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[quote]QUOTE: Originally posted by BNSF SD70MAC If AC is not as good as DC then why did the BNSF buy so many SD70Mac's? Why couldn't thay have just got the SD70M's instead? I mean the locomotive is the still the same thing but only the big differnce is the traction motors right? BNSFrailfan. [/quote] BNSF runs many coal trains, so there is a need for AC's. And many of those 70MAC's came from BN, which also ran a lot of coal trains. SD70MAC's can replace SD40-2's on almost a 1-1.5 basis, meaning 3 70MAC's can replace 5 SD40-2's. SD70MAC's produce more tractive effort than SD70M's, about 28,000 lbs. more, making them much more sutable for low-speed heavy hual service. Also AC traction motors can't burn out like DC can. If a DC powered unit stalls on a grade or goes below the minimum speed (usually about 8 Mph) for too long, chances are the traction motors are going to get fried. AC, on the other hand, can go down to as low as 1 Mph and still pull without risking traction motor damage.
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