James,
I wanted to offer a few more thoughts on DoD generators. Most of the generators I found on Government Liquidations were Mil Std Generators. This family of generators was designed in the 1970s and manufactured into late 1980s to early 1990s. The DoD is selling of the generators because they are old, and compared to newer DoD generators they consume more fuel, require more regular maintenance (PMCS), are less reliable and are more expensive to repair if you can get the parts.
The Mil Std Family are tough generators designed to run in environmental extremes. They are not your typical consumer generators and out perform most same kW commercial generators. Most Mil Stds (5 kW +) are designed to produce 110-125% of nameplate kW continuously , 0.8 Power Factor, up to 5,000 Ft. elevation (normal de-rating for a generator set is 3.5% per 1,000 ft & commercial generators are rated at sea level to no more than 1000 ft. elevation). The alternators are oversized to improve efficiency and power quality, to operate at high temperatures and to start motors (the generators have phenomenal motor starting capability). The alternators are brushless and controlled by voltage regulators so the power quality is good (significantly better than residential gasoline generators). The engines are a bit over powered compared to commercial sets, contributing to the motor starting, altitude and power quality performance. Electronics in the generators will be simple relays and black boxes with resistors, diodes, capacitors & simple transistors. Good electronic shops should be able to troubleshoot them. The generators are also designed to be repaired and can easily be disassembled. Most wiring harnesses are marked with wire numbers, though the circuits are more complex than in newer generators. They are heavy and will withstand off road transport without damage. DoD has published fairly complete maintenance manuals that can be found on the web that are quite a bit more detailed than most commercial generator set manuals.
In terms of problems, the most likely problems will be in areas with moving parts (engines), the fuel system, and set specific electronic parts with high failure rates. The 15, 30 & 60 kW generators are known for voltage regulator failures, for example. I believe a good technician could probably replace the voltage regulator with a current model from Basler or one of the other commercial VR manufacturers. 8 years ago there were vendors who could rebuild the injectors, injector pumps and engines, though I don’t know about availability today. Many of the other components that corrode or fail could be replaced with commercial components (radiators, fuel tank, fuel pump, wiring, toggle switches, etc.)
Downside to sets: All the generators use engines that have been out of production for probably 15 years. The Onan diesel engines in the 3, 5, & 10 kW generators were only used in the DoD generators. Onan stopped making them back in the early 1990s. Spare parts were available past 2000 but DoD has stopped purchasing most spare parts for these sets so the industrial base for spare parts is shrinking and requires a serious search to find the few parts available. The 15 & 30 use White-Hercules engines that were sold commercially, but these companies are no longer in the diesel engine business so I’m not sure how available parts will be. The 60 kW also uses an engine previously sold commercially, but the manufacturer doesn’t make diesel engines any more either. The generators were designed to run on 1980s fuels. Fuel injectors and injector pumps should wear out prematurely from the Ultra low sulfur diesel fuel sold today. They are all good diesel engines, but if you have engine problems it may be tough to find spare parts. All the sets contain main alternators custom built for the generators, though local motor rewinding shops can probably fix damaged windings. The alternators have a long life outside bearing but are supported by the engine flywheel on the other end so they would be difficult to re-purpose into a different generator set. The sets use a 24 VDC starter and control system, so cars can’t be used to jump start them. They are noisy too. Soldiers joke about finding command posts out in the field by listening for the Mil Std generator noise. After the SHTF Mil Std generators will advertise for quite a distance that you have power and potentially other supplies, though the noise is probably no higher than your typical residential gasoline generator.
Selecting generator size: Most users don’t size their diesel generator sets correctly for optimal generator set performance and fuel consumption. Army Field manuals recommend an average load of 80%. This balances having some reserve capacity for peaks and motor starting against optimal engine loading and fuel consumption. Diesel engines work best at high load. At low loads diesel engines consume more fuel per Hp of output increasing kW-Hr fuel costs. At low loads Mil Std generators will also “wetstack” which can lead to sticking rings, dirty injectors, improper new engine break-in and other engine problems. If you go to engine manufacturers they will have graphs of fuel consumption versus load. The graphs will have non-linear curves that show optimal engine fuel efficiency normally somewhere between 60-90% of engine capacity. For the Mil Std generators, at 100% electrical load the engine is probably at no more than 70% mechanical load (the engine has enough hp to power 125% load + another 15% for elevation), so operating the set at even 30-50% electrical load will be wasting fuel. After the SHTF my house will provide shelter for many years with minimal maintenance, I can filter water, potentially grow food, but my fuel supply could be a finite resource with a shelf life that can’t be replenished. Don’t purchase an oversized generator that consumes more of your finite fuel resources than a properly sized generator would. Personally I’m accumulating multiple generators of different sizes that will allow me to run the optimal generator set for the load maximizing the life of my fuel supply. This also provides redundancy. If you need help determining how much power you need recommend you read a basic electrician’s handbook or you can download a copy of FM 4-424, Theater of Operations Electrical Systems, off the web. When examining loads look at night vs day, peak loading, standard loads, and motor starting. Consider batteries and solar for periods of light loads to minimize generator operation. Induction motors place especially high starting loads on generators. Mil Std generators will put out 300% of rated load for the few seconds required to start spinning an induction motor allowing a smaller generator to run loads with large induction motors (motor starting depends on the engine, VR and alternator design). If you have inductive loads, before purchasing a commercial generator check with the manufacturer about their peak output watts or how large a motor they will start. My father purchased a 1,750 Watt gasoline generator that wouldn’t start an induction motor that used 450 Watts, once spinning.
I agree with the writer who didn’t recommend purchasing a DoD generator unless you had the skills to maintain and repair it. I have those skills and I wouldn’t purchase one unless the price was right and the generator was going to be a back up to a back up that I was going to tinker with. The Mil Std sets might be a good fit if it wasn’t going to be operated for many hours (negating the fuel consumption issue) and the poor spares availability could be minimized by purchasing 2 or 3 of the same set size, allowing cannibalization of a set to keep the another set running.
If you are interested in purchasing one try to learn as much as you can about it’s prior history before purchase. As JWR said, try to check the condition of the oil, look at the coolant, check the air filter element, check the hour meter, does it have excessive corrosion on the sheet metal, does it look like it’s been taken care of, do the doors swing freely like they have been lubricated, look in the fuel tank for sediment, are there signs of fluid leakage in the bottom of the skid, drain the fuel filter water separator and check for water or condition of the fuel if present, check the wiring harness’s for fraying, check the control boxes for corrosion, do the rotary switches move freely, are the output terminal lug nuts stripped, try to find out when it was last started (after a couple years the fuel will gum up the injector pumps), and check to see if it’s been rebuilt. Generator sets in better shape, with less corrosion, and fewer hours are more likely to provide trouble free operation, though corrosion and condition is not an absolute indicator as the sets are so tough. – Greg X.