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TickTock
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1 gid *mostly* equals 80Wh

Sat Aug 11, 2012 3:48 pm

My recent observation that my car came back with more gids on an 80% and 100% charge while still drawing the same power from the wall led me to go back and check more logs on the value of 1 gid. Using three turtle to 100% logs (so non linearity won't be considered a factor), I computed the total energy into the battery as the integral of V*I*delta_t and compared to the power from the wall for the same charge. Then I divided both by the number of gids that charge added:

11/21/2011:
input:
gid start: 6
gid stop: 256
wall start(kWh): 508.93
wall stop(kWh): 531.57
battery start(kWh): 0
battery stop(kWh): 20.02
computed:
charger efficiency: 88.4%
wh/gid into battery: 80.0
wh/gid from wall: 90.6

7/6/2012:
input:
gid start: 6
gid stop: 217
wall start(kWh): 2857.34
wall stop(kWh): 2878.11
battery start(kWh): 0
battery stop(kWh): 18.50
computed:
charger efficiency: 89.1%
wh/gid into battery: 87.7
wh/gid from wall: 98.4

8/11/2012:
input:
gid start: 5
gid stop: 232
wall start(kWh): 2979.18
wall stop(kWh): 3000.01
battery start(kWh): 0
battery stop(kWh): 18.82
computed:
charger efficiency: 90.4%
wh/gid into battery: 82.3
wh/gid from wall: 91.8

I think since the efficiency (power_into_battery/power_from_wall) is pretty consistent, the power_into_battery computation should be valid --> although 80Wh may be the nominal target for 1 gid, it can be off by as much as 10%. Just something to keep in mind if you are counting gids and cutting your range close. Maybe my car just got out of cal and they recalibrated it for me when it was [Edit]at the Nissan Maricopa testing facility[/Edit] (between the 7/7 and 8/11 measurements), but I am going to be more cautious using a gid as an accurate unit moving forward.
Last edited by TickTock on Tue Jul 23, 2013 9:42 am, edited 1 time in total.

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Stanton
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Re: 1 gid *mostly* equals 80Wh

Sat Aug 11, 2012 5:03 pm

You keep excellent (historical) data. This is very interesting, but I'm beginning to wonder if/when we'll be able to get an "absolute" capacity reading on any given battery pack.
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smkettner
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Re: 1 gid *mostly* equals 80Wh

Sat Aug 11, 2012 5:28 pm

I don't think battery capacity is as easy as measuring a gallon of gasoline. More like trying to measure a rubber band.
1 bar lost at 21,451 miles, 16 months.
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RegGuheert
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Re: 1 gid *mostly* equals 80Wh

Sun Aug 12, 2012 6:22 am

Stanton wrote:You keep excellent (historical) data.
+1 ...and you publish it! Thanks, TickTock!

Just a few thoughts on this new data:

- It seems like the reports back from Nissan based on the Casa Grande testing are on the level. Hopefully we will hear more details from them soon.
- Based upon TickTock's measurements of energy accepted by the battery, it appears his battery has lost about 6% capacity in 9 months. This is 6% of the capacity 9 months ago, not original capacity. However, these two measurements are with the battery at different temperatures, so the number may be off (since it's possible the battery has different capacity at different temperatures). It would be interesting to have these measurements again in November.
- I wonder if the calibration had somehow degraded or if they have merely recalibrated at a different temperature point. I would suspect the latter, since I would think temperature compensation would handle temperature variations fairly well. So I'm wondering what may have moved off cal? I wouldn't expect voltage measurements to move much over time. Do the Hall-effect sensors degrade over time?
- The car will have to use something as ITS absolute energy reference, and I will assume that is GIDs. That implies that not only did the car think it had less energy available but that driving efficiency would be higher. Energy consumed reports by the car should also have been low.

Hopefully Nissan can use what they have learned to improve the accuracy of the instrumentation in the LEAF.
RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
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jpa2825
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Re: 1 gid *mostly* equals 80Wh

Sun Aug 12, 2012 8:12 am

@TickTock -what is your method of charging? L2 I presume with that efficiency. I have heard tale of expecting 75% efficiency from wall to battery in other threads.
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TonyWilliams
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Re: 1 gid *mostly* equals 80Wh

Sun Aug 12, 2012 8:12 am

RegGuheert wrote: (since it's possible the battery has different capacity at different temperatures). It would be interesting to have these measurements again in November..


