Dumb question: Would an SD60M be the same as an SD60MAC because I've not heard of an SD60MAC. Further dumb questions: Is there such thing as an SD70M? SD80M? SD90M? I doubt it as I have not heard of those either. Thank you, Jas
AC stands means Alternatin Current which is the type of current supplied to the trucks. I'm not sure how Alternatign Current works but I do know AC trucks are generally know to have a much higher tractive effort than standard trucks. I don't know why SD60's never seem to be equipped with AC electronics and trucks. Technology probably didn't develop until EMD's development of the SD70. NS has GP38-2AC, but they were rebuilt that way. As for SD70M, SD80M, and SD90M, I believe it is much more economical to purchase a MAC because of the higher tractive efforts of the trucks and the Radial trucks to lesson wear on rails.
I knew that the "AC" portion means "Alternating Current" for the power. So if the "AC" is left off, using the SD60M in my example, that would mean EMD's SD60M production units are DC units?
There were a total of 4 SD60MAC's built, all by the Siemens/GMD Group for Burlington Northern. They were in testing and in service from the early 1990's until 1998. There were SD60MAC, SD70MAC, SD70IAC, SD80MAC, SD90MAC, and SD9043MAC model designations for EMD's AC units. (maybe more, not certain of that) Also, the latest SD70ACe units are the emissions improved version. The SD70MAC variations are by far the most established base of EMD AC units. For DC, the SD70, SD70M, and SD75M's are the latest model designation. (So, there are no DC SD80's or SD90's) Yes, the SD60 and SD60M's are also DC...with the four aforementioned 60MAC's the exception. Economically speaking, the AC units are more expensive and thus the DC units are still attractive for some applications. (UP is still receiving their SD70M's on a daily basis I think, well over 1200 of 'em last I heard) The AC units are supposed to be more durable over the long haul pulling heavier loads at low gear ratios, such as coal and grain. References to locomotives such as the NS GP38-2AC or the BN's GP38AC's are NOT the same as the new AC units. These refer to AC alternators, rectified to provide DC to the traction motors. Whereas, the the new AC units actually have AC Traction Motors to drive the wheels. The trucks on most AC units are radial trucks, meaning they turn on individual axis instead of the entire three axle truck turning together. This provides increased tractive effort because greater wheel surface area is applied to the rails. This complements the AC traction motors but is not directly tied to AC technology. I'm sure someone will shoot holes in my explanation, but hopefully I'm close. [ 22. July 2004, 00:29: Message edited by: Doug A. ]
