CV settings on Loco Decoders

[mikejj101]

I am trying to get my head around all the different CV acceleration/deceleration settings on various decoders.

I was under the impression that NMRA standards meant that all the settings regardless of manufacturer would produce the same results. How wrong am I !

I have Hornby TTS and Hornby factory fitted DCC locos as well as a variety of other decoders.  I yesterday installed a Zimo MX decoder into a DCC ready Hornby loco and without altering any of the CV settings(apart from the address of the loco) it performs beautifully with nice slow acceleration and speed etc. I then installed a DCC Concepts ZEM decoder in another DCC ready Hornby loco and it performs like a manic runaway. The paperwork for the ZEM states that it shouldn't need any adjustment ! 

OK - so I then read the CV values from the first loco with the Zimo and print out a copy. I then program the second loco with the ZEM using the same values of CV's 2,3,4,5,6. The loco still reacts like a runaway. The eventual working CV settings for the ZEM are totally and completely different from the Zimo. Comparing to the Hornby decoders they are completely different again. The Hornby decoders vary in manufacturer when read between Hornby Hobbies and Atlas Model Co. The CV settings also vary between the Hornby. What works with branding does not work with another.

Is there anywhere a complete listing in an understandable, in laymans terms, form that covers all the different decoders ?

[Rog RJ]

No, there's no listing of settings and there never can be because all models, even two or more of the same model from the same manufacturer will have slight mechanical and electrical differences such as friction and component tolerances.

 

Different makes of decoders use different formulas for acceleration and deceleration, for instance.  Hornby may make there decoders so that every increase in the acceleration rate (CV 3) will increase the time to reach max speed by one second.  A different maker may choose two seconds per step to reach max speed.  The differences are many and varied.  Carefully reading the information sheet or manual that comes with each decoder can give some idea of what to expect but many are pretty sketchy.

 

Keeping your own record of what settings work best for you is probably the best option.

[DEREK123]

Hi Mike ( and thanks Rog )

I could not agree more.

I am having trouble CVing and  understanding different manufacture settings  😳

If anyone can enlighten us ( perhaps with a list as suggested by Mike ) it would be really good ( as a beginner I too am totally confused !! 😀

 

Derek

[2e0dtoeric]

Don't overlook the fact that some loco's behave like greyhounds leaving the trap on analogue, while others are like exhausted snails, so they will behave just the same with DCC.

It depends on the motor behaviour, intermediate gear ratios, etc.

As a result - no one set of cv's will work the same on different loco's.

[96RAF]

NMRA clearly defines how CV3 (and also CV4) works. Manufacturers are recommended to use this methodology but it is not mandatory that they do.

 

Simply put: - Value in CV3 times 0.896 divided by speed steps in use (14/28/128 as applicable).

 

Configuration Variable 3  Acceleration Rate determines the decoder's acceleration rate. 

The formula for the acceleration rate shall be equal to (the contents of CV#3 * 0.896) / (number of speed steps in use). 

For example, if the contents of CV#3 =2, then the acceleration is 0.064 sec/step for a decoder currently using 28 speed steps. 

If the content of this parameter equals "0" then there is no programmed momentum during acceleration.

 

In the example above that is 0-max time is less than 1.8 seconds.

 

More examples:

Using a TTS decoder default value of 15 for CV3 the accel rate is 0.105 seconds per speed step or 0-max in 13,44 seconds..

Using my ordinary decoders setting value of 5 for CV3 the accel rate is 0.035 seconds per speed step or 0-max in 4.48 seconds.

 

I shall have to check those times on track and see how closely they are to the formula.

 

As stated by others each loco performance is governed by many things, such as lubrication and wear, etc as well as the load being pulled - or stopped.

Rob

[mikejj101]

Thank you all for your responses.

I'm still confused on how I change the speed step settings between 14/28/128?

Using your formula of CV3 value x o.896 and then divided by the speed step setting?

The DCC Concepts decoder ZEN instructions from their website suggest :

CV2 = 010

CV3 = 035

CV4 = 025

CV5 = 165

CV6 = 090

I've used these figures but the loco is still travelling far to fast on start up.

What would you suggest I do to slow everything down?

[Howbi]

What value do you read in CV29?...........HB

[Rog RJ]

Try setting CV2 to 5 to reduce the starting speed.  If that improves it, you could then try reducing it further.  If the loco won't start to move with a smaller value, try increasing it in stages until it does start OK.

[Fishmanoz]

128 speed steps is the default and is set in CV29 bit 1.  Visit the 2mm Organisation web site for a handy CV29 calculator.  http://www.2mm.org.uk/articles/cv29%20calculator.htm

[mikejj101]

Hi all,

CV29 = 000

Thanks for the tip on the CV29 calculator

[Chrissaf]

With a value of 0 in CV29 then you have speed steps set at 14. Set it to 2 for for speed steps set to 128 or 6 (optional) if you want to enable DC operation as well. See the CV29 calculator for confirmation of these CV29 values.

.

Note also, that if you have a loco fitted with directional lighting, then you usually have to set speed steps at 128 in CV29 for the lighting to work.

[jane1707819582]

Thank you all for your responses.

I'm still confused on how I change the speed step settings between 14/28/128?

Using your formula of CV3 value x o.896 and then divided by the speed step setting?

The DCC Concepts decoder ZEN instructions from their website suggest :

CV2 = 010

CV3 = 035

CV4 = 025

CV5 = 165

CV6 = 090

I've used these figures but the loco is still travelling far to fast on start up.

What would you suggest I do to slow everything down?

 

 

hello mike

set  cv 2 to 1

set c.v 3 to 128.

 set  cv 4 to 90 .

 what does this do to your loco ?