Motor Powering Generator Efficiency

[dingpud]

What do I look for to determine the efficiency factor to know how many watts I can get out of a generator given a specific known HP sized engine?

Example:
12.6 HP gives 9395 Watts from the standard HP to Watts conversion... however on a Markon generator, the spec sheet says that a 12.6 HP engine will provide 7500 Watts.

I am sure that number is composed of data from days of testing, calculations, safety factors, etc. I wanted to see what I could calculate for a 9.9 HP engine but wasn't sure where to start. Is there an industry standard / assumed 80% efficiency factor?

Any thoughts?

Markon link for reference: https://www.cumminsgeneratortechnologies.com/www/en/referenceapplications/apu/MARKON_Brochure.pdf

 

[SteamKing]

Typical automotive alternators have efficiencies in the range of 70-80%. Some smaller alternators can go as low as 60%:

http://en.wikipedia.org/wiki/Alternator_(automotive)

Your alternator seems to be on the high end of the range.

 

[Chronos]

You reach a price point for alternator efficiency. An extremely efficient alternator [~90%] would not be cost efficient. It is more practical to use a bigger motor.

 

[themotorman]

The most efficient system is for a high speed gas engine with a converter to deliver the electrical output as needed. This is because the size and weight for a given generator power go down with RPM. Conversion of the electrical output from the generator by electronic converter is over 90% efficient. The older gensets running at 1800 or 3600 RPM so they could put out 60 Hz is really old school thinking.