Waiting until November won't provide accurate data either, unless you think degradation STOPS, and will wait until November to then measure the battery at a lower temp. The only way to make that measurement is now (and attempt to prove the temp compensation theory), by cooling the battery.

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TickTock
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Re: 1 gid *mostly* equals 80Wh

Sun Aug 12, 2012 8:22 am

jpa2825 wrote:@TickTock -what is your method of charging? L2 I presume with that efficiency. I have heard tale of expecting 75% efficiency from wall to battery in other threads.

Yes. L2 with an AV EVSE and an EKM-25IDS power meter.

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TickTock
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Re: 1 gid *mostly* equals 80Wh

Sun Aug 12, 2012 8:25 am

RegGuheert wrote:
Stanton wrote:You keep excellent (historical) data.
+1 ...and you publish it! Thanks, TickTock!

Just a few thoughts on this new data:

- It seems like the reports back from Nissan based on the Casa Grande testing are on the level. Hopefully we will hear more details from them soon.
- Based upon TickTock's measurements of energy accepted by the battery, it appears his battery has lost about 6% capacity in 9 months. This is 6% of the capacity 9 months ago, not original capacity. However, these two measurements are with the battery at different temperatures, so the number may be off (since it's possible the battery has different capacity at different temperatures). It would be interesting to have these measurements again in November.
- I wonder if the calibration had somehow degraded or if they have merely recalibrated at a different temperature point. I would suspect the latter, since I would think temperature compensation would handle temperature variations fairly well. So I'm wondering what may have moved off cal? I wouldn't expect voltage measurements to move much over time. Do the Hall-effect sensors degrade over time?
- The car will have to use something as ITS absolute energy reference, and I will assume that is GIDs. That implies that not only did the car think it had less energy available but that driving efficiency would be higher. Energy consumed reports by the car should also have been low.

Hopefully Nissan can use what they have learned to improve the accuracy of the instrumentation in the LEAF.


Thanks for all the encouragement. I do have a lot more data on incomplete charges (n-80%) just not many from turtle to 100 since I do try to avoid both of those levels. If I can get my boys off Minecraft for an hour or so I will plot wh/gid over time to see if it tracked temperature up until the service.

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Stanton
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Re: 1 gid *mostly* equals 80Wh

Sun Aug 12, 2012 9:58 am

TickTock wrote:Thanks for all the encouragement. I do have a lot more data on incomplete charges (n-80%) just not many from turtle to 100 since I do try to avoid both of those levels. If I can get my boys off Minecraft for an hour or so I will plot wh/gid over time to see if it tracked temperature up until the service.


I have that SAME problem with one of my sons :lol: Oh well, guess there's worse things they could be doing :roll:
I also wanted to comment that I appreciate the fact you post excellent info on a difficult subject without all the venom I see in some other posts/folks regarding the heat+battery issue.
2011 Blue Ocean SV w/floor mats & window tint
12v LiFePO4 battery & FIAMM 74100 horns
Wet Okole seat covers (front)
Tor's low-power heater mod
2013 sun visor
3G modem upgrade
L2 EVSE Upgrade
Battery Pack replaced (Rev E) @51 months and 41k miles

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TickTock
Posts: 1701
Joined: Sat Jun 04, 2011 10:30 pm
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Location: Queen Creek, Arizona
Contact: Website

Re: 1 gid *mostly* equals 80Wh

Sun Aug 12, 2012 10:27 am

OK. I did see some temperature dependance on the gid unit. I added two more sets to my plot 0 to 100 and 0 to 80 wall energy. For these, I compute the wh/gid=delta_wall_power/delta_gids then multiply that by the final gid value to approximate the wall power required to go from zero to 80% or 100% charge. When I do this, the seasonality almost disappears and the loss over time is more gradual. Full disclosure: I did delete a few anomalous datapoints that were far off the trend. I am attributing those to days I ran the climate control to pre-heat/pre-cool the car and/or topped off away from home. I am missing a huge chunk of data for this computation during the winter (I got lazy and was only recording data in the morning so don't know what the starting gid value was).

Definitely much less alarming degradation than looking at gid count alone. I can now see why Nissan didn't want us looking at it.
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