# Shifting Gear Sound???



## Homeless by Choice (Apr 15, 2016)

There is a maybe 10 mile long 1-2% grade near me. Then the grade levels to near zero. The three engine trains are just snorting along, heavy black smoke and all. Once they are on the level area, the engines seem to shift gears. It sounds just like a diesel truck when it makes an up shift and the engine RPM drops. What is mechanically happening?

All that I really understand about diesel electric power is that the diesel engine turns an alternator which produces voltage and frequency. Then the traction motors use that to produce wheel torque. Where, how does the change in engine RPM come into play? Is there a transmission between the engine and the alternator? Please explain.

Thanks in advance,
LeRoy


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## time warp (Apr 28, 2016)

I know in the old days they used transition contactors to keep the wheel speed in the torque range of the diesel engine. 
I'm sure it's different technology now, but there would have to be a means to keep the engine rpm and wheel speed within certain parameters, otherwise the generator heat would be tremendous.
Excellent question. Maybe someone else has a better answer .


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## wvgca (Jan 21, 2013)

it's basically just a big generator or [AC alternator in the newer ones], no transmission, direct coupling, 
When under a heavy load, the motors can be run up to full throttle to generate maximum current, when the load is lightened [for example, by a change to level grade], the maximum current isn't needed, so the motor will slow down and produce less current, just what is needed to maintain desired speed .. 
When braking with the engines [not air brakes] some loco's are equipped with what is called 'dynamic brakes', nothing more than a really big heating element array, the wheel motors receive no power from the generator, but generate power on their own from weight and momentum, and this energy is dumped into the dynamic brake array, and produces huge amounts of heat, and slows the train down ..further electric braking is assisted by the huge fans that cool the dynamic brake array


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## Homeless by Choice (Apr 15, 2016)

wvgca said:


> it's basically just a big generator or [AC alternator in the newer ones], no transmission, direct coupling,
> When under a heavy load, the motors can be run up to full throttle to generate maximum current, when the load is lightened [for example, by a change to level grade], the maximum current isn't needed, so the motor will slow down and produce less current, just what is needed to maintain desired speed ...


Most of the engines in my area have dynamic braking.

One more question, Are the engine RPM's synchronized? Or are they individually set to maintain a desired speed? I am just curious/noisy.

Thanks for the quick reply,
LeRoy


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## wvgca (Jan 21, 2013)

Homeless by Choice said:


> Most of the engines in my area have dynamic braking.
> 
> One more question, Are the engine RPM's synchronized? Or are they individually set to maintain a desired speed? I am just curious/noisy.
> 
> ...


no idea on that, i will ask at coffee if i remember, one working CN engineer, and a few retired CN / CP ..
none of them much of an excuse to talk


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## wvgca (Jan 21, 2013)

this may be of interest to you ...
operator manual for the SD40 ..

http://www.kirara.co.uk/info/SD40 - Operator's Manual/

link doesn't post properly .. copy / paste
kirara.co.uk/info/SD40%20-%20Operator's%20Manual/


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## wvgca (Jan 21, 2013)

talked to the cn engineer at coffee tonight, he said that if they were all the same model, with gearing [top speed] the same, the engines would all be 'close', and were controlled off the lead unit mu, but sometimes there would be up to a 200 amp difference on the loading, especially at lower speeds ..


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## Homeless by Choice (Apr 15, 2016)

wvgca said:


> this may be of interest to you ...
> operator manual for the SD40 ..
> 
> http://www.kirara.co.uk/info/SD40 - Operator's Manual/
> ...


Here is what your reference says:

*Throttle Lever

The throttle lever actuates switches within the controller to establish low voltage electrical circuits to the rn engine governor for purposes of controlling engine speed. The throttle has ten positions namely, STOP, IDLE and running speeds 1 through 8 as shown in Fig. 2-6. Each of these positions is shown in the illuminated indicator in the upper left hand corner of the controller.

To stop all engines, the throttle lever is pulled out away from the controller and then moved one step beyond IDLE to the STOP position. The IDLE position is as far forward as the throttle lever can be moved without pulling it away from the controller.

Each running notch on the throttle increases locomotive power by increasing generator excitation or engine speed or both. At time of locomotive start each notch provides a fixed and immediate level of generator excitation. This level brings about an immediate and fixed response to throttle position during starting.
*

Unfortunately the manual goes from Fig. 2-5 to Fig. 2-7 but I now understand a lot more.

Thank you and your buddies for all their help,
LeRoy


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## time warp (Apr 28, 2016)

I'm glad you brought this up, LeRoy.
I now want to dig into this myself to see how things have changed from the early days to current technology.
I understand dynamic braking , but the subject of generator/alternator loading to affect the output fascinates me.


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## mikek (Dec 29, 2013)

Has any line used electric locos (like the GG1) for hilly country whereas locos going downhill would generate power for use by locos going uphill? Seems like a lot of bother, but I don't know how much fuel could be saved/versus the cost of the wiring and the logistics and schedule nightmares.


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## wvgca (Jan 21, 2013)

time warp said:


> I'm glad you brought this up, LeRoy.
> I now want to dig into this myself to see how things have changed from the early days to current technology.
> I understand dynamic braking , but the subject of generator/alternator loading to affect the output fascinates me.


here's a link that explains some of principles of 'old school' ALCO generator / traction motor principle, with quite a few images
http://www.rr-fallenflags.org/manual/IS-800A.pdf

interesting reading, very similar to the old DC welders I have on the farm, belt driven in my case


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## time warp (Apr 28, 2016)

Many thanks! I haven't talked about this kind of stuff for years and years. My old brain is Rusted up!
I can't really remember seeing a belt drive welder, but apparently my parents thought that I was belt drive when I was a kid!,


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## Homeless by Choice (Apr 15, 2016)

wvgca said:


> this may be of interest to you ...
> operator manual for the SD40 ..
> 
> 
> kirara.co.uk/info/SD40%20-%20Operator's%20Manual/





wvgca said:


> here's a link that explains some of principles of 'old school' ALCO generator / traction motor principle, with quite a few images
> http://www.rr-fallenflags.org/manual/IS-800A.pdf
> 
> interesting reading, very similar to the old DC welders I have on the farm, belt driven in my case


My curiosity is satisfied and my questions are answered. I read and downloaded both of these manuals and have them stored on my computer for future reference.

You guys are great.
Thank you,
LeRoy


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## wvgca (Jan 21, 2013)

Homeless by Choice said:


> My curiosity is satisfied and my questions are answered. I read and downloaded both of these manuals and have them stored on my computer for future reference.
> 
> You guys are great.
> Thank you,
> LeRoy


i added more links to loco manuals this morning in the thread
SD40 Operators Manual [1:1] 
brain fart, forgot how to post link to thread, lol


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## Homeless by Choice (Apr 15, 2016)

wvgca said:


> i added more links to loco manuals this morning in the thread
> SD40 Operators Manual [1:1]
> brain fart, forgot how to post link to thread, lol


I found what you are referring to at:
http://http://www.modeltrainforum.com/showthread.php?p=1202537#post1202537

First, thanks for the additional information,

Second, I also was trying to remember how to post a link to another thread. Somehow I accomplished it but I don't know how.

LeRoy


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