Overview#
The Generac SD1250 (also designated IDLC1250) is a 1,250 kW standby (1,125 kW prime) industrial diesel generator set powered by a Mitsubishi S12R-Y2PTAW-1 49.0L V12 engine. Rated at 1,563 kVA standby and 1,406 kVA prime at 60 Hz, it is EPA Tier 2 certified for stationary emergency applications. The genset features the InteliGen NT controller with electronic governing and plus or minus 0.25% steady-state frequency regulation.
Engine and alternator#
The Mitsubishi S12R-Y2PTAW-1 is a 4-cycle, 49.0-liter (2,992 cubic inch) V12 diesel engine delivering 1,881 hp at 1,800 RPM. Key specifications include a 14.5:1 compression ratio, 6.69-inch bore, 7.09-inch stroke, 4-valve cylinder heads, aluminum pistons, and a drop-forged steel crankshaft. The lubrication system uses a gear-driven oil pump with cartridge filtration and a 158.5-quart (150L) crankcase capacity.
The standard alternator is the Generac K2112064N22, a 4-pole rotating-field design with Class H insulation on both rotor and stator. It features permanent magnet excitation, analog voltage regulation with plus or minus 0.5% steady-state accuracy, and total harmonic distortion below 5%. Motor starting capability is 7,709 skVA at 30% voltage dip on 277/480V with the standard alternator.
Power ratings and fuel consumption#
At 277/480V three-phase and 0.8 power factor, the SD1250 delivers 1,250 kW standby (1,882 amps). It is also available at 346/600V (1,505 A). The cooling system supports operation at up to 104 degrees F (40 degrees C) ambient with the standard 40-degree package, or 122 degrees F (50 degrees C) with the optional 50-degree ambient cooling system.
Fuel consumption at standby ratings: 114.0 gph at 100% load, 82.9 gph at 75%, 56.4 gph at 50%, and 32.2 gph at 25% load. Total fuel pump flow is 127 gph (479 Lph).
Physical dimensions#
The open set measures 215.7 x 93.0 x 115.1 inches (5,478 x 2,362 x 2,924 mm), weighing 26,045 lbs (11,814 kg). With a 24-hour integral base tank (2,500 gallons usable), the dimensions extend to 243.0 x 116.0 x 148.0 inches. Sound attenuated enclosures are available up to Level 2 at 404.0 x 262.0 x 150.0 inches.
Cooling system#
The SD1250 has separate jacket water and aftercooler cooling circuits. Jacket water coolant flow is 489 gpm (1,851 Lpm) with a 95-gallon (360L) capacity. The aftercooler circuit flows 90 gpm (341 Lpm) with a 50-gallon (189L) capacity. Heat rejection to coolant is 1,829,820 BTU/hr (536 kW). The unit-mounted radiator uses a pusher fan (88-inch diameter) at 710 RPM, drawing 66,100 scfm at the 40-degree C cooling package rating.
Our service experience#
The Mitsubishi S12R is a well-proven engine in this power class with a solid track record. At 1,250 kW the engine operates at 276 psi BMEP, which is moderate for the displacement. The dual-circuit cooling system requires separate coolant sampling and maintenance for jacket water and aftercooler circuits. We recommend oil analysis every 250 hours to track engine wear trends, particularly for the 12-cylinder valve train.
