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Carwings miles/kwh figures higher than Leaf's by 10% to 35%

Posted: Sat Mar 26, 2011 8:06 am
by evnow
Opening a new thread here to track this problem.

Carwings shows efficiency that is different and higher than what Leaf shows. I've been tracking this for a number of days now. Every day I note down Leaf's efficiency i.e. miles/kwh figure and reset it.

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As you can see the carwings can be higher anywhere from 10% to 35%.

This is the response Nissan sent to Andy on this problem ...
Discrepancy between carwings energy economy, and the miles/kWh indicated in the car

I apologize for the inconvenience. The shown average energy economy is different on the vehicle and website because the vehicle calculates with power-loss in motor. However, the website excludes power-loss in motor. This is actually a known issue that we are working to correct. Unfortunately, it will take some time for this to be accomplished. If you have any additional questions, please do not hesitate to contact us.

Re: Carwings miles/kwh figures higher than Leaf's by 10% to 35%

Posted: Sat Mar 26, 2011 9:47 am
by DaveinOlyWA
http://www.mynissanleaf.com/viewtopic.p ... 1&start=70

check out my math. this only lends to the confusion i am afraid

Re: Carwings miles/kwh figures higher than Leaf's by 10% to 35%

Posted: Sat Mar 26, 2011 10:21 am
by evnow
Dave, too convoluted. If you do the calculation using numbers carwings shows - their m/kwh = miles / (motor+accessories-regen).

Can't remove regen - that needs to be part of the equation. May be if we reduce regen by a large % we can get close to the Leaf figure ?

Re: Carwings miles/kwh figures higher than Leaf's by 10% to 35%

Posted: Sat Mar 26, 2011 10:35 am
by TomT
I'm typically seeing a difference of about 40 percent between the car and Carwings...

Re: Carwings miles/kwh figures higher than Leaf's by 10% to 35%

Posted: Sat Mar 26, 2011 10:40 am
by MikeD
This has probably already been addressed, but has anyone checked the odometer mileage readings against road mile markers, i.e. how accurate is the odometer? Also is the method for measuring distance traveled clearly documented somewhere, i.e. does it depend on the average radius of a drive tire? (Someone may be able to link me to a previous post about this).

Re: Carwings miles/kwh figures higher than Leaf's by 10% to 35%

Posted: Sat Mar 26, 2011 10:48 am
by DaveinOlyWA
Odometer checked and is accurate to within a tenth over 20 miles.

Now power used by motor does not differentiate from where it comes from so regen must be removed to find efficiency of power used as related to power from the wall

Re: Carwings miles/kwh figures higher than Leaf's by 10% to 35%

Posted: Sat Mar 26, 2011 11:02 am
by evnow
I did some calculations, here is my best fit formula. I get to within 5% of Leaf m/kwh.

Code: Select all

Leaf m/kwh ~= car wings miles / (motor_kwh + accessories_kwh - 0.41*regen_kwh)
This also fits with what Nissan said - " ... website excludes power-loss in motor".

So, this is my guess. The regen figure shown by carwings is the theoretical max regen possible. The actual regen could be about half of that max (once we take into account the losses in the generator, into battery, out of battery etc). So, using 41% above to get the actual useful regen captured, gives us a figure close to that of Leaf.

update : We can also do this by adding a loss to the Motor energy consumption reported i.e. increase the consumption by some %. I get the best fit by using 21% increase (i.e. multiplying by 1.21).

Code: Select all

Leaf m/kwh ~= car wings miles / (motor_kwh * 1.21 + accessories_kwh - regen_kwh)
update : Changed above to 41% instead of 44%, which gives the best fit using squares of difference.

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Re: Carwings miles/kwh figures higher than Leaf's by 10% to 35%

Posted: Sat Mar 26, 2011 4:03 pm
by garygid
Yes, CARWINGS appears to handle Regen incorrectly in its calculation of miles per kWh. Regen delivered to the battery is substantially higher than the amount of Regen energy that is recovered from the battery.

Also, they appear to be calculating the kWh used by the motor (and accessories), NOT the kWh supplied TO the LEAF to charge it.

Re: Carwings miles/kwh figures higher than Leaf's by 10% to 35%

Posted: Sat Mar 26, 2011 5:05 pm
by DaveinOlyWA
Carwings seems to handle EVERYTHING "differently".

i have a question and i guess it would be easy enough to check, but if i were to accept the "i agree" screen say a mile after i took off, would carwings not record that mile?

would this explain the discrepancies in the mileage calculations?

Re: Carwings miles/kwh figures higher than Leaf's by 10% to 35%

Posted: Sat Mar 26, 2011 5:57 pm
by evnow
DaveinOlyWA wrote:i have a question and i guess it would be easy enough to check, but if i were to accept the "i agree" screen say a mile after i took off, would carwings not record that mile?

would this explain the discrepancies in the mileage calculations?
Interesting - not tried that. I've not even read the message - I thought it was about uploading data and not recording it.