Stoaty
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Only 18 KWh Usable Energy for MY Leaf--Retest Shows 20.3 KWh

Thu Oct 06, 2011 8:14 pm

I have been noticing for a while that my Leaf doesn't seem to be doing quite as well as I expected in terms of range. Nothing earth shattering, but noticeable--even though I drive extremely conservatively. Now that I have my SOC meter (thanks, Gary) I have some figures that may back this feeling up. Assumptions (which may not be correct):

--a gid is a fixed amount of energy for a particular Leaf battery at a particular stage of its life (i.e., gid may represent a lower amount of energy as battery capacity declines)
--281 gids represent the entire usable energy for the Leaf
--the Leaf battery is charged at a rate of 3.3 KW when charging at 240 volts and 16 amps

Data:

Charged to 80%
Drove 46 miles, using 123 gids (224 gids minus 101 gids)
Charged back to 80% (224 gids again) in 2 hours, 25 minutes (=2.417 hours)
Trip Efficiency (dash) = 5.8 miles/KWh

Calculations:

Total KWh added to battery = 3.3 * 2.417 = 7.975 KWh
1 gid (for my battery) = 7.975/123 = .0648 KWh = 64.8 wh
Total usable battery capacity = 281 * .0648 = 18.2 KWh

As a check on the KWh used for the drive = 46 miles/5.8 miles per KWh = 7.931 KWh (almost exactly the same)

Approaching the problem from the miles driven angle:

Total available miles = 46 * (281/123) = 105.1 miles

Total usable battery capacity = 105.1 miles/5.8 miles per KWh = 18.12 KWh

Assuming these calculations are correct, my battery usable battery capacity = 18.2/21 = 86.8% of expected 21 KWh

Note: in another thread, surfingslovak guessed that a gid is 75 Wh, which would give a usable battery capacity of 281*75 = 21.075 KWh

Comments, pointing out calculation errors or invalid assumptions, etc. welcome. For those with a SOC meter, how many Wh is a gid on your Leaf using same method?

Addendum 10/8/11:

OK, here is a follow-up with more data from today:

Charged to 100% (273 gids) this AM
Drove 49 miles to Claremont
At destination read 130 gids (143 gids used for trip)
Efficiency on center console - 4.7 miles/KWh; efficiency on dash estimated to be 4.6 miles/Kwh (usually reads 0.1 lower on dash)

Calculations:

Total estimated range = 49*273/143 = 93.5 miles
Usable battery = 93.5/(4.7-.1) = 20.3 KWh
Capacity = 20.3/21 = 96.8% of expected

If we assume that the pack showed only 273 gids at 100% charge because the cells were slightly out of balance, the calculations change to:

Total estimated range = 49*281/143 = 96.3 miles
Usable battery = 96.3(4.7-.1) = 20.93 KWh
Capacity = 20.93/21 = 99.7% of expected

Either way, the results are very close to expected. Now, why the discrepancy? I believe that the KWh needed to recharge in my first test may have been low due to the Leaf perhaps charging at a higher rate for the middle of the battery, as suggested by a poster above. The calculation in my first test based on miles driven, gids used, and efficiency had an assumption that I forgot to mention, and one which was probably the culprit. I didn't actually measure the 5.8 miles/KWh in the first test, because every time I drove my work commute and measured (which was many, many times), the result always came out 5.8 (or occasionally 5.9).

Why would the efficiency change? For most of the summer, the temperature was running about 70 in my parking garage and 90-95 during the day at work (and my car was parked in the hot sun). The day I did test #1, I now realize that the temperature had suddenly changed to 55 in my condo garage, and about 60 degrees while I was at work. It seems that the efficiency may be less when the battery is colder. I noticed the difference today when I drove to Claremont also (exact same speed, etc.): efficiency was 4.7 miles/KWh, while 1-2 weeks ago it was 5.2 miles/KWh. Again, the weather today was running 55-60 degrees, a lot cooler than the last time I drove to Claremont.

Of course, there could be other reasons; perhaps I am not driving the same now (but pretty sure I am). I think the reason I have been noticing a decrease in range is due to a decrease in efficiency, not a decrease in pack capacity. I will post this as an addendum in the first post of the thread and change the title.
Last edited by Stoaty on Sat Oct 08, 2011 4:42 pm, edited 1 time in total.
2011 Leaf with 62,000 miles given to Nephew
2013 Tesla Model S85 with 251 miles rated range at full charge
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TickTock
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Re: Only 18 KWh Usable Energy for MY Leaf?

