Decoder programming - limit top speed

[AndrueC]

I have a Dapol N Scale Class 121. It has a Dapol Next 18 Imperium decoder fitted and the top speed is insane - I have to set the speed to no higher than 5 out of 28 on my NCE PowerCab to get a fairly realistic speed. Quite frankly it's too scary to run at step 28.

 

So I've tried setting CV 2 to be 1 then CV 5 to be various values and CV 6 to be half CV5. Nothing I've done appears to make any difference.

 

CV 29 has a value of 6.

 

When I put the decoder in a different loco the speed is fine so presumably it's some kind of gearing issue in the 121 (it also has a noisy whine). Anyway I don't understand why nothing I do with the CVs is having any affect on speed so can anyone explain?

 

Thanks.

[WIMorrison]

Firstly, why are you using 28 Speed Steps? You should be using 126 these days.

 

Secondly, if you use a Zimo decoder then you can set the voltage provided to the motor independently of the setting in CV5 which allows you to tame excessively fast locos but still get a decent range of speed steps - especially using 126 speed steps ;)

[34theletterbetweenB&D]

2 hours ago, AndrueC said:

Anyway I don't understand why nothing I do with the CVs is having any affect on speed so can anyone explain?

I would take that up with Dapol if you want an explanation, as it is a combination of their product offerings.

[jamesed]

Maybe start with a reset which is cv8=4 for Lais / Imperium.  That will clear anything odd like consist settings etc. which can affect speed settings.

 

With the Lais cv set you must have cv29 set to 128 speed steps for 3 point speed curves. Your cv29 value of 6 indicates that you have 128 steps enabled and dc running enabled.  Just for now, try turning dc off and set cv29 to a value of 2.  If you want dc on then you can go back and change it later once you have got the speed steps for dcc correct. 

 

Next, you must have a value other than zero (which is the default) for all of CVs 2, 5 &6. CV values need to be in the range of 1-255.  So, start maybe with cv2=2, cv5=160 and cv6=60.   See how that works and adjust as required.   

[CFL]

CV 5 = 160 should see it fly off at the curves. It is a bubble car isn't it? Not an ICE.

[AndrueC]

9 minutes ago, CFL said:

CV 5 = 160 should see it fly off at the curves. It is a bubble car isn't it? Not an ICE.

That's not the point. The point is that it doesn't matter what I set CV 5 to be because the top speed is always the same.

[CFL]

Oops.

I see you tried the decoder in a different loco but you don't say whether you tried a different decoder in the recalcitrant vehicle.

 

 

Edited April 24 by CFL
Wrote first, thought afterwards. Again.

[Izzy]

The decoder hasn’t been locked somehow to prevent cv changes has it? I have looked at the Dapol Imperium profile in JMRI but can’t see one although I have read there is some mention of cv15. It’s a bit confusing TBH. Thought it worth a mention though just in case. 
 

The other thought is that you might need to knock cv5 down really low to see an effect with the 121. Try a silly figure such as 50 and 25 for cv6 to see if there is a difference. If there is at least you’d have a benchmark to go on. 

 

Bob