Engineer-Joe posted:Hot Water posted:......since I spent so much time with the SD70MAC units on the BN, out in the Wyoming Powder River Basin coal fields (1991 thru 1998), prior to my retirement.
If you would indulge us please, of your opinion on the SD70MAC units overall. I have always been a modern diesel fan and not experienced with real trains. It is always good to read an experienced RR person's inside info. I feel that these units were the pivotal units leading the AC trend that seemed to take over now.
Joe,
During my 36 1/2 year career with EMD (June 1 1962 thru December 24, 1998) I always felt that the SD40-2/SD45-2 were the best units I ever worked with. Until the SD70MAC units! Sure the new new "MACs" had the typical "new design" bugs, especially the KNOR Electronic Airbrake system, but once the Semens people from Germany understood the unbelievable temperature extremes that the AC Inverters and their own computers had to work with, i.e. a coal train be loaded in the Powder River Basin of Wyoming at temps as cold as -35 degrees F, proceed to Houston Texas area, and unload the coal at 85 degrees F with 90% humidity, all within 3 days running time, the units became VERY reliable.
In training the various Engineers and Road Foremen out of the Gillette, WY terminal, it quickly became apparent that a pair of SD70MAC units on the headend of 18,000 tons of coal, with another DPU SD70MAC on the rear, you could almost defy the laws of physics on the BN/BNSF Orin Subdivision. During the occasional "hot day", if the inverters got hot enough, they would automatically power-limit, and you would stall on the ascending grade. No problem; simply apply the train air brakes and stop, place the units in "neutral" and Reve the engines up to blow cooling air through the traction inverters. After about 10 or 15 minutes, you could call up the inverter temperature screen on the computer, and make sure that they had cooled down to "normal".
Then, with the air brakes still set, place the rear DPU in forward throttle 6, and the lead units in forward throttle 6, thus straining against the train, so then when the air brakes are released, the train will NOT roll backwards. As the brakes release, the rear DPU is placed in throttle 8, and the lead units placed in throttle 7. Still holding the independent brakes on, when the train is fully released and the rear DPU begins pushing in any slack, ease down the independent brakes to about 30 psi, and place the lead units in throttle 8. Ever so gradually the train begins to move forward up the grade, as the Engineer lowers the independent brake down to about 10 pis, they all the way off. There is no wheel slip, and the train slowly accelerates up the grade to about the balance speed of 10 to 15 MPH.
Such action with DC traction SD40/SD40-2 units would pretty much destroyed all the DC traction motors, by causing massive stall burns on the copper commutators. No problem for an AC traction SD70MAC!
Having no practical experience only leaves me to read up on what I can get my hands on. I haven't seen much comparisons of say the SD70MAC to the SD70M units for example.
The SD70MAC units are AC traction, while the SD70 is DC traction.
I have read some general comparisons to the GE's of the same time frame.