Thu Oct 06, 2011 10:10 pm

Stoaty wrote:Data:

Charged to 80%
Drove 46 miles, using 123 gids (224 gids minus 101 gids)
Charged back to 80% (224 gids again) in 2 hours, 25 minutes (=2.417 hours)
Trip Efficiency (dash) = 5.8 miles/KWh

Calculations:

Total KWh added to battery = 3.3 * 2.417 = 7.975 KWh
1 gid (for my battery) = 7.975/123 = .0648 KWh = 64.8 wh
Total usable battery capacity = 281 * .0648 = 18.2 KWh

As a check on the KWh used for the drive = 46 miles/5.8 miles per KWh = 7.931 KWh (almost exactly the same)

Approaching the problem from the miles driven angle:

Total available miles = 46 * (281/123) = 105.1 miles

Total usable battery capacity = 105.1 miles/5.8 miles per KWh = 18.12 KWh


I think I have my doubts if gids are as absolute as we think The highest I've recorded on a 100% charge is 239. If I use that as 100%, then I get only 16.8kWh capacity.

My Data:
Charged to 80% (200 gids)
Drove 50.4 miles, using 157 gids (200 gids minus 43 gids)
Charged back to 80% drawing 12.9 kWh (from installed power logger)
Trip Efficiency (dash) = 4.6 miles/KWh

Calculations:

Total KWh from the wall = 12.9 KWh
KWh used for the drive = 50.4 miles/4.6 miles per KWh = 11.0 KWh --> 85% charging efficiency
1 gid (for my battery) = 11/157 = 70.0wh
Total usable battery capacity = 239 * .070 = 16.7 KWh

Approaching the problem from the miles driven angle:

Total available miles = 50.4 * (239/156) = 77.2 miles

Total usable battery capacity = 77.2 miles/4.6 miles per KWh = 16.8 KWh


If I assume 281 as 100% then my battery capacity appears to be a little higher (19.7 kWh) but I don't think 281 is the right number for me.

SanDust
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Re: Only 18 KWh Usable Energy for MY Leaf?

Thu Oct 06, 2011 10:16 pm

Not completely sure I follow how you're calculating this, but the 3.3 kW is what is delivered to the onboard charger not to the battery. It would also be better if, like TickTock, you were measuring rather than calculating from the wall.

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garygid
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Re: Only 18 KWh Usable Energy for MY Leaf?

Fri Oct 07, 2011 12:34 am

TickTock,
So far, you are the only one reporting this "250-based" SOC
(roughly 198 gids, or 70% "SOC", for an 80% charge).

198 = 128 + 64 + 4 + 2 (no 32 bit)
281 - 249 = 32
198 + 32 = 230 (if the 32 bit was on)
230/2.81 = 81.8%

So, maybe the 0010000 (32) bit is stuck OFF in your car or Meter ...
BUT the log of "gids" that you sent did not have "jumps" in it,
so it appears like the data is just low coming out of your car.

Please try your meter on another LEAF.

Thanks, Perplexed :D
See SOC/GID-Meter and CAN-Do Info
2011 LEAF, sold in 2015
2010 Prius, 2014 silver Tesla S
Nissan EVSE, mod to 240/120v 16A
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LEAFfan
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Re: Only 18 KWh Usable Energy for MY Leaf?

Fri Oct 07, 2011 12:46 am

If the raw numbers vary that much, I would think the SOC% would be more important. My SG has never reached 80% (76.8) yet after an 80% charge. I'm going to see if the QC will take it to 80% tomorrow.
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planet4ever
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Re: Only 18 KWh Usable Energy for MY Leaf?

Fri Oct 07, 2011 1:46 am

SanDust wrote:Not completely sure I follow how you're calculating this, but the 3.3 kW is what is delivered to the onboard charger not to the battery.

16A * 240v = 3.84 kW, not 3.3 kW. It is my belief the 3.3 kW is what the charger is capable of delivering to the battery, not what it can accept from the wall.

Ray
End of April 2013: Traded my 2011 SL for a 2013 S with charge pkg.

Stoaty
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Re: Only 18 KWh Usable Energy for MY Leaf?

Fri Oct 07, 2011 7:01 am

planet4ever wrote:16A * 240v = 3.84 kW, not 3.3 kW. It is my belief the 3.3 kW is what the charger is capable of delivering to the battery, not what it can accept from the wall.

Yes, and 3.3/3.84 = 86% which is very close to the efficiency measured previously for 240 volt charging.
2011 Leaf with 62,000 miles given to Nephew
2013 Tesla Model S85 with 251 miles rated range at full charge
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abasile
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Re: Only 18 KWh Usable Energy for MY Leaf?

Fri Oct 07, 2011 7:23 am

It seems to me that 18 or 19 kWh could be the amount of usable energy after factoring in discharging losses. Assuming that 24 kWh is the "ultimate" capacity and that the "usable" capacity is closer to 20 or 21 kWh, a discharging efficiency in the ballpark of 85 - 95% could bring us down to 18 or 19 kWh actually available to the motor and accessories.

