Their data shows a peak efficiency of 250 g/kWh @ 4.8 kW output. That’s 0.410 lbs/HP h for those who actually find these units useful. This is not too shabby, if it proves accurate.

For what it’s worth, I recently measured the fuel consumption of my 2-71 Detroit Diesel from Affordable Power. The numbers are not good and I will probably be replacing it with a Lister 8-1.

The following data was collected with a fuel temperature of 15 degrees F and has been volumetrically normalized for 60 degrees F. The test fuel was #1 diesel. Test loads were provided by electric heaters, measured with a Watts-Up meter.

Load: 0 kW
Fuel Consumption: 0.90 gallons/hour

Load: 1.76 kW
Fuel Consumption: 1.02 gallons/hour
Est. BSFC: 2.68 lbs/HP h

Load 3.52 Kw
Fuel Consumption: 1.13 gallons/hour
Est. BSFC: 1.49 lbs/HP h

I did not have a larger load to test, but if these numbers are extrapolated (0.90 gal/hour + 0.0653*LOAD gal/hour), I would expect the full rated capacity of 12.5 kW to consume about 1.68 gallons/hours. This would have a BSFC of 0.622 lbs/HP h. Absolutely terrible! Get a lister 8-1 instead.

Obviously the Lister has inertia out the ying-yang. Those “old school” ST alternators like many people use with Listers has plenty of iron in the magnetic path and so saturation isn’t a problem.
The trade-off is, of course, weight. I couldn’t very well move 1500 lbs of Lister and ST around like I can, say, my Generac 7000XLT.

Inertia can be easily added to a belt-driven generator. I have a 10KW genset that I built using I Riggorini twin cylinder high speed air cooled diesel engine. I built it to run a concession stand which is mostly resistive loads. I needed it to be quite light so that I could move it around easily.

A second use was as the backup generator for my restaurant’s refrigeration. In that capacity it needed LOTS of surge power. To provide that surge power I fabricated an approx 30 lb flywheel made from a piece of 1″ thick cold rolled plate. I machined it to accept a TaperLoc hub which enables it to be easily attached and removed from the generator’s shaft. This is the best of both worlds – a lightweight generator for easy portability and surge capacity when it’s needed.

Speaking of, I used my Generac to power a concession stand 12 hours a day, 6 days a week for over a year. It quit at the end of that time but only because it had collapsed the aluminum pushrods. I replaced them and the generator resumed service. The engine is still tight and it uses no oil. I suspect that the pushrod problem was my fault for not keeping the valve clearance adjusted.

It certainly wasn’t my first choice – the noise is almost intolerable – but it’s what I had on hand and it did the job. You really can’t plaster all high speed generators with the bad rep that the throw-away generators sold by the big box stores have rightly earned.

John

That Equals 1.028 lbs fuel per hour. A US gallon weighs about 7 lbs winter/summer average, so that is 0.718 gallons per hour. This is slightly worse than the 7% rule which states consumption should be 7% of the KW load.

The Lister 12/2 puts out 100 foot lbs, so it wins over a gas engine on gen start up which goes to triple the HP load rating. This means that if you want to put a starting inducitive (motor) load across a generator, it had better be 3 times the electric motor’s rating. So a 4 HP motor attached to a load will need a 12 hp/ 9 KW genset. Gensets can be different unless they are connected to batteries direct, so start up should be decoupled and the batteries kicked in gradually if your gen is not over the load by three times. Twice is dicey.

Don’t try to run a gas engine 24-7 for a year running any sort of load. It will last about 4 months unless it is long stroke with stellite valves. Few of them around anymore. B & S used to make one for pumps.