# Check math please - kWh to Ah - electric car

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Gents,

(full text below as NYT will pull it soon)

"The Leaf's rating is based on a formula from the E.P.A. in which 33.7 kilowatt hours of electricity is equivalent to one gallon of gasoline.

"The tough part with an electric vehicle is we have no gallons. We have no gas," Mr. Perry said. "But we understand the need to provide a comparison and that's what the formula does.""

I calculated that one "gallon" of gas is equal to 2.8 Ah. I don't want to show my math because it might skew your calculation.

If the Nissan Leaf gets the equivalent of 73 MPG on its electric motor, does that mean only a 2.8 Ah battery will last for 73 miles?

---FULL TEXT OF ARTICLE---

Nissan Says Its Electric Leaf Gets Equivalent of 99 M.P.G.

DETROIT ? The federal government has rated the Nissan Leaf, the battery-powered car scheduled to go on sale next month in five states, as getting the fuel equivalent of 99 miles a gallon, Nissan said Monday.

The Leaf?s fuel-economy label.

The Environmental Protection Agency, which tests vehicles for emissions and fuel efficiency, has determined Leaf?s official range to be 73 miles on a fully charged battery, much less than the 100 miles previously claimed by Nissan.

Both figures will appear prominently on the Leaf?s window label, which shows the estimated yearly electricity cost as \$561. The E.P.A. calculates annual fuel costs as \$867 for the Toyota Prius hybrid and \$1,669 for Chevrolet?s Malibu, which like the Leaf, is classified as a midsize car.

The E.P.A. puts vehicles through five tests to simulate varying driving conditions and levels of climate-control usage.

Because drivers cannot simply stop at a gas station and refuel, the Leaf?s range is expected to weigh heavily on shoppers? minds. Adding to any confusion they might feel, the Leaf will have a second sticker from the Federal Trade Commission ? it regulates advertising by alternative-fuel vehicles ? displaying the car?s range as 96 to 110 miles.

?Driving behavior, temperature ? those things do affect your range,? said Mark Perry, the director of EV and Advanced Technology strategy in North America for Nissan. ?We?re trying to be very open so folks are making the right decision for them. We don?t want them to be surprised.?

The E.P.A. calculated the 99 m.p.g. equivalent figure by combining ratings of

106 m.p.g. in city driving and 92 m.p.g. on highways. The Leaf?s rating is nearly double that of the Toyota Prius hybrid, which is 50 m.p.g.

The agency has not concluded its tests of the Chevrolet Volt, a plug-in hybrid that also goes on sale next month in parts of the United States. The Volt, unlike the Leaf, has a gasoline engine that allows the car to remain operational after the battery, which General Motors says has a range of 25 to 50 miles, is depleted.

?Their calculation is a little bit more straightforward than ours, so I suspect they may have gotten through the process a little faster,? a G.M. spokesman, Rob Peterson, said in explaining why the Leaf results were finished first. ?At this time we don?t have a definitive number.?

The Leaf?s rating is based on a formula from the E.P.A. in which 33.7 kilowatt hours of electricity is equivalent to one gallon of gasoline.

?The tough part with an electric vehicle is we have no gallons. We have no gas,? Mr. Perry said. ?But we understand the need to provide a comparison and that?s what the formula does.?

Mr. Perry noted that electricity costs ? assumed to be 12 cents a kilowatt-hour for the purposes of the label ? varied widely in different parts of the country and in some cases depending on what time of day the car was plugged in.

The Leaf?s window sticker will list the car as needing seven hours to charge via a 240-volt outlet and consuming 34 kilowatt-hours every 100 miles. It will show the Leaf, which has no tailpipe, as receiving the best possible scores for emissions of greenhouse gases and other pollutants.

Nissan dealerships in California, Oregon, Washington, Arizona and Tennessee will start selling the Leaf in December. Sales will begin in Texas and Hawaii in January, followed by additional states later in 2011.

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What is the battery's voltage? 2.8 AH is only part of the data.

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A gallon of gas contains around 35MJ or about 9.7kWh.

If the battery is ~3500V.

1) Your numbers are *way* off. 2) There ain't no such thing as a free tank of gas.
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>(full text below as NYT will pull it soon)

Don't forget Friction dumbass. All cars have very high frictions eating = away your energy. That's why you're stuck in snow easily.

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snipped-for-privacy@4ax.com...

g away your energy. =A0 That's why you're stuck in snow easily.

You are an idiot. He did not say anything about friction. He declared the content of the energy source. You are even more stupid than theghost troll is, and that is some feat.

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12V.
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I don't where I grabbed my numbers. :-)

Here is my real question I guess:

"The Leaf's rating is based on a formula from the E.P.A. in which 33.7 kilowatt hours of electricity is equivalent to one gallon of gasoline."

Given: 33.7 kWh = 1 gallon of gas

What size 12V battery would be required to drive the claimed 73 miles?

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Put about 300 of those in series and you're close.

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Whoops, looking again, I see that gasoline contains about 35MJ/l (not gallon), so make that 130MJ/gallon or about 37kWh. Close enough.

37kWh == 37,000VAH/12V = 3100Ah
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Sounds good.

Wow.. so that's going to be a big ass one (physical measurements). I wonder how big it would be.

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That is about 15 golf cart batteries, the typical electric car load but I bet these guys use lithium batteries.

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