Top Speed DC vs. DCC

[Jerrys HO]

I was reading up on a few links I have saved and came across this info that I had remembered seeing in another post and thought it was an interesting analogy.
Post where someone had inquired:
http://www.bachmanntrains.com/home-usa/board/index.php/topic,19691.0.html

Post where I found this: http://www.members.optusnet.com.au/nswmn2/DCC.htm#TopSpeed
I have observed and many others have reported that when they've install a decoder into a loco, the loco goes much slower at Top Speed in DCC than what it did in DC.

Depending on the type of DC Power Pack (Controller) being used, while they are rated at 12 Volts DC, they put out much more than 12 Volts. Many especially the early types provide an "unregulated" DC supply provided by a suitable drop down Transformer, Rectifier and then some form of Rheostat. Later Power Packs had simple electronics instead of the Rheostat. In both cases these Packs the "12" Volts supplied to the Rheostat/Electronics was not REGULATED and provided voltages up to 20 Volts DC. Later more complex electronic Power Packs provided regulated 12 Volts DC. These units would provide a maximum of 12 to 14 Volts DC.

For DCC equipped locos, I measured some decoder motor outputs for some comparison test to see why the locos ran slower in DCC to DC.

Test Conditions:
NCE DCC Power Pro 5 with a Track Voltage of 14.2 Volts DCC (NMRA Nominal DCC Track Voltage) measured with my Pricom DCC Pocket Tester.
Decoder's CV 5 programmed to "255" if applicable and Internal Speed Tales set - CV 29 at "34" and CV 3 & 4 at "0").
Throttle set at Speed Step 28 out of 28 (Full Speed).
Loco "blocked" and running at full speed with wheels slipping (loco stationary).

Listed below are the DC voltages at the Motor Terminals while operating:

Soundtraxx Tsunami - 11.6 Volts DC.
Soundtraxx DSD-100LC - 12.6 Volts DC.
TCS MC2 - 11.6 Volts DC.
NCE D13SR - 13.0 Volts DC.
Lenz 1034 - 12.3 Volts DC.
TCS T1 - 11.3 Volts DC.

With 14.2 Volts applied to the track, this shows that the decoder electronics "drop" between 1 to 3 volts. This I would consider normal. Inside the decoder, the electronics has a bridge rectifier and transistors/FETs etc to make the DC for the PWM motor drive voltage etc, that have "voltage drops" across them.

With a voltage to the Motor in DCC being in the range 11.6 to 13.0 Volts DC when compared to what the same motor had in DC, 12.0 to 20.0 Volts DC, there could be a verly large variation up to 100% higher for DC. No wonder the loco goes faster in DC.

One other thing to consider in "top speed" running, is the DCC track voltage. NCE is operating at 14.2 Volts DCC, the "nominal" NMRA recommendation for HO. Of the other U.S. made DCC systems, some operate around the same 14.2 volts DCC but others operate with a higher voltage. I have measured 22.5 Volts DCC on a European DCC system. The Europeans seem to want their locos to go "faster". Have you noticed how bright the incandescent headlights are on these systems or they have blown.

A note on Top Speed I have never understood, if the prototype of the model you have went at 100 MPH, why you would want the model to go at 100 scale MPH. That would be 3 feet in 1.75 seconds and 30 feet in 17.5 seconds. I guess some people have extremely long layouts, but for me I want the "operating" experience to last a little longer and with my track laying abilities, I would have to install safety nets around the layout. These above speeds are for toy trains, not for the serious modellers that go to added expense of using DCC to "play" trains.

I have visited the La Mesa Club's Tehachapi Loop layout in San Diego that is 125 feet long and operated on some "smaller" layouts when I attended the NMRA 2011 Convention in San Jose/Sacramento USA and many layouts here in Australia (not quite as big as the Tehachapi Loop layout) and not once did I see a train "driven" at more than 30 MPHs. These observations and my own personal preference, why would anyone want to operate a train at greater than 30 scale MPH, in HO.

