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Old 04-27-2009, 01:38 PM   #18 (permalink)
Join Date: Dec 2007
Location: Bay Area
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The Miata - '01 Mazda MX-5 Miata
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Not seeing a violation of any thermo laws...

The BTU figures are used as a comparison metric. Electric power trains aren't constrained by the btu content of gasoline. We could report in terms of mi/MJ - a unit that I've seen pop up more and more frequently...

Miles per MegaJoule

1KwH = 3.6MJ
1 gallon of gasoline (125,000btu) = 131.9MJ

3-4 miles/kWh - lets say 3.5 miles - this would be socket to wheel figures....

That's 3.5/3.6 mi/MJ = .97 mi/MJ

Compared to a 50mpg car - pump to wheel....

That's 50/131.9 mi/MJ = .38 mi/MJ

But doing so is missing the point. If I were completely new, and potentially open to the concept of driving more efficiently, I would feel alienated by this awkward unit. If I'm comfortable, I'm probably more likely to continue reading.

Does anyone have any literature with respect to an electric motor and the carnot heat cycle? That is, what's the equivalent/comparable isotherm compression stage for an electric motor and etc.? I've had red flags pop up in my head while reading that comparison. I even dusted off the old thermo book and heat transfer - nothing
Cars have not created a new problem. They merely made more urgent the necessity to solve existing ones.
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