EMD MP15AC

The EMD MP15AC is a 1,500 hp diesel road switcher locomotive built by General Motors' Electro-Motive Division between August 1975 and August 1984. A variant of the EMD MP15DC with an AC/DC transmission, 246 examples were built, including 25 for export to Mexico, and four built in Canada.

Development
The MP15DC's standard Blomberg B trucks were capable of transition and road speeds up to 60 mph, allowing use on road freights. Soon there was a demand for a model with an advanced AC drive system. The MP15AC replaced the MP15DC's DC generator with an alternator producing AC power which is converted to DC for the traction motors with a silicon rectifier. The MP15AC is 1.5 ft longer than an MP15DC, the extra space being needed for the rectifier equipment. The alternator-rectifier combination is more reliable than a generator, and this equipment became the standard for new diesel-electric locomotive designs.

The MP15AC is easily distinguished from the DC models. Instead of the front-mounted radiator intake and belt-driven fan used on all previous EMD switchers, these have intakes on the lower forward nose sides and electric fans. Side intakes allowed the unit to take in cooler air, and the electric fans improved a serious reliability issue found in its earlier DC sisters.

Engine
The MP15 used a roots-blown 12-cylinder 645E engine. The engine is rated at 1,500 hp. The 645 series, introduced in 1966, was EMD's standard engine through the 1980s.

Original owners
The six largest buyers, Milwaukee (64), Southern Pacific (58), Seaboard Coast Line Railroad (45), Nacionales de México (25), Long Island (23), and Louisville & Nashville (10), were all buying road locomotives with AR10 alternators throughout the 1970s, so the similarly equipped MP15AC was easily kept in good repair. 36 more units were sold to 8 other customers.