SD40-2 Transition

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SD40-2 Transition

Postby Engineer Spike » Mon Feb 27, 2017 9:17 pm

I have noticed that SD40-2 units do upward transition at about 23 mph. Backwards transition happens at about 18 mph. One strange feature is that even if the speed remains above 23 mph, placing the throttle in #1 notch, or idle produces backwards transition. It will not do forward transition, until the throttle goes back above #5 throttle. Why is this required?
"Boston and Maine Hudson River Bridge, westward track...no defects...... Boston and Maine Hudson River Bridge, westward track... no defects."
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Re: SD40-2 Transition

Postby WVU » Thu Mar 16, 2017 6:14 pm

On the SD40-2, the Transition Settings is controlled by "E/I" which means Main Generator Voltage/Main Generator Current. The TR11/12 Module receives a scaled down MGV and MGA signal that makes transition happen. The older GE's used a speed input from the Axle Alternator and so does the new SD40-3 units CSX has to control Transition but EMD's use E/I. It just so happens to happen in the area of 23 mph for Forward Transition and like you said backwards Transition is in the area of 18 mph. You also have another feature with the SD40-2 called Transition Delay (TDR) what this does is this, lets say you make Transition and the load is so heavy in Parallel that the unit slows down and makes Backwards Transition and the unit goes back into Series, by this happening the MGV/MGA Limits will change and the new setting will allow you to go in the area of 28 mph before the unit makes Transition again. For this TDR circuit to work, the timing has to be set properly on the TDR relay.
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Re: SD40-2 Transition

Postby Engineer Spike » Sun Mar 19, 2017 9:06 pm

Good technical details. Still, why does reducing throttle to #1 produce backward transition, and why does it have to be advanced to #5 to do upward? This happens at speeds well above the 18-25 mph range. I have wondered about this because my line is a roller coaster. If I tried notching down, to use the grade, there would be not much power, until 5 was reached, and transition happened.
"Boston and Maine Hudson River Bridge, westward track...no defects...... Boston and Maine Hudson River Bridge, westward track... no defects."
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