Is there a way to adjust decoder to get same slow speed crawl as on DC?

tony22 Apr 16, 2010

  1. tony22

    tony22 TrainBoard Member

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    I just got my Tuscan Red N scale Kato GG1 and ran it through its paces. It was a little noisier than my Brunswick Green jobs but after a few hours of break in it was fine. I noticed something, though, that I've seen with a few other engines after converting to DCC - on DCC I can't seem to achieve the same slow speed crawl as when the engine was on DC power. Is this normal?

    In this case, and I kid you not, on DC the GG1 took 242 seconds to go 1 inch. That's .0375 smph! :tb-shocked: Now I'm not suggesting an engine needs to be run at this speed during normal operations, but when I dropped in the TCS decoder I got abot 1 smph minimum.

    Don't throw anything at me yet! :pbiggrin: It's really a question of whether decoders can be adjusted any better in the low end. CV2 is set to 0 on the TCS. I tried setting it to 1 (assuming that maybe 0 was not really "minimum" but some default value) and it didn't help. Is this a BEMF thing?
     
  2. redone1992

    redone1992 TrainBoard Member

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    It may be that bmf may not be on ?
    I have installed tcs decoders in loco,s and improved the slow speed.
    Im on the road now so idont have the tcs manual to look at fo the cv,s.
    You could do a reset with cv 8 by entering 2 for data .
     
  3. Gats

    Gats Staff Member TrainBoard Supporter

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    Try disabling the BEMF and set the dither CV's 56 and 57. Remember the higher CV5 and 6 are set, the less fine resolution you have at lower speeds
     
  4. retsignalmtr

    retsignalmtr TrainBoard Member

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    try setting cv3 to 31, cv4 to 0 cv5 to 255 and cv6 to 150. then adjust cv2 higher (around 50) then readjust cv2 down until you get the slow start.
     
  5. tony22

    tony22 TrainBoard Member

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    Good tips. I'll give them a try and report back. redone, I'm pretty sure BEMF is on by default with TCS decoders.
     
  6. Powersteamguy1790

    Powersteamguy1790 Permanently dispatched

    Turn off the BEMF on the decoder. Then set CV 2=0. Then adjust CV 2 to a value that just starts to get the locomotive moving. At this point turn the BEMF on and adjust the CV's that control the BEMF to get the desired slow speed that you want.
     
  7. CSX Robert

    CSX Robert TrainBoard Member

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    Personally, I have not been happy with TCS's "self adjusting" Bemf implementation - there on no CVs to fine tune it's performance. With the TCS decoders I have experimented with, I can get better low-speed performance using dither instead of Bemf, but I can get even better low speed performance using Digitrax's Bemf.
     
  8. tony22

    tony22 TrainBoard Member

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    Bob, should I adjust CV5 first to bring down the top speed to a proper value? I'd heard that will "open up" the usable range across the speed steps since the unneeded voltage range will have been cut out.
     
  9. Powersteamguy1790

    Powersteamguy1790 Permanently dispatched

    Give that a try Tony. Set CV 5 to 100 and CV 6 to 50. You might have to play with the values of CV 2, 5 & 6 once the BEMF is turned off. When you find the right combination, turn the BEMF back on and fine tune the starting speed.
     
  10. MK

    MK TrainBoard Member

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    With my experience with Digitrax and TCS (newer gen. with BEMF) decoders is that you get better slow speed with BEMF turned off, as others has mentioned. For TCS I believe it's CV60=0 since I just installed a few a few weeks ago. With BEMF off, the motor seems to have a slower start speed.

    So as to not complicate matters, I suggest you just turn BEMF first and only and see if that does the trick. That does it for me and I don't have to muck around with the other CVs.
     
  11. tony22

    tony22 TrainBoard Member

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    Turned off BEMF (it's CV61). Did the CV2 adjustment. But as CSX Robert says, the TCS decoders have "self adjusting" BEMF. I don't think there are any CVs to tweak it. The alternative I think is to use dither (CV56 and 57), but I've never used that. Not suer what to do.

    I found some guidance for dither here

    http://www.bromsgrovemodels.co.uk/TCSDecoders1.htm#Dither
     
  12. tony22

    tony22 TrainBoard Member

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    Hmm, that seems to have worked pretty well.

    I adjusted CV2, CV56, and CV57 and got my crawl speed down to .0366 smph. Pretty nice, but at those sorts of ridiculous low speeds you can see the digital nature of DCC. With the stock DC board at minimum DC voltage the GG1 moved very very smoothly. At the same approximate speed on dither in DCC the engine moves in a more "discrete" sort of manner. BEMF tends to produce more of that sort of smooth gliding at low speeds. Maybe I can make it better by playing with the dither voltage and frequency a bit, but I can see where it can become a pain real quick.
     

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