Xbox Dynamic Brake Issues On Csx Sand Patch Grade

Discussion in 'Technical Reports' started by CrazyDash, Jan 5, 2021.

  1. CrazyDash

    CrazyDash Well-Known Member

    Jul 17, 2020
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    Now just looking at this image. Do you notice how the speed line is rapidly going up and down? You can clearly see something is not right here. This part of the image you see is on the section from Sand Patch to Rockwood which is mostly downhill. As what would anybody do, I use the dynamic brake when going downhill. However, the effectiveness of the dynamic brake changes substantially. First it has almost little to no effect, then the train begins to decelerate rapidly. This kept repeating. The more dynamic brake you apply, the more the fluctuation in effectiveness of the brakes increases. As you can see on the left, I heavily oversped at the beginning of the downgrade. I had the dynamic brakes set to 8 and the train would not slow down at all. It forced me to set the automatic brake to max just to get the train down to the speed limit. My consist was 2 SD40-2's on the front of the train, and 50 autoracks behind me. My train was about 5k tons. My train should not have had too many problems going down the grade. The only thing I could think of that could be causing this is the second SD40 was doing something that was giving the dynamic brakes a hard time in the lead loco. I don't know what else could be causing this to happen. If this is not a bug, is there a way to avoid this from happening?
  2. involvedmass

    involvedmass Member

    Sep 19, 2020
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    Looks to me like you were just to late with applying the dynamic brake in the beginning at least. Keep in mind that the dynamic brake does not apply with full power instantly, it will gradually increase quite slowly until it reaches your set braking power.

    As for the constant up and downs, I have no real explanation. However, it does look like you are keeping the train moving at pretty much exactly the line speed. This will make it almost impossible for you to react in time when the gradient of the slope changes and becomes steeper. I would recommend trying to keep at 2-3 mph below the limit, and as soon as the speed starts to increase you apply more dynamic brake.
  3. geloxo

    geloxo Well-Known Member

    Nov 21, 2018
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    You still need both pneumatic and dynamic for heavy trains. Take into account that dynamic uses the locomotive mass to reduce speed (it forces only locomotive to slow down and locomotive forces wagons to stop pushing it) while pneumatic reduces speed on whole train. You can use dynamic to prevent that train overspeeds and to slow it down on moderate downhills but that´s all.

    Last edited: Jan 5, 2021
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  4. Crosstie

    Crosstie Well-Known Member

    Dec 8, 2016
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    This is all good advice. It takes judicious use of both the dynamic and automatic brakes to manage a heavy train on the downgrade. First use the train brake to slow down before the grade increases, then use the dynamic brake to maintain a constant speed. As the grade changes, adjust the brakes slowly.

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