the integrated 800 which has the transformer built in. I could see them coming out with the higher power version for N/A if the market grows, but until then I can see why it's cheaper/easier for them to let the consumer supply the N/A power supply separately. 
If there is one thing I've learned from my experience with DCC is that there is no fits-all solution; each person has unique demands and so what is value to one person is paying for unnecessary features to another. I think that's what causes a lot of frustration. It also seems to me that many of these so-called standards have been driven by the manufacturers or special interest groups and have lacked adequate input from the consumers. 

Keith


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## StanleyAmes (Jan 3, 2008)

There seems to be a lot of confusion on the maximum DCC track voltage allowed by the standards and why this number was chosen.

From a Decoder standpoint decoders other then N scale decoders must accept a DCC track voltage of at least 27 volts DCC. 27 was initially chosen because it is more than twice the 12 volts DC and under the 30 volt standard component part max voltage.

From a systems standpoint the Maximum DCC track voltage was set to 22 volts DCC. 

This number was chosen in 1992-1993. This was before LGB developed its Large Scale DCC products. In large scale at that point in time you had the majority of the manufacturers at 18 volts DC and LGB at 24 volts DC. However an LGB locomotive at 22 volts DCC will operate about as fast as the same locomotive at 24 volts DC. The reason is simple. What is important is the voltage to the motor and LGB uses Diodes to drop the voltage to the motor so that the lights turn on before the motor operates. A track voltage of 18 volts DCC was chosen as the typical DCC track voltage for DCC in Large Scale which at the time provided a good top end speed for most product in the market (except for the LGB track cleaning locomotive which needed at least 20 volts DCC.)

Please note that DCC was the first standard to recognize that Large Scale trains had a higher operating track voltage but even today we still have no industry wide common DC track voltage in Large Scale as the different manufacturers continue to build to different maximum voltages.

From a Large Scale Perspective one key issue is that since 1992 many manufacturers have raised the voltages so that with some locomotives you now need close to 24 volts DC to the motor to get acceptable maximum speed so that what was once a good maximum is now barely adequate from a max speed perspective for some locomotives.

Stan Ames


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## jimtyp (Jan 2, 2008)

Stan, I agree that the max G scale track voltage for DCC should be increased to at least 24v, so locos run closer to the DC operation of the same loco. 18v is way too low as decoders drop the voltage as well. Even at 24v with the decoder dropping voltage to the motor it still won't compare to DC operation but at least it would be closer. Ideally I think it should be higher, maybe 26v to accommodate the drop in voltage by a decoder. But I don't know if going to 26v would cause problems with non DCC components, such as passenger cars that are lit from track power? 

I think raising the min and max voltage would encourage more folks to run DCC in G scale. As I said I was ready to give up on DCC because my locos wouldn't run any where near prototypical speeds when my power station was putting out 18v to the track, thus about 16v to the motor through the decoder.


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## Guest (Oct 24, 2008)

The "gearless" or "bipolar" motors that were wound on the axle themselves are a hack. First they were AC motors. Second, they were inefficient. Third, they were limited in horsepower, hence some locos like the Biploar Electric had LOTS of motors. The reason that they were used is that only part of the originally very heavy motors were sprung, the armatures. The fields were fixed to the loco.

These motors weren't used in designs past the 1920's or so because much better motors were devised that could fit in the trucks, were much more efficient due to better magnetic coupling between the armatures and the fields and were still reliable.


- gws


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## Steeeeve (Sep 10, 2008)

Seems siemens has improved on them a little bit. 

In any event, Aristo uses plastic gears and a worm drive because of the location of the motor. Why don't any of these manufacturers so what all trains do and have the motor parallel with the axle and run the gear reduction to it? You'd get 3 motors per truck on 3 axle trucks which is the standard. Is the space too small?


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## krs (Feb 29, 2008)

Posted By jimtyp on 10/21/2008 11:40 AM
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?



From a systems Engineering point of view, the maximum DCC track voltage should be equal to the maximum DC trackvoltage plus the expected voltage drop due to the decoder.

NMRA follows that principle in H0 - the maximum DC track voltage there is defined as 12 VDC and the maximum DCC track voltage recommended is 14 volts DCC allowing a two volt drop through the decoder which is reasonable. That ends up powering the motor in the engine with the same maximum voltage regardless if the layout is powered by a DC or DCC system.


Using the same logic, the maximum DCC voltage for G Scale should have been 26 volts DCC, again the maximum DC voltage used in G Scale which is 24 volts plus the drop through the decoder.

From a system point of view, I'm talking track voltage - if a booster or Central Station has an internal voltage drop due to the design, that needs to be taken into account by the manufacturer. The booster should be a "black box" with a 24 volt DCC signal as measured at the output terminals.

The 24 volt and 27 volt minimum required for smaller scales and H0 and larger DCC decoders is really derived from the maximum specified DCC track voltage (22 DCC in the current NMRA spec) plus a safety margin - in this case of 5 volts which is also reasonable.


So ideally, the G-Scale DCC track voltage should be 26 volts and the minimum DCC Decoder voltage should be 31 volts - 30 volts is probably OK.
Trouble is, as Stan has already pointed out, the higher you make the voltage spec the more expensive the parts become. There are very few Large Scale DCC decoders that actually specify 27 volts or more as their max. decoder voltage. In fact most manufacturers don't specify that voltage at all!

Last time I checked Zimo , they specified 24 volts as the maximum voltage for their Large Scale decoders - they at least did have a spec, most manufacturers don't.


PS: Sorry - I wrote this without realizing there was a second page to this thread.


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## krs (Feb 29, 2008)

Posted By Road Foreman on 10/21/2008 12:33 PM
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.. 



Bob -

There are really two different circuits involved in what you describe.

One is a simple zener diode transistor regulator set to around 6.5 volts (even though LGB calls it 5 volts) to drive their "5 volt" lamps - so the lights stay on at constant brightness from about 6 volts to 24 volts, and secondly there is a roughly 5 volt "voltage dropping' circuit between the track pick-ups and the motor.


But this "voltage dropping" circuit or "delayed start" circuit as LGB called it was introduced with the first RhB electric loco with the moving pantographs so they would operate properly. 
When one reversed direction, and then applied track voltage, the rear pantograph had to be raised and the front pantograph had to be lowered - all before the engine started to move. So this "voltage dropping" circuit was added to this engine to be able to power the pantograph motors and "delay" the start of the loco motor.

For those engines with that circuit - yes, the motor will actually only see about 19 volts with 24 volts on the track, but not all LGB engines include that "voltage dropping" circuit. Many LGB engines will move with less than 5 volts on the track.

I don't think any of the current NMRA specs took any of these LGB parameters into consideration, not the 22 VDCC max to the track spec nor the 27 volt Decoder max spec.

Lenz developed the original MTS system for LGB and was also the father of DCC, so it's no wonder the two systems are very similar, but for years at the beginning, LGB kept saying that MTS does npt equal DCC; in fact they positioned MTS as superior to DCC and specifically geared for Large Scale whereas DCC focused on H0 and N scale.


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