Locomotive running out of control

[AyJay]

Can anyone offer a suggestion as to what was going wrong and what I can do to put it right?

Today I had a running session of my locomotives, the first time that most of them have been run in several months.

All ran well, except one...

This locomotive was running round my layout at a very high speed, certainly faster that I would run it.

Yet when I went to stop it, it continued to run for a very long time, deceleration was barely there.

When it did eventually stop, I decided to start it again, on the lowest speed setting on my controller. It should have started crawling away slowly, but it immediately went at it's previous speed and the same happened again.

Turning to the handbook for my controller, an NCE Powercab, I looked for anything that could offer an explanation for this strange behaviour and found a section to do with acceleration and deceleration.  I followed the instructions but it made no difference.

The locomotive is the Serlby Hall by Hornby. The DCC decoder is from Digitrains, same as is fitted in all my locomotives and it's something that I would have fitted myself from new a few years back.  None of my locomotives have ever behaved like this before and none of them are mistreated.

I don't understand DCC very much, I have only done the basics to get things going.

Can anyone suggest what the problem might be? Could the decoder have 'blown'?  Has a setting changed and I just need to reset something?

Thank you.

[73c]

I have a Bachmann 2-car emu that does similar, takes off like a cat with it's a**e on fire every time power is applied. I've changed the decoder but still does it, so will be interested in the responses to your problem. 

[gordon s]

Personally, I would put it on the programming track and enter the data as if it were a new loco. I would also switch off the capability to run on DC.

 

As a matter of course I remove all capacitors/chokes in the circuit as they can cause some strange effects.

 

There should also be a CV to reset the decoder back to factory settings, which is always a good starting point.

[4firstimes]

I have faced a similar situation With farish class 20 after replacing the chip with the likes of digitrax and Lenz . The locomotive has been re programmed several times reset an equal number of times. Following a suggestion from a follower of the NCE Dcc forum to put a RC filter or snubber across the furthest end of each DCC bus runner .
If you are using high power boosters or very long bus runs greater than around 60 feet then consider using two snubbers at the end of each bus. 
Having installed snubbers on my layout I haven’t experienced any similar problems .  

The advantage and it may be a personal choice; a RC filter is designed to reduce or eliminate voltage spikes on long runs  of the Dcc bus wire. I understand a RC filter May  reduce the chances of decoders being damaged from inductive voltage spikes . I have noticed an improvement in running , which may be due preserving the DCc waveform accuracy .

I am only familiar with those RC filters provided by NCE , but I believe similar filters are available from other manufacturers.  DCc concepts  used to have their own version listed on their website . There are numerous views on the effectiveness of “snubbers” in DCC , but for a small outlay and if you are experiencing issues with run away locomotives,  fitting a Snubber or RC filter may prove advantageous. 

[AyJay]

Good morning all. 

Yes, I do have 'snubbers' (did wonder what they were called) on both ends of my layout, also supplied by Digitrains. The length of the run from the controller is 8 - 9 metres. 

My understanding of the purpose of the snubber, is that the power feed acts as a transmission line that needs to be balanced with a load at the end to prevent signal reflections.

I omitted to add that while this was going on, I had several locomotives on the track at the same time and one of them was running (normally), so that rules out the controller and the track.

Right now, I am favouring resetting the locomotive decoder on the programming track; I have never done that before so I just hope that NCE write clear instructions?

I also note that there is a 4-wire connection from the locomotive to the tender, so it is unlikely that I opened the locomotive and caused damage there.

[Pete the Elaner]

Instructions for factory resetting your decoder will not be in the Powercab manual because it is simply a CV change.

With many decoders, you need to set CV8 to a value of 8. You cannot actually change CV8 but trying to to send this triggers a reset.

Not all decoders use this CV & value, so you need to check with the decoder instructions.

I have had runaways but only with some of my locos & it only happens when power is suddenly applied to the layout, like after clearing a short or when power is momentarily restored after reading a CV from the programming track. Disabling DC has stopped this happening.

[Nigelcliffe]

54 minutes ago, AyJay said:

Good morning all. 

Yes, I do have 'snubbers' (did wonder what they were called) on both ends of my layout, also supplied by Digitrains. The length of the run from the controller is 8 - 9 metres. 

My understanding of the purpose of the snubber, is that the power feed acts as a transmission line that needs to be balanced with a load at the end to prevent signal reflections.

 

DCC is not a transmission line.   There is no "reflection".   

The snubber acts to filter spikes, nothing else.   As such it may be useful in some situations, and do nothing in others.  

 

- Nigel

[AyJay]

I fixed it!  Really am not sure what I did to cause this to happen, but I went for a complete reset of the decoder after I found that the short address was set to 255 instead of 3. 

Anyway, it all works fine now.  Thank you all.

[gordon s]

Glad to hear it's fixed and all OK. I can't recall if a factory reset means DC operation is on or off. Might be worth checking with your NCE Powercab. I have one upstairs, so can talk you through it if you get stuck....

[Michael Hodgson]

21 hours ago, 73c said:

I have a Bachmann 2-car emu that does similar, takes off like a cat with it's a**e on fire every time power is applied. I've changed the decoder but still does it, so will be interested in the responses to your problem. 

 

Stop giving the cat a vindaloo!

[73c]

11 hours ago, Pete the Elaner said:

Instructions for factory resetting your decoder will not be in the Powercab manual because it is simply a CV change.

With many decoders, you need to set CV8 to a value of 8. You cannot actually change CV8 but trying to to send this triggers a reset.

Not all decoders use this CV & value, so you need to check with the decoder instructions.

I have had runaways but only with some of my locos & it only happens when power is suddenly applied to the layout, like after clearing a short or when power is momentarily restored after reading a CV from the programming track. Disabling DC has stopped this happening.

When I swapped the decoder, the one already in it was a Bachmann changed that to a Lais dcc chip. Having just looked up the manual for it, it says it 

can be reset by changing CV8 to 2. I'll give this a go and check the setting for DC when next in the loft.

[RAF96]

If the decoder is reading the address back as value 255 likely it was simply not reading the decoder for whatever reason.