# Efficiency, What are your Miles Per KWH?



## atzi (Jun 26, 2008)

I have been studying the question of efficiency in the EV conversions and would like to here your numbers.

 I purchased a KW meter to measure usage.
 Two ways to figure efficiency:
  How much KWH from the electric company you use to recharge your EV and drive so many miles.
 and 
 How much energy or watts, based on onboard meters, odometer, voltmeter and ampmeter are you averaging at different speeds at level grades. Include your vehicle type and weight.​


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## atzi (Jun 26, 2008)

*Well...............
Here is what I found *after recording a few hundred miles of charging and writing down the figures off the meter. A 30 mile round trip driving from 40mph to 60 mph, some hills, with no charging at work. The odometer reading 176379 to 176409 took 12KWH. TVA charged 12 cents a KWH, so the charge cost me *$1.44 to drive 30 miles or $.048 per mile.*


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## sailfish11 (Sep 15, 2007)

Hmmm, I would have thought it would be cheaper than that. My Prius gets 50 mpg. At $2 gal, that's only .04/mile. I realize an ICE has other costs associated with it (oil changes, impact on environment), and that gas prices can go up, but still, I'm surprised the EV isn't cheaper at the 'pump'.


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## dtbaker (Jan 5, 2008)

atzi said:


> How much energy or watts, based on onboard meters, odometer, voltmeter and ampmeter are you averaging at different speeds at level grades. Include your vehicle type and weight.​


my car 'zappy' has been on the road for a week now. It is a 1997 suzuki swift with 12x8v (96v) FLA batteries and a 8" adc motor. I have not gotten the finished car on a scale yet, but its probably right around 2400#.

I kept track of the cumulative charge it took for the first 100 miles or so. It came out to .41 kWhr/mile. I currently have old over-width (bald) tires that came with the car, which are probably fairly high rolling resistance. This is during the break-in period for brushes, batteries, and I do not have a hood or bumper on yet for the aerodynamics are bad. I expect the efficiency to improve to maybe .3 once I break in, have hood, belly pan, and new tires. The driving was typical suburban rolling hill, not trying to take it particularly easy average...

I just installed metering, so I did not even know how many amps I was pulling usually. Now, I find it hard to give a very good estimate of average amps at any particular speed because we really don't have ANY roads that are very flat for long enough to come to a steady state. I know that 'easy' acceleration from a stop is about 100amps, and more usually I pull it up to 200 to get going. In traffic I have been pushing 300 for short periods to get up to speed.

as far as cost, I am in the unusual position of getting PAID by local utility co to generate my grid-tied electricity. Our utility rate is .09, and I get a gross payment of .13/kWhr offsetting that. I sizd my PV to cover the house AND some extra for the car, so it depends on how you amortize the cost as to what my true operating cost is.....


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## atzi (Jun 26, 2008)

dtbaker said:


> my car 'zappy' has been on the road for a week now. It is a 1997 suzuki swift with 12x8v (96v) FLA batteries and a 8" adc motor. I have not gotten the finished car on a scale yet, but its probably right around 2400#.
> 
> I kept track of the cumulative charge it took for the first 100 miles or so. It came out to .41 kWhr/mile.
> I just installed metering, .... we really don't have ANY roads that are very flat for long enough to come to a steady state. .........


Thanks for the info. I'm interested to see what are others efficiency, so I know where I stand and can improve upon. I like the metering part because of so many variables including the gassing of battery pack at the end of the charge. 
You are so right about no flat land, and in the real world you have to stay up with traffic. 
I bet once your batteries are broken in and the weather warms up you will be as low as 300 watts a mile. 2400 pounds is very light, it is a great advantage thats all your pushing. My Saturn weighs in at 3400.
see: http://www.saturn.lynnautorepair.com/node/332 about the metering setup.


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## dtbaker (Jan 5, 2008)

atzi said:


> I bet once your batteries are broken in and the weather warms up you will be as low as 300 watts a mile.


I hope so.... 

I started a new measurement period to see if batteries/brush breakin really matters. Only 16 miles into this second session, the average has dropped to .39 kWhr/mile... so it may be changing! Interesting. I have new wheels and tires coming probably next week, which I hope will make a bigger difference.

I plan to put up a 'performance update blog' on my homepage at www.envirokarma.org and update the kWhr/mile periodically as I make significant changes (like different wheels/tires, hood, block grill, etc) You might wanna go sign up with the 'change detection' button to watch my page for updates.

I did attempt to see what a steady state speed is at 100 amp output (for 96v system), and it seems to be right around 40mph on the flattest section of road I can find (with too-wide tires and no hood still) which is near the top of my second gear.... I don't have a tach, but could work out the rpm manually. I have marked 45mph as my top shift point with the motor at 5000rpm.

right now, I have GOT to catch up on the site and post the final days of work and pictures to the point I have it now.... Then figure out how to work my new digital camcorder and get something up on utube.


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## dtbaker (Jan 5, 2008)

one more little update on measurements....

I am measuring the kWhr that I put in using the running total showing on a kill-a-watt meter at the plug... which COUNTS whatever I am losing from the charger, etc. So while it may take less to actually operate the car (measured a the motor), using the kW meter at the plug does shw what it actually consumes in total.

I am not making any special pains to be super conservative... just trying to keep up with traffic. I am not a lead foot, but sometimes in traffic you HAVE to put the pedal to the metal just to keep up. 

I will continue to report any changes in efficiency as I add hood, bellypan, etc on my site at www.envirokarma.org


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