Why does the diesel need to run above idle power when using dynamic brake? Are there fans on the resistor banks that need to run and if so why didn't they design the fans to run off of the power being generated from the traction motors during dynamic braking?
Most North American diesel locomotives need to have the engine run faster in dynamic braking to run the traction motor cooling fans.
KPykkonen Why does the diesel need to run above idle power when using dynamic brake? Are there fans on the resistor banks that need to run and if so why didn't they design the fans to run off of the power being generated from the traction motors during dynamic braking?
You need to do three things in dynamic braking. Cool the grids, cool the traction motors and provide excitation for the traction motor fields (it's how you control the amount of braking).
EMDs have always used the power running to the grids to run the grid fans. GE started doing it with the last Dash 7s. Before that, they used the mechanically driven radiator fan for the job.
EMDs use mechanically driven traction motor blowers and GE uses motor driven blowers, but in both cases, you need to rev up the engine to speed up the blowers.
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
That makes sense, thanks for the explanation
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