Comments on: Calculating the Volts EPA Rating, More than 100 mpg?

By: Zero X Owner

Zero X Owner — Wed, 24 Dec 2008 21:55:59 +0000

Remember, the lower the number of kW-hr/100 miles, the more efficient the vehicle.

By: Zero X Owner

Zero X Owner — Wed, 24 Dec 2008 21:54:05 +0000

Dave G had it best, but Dave’s and my numbers don’t match and he has everything being far more efficient that the Tesla Roadster on kWh/100 miles, which I highly doubt. The difference is probably in how conservative the power pack management estimate is, as I can’t imagine that the Prius et. al. don’t use electric motors that are twice as efficient at the Tesla Roadsters (indeed, I’m pretty sure that’s not possible, with the already extremely high efifciency of existing electric motors). Dave G seems to be assuming a 40% of capacity usage (40% to 80% range), which is in line with existing nickel power packs in most current hybrids and some electrics. But I distrust the results using that. Again, consider that a Tesla Roadster is already EPA rated at 32.5 kW-hr / 100 miles mixed city/hwy.

Can someone resolve this difference with Dave G’s results?

By: Zero X Owner

Zero X Owner — Wed, 24 Dec 2008 21:42:31 +0000

The correct EPA rating is now in number of kW-hr/100 miles (that’s number of kilowatt hours per 100 miles.

The lower the number, the more efficient the vehicle is. The Tesla Roadster, for example, is EPA rated at City: 32kW-hr/100 miles, Hwy: 33kW-hr/100miles. My Zero X motorcycle (full electric) averages 2kW-hr/100 miles in real world driving (7,000 miles street riding, so far, with zero maintenance). That means that my Zero X motorcycle is more than 16 times more efficient than a Tesla Roadster.

Here’s my best guess at the Chevy Volt EPA rating using power pack only, with the propsed 16 kW power pack and a 40 real world mile range. To maximize power pack life, using a lithium ion base, and being extra cautious, the power pack would never exceed 80% (also makes the recharging faster) and never go below 40% (real world indicates that a 20% to 100% range, managed extremely rigorously, would be possible with about the same power pack life span), which means thaht 40 miles would use 40% (80% minus 40%) of the power pack capacity (16kW).

Now consider that 100 miles is 2.5 times 40 miles.

The calculation: (16kW-hr times 40% times 2.5) divided by (40 miles times 2.5) = (16*0.40*2.5) kW-hr/ (40*2.5) miles = 16Kw-hr/100 miles

This means that the Chevy Volt, with a propsed curb weight 800 pounds heavier than the Tesla Roadster, using more conservative power pack management, would be twice as efficient than the Tesla Roadster, which I doubt. This tells me that GM is confident enough in the battery performance, after their extreme testing of two manufacturers, that they are using the most agressive power management possible (probably 20% to 100%, which equals 80% of power pack capacity), in which case the calculation becomes:

(16kW-hr times 80% times 2.5) divided by (40 miles times 2.5) = (16*0.80*2.5) kW-hr/ (40*2.5) miles = 32Kw-hr/100 miles

This matches the Tesla Roadster efficiency exactly, though the CHevy Volts looks to have a higher curb weight by 800 pounds. The difference – probably in improved battery performance from 2008 (the 2008 Tesla Roadster EPA ratings date) to 2010 expectations for the CHevy Volt release.

It wouldn’t surprise me if, based on this, that Tesla is already capable of getting below 30kW-hr/100 miles from their latest power packs, on the weight difference.

I think my work is reasonable based on the final results, but if someone else can improve on it, please chime in.

Note: This is the correct metric for series hybrids, such as the Chevy Volt. For parallel hybrids the gas fueled portion can be converted from miles per gallon to the new metric kW-hr/100 miles and each portion averaged, weighted by miles for a combined result of a single number in kW-hr/100 miles.

By: 2010 Volt Revealed...just now! - Page 4 - Zilvia.net Forums

2010 Volt Revealed...just now! - Page 4 - Zilvia.net Forums — Mon, 13 Oct 2008 20:27:29 +0000

[...] John. GM-VOLT : Chevy Volt Electric Car Site

By: Dan Petit

Dan Petit — Mon, 13 Oct 2008 14:48:24 +0000

The incredible and astonishing thing about regenerative braking is not so much the power it recovers, but
THE BRAKE PAD WEAR IT PREVENTS!
When scanning the processor of my neighbor’s 2001 Prius, which had 113,000 miles on it at the time, as I was analyzing the systems waveforms (which is what I teach to auto techs), and I repeatedly asked how many miles he had on it. ( I hadn’t seen the odometer).
He repeated 3 times to my skeptical 3 questions of how many miles it had on it all during the 45 minute scan.
When I got out to inspect the pads, THEY STILL HAD 30 TO 40 PERCENT PAD LEFT on the originals! How many front brake jobs would have been needed? 2 front brake jobs and probably a rear brake job as well. THESE ARE THE SORTS OF TERRIFIC THINGS THAT ALL THE NEW ENGINEERING WILL BRING TO THE CONSUMER.
(Yes there will likely be more fuel system cleanings if “TOP TIER” fuels are not used by owners.)
Note: I have always used “TOP TIER” fuels in my motorhome (which I am selling to make way to buy a Volt), and, the fuel has never gone stale the twice-a-year I fill up the tank in it.
(Shell 87, if I am allowed to say so).

Dan Petit, Austin, TX