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Hornby HST DCC conversion issues


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So I've converted an early Hornby HST to DCC and fitted it with a Hornby TTS Sound decoder and the Blackcat LED lighting mod. It runs fine around the test track for about six laps and then stalls, sounds the horn and then restarts. I swapped out the decoder for a LaisDCC one and it doesn't skip a beat, controller reports around about 200mA being drawn for either decoder. I thought perhaps the Hornby decoder might be a bit less tolerant of a dirty track, so I tempoarily fitted a large stay alive (15000uF) to the TTS decoder. This involves soldering wires across the bridge and I've used a connector for easy removal. Picking the loco up from the track whilst running showed about 2-3 seconds of stay alive but still the same symptoms of stalling after a few laps. I came to the conclusion that its down to a 'loss of comms' so I implemented the all wheel pickup mods in the article below:- 

 

http://www.halton96th.org.uk/article10.html

 

I couldn't get the replacement collector assembly (part X8515) so I used the PCB with modified coach collector approach. This proved problematic as the bogie rides too high causing derailments plus the collectors seem to cause alot of friction. So I swapped the old front bogie back in but left the rear one in meaning that 6 of 8 wheels are still picking up. Its a great improvement but I am wondering whether the most significant change was the CV changes as per the article:-

 

If necessary adjust CV150 to value 1 (regime 2) and/or CV151/152 (regime 1) or CV153/154 (regime 2) to suit the running characteristics of the Ringfield motor.

 

Does anybody have any experience of 'tuning' these TTS decoders for use with the Ringfield motor? I suspect some top speed has been lost since the last changes, I'll do some comparison with that LaisDCC decoder. I've yet to see it hauling loads too, which might be more of a problem without the traction tyres.

 

Thanks.

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I am glad my article was of some use, if not the final fix.

If the lighting kit is pulling near to max current for the function output (100mA)  it can make the TTS decoder jittery. The function outputs are not self protecting like the motor circuit so overloading them can damage the decoder. I have found some lighting kits too bright anyhow so added an additional 1K resistor in the blue wire to pull the current down.

CV150 is a good starting point, then go to fine adjustment of either CVs 151/152 or 153/154 as applicable to your 150 setting. There is a science behind adjusting motor PI values but trial and error works just as well. 

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23 hours ago, RAF96 said:

I am glad my article was of some use, if not the final fix.

If the lighting kit is pulling near to max current for the function output (100mA)  it can make the TTS decoder jittery. The function outputs are not self protecting like the motor circuit so overloading them can damage the decoder. I have found some lighting kits too bright anyhow so added an additional 1K resistor in the blue wire to pull the current down.

CV150 is a good starting point, then go to fine adjustment of either CVs 151/152 or 153/154 as applicable to your 150 setting. There is a science behind adjusting motor PI values but trial and error works just as well. 

 

Thanks, did you find any issues with extra friction created by added more collectors when hauling loads? 

 

I've just carried out some testing and it takes 7.9 secs to cover a 4.2m oval test track with CV150=1. Resetting the decoder gives slightly better speed but its negligible really, still looks like a slow top speed for an HST. The CV change also re-introduced a little bit of stalling, not as bad, so maybe the extra collectors help? I haven't tested without the LEDs yet, so cannot about what load they are drawing.

 

Swapping the other controller in gives me a lap time of 6.4 secs which 'looks' more like it. I'm actually coming to conclusion that a second decoder for motor control is the way to go given the relatively low cost.

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