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"a big diesel probably uses 25% of peak fuel at idle" I have a very hard time believing this, especially for diesels, which idle much more efficiently than spa

"a big diesel probably uses 25% of peak fuel at idle" I have a very hard time believing this, especially for diesels, which idle much more efficiently than spark-ignition engines. Where did you get this figure? What I'm also surprised by was the fact that they hadn't already allowed unstable voltages from the generators to be used. A modern switching powersupply can operate down to, what, 80 volts? EDIT: rdl, for some reason I can't reply to your reply. Replying here. Thanks for the info. Now that I think back, I recall reading that diesels operate with an air/fuel ratio as high as 80:1 at idle. 1/4 would put them at 20:1 at full load, which I can beleive, because diesels don't typically operate at stoichiometric even under full load, which would be ~15:1.

rdl 14y ago
2MW Cummins use about 130 gallons/hour at max load. At 1/4, about 34 gallons/hour. You can't idle them at low loads for long periods without damaging them. That's basically 1/4. You usually want it to be more like 50-75%. So "no real load" is artificially set higher than engine idle to keep the system functional, using a load bank. (what you actually do is have N generators and just use some of them, or have different sizes and use the right ones to sort of match the load) The output from the generators is going into the UPS. The UPS input is probably pickier than any switchmode power supply. Especially because most big UPSes let you set in software how picky they are about input power before they switch to battery, and they apparently had it set to conservative mode.