Runaway Train and CV29

[Chrissaf]

Hello, I've put this here in general rather than Hornby DCC because I believe the issue is with the decoder not the train. The train is R2702 HST which was fitted with sound by Howes a few years ago. All my trains have been in storage for two years now and are being given some track to run on as the new layout takes shape. 

This HST is a proplem though. Used to be fine, but now once given some throttle it won't stop. I've done CV8 to 8 and I've read that CV29 can be used to sort this problem out by turning off the DC function, however I can't find a simple explanation for it. Binary maths and DCC is not my strong point.

Anyone know how to sort it, if indeed this is the right path to take anyway?

 

 

[Chrissaf]

This web page gives the simplest explanation of CV29 available, with an online tool to do the maths for you.

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http://www.2mm.org.uk/articles/cv29%20calculator.htm

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Basically read your current value of CV29. Enter the value of CV29 you read into the CV29 box and click the 'Back Calc' button (see yellow highlight in image below).

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Clicking the 'Back Calc' button will populate the vertical column with ticks in the boxes of the functions that have been enabled for your particular value of CV29 that you entered into the CV29 value box.

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Then untick the 'DC Operation' tick box. This will give you the new value to write to CV29......(see yellow highlight in image below).

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In the example above, CV29 = 6 and the two boxes ticked are the decimal 2 and decimal 4 boxes.......2 + 4 = 6

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Decimal 4 is the 'DC Operation' tick box. So if 'DC Operation' is disabled in the above example, one would write a value of 2 to CV29 to replace the current 6 value.

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If you want to expand your knowledge of Binary / Decimal conversion, then download and read my tutorial from here (link circled in red):

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https://octaviancs.com/railmaster/binary.php?id=binary

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See pages 8 to 11 in the tutorial for CV29 specific info.

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[RobOO]

Thanks for the reply.

Regarding my logic and thought process, I thought I explained that in the post. The section we're in now is Hornby DCC. While it's a DCC issue it's almost certainly nothing to do with Hornby as the decoder is ESU. I wouldn't want to have people think my Hornby DCC (TTS) or Saphire train isn't working.

Now to look at this problem again; time for coffee!

 

 

[RobOO]

Okay, HST number two is out now and thats doing the same thing. Bachmann 47 and 108 with ESU SWD are fine, as is Heljan with the same. Just Hornby locos (HST) not liking something..............I'm going to try my Class 50 now.

[Rog RJ]

Runaways are very often caused by poor electrical pickup from the track, but there are other reasons too.  Make sure all the track and wheels (including the pickups on the back of the wheels) are clean, dirt is probably the number one cause.

[96RAF]

The DCC section is for DCC related items, no matter the manufacturer And is exactly the right place for the discussion.

The General section is for oddly general things.

There is no mention of the track connection method which may be the culprit, i.e. if a Hornby connection product is there a DC capacitor installed.

Rob

[RobOO]

Thanks Rog. I was aware of the track issue and have given it a good clean. The funny thing is the two HSTs are basically new. They were fitted for sound and ran for a few weeks (which is actually minutes really in actual terms) then we decided to move house and I had to pack everything away. The other locos have seen more action. 

[RobOO]

Perhaps this isn't DCC related at all? 

I'm doing this on the fly as you can probably tell. I've just noticed that HST no2 doesn't runaway when its just the powercar and dummy, only when the rake of 7 coaches is attached.

I'm just going to reset no.1 again and see if its the same.

More coffee methinks!

[RobOO]

The DCC section is for DCC related items, no matter the manufacturer And is exactly the right place for the discussion.

The General section is for oddly general things.

There is no mention of the track connection method which may be the culprit, i.e. if a Hornby connection product is there a DC capacitor installed.

Rob

 

I'd say this was odd but hey ho, I appreciate any help from more seasoned and experienced modellers. Regarding connection, it's the same as last time which worked fine. It's a main bus with droppers to it about every two feet or specifically where needed. The only thing that's different at the moment is I do have two ends where the circuit isn't connected as the layout isn't complete yet. I do have DCC concepts powerbus terminators to fit but I'm not quite at the end yet.

Also, you may have read my strange or odd behaviour regarding the runaway only while hauling the rake. People laugh when you tell them you have a model railway, I wish they understood it really isnt for children!

 

[RobOO]

Well I'm now convinced it's the model. I can't be messing around with this. I'm going to send them both in for repair/service. Makes me wonder if my 3rd one which has never been run will work either when I get round to fitting it for sound?

[RobOO]

This web page gives the simplest explanation of CV29 available, with an online tool to do the maths for you.

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http://www.2mm.org.uk/articles/cv29%20calculator.htm

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 Thanks for that. It turns out my maths and reasoning were correct but it's nice to have that confidence it's right from your link.

