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JRMichler · 08-31-2011, 02:32 PM

Just for the fun of it, let's calculate potential savings. First, get the alternator efficiency up to 90%. Second, change all lighting to the latest technology LED. Third, a more efficient (ECM?) blower motor. The total electrical load would drop from 20 amps down to about 6 amps, for a savings of 14 X 13 volts = 180 watts. The engine power needed would drop from 260 / 0.5 = 520 watts down to 6 X 13 / 0.9 = 87 watt, for a savings of 430 watts.

430 watts / 746 = 0.58 hp. Multiply by 0.4 lbs fuel per hp-hour = 0.23 lbs per hour fuel saved = 0.039 gallons per hour. Assuming 40 MPG at an average speed of 40 MPH, the fuel used would drop from 1.00 gallons per hour down to 0.961 gallons per hour. MPG would increase from 40 MPG up to 41.6 MPG. Those getting better mileage would get a larger gain, those getting less mileage would get a smaller gain. Certain practical realities, such as the fact that engine efficiency decreases at lower loads, will make the real world MPG gain less.

If I put in LED bulbs, it will be for reliability, not MPG. I can also get reliability by replacing every single bulb when the first one burns out.

08-31-2011, 02:32 PM	#3 (permalink)
JRMichler Master EcoModder Join Date: Feb 2011 Location: Phillips, WI Posts: 1,016 Nameless - '06 GMC Canyon 90 day: 37.45 mpg (US) 22 Maverick - '22 Ford Maverick XL 90 day: 49.27 mpg (US) Thanks: 188 Thanked 467 Times in 287 Posts	Just for the fun of it, let's calculate potential savings. First, get the alternator efficiency up to 90%. Second, change all lighting to the latest technology LED. Third, a more efficient (ECM?) blower motor. The total electrical load would drop from 20 amps down to about 6 amps, for a savings of 14 X 13 volts = 180 watts. The engine power needed would drop from 260 / 0.5 = 520 watts down to 6 X 13 / 0.9 = 87 watt, for a savings of 430 watts. 430 watts / 746 = 0.58 hp. Multiply by 0.4 lbs fuel per hp-hour = 0.23 lbs per hour fuel saved = 0.039 gallons per hour. Assuming 40 MPG at an average speed of 40 MPH, the fuel used would drop from 1.00 gallons per hour down to 0.961 gallons per hour. MPG would increase from 40 MPG up to 41.6 MPG. Those getting better mileage would get a larger gain, those getting less mileage would get a smaller gain. Certain practical realities, such as the fact that engine efficiency decreases at lower loads, will make the real world MPG gain less. If I put in LED bulbs, it will be for reliability, not MPG. I can also get reliability by replacing every single bulb when the first one burns out.