PC Sherman Hill Sd70ace Dynamic Brakes

Discussion in 'Troubleshooting' started by 777Gaming, Dec 1, 2021.

  1. 777Gaming

    777Gaming Well-Known Member

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    I've noticed that when applying any form of the airbrake (automatic or independent), it forces the dynamic brakes off. They are still in full power, but they aren't working. As far as I am aware, dynamics aren't supposed to do this in real life, only when the train is put into emergency do the dynamics cut out, not just a tap on the automatic to help out. Now maybe I'm wrong, as one of the streams pointed this out as "normal," though I have never heard of this before, and it doesn't happen on other locomotives. 20211201181248_1.jpg
    (Automatic brake is in "Initial Reduction" in this screenshot)
     
    Last edited: Dec 1, 2021
  2. wxtr7

    wxtr7 Well-Known Member

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    Bail the independent off. Apparently irl the SD70ACe disables the dynamics if the independent brake is applied (since the loco brakes work against the dynamics), which applies with the auto brake. The dynamics will spin back up once the brake cylinder is back to 0.
    Rule of thumb I follow, always bail off the independent when applying the train brake, until you slow enough and actually need the loco's brakes.
     
  3. 777Gaming

    777Gaming Well-Known Member

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    Hmm, didn't know that. Not sure how I feel about that.
     
  4. Michael Newbury

    Michael Newbury Well-Known Member

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    When you do a bail off of the independent brakes it will only release the loco brakes, and then the dynamic brakes will kick back in.
     
  5. Wesley Alves

    Wesley Alves New Member

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    Am I the only one that can't hold the Sd70 to the speed limit on the downhill parts? I noticed what you said about the dynamic brake being forced off but even when bailling off, It's still not enough.. even in Sand Patch. I need all 3 brakes to slow down the train and sometimes It's still not enough.
     
  6. Michael Newbury

    Michael Newbury Well-Known Member

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    Trick is when you get to the start of the hill notch down to zero, then wait until half of your train has made it over the crest of the hill. Then apply minimum train brake, then bail off the independent brake. Then put the dynamics into setup as you start to see your speed slowly increase start applying the dynamic brakes as needed. By doing this you should be to find that you can keep the speed at a safe 30 miles per hour.
     
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  7. Wesley Alves

    Wesley Alves New Member

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    I'll try that, thanks.
     
  8. damarjatiaji

    damarjatiaji Guest

    The key is don't drive too fast, real life train runs on Laramie Subdivision (aka The Sherman Hill) are rarely runs more than 30 mph, or even 25 mph.
    The speed limit is just a limit, not your target. Trust me, 25-30 mph is your comfort zone around Sherman Hill. Above that, you will begin to struggle to control or maintain the train's speed downhill.
     
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  9. breblimator

    breblimator Guest

    Brake Cylinder (BC) has to indicate ZERO for dynamic brakes to kick in
    ... which is the effect of 'bail off', like others posted a few times above :) BR o7
     
    Last edited by a moderator: Dec 2, 2021
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  10. Nick Y

    Nick Y Well-Known Member

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    Just a point to note (and Matt has said this on a few of his Sherman Hill streams), dynamic brakes are only effective until about 30 or 35mph. Once above that speed, they become less effective and will eventually have no power to control the train down the steep grades.

    I've run several timetable services on this route now with varying cargo and I've always been able to control the descents using dynamics only through balancing (easing off when speed drops and adding more when speed increases). The highest speed I got to on those downhill sections was 29mph.
    If you're trying to run at line speeds then dynamics will not work at all and you'll be using your air brakes (automatic brakes) which once those brakes get below about 65psi, you'll have no brakes left to apply and have a runaway train.
     
    Last edited: Dec 2, 2021
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  11. bartolomaeusz

    bartolomaeusz Well-Known Member

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  12. bartolomaeusz

    bartolomaeusz Well-Known Member

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    Thanks Nick Y; this helps a lot. I've had a couple runaways going into Cheyenne. I endeavor to hold it between 10 and 20 on the grade.
     

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