In other words, it doesn't seem likely that your average efficiency of 5.8 miles/kWh accounts for charging and discharging losses. I believe it is merely an indication of how efficiently the available energy is being used. Of course, with more efficient driving and lower discharge rates, I would expect the discharging efficiency to be higher.
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edatoakrun
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Re: Only 18 KWh Usable Energy for MY Leaf?

Fri Oct 07, 2011 8:29 am

abasile wrote:It seems to me that 18 or 19 kWh could be the amount of usable energy after factoring in discharging losses. Assuming that 24 kWh is the "ultimate" capacity and that the "usable" capacity is closer to 20 or 21 kWh, a discharging efficiency in the ballpark of 85 - 95% could bring us down to 18 or 19 kWh actually available to the motor and accessories.

In other words, it doesn't seem likely that your average efficiency of 5.8 miles/kWh accounts for charging and discharging losses. I believe it is merely an indication of how efficiently the available energy is being used. Of course, with more efficient driving and lower discharge rates, I would expect the discharging efficiency to be higher.


Updated Carwings energy usage reports seems to indicate approximately 20.4 KWh capacity was correct as a function of dash (or perhaps nav screen) m/kWh, at least for my car on one day last month, at about 85 F degrees, as I posted below. Of course, that does not mean you are not picking up numbers from somewhere before the CW "usable" or "to the wheels" calculation, as you suggest, and I agree it’s unlikely the dash is reflecting Charging loses.

I appreciate you folks’ efforts, and have been following your progress with interest, but so far I have actually become a bit more tolerant of Nissan's decision to omit a SOC as a percentage of what is a (significantly?) variable battery capacity. What I'd like is a gauge showing total usable kWH, available to the wheels.

Has any other EV manufacturer done this?

On 9/7 I drove the same route from my home to Burney Falls State Park again at slightly higher speed with more (still not much) AC use. When I reached my driveway, at 87 miles, I still had (less than) one bar, so I drove until I got the "very low battery" warning and simultaneously lost the last bar, at 91.5 miles. I got home with 93.4 miles, and between 5,500 and 6,000 ft. of ascent and descent, at an average speed of about 40 mph (those last 6.4 miles were up and down a hill at low speed). Since the last 1.9 miles after the "very low battery” warning were at about 20 mph and required about 150 ft. net descent with regen, I was probably still very close to the VLBW point capacity, when I parked.

According to CW, on this drive I used 18.7 kWh to drive 91.1 miles at average energy economy of 4.9 m/kWh.
I rechecked 2 other recent drives of 85-105 miles and each time CW has erred, under-reporting distance traveled, as compared with both my odometer and Google Maps, by 2.5%, +/- 0.1%.

Has anyone else-before or after the NTB11-041 update-seen this same odometer/CW mileage disparity?

If so, do you suppose this may reflect the similar discrepancy between the dash and screen numbers, as widely reported?
My car shows 4.3 m/kWh on the dash and 4.4 on the screen, as average since delivery.

Extrapolating from the chart, it appears CW may be saying the 1.7 kWh (8.5% from the chart, of 20.4 total kWh-anyone have a better number?) I had left at or near VLBW implies total available battery capacity of about 20.4 kWh. So, from the limited info I can gather, looks to me that Carwings may now be accurate as to energy use.

Posts from others who can take the charge lower could verify this...

Comments from the SOC meter crowd, and also those who have metered L2 charging and can determine charge efficiency, as a % from Carwings reports, would also be greatly appreciated...

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Stoaty
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Re: Only 18 KWh Usable Energy for MY Leaf?

Fri Oct 07, 2011 9:04 am

abasile wrote:It seems to me that 18 or 19 kWh could be the amount of usable energy after factoring in discharging losses. Assuming that 24 kWh is the "ultimate" capacity and that the "usable" capacity is closer to 20 or 21 kWh, a discharging efficiency in the ballpark of 85 - 95% could bring us down to 18 or 19 kWh actually available to the motor and accessories.

Interesting thought, but that doesn't square with the reports that the best way to get the actual mileage available to you is to multiply the miles per KWh from the dash by 21 (or 20.4). Although not tested by a complete discharge of the battery, my results suggest that--at least for my car--I should be multiplying the miles per KWh from the dash by 18.2 to get the total miles available on a full charge. Either the rule of thumb needs to be changed, or if the original rule holds true for others then my capacity is lower as indicated by my calculations.
2011 Leaf with 62,000 miles given to Nephew
2013 Tesla Model S85 with 251 miles rated range at full charge
Leaf Spy Manual
Battery Aging Model Spreadsheet

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