 

[Howbi]

@RobOO........you haven't said yet, have you reset CV29 to a value of 2 and tested the locos?..........we always like to see feedback as it's good info for others who may be experiencing a similar problem......... 😀..........HB

[RobOO]

I set CV 29 to 34 which appeared to be the right thing to do???

Anyway, what with all the weird behaviour runing away laden but not light and having the same problem on both HSTs when all the other locos are fine I think I'll send them off for a proper service/repair (which is annoying as they are the newest least used trains I have. I've got three, swallow, executive and BR blue and the BR blue is still in the box waiting on funds for sound decoders and a complete layout to run on!)

You think I should set CV29 to 2 then? I read it before trying the change to 34 and it was 14.

[Howbi]

A value of 14 would indicate that Railcom is 'on'........this should be 'off' if not being used on your layout........so for normal 2 digit addressing +128 speed steps and DC running 'off' then a value of 2 is correct........your value of 34 indicates you are using 4 digit addresses + 128 speed steps..........if this is incorrect then your loco will not respond.........try a value of 2 and see how it works.........all  my locos are changed to CV29 value 2 as soon as bought, whichever decoder inc sound from ESU, TTS & Econami........HB

[RobOO]

A value of 14 would indicate that Railcom is 'on'........this should be 'off' if not being used on your layout........so for normal 2 digit addressing +128 speed steps and DC running 'off' then a value of 2 is correct........your value of 34 indicates you are using 4 digit addresses + 128 speed steps..........if this is incorrect then your loco will not respond.........try a value of 2 and see how it works.........all  my locos are changed to CV29 value 2 as soon as bought, whichever decoder inc sound from ESU, TTS & Econami........HB

I am using long addressing as I find it easier at the mo using the Elite. If I want a HST then its 43+either 1,2 or 3. So my Swallow HST is 433. If I use Railmaster then I suppose the address wouldn't matter so much would it as there's option for better description of the loco.

I'll try your suggestion tomorrow night if I get time. Thanks.

[Fishmanoz]

If yo user CV29 to 34 you have 128 speeds steps on (correct), long addressing on (correct) and DC Running off, also correct.  With this set, you cannot get DC Runaway so if the locos continue to take off, it something else and very unusual. 

[RobOO]

If yo user CV29 to 34 you have 128 speeds steps on (correct), long addressing on (correct) and DC Running off, also correct.  With this set, you cannot get DC Runaway so if the locos continue to take off, it something else and very unusual. 

That's exactly what I've done on both HSTs and both are doing this odd behaviour; no other locos do this. 

[RobOO]

If they weren't both proffessionaly fitted with sound I'd be tempted to take out the decoder and try another one in them.

[96RAF]

How about putting BEMF off or at least back to default.

It may be OK light load but overcompensating with a load and applying max chat.

Rob

[Fishmanoz]

What about checking with Hornby whether the decoders need firmware upgrade. 

[96RAF]

Whilst I know the basic decoder firmware (not the sound files bit) can be updated on TTS decoders I don’t know if the more basic decoders can be done, although there would seem to be no reason why not. The awkward bit apparently is getting good connection with the decoder using the update kit probes, normally achieved using a bench jig.

Rob

[Howbi]

The op mentioned ESU decoders ..... HB

[RobOO]

The op mentioned ESU decoders ..... HB

This is why I didn't put it in Hornby DCC as I knew confusion would arrise. These are both Pro fitted aftermarket ESU SWD which worked perfectly well on my previous layout (although they weren't run for very long it was enough to know there were no problems).

[RobOO]

A value of 14 would indicate that Railcom is 'on'........this should be 'off' if not being used on your layout........so for normal 2 digit addressing +128 speed steps and DC running 'off' then a value of 2 is correct........your value of 34 indicates you are using 4 digit addresses + 128 speed steps..........if this is incorrect then your loco will not respond.........try a value of 2 and see how it works.........all  my locos are changed to CV29 value 2 as soon as bought, whichever decoder inc sound from ESU, TTS & Econami........HB

I've just tried CV29 as 2 and the loco behaved the same way, ie worked ok light and runaway under load.

[Fishmanoz]

RobOO, my apologies for confusing this with TTS when you clearly said ESU, and then I confused Rob too. But this is absolutely the right sub-forum for the topic which is why the mods moved it here.

 

I like Rob’s BEMF suggestion, worth checking out the ESU manual on that one and having a fiddle. 

 

Then not not sure if it will prove anything but can you try to see how they behave on a DC track?  You’ll have to add 4 to CV29 to do it though. 

 

And lastly, could you please stop using that blue button and unnecessarily copying our posts back at us, including then sometimes putting your own content in the yellow box, most confusing and space wasting.  Just use the box and the bottom of the page and the proper green Reply button, just like all of us have.