I was reading somewhere on the web that each locomotive manufacturer has a different set up when it came to dynamic braking. I read that EMD units would slow the prime mover to idle while the dynamic brakes were engaged. The GE and ALCO units would run at notch 8 while in DB because the fans were powered directly to the drive shaft.
Everything I saw on the web was talking about the older units. Is this still true on the newer units, especially the GEs?
Will
That was true of Uboats and older Dash 7 GEs - the engine had to rev to keep the cooling fan going. The DB grids were in the intake air flow side of the radiator cab. Newer GEs, like all EMD's use taps on the DB grids to power the DB cooling fans. The diesel engine only has to rev enough to provide excitation for the traction motors (This applies to DC units. ACs are a bit more complicated)
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
1960-70 era EMDs revved up the prime mover in dynamic to... Run 5 speed, was it? Or more? because the traction motor blower was driven directly from the prime mover, and the traction motors still needed cooling. The GP50/SD50 got away from that somehow-- I remember how strange it was to hear SFe GP50s rolling the York Canyon coal downgrade with the engines at Run 2 speed or whatever it was.
timz 1960-70 era EMDs revved up the prime mover in dynamic to... Run 5 speed, was it? Or more? because the traction motor blower was driven directly from the prime mover, and the traction motors still needed cooling. The GP50/SD50 got away from that somehow-- I remember how strange it was to hear SFe GP50s rolling the York Canyon coal downgrade with the engines at Run 2 speed or whatever it was.
Thanks for the memory jog.... Two speed DB did come out with the 50 series. It sensed TM amperage and would rev up the engine to speed up the TM blower. I think it was further evolved into 3 speed DB (1, 3, 5?) That all went away with motor driven TM blowers on Dash 8s and 70 series.
I always thought that you needed engine revs on the generator to get the excitation voltage on the traction motors needed to have the traction motors function as generators. In dynamic brake mode, the motors are taken out of series-wound configuration, the motors are rewired so the field windings get voltage from the generator needed to generate magnetic field, and the rotors are wired to the dynamic brake resistor grids to provide the braking force.
The engine wasn't so much as delivering power (except against bearing friction and the like) so much as spinning fast enough to deliver enough generator voltage to get the required braking effect.
Of course engine revs run the main blower because you need traction motor cooling.
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
Some newer EMDs use electric powered traction motor cooling fans, SD70M, SD75M, SD80MAC, and SD90MAC. However the SD70MAC uses a drive off the diesel engine, the presence of a blower bulge or lack there of tells the tale.
Someplace else I read that the Dynamic Brakes may require the older EMD units to go as high as notch 6. I believe that some of the NS operating rules or employee timetables refer to that also.
- Paul North.
Paul Milenkovic I always thought that you needed engine revs on the generator to get the excitation voltage on the traction motors needed to have the traction motors function as generators. In dynamic brake mode, the motors are taken out of series-wound configuration, the motors are rewired so the field windings get voltage from the generator needed to generate magnetic field, and the rotors are wired to the dynamic brake resistor grids to provide the braking force. The engine wasn't so much as delivering power (except against bearing friction and the like) so much as spinning fast enough to deliver enough generator voltage to get the required braking effect. Of course engine revs run the main blower because you need traction motor cooling.
Field voltage is only about 50 volts and field current is about 925 amps , the AR-10 can do that in idle...
Paul, there has been times when I have been troubleshooting a Extended Range Dynamic Braking problem on a EMD Dash 2 unit and I have reached over and turned the "Engine Run Switch" OFF so I don't have to listen to the unit running in notch 4 to make it eaiser to communicate with another electrician when trying to solve the problem. You are still exciting the Traction Motor Fields even if the unit is not running in notch 4.
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