Multiple unit question

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David Collins
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Multiple unit question

Unread post by David Collins »

I've noticed quite a few times when a crew starts a train, the lead unit will throttle up, but the trailing units behind the engine stay in idle for a bit and then anywhere between 15-30 seconds later they'll throttle up. I thought this was only a thing on modern locomotives until I watched a Danny Harmon video with a lashup of two SD40-2's doing the same thing, the lead unit loads first and then the second unit starts throttling up a little later. My question is how/why do crews do that?

Thanks in advance.

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SD80MAC
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Re: Multiple unit question

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Different engines start loading at different times. An EMD is going to increase RPMs before and faster than a GE. Even two of the same model don't always load in-sync. There's nothing the engineer can do to change that. I was on a train with 2 C40-8Ws once, and every time the engineer would go above notch 2 on the throttle, the trailing Dash 8 would bump us in the rear as it loaded faster than the lead one.
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David Collins
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Re: Multiple unit question

Unread post by David Collins »

SD80MAC wrote:
Tue Mar 14, 2023 1:10 pm
Different engines start loading at different times. An EMD is going to increase RPMs before and faster than a GE. Even two of the same model don't always load in-sync. There's nothing the engineer can do to change that. I was on a train with 2 C40-8Ws once, and every time the engineer would go above notch 2 on the throttle, the trailing Dash 8 would bump us in the rear as it loaded faster than the lead one.
I should have attached this, I have a video of the PRR heritage unit leading a 17N at Millbury a few years ago, it's at like half power but the trailing units are in idle, but when they went by my friend at Vickers, they were throttled up.

Here's the link:

https://www.youtube.com/watch?v=JXbLxGuxtW4

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SD80MAC
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Re: Multiple unit question

Unread post by SD80MAC »

The second unit in that video is definitely online and working, the SD70 is not. It's entirely possible a crew member walked back and put the SD70 online between Millbury and Vickers. There is no way to do that remotely. The newer units will also take themselves offline if they develop any kind of a problem, or will limit the amount of power they put out. On the SD70ACes, you can also set them to "Dynamic Only", meaning they won't provide power but will provide dynamic braking.
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Re: Multiple unit question

Unread post by David Collins »

SD80MAC wrote:
Tue Mar 14, 2023 3:10 pm
The second unit in that video is definitely online and working, the SD70 is not. It's entirely possible a crew member walked back and put the SD70 online between Millbury and Vickers. There is no way to do that remotely. The newer units will also take themselves offline if they develop any kind of a problem, or will limit the amount of power they put out. On the SD70ACes, you can also set them to "Dynamic Only", meaning they won't provide power but will provide dynamic braking.
Gotcha, thank you!

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