# Double heading w/ DCC



## riderdan (Jan 2, 2014)

Still working in the garden (the terrace is almost done, probably will lay track after Easter) and starting to work on motive power. I'd like to run a locomotive and powered tender that I have, but they run at different speeds. The tender is about 20% faster than the loco, and running DC it tries to "push" the loco around the track, which leads to some uneven running.

My question is, if I equip both of these with decoders, will it be possible to match their speed so that they're working together rather than against each other? Is there a special type of decoder needed, and how would I go about programming the two decoders such that the loco and tender match speed?

Thanks,

D


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## East Broad Top (Dec 29, 2007)

Most definitely. The ability to program specific speed curves for individual locomotives so they can run together in a consist at the same speed is one of the hallmarks of DCC. At the most basic level, you can set start and top speeds via CV2 and CV5 respectively. That will make sure your locos start moving at the same throttle setting, and all move at the same speed when at full throttle. You can then customize the speed curve between those points to better match speeds through the speed range. At more advanced levels, you can create a totally custom speed curve to really fine-tune locomotive performance. 

Google "DCC Speed Matching" and you'll get a bunch of links, including written and video "how-tos." 

Later,

K


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## Greg Elmassian (Jan 3, 2008)

What DCC system do you have?

Greg


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## Dan Pierce (Jan 2, 2008)

What engine and powered tender? Do either have MTS?
The LGB units should run at the same speed as they have the same motor inside and the same gearing.
If these have no internal electronics, then the slow one has a bad motor.

There are engines and tenders that have electronics that take a plug and play LGB 55020/55021 and if your engine has this and your tender does not then there will be a speed difference.
And you can not run a mts and non mts unit together .


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## riderdan (Jan 2, 2014)

Thanks for the replies.

I haven't purchased a DCC system yet--I'm leaning towards NCE, but still researching the options. A $500 DCC system and a pair of decoders will put a strain on my train budget, so I probably won't actually buy the system until I get my tax refund  

The locomotive is from Piko, but the tender is LGB. It's an older tender out of a 2015D set. It does not appear to have the MTS connector.


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## Greg Elmassian (Jan 3, 2008)

Consisting is easy with the NCE system, it the system of choice for me. It supports both advanced and basic consisting.

Greg


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## Dan Pierce (Jan 2, 2008)

Since the units have different motors and are from different manufacturers, decoders can be programmed to fix the speed differences.
There are settings for start voltage, max speed, acceleration and de-acceleration plus a speed step table for the 28 speed steps.

While waiting for $$ to buy a system, download the decoder and command station manuals and read up on the units you are thinking of buying. And you can both locos to the same address, or look at the ability to consist the locos. This allows you to keep different address for each motorized unit, but run them as one.

And remember all decoders are not the same, you usually get what you pay for.
Watch for maximum voltage and current ratings and most decoders are rated for max light/smoke motor current combined.

I run 24 volts thus I look for 30 volts or more for the voltage rating.
Other systems output less voltage, but if you bring a loco to someone's layout like mine or even Greg's the lower rated decoder may fail.


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## riderdan (Jan 2, 2014)

So, if they both have a decoder programmed correctly, it'll work. It sounds like I will have to manually adjust the speed settings of the tender to get it in sync with the loco, since the decoders don't actually measure speed, just voltage. Is that correct?


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## Greg Elmassian (Jan 3, 2008)

The decoders don't actually do voltage either, it's pulse width modulation, but often the word "voltage" creeps into documentation.

Basically speed 0 is no pulse and speed 126 is on all the time, and (supposedly) speed steps between them are percentages of "on time" pulse of full voltage. (note that I am referencing 128 speed steps but this is also true for 28 speed step mode).

Try the simple settings that Kevin suggested in the first reply. That is usually good for 90% of the cases.

Greg


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## Dan Pierce (Jan 2, 2008)

The full speed/last speed step is limited by the CV controlling the top speed.
And in some decoders there is a maximum motor voltage setting which is another limitation. 
A use of these settings would be to limit the speed of slow engines to make them more realistic, plus you get the benefit of having a lower voltage range (like a shay at 12 volts) and having 128 speed steps instead of 24 volts having 128 steps. 

Also useful if an engine has a 12 volt motor (Accucraft has 12 volt motors and I am working on a C16 that has a 12 volt pittman motor).


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## Greg Elmassian (Jan 3, 2008)

Dan, I'd be very interested in a decoder that REALLY limits maximum motor voltage, I have never seen one, and I have an application for one (a 10v motor on a 13v DCC system)..

Please let me know which decoders actually limit motor voltage, not just limit top speed by PWM.

Greg


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## Dan Pierce (Jan 2, 2008)

Look at CV57 in the zimo manuals. Not sure how it works.
CV60 is light dimming and that is a pulse control.


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## Cougar Rock Rail (Jan 2, 2008)

The new Maerklin/LGB decoder in the Allegra has the same ability with one of it's CV's--similar description there too. It also has a forward and reverse trimming ability which compresses the speed and sound together if you want to.


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## Greg Elmassian (Jan 3, 2008)

Dan, it just limits the speed, by setting a max pwm.

To reduce the voltage takes analog circuitry, large and heat producing. The electronics are just not there to do this.

The only way decoders are so small, and can handle many amps is using FET transistors and modulating the track voltage by being on longer or shorter periods. 

The only easy way to actually reduce the actual voltage is put diodes in series with the track pickups. I also run Z scale and many of the motors won't handle over 9 volts.

Unfortunately many manuals use the term "voltage" where it's really shorter or longer duration pulses. If you put a scope on the motor outputs you will see this.

Greg


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