[urq] NAC : Electrical draw on an average car...
Louis-Alain Richard
laraa at sympatico.ca
Thu Mar 5 14:52:06 PST 2009
HI everyone,
I want to write a text about the pros and cons of the Start&Stop and
regenerative braking systems that will be popular very soon on non-hybrid
cars.
Now, I need to evaluate the average and peak amperage draw of an average
car. Peak is at 75 amps, average is 20 amps in my calculations.
Second, from what I know, an alternator is only efficient at 50-60%. Is this
true ?
Third, a gasoline engine efficiency is around 30%, right ?
So, from that, at peak draw (winter driving, all lights, rear defrost, seat
heaters, blower, etc) :
- 75A at 14V = 1050 W
- Engine draw is double. 2100W.
- At 30% efficiency, those 2100W needs 7000W of fuel energy. That is 7kW/h
for an hour of driving.
- Fuel energy is 10 kW/h/liter
(http://en.wikipedia.org/wiki/Gasoline#Energy_content)
Thus, those 75A during 1 hour are worth 70% of a liter of gas : in Qubec
today, that is 65¢.
During summer, amperage would be 1/3, so 22¢ an hour.
Are my calculations OK ? Can I print this ? :-)
Louis-Alain
1983 Quattro
(whose 150mA draw is still an unsolved mystery.)
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