# Different loco performances



## MikeL (Mar 21, 2015)

Hi everyone,

Let me try to explain the situation: I have two locomotives that had DCC decoders installed for me (I assumed they were the same type of decoder, not sure).

When I start the throttle for my CP loco, its takes its time, some nice realistic sounds, accelerates slowly, then gets to speed.

When I start my CN loco, it gets to speed right away, no nice gradual acceleration.

I realize this isn't a lot of information, but does this sound like a loco issue or a decoder issue? I went through my Digitrax Zephyr manual in the hopes of finding information on acceleration, but nothing 

Thanks


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## mopac (Feb 24, 2011)

You need to find out what decoder was put in and then get a CV chart for that decoder.
There are CVs for momentum accelerating and decelerating. I always change these CVs
because I don't want them to be like a jack rabbit.


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## wvgca (Jan 21, 2013)

add some momentum, cv 3 , to the CN loco ...
add some on cv 2 so that it just barely crawls at speed step one also


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## mesenteria (Oct 29, 2015)

CV2 is "V-Start", or the initial voltage allotted to the motor by the decoder when you enter speed step #1 on your throttle. Each drive has its own unique characteristics due to hand-assembly and other variances. So, each will have its own requirement for starting voltage to begin to turn the drivers, just creeping along at Speed Step #1. If it's a sticky drive, needs some wearing-in, you'll need more voltage in CV2, meaning programming it with a higher number. Whichever decoder you're dealing with, it may take a value of as much as 50 (my Bachmann Spectrum Heavy 4-8-2!!!, so don't say it won't happen). Some exceptionally smooth drives may only need a value of 1 (my Lionel HO Challenger).

Entering programming on the main, NOT Paged or Broadcast mode, but Ops Mode or Programming on the Main, acquire CV2 on the correct address active on your throttle (this is important...double check to make sure you have the correct address active), and begin to set higher and higher values, increments of 5, until your drive begins to move the loco.

Before you do this, you set the first speed step on your display. Click your knob, or twist it, and get that first speed step showing, then enter POM or Ops Mode, whichever your system calls it, acquire CV2, and start at "01". Enter. Then 5, Enter, 10, Enter, until you see it starting to crawl.

Note that a warmed up drive will require less start voltage than when it is cold....typically. Your CV2 setting might be great on your warmed up locomotive, but when you go to that first speed step next day, it may not move. Moving along to Speed Step 2 or 3 should get it moving.

CV3 is "inertia". It means the mass of the engine or the entire consist is slow to accelerate. I typically set mine mid-range for the range of values that CV needs.
CV4 is "Momentum", meaning once it's at speed, the tonnage would rather remain at speed, all things being equal. Of course, in Newtonian physics, this would be in a vacuum and well outside a gravitational well. But, I digress. Again, I set mine near 40-60% of the maximum value for that CV and decoder.


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## Cycleops (Dec 6, 2014)

To simplify things a bit CV3 acceleration is how quickly or slowly the loco gets up to speed you have selected. CV4 momentum is how quickly or slowly it comes to a halt after shutting the throttle, shut the throttle quickly to better see this. Set the start voltage(CV2-low value best) mid range speed and top speed need to be adjusted. Just experiment by adjusting the CVs and see how they respond.
Information on all the CVs will be on the manufacturers site plus tips on how to adjust for best running, but you don’t know which make you’ve got so go to CV8 and read it, this will give a number which will relate to a maker. Go their site for a manual. Here’s a pdf of the codes: https://www.nmra.org/sites/default/files/standards/sandrp/pdf/appendix_a_s-9.2.2.pdf Your number should be in the binary column.
If you want to run the two in a consist you’ll need to match them near as poss. How to run them like this will be in your Digitrax manual.

Have fun.


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## tkruger (Jan 18, 2009)

Adjusting the decoders is key in this case even if they are geared different the decoders can make them run together. One word of caution based on experience. Make sure that both of the locomotives are properly lubed and serviced before matching them. I say this because if you service them as a pair in the future they may not be in sync after the cleaning. It is amazing the effect of clean contacts and an lube can make on performance.


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## MikeL (Mar 21, 2015)

Thanks everyone. I made some good (and slow) progress tonight - your explanations greatly helped.

There seems to be something strange when I set the CVs values. I start with CV02, I set the value at 10 (for example). I follow the procedure (CV-WR, then Exit) and then go to CV03. When I try to set the value, it is at the value previously set (in this case 10 for CV02). Same thing for CV4, the value is at 10. Is it actually at 10 or is it just reading the previous setting?

Mike


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## mesenteria (Oct 29, 2015)

MikeL said:


> Thanks everyone. I made some good (and slow) progress tonight - your explanations greatly helped.
> 
> There seems to be something strange when I set the CVs values. I start with CV02, I set the value at 10 (for example). I follow the procedure (CV-WR, then Exit) and then go to CV03. When I try to set the value, it is at the value previously set (in this case 10 for CV02). Same thing for CV4, the value is at 10. Is it actually at 10 or is it just reading the previous setting?
> 
> Mike


If your DCC controller is functioning properly, and your decoder, and you are following the correct procedure for altering CV values and saving them to the decoder, then the CV's should retain the last value you set for them. 

To check, you can re-enter the correct mode of programming, and save a grossly (but within range) inflated value to any one of the three CV's we've discussed. Exit, and then crank the throttle up to 50. What happens? If it is saving them, the first speed step should have your loco moving along instantly and rather much more quickly than you'll be comfortable with for that first speed step. Or, if you only do it to CV3, it'll take a long time to get up to speed, mimicking a laboring locomotive attempting to lift a heavy consist. Or, if you do it to CV4, when you get it to speed and then quickly shut off all speed steps, rendering your display reading '00', the locomotive should begin to decelerate very slowly, perhaps taking 30 seconds to come to a complete stop.


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