Uneven acceleration and slow top speed in DCC

[Hampshire Stu]

 

Hi All,

I'm running a Hornby e-link with my 1980s Class43 HST newly converted to DCC with a basic R8249 chip. First of all it's runs more slowly than in DC taking 52sec to complete a set distance rather than 37sec when in DC.

Second, it accelerates nicely up to 50mph but increasing the speed slider further results in a train moving no faster.

I realise there's very little I can change on this chip and I won't be buying any more but is there anything I can to get the acceleration even?

Thanks loads guys

Stu

[Augustus Caesar]

Hi Stu

Welcome to the forum...

I have one of  those HST's from the 80's and have converted it to DCC successfully using a chip as you describe and also installing lights from Black Cat Tech (surface mount LED's on a very small circuit board) and the loco runs brilliantly.

Two things first... have you thoroughjly cleaned the loco motor by stripping it down?

Have you removed the capacitor from the motor which would have been installed when first built?

These two points are crucial before anyone can go further and I suspect these questions would be everyone's first ones asked of you. Checking wheels for dirt, track also etc. will help too.

[Howbi]

Hi Stu, welcome to the Forum........first consideration is the age of this motor some 30 yrs, who knows what work it's done?........2nd, have you turned off DC running in CV29?........you can experiment by changing CV3, acceleration rate and also CV10 for back EMF cut-off..........HB

[Hampshire Stu]

Thanks guys for the welcome and speedy replies:) I removed the capacitor you mentioned and cleaned it up the best I can, dismantling the gears but stopped at pulling the two sections of the ringfield motor apart as I didn't want to break it and it wasn't looking willing! So I cleaned the commutator from the outside, turning it as i went. It runs really well in DC mode just somewhat slower in DCC. Funnily enough I've put the Blackcat LED lights in too! A great addition.

I turned on DC running in CV29 so I could check it was faster in DC mode. It hasn't affected the top speed being on. Anyway I shall play with CV 3 and 10 and report back. It's the uneven acceleration that most frustrating.

Cheers!

Stu

[Flashbang]

Hi

My rule when converting older models to DCC is to use the very best decoder I can afford.  I use Lenz Silver or Zimo in older models!

The Hornby R8249 is a very basic decoder and doesn't allow too many CVs to be adjusted.  Speed curve is one and setting CV5 and CV6 to the correct setting is IMO vital for good performance.

Assuming the model ran faultlessly and correctly on DC before conversion - Poor DC operation equals even worse DCC operation!

[sparrow hawk]

Hi

The only time I seem to get speed problems is with the Back EMF settings, not sure if your  decoder has the ability to turn on or off. Or to adjust the  values of the back EMF.

Bach EMF is designed to alter the speed ,so that it is constant around curves and inclines. Not sure if this affects a ringfield motor, but worth looking at your decoder manuel,to see if this can be changed.

Good luck

 

Roy.

 

[Hampshire Stu]

Many many apologies for not replying sooner... as a newbie I can only post twice in 24h so I was locked out. I might have spammed you all apparently 🤔

Anyway, CV10 was the most interesting. It can be adjusted from 1-128 and the value you enter is where in the speed stepping the bEMF cuts out as I understand it. I changed it from 128 (on all the time) to 32 and this worked a treat in resolving the uneven acceleration as I adjust the throttle slider up however it introduced a jolt reduction in speed as it passed speed step 32 as the bEMF cutout. To be expected I guess.

Anyway, it's not too bad and I think will be the best I can achieve with this decoder. I'll upgrade it at some point. I've fitted an 8-pin harness so it's an easy unplug old and plug in new.

Thanks Flashbang, I'll look at Lenz and Zimo. The Hattons ones look ok (now I've learnt what to look for!) and are a good price. Anyone tried these?

Thanks all anyway for your help. I've learnt a lot.

Stu

[96RAF]

As you are using an eLink you must be using RM and it has its own irregularities when it comes to speed control.

 

You might like to deselect scale speed if set and see if that makes a difference.

 

A general accel value is 5 but value 15 (same as TTS decoders which are basically an R8249 core) may help in/out of synch with BEMF settings and/or scale speed. At some point you may hit a sweet spot for that loco.

[Hampshire Stu]

Ah ok thanks RAF96. When I'm next at the helm I'll try that and report back any success.

Cheers everyone!

Stu

[Hampshire Stu]

Hi all

The scale speed setting makes no difference so I've reset everything back to how it was at the start.

I've calculated the scale speed of the loco itself and it came out at 126mph! Perfect! Although it does feel incredibly slow compared to what were clearly crazy DC speeds. So I'm stuck with all the acceleration taking place within the first 50ish speed steps of 128. And deceleration not commencing until it's counted down the speed steps from 128 to 50ish. I've emailed hornby to see if there's an answer and will post here if there is.

Stu

[96RAF]

No one seems to have mentioned altering the normal acell / decell CVs. Try setting them to 5 or 15 for reasonable response times, or 50 to 100 for 'takes forever' inertia.