I have reduced the Top Speed of all of my locos to 30 MPH, see My 30 MPH Max Speed Table and my Blog entry.
End of article....

Found it interesting and thought it may help others that are used to DC versus DCC.

Jerry 

[richg]

Nice job Jerry. Nice to see Facts, not opinions.
I have seen about the same in some post in other forums about DC speed versus, DCC speed. Just not to the detail in your message. This is something anyone can reproduce if they doubt your results.
Takes all the fun out of playing with trains. lol.
I have always used a stop watch with measured section of track and a calculator.

It will not happen but your message would be a nice sticky or FAQ which many never read anyway.

Rich

[Jerrys HO]

Rich

When I joined this forum I kept reading your replies and they all said the same thing--- save and store in your favorites. Well just about everything I can get my hands on regarding DCC, I save and read over and over.

Thanks

Jerry

[richg]

Is it possible to reference you when I see the same questions in another forum?
What I plan to do is save the link to this page in my Browser and just include the link in a different forum when I see the same question. A few still do not want to believe the answers they get when using a measured distance and stop watch.
Again, some nice realistic numbers. This can be applied to any scale.

Rich

[glennk28]

Keep the top speed below Mach 1!   8^))     

[Jim Banner]

... A note on Top Speed I have never understood, if the prototype of the model you have went at 100 MPH, why you would want the model to go at 100 scale MPH...

... I have reduced the Top Speed of all of my locos to 30 MPH ...

Jerry

I agree with your measurements but am having trouble with some of your conclusions.  If I regularly see trains running through the countryside at 80 mph, why wouldn't I want to see them running at a scale 80 mph on my layout?  If the real thing takes 11 seconds to cover 1/4 real mile of scenery, why wouldn't I want to see my 1/87 model cover 15 feet of scenery in 11 seconds?

I don't know of any fans of the Acela or the ICE who would be happy watching their models of same putzing along at 30 mph.

In spite of that, there is much to be said for running our trains slowly when a group of us is operating our trains.  As you pointed out, we rarely have anything approaching scale distances on our layouts.  One solution is distance compression, calling every ten feet along our tracks a mile.  This means that if we limit our trains to say 60 compressed miles per hour, we cover only 600 real feet of track in one real hour at a scale speed of only 10 mph.  Most people do not like running that slowly.  The common alternative is to use time compression, calling every 10 real seconds a compressed minute.  Now we can cover that 600 real feet of track in 10 real minutes or 60 compressed minutes running at a scale 60 mph.  But that creates a problem for operators switching trains - their time is difficult to compress.  A work around is to run the trains slower, say at 30 scale miles per hour, which helps stretch the distance without requiring as much time compression.

Bottom line, running extra slow can be a good solution when operating trains but operating them at scale speeds can make them look more like the real thing.

Jim

[Jerrys HO]

Jim

I am sorry to say that none of those quotes are mine, I just found it interesting to read and remembered the other post about the Dynamis running slow.
I do agree with you on:

If I regularly see trains running through the countryside at 80 mph, why wouldn't I want to see them running at a scale 80 mph on my layout?  If the real thing takes 11 seconds to cover 1/4 real mile of scenery, why wouldn't I want to see my 1/87 model cover 15 feet of scenery in 11 seconds?

Wish I could take credit for the measurements though.

Jerry

[Jerrys HO]

Rich

Is it possible to reference you when I see the same questions in another forum?

Sorry I missed your question. Yes you can reference me or just used the link in which I found it.
Like I answered Jim, I wish I could take credit for this. I tripped over it while I was broadening my knowledge on DCC. The link has a lot of detailed information and kind of breaks it down so a caveman can understand.

Jerry

[poliss]

I know what you mean about the 22.5v from European systems. I think the power supplies have been changed in the last year or two and now they put out a much more reasonable and better regulated 18v.