Loksound v4 decoder

[Dmudriver]

Hi all

 

I've just bought one of the above with the LMS Mogul sound to fit into my "0" gauge Ivatt tank. I've synchronised the chuffs using CVs 57 and 58 and I'm well pleased with it. I'd like 2 speakers, but I can only get one in - but that's another matter!

 

When running the loco was jerking a lot with the sound on, but running perfectly without it. I spoke to SWD and Caroline advised me to alter CVs 52 to 55. I read the instructions and did some alterations and it's a lot better now, if not perfect.

 

However, I don't understand what I was doing!! Obviously altering the effect of back EMF, but could someone please explain to me (preferably in words of one syllable!!) what back EMF is and how altering it affects performance, particularly the jerking? Alternatively, could you point me in the direction of some simple text that explains it, please?

 

With thanks in anticipation of your replies.

 

(Somewhat bemused) Rod

[smokebox]

Back emf is generated when the motor turns. The bemf varies according to whether the loco is going along the flat or uphill or downhill and how much load the loco is pulling/pushing. The size of any flywheel(s) will also affect bemf. The decoder monitors this bemf and varies the decoder output to try to maintain a constant speed.

The jerkiness is due to the decoder over/under compensating for the detected bemf

[Dmudriver]

Thanks for the reply, smokebox. It was helpful and I'm gradually coming to terms with what emf and back emf are. However, the next question is what sort of values should I have in CVs 52 to 55?

 

I've got a written record of what the original settings were on this decoder, but I've an LS v3.0 DCC decoder in an 03 and various V3.5 XLs in other locos. As a start point I'll see what they are set at. That may provide a clue: I haven't had to alter one of them, just fitted them as they came and they worked fine.

 

Will post the results later - it may be a day or two!!

 

Rod