Weatherman
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Re: Battery Aging Model

Mon Oct 15, 2012 8:05 pm

I'm not sure that's the appropriate direction to take, since it makes the heat-induced degradation rate in Honolulu very close to the rate in Phoenix.

I'd be more inclined to steepen the heat-induced curve by doubling every 5 or 8 degrees but assume "normal" is a lower percentage of the total loss per year. The cycling losses would, then, represent a larger percentage of the total loss and the sum total loss rate would be more linear.
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abasile
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Re: Battery Aging Model

Mon Oct 15, 2012 8:08 pm

Stoaty wrote:Based on the Prius study of solar loading, parking in the sun full-time can cause a 10% (low solar load) to 24% (high solar load like Phoenix) increase in battery aging compared to avoiding parking in the sun completely. The solar loading depends on geographic location. Of course, the Leaf may be designed in such a way that the solar loading factor would be less.
I would expect the LEAF's battery temperature to be somewhat less dependent on solar loading than the Prius battery. The Prius vents its battery pack via the passenger cabin, which in full sun can be far hotter than the outside ambient temperature. The LEAF's battery, under the car, would more closely track the temperature of the pavement below, which might not be too much higher than ambient if it is parked in the same spot all day, particularly with other cars around.
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Weatherman
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Re: Battery Aging Model

Mon Oct 15, 2012 8:23 pm

I would agree that solar loading doesn't seem to be a big issue with the LEAF battery (something Nissan got right in the design?). Over the past summer, even with the heatshield in the windshield, cabin temps in my car got up around 110F and held that high most of the day. But, with outside air temps in the lower to mid 90s, I never saw seven bars on my battery's temperature gauge.
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Stoaty
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Re: Battery Aging Model

Mon Oct 15, 2012 8:24 pm

Weatherman wrote:I'm not sure that's the appropriate direction to take, since it makes the heat-induced degradation rate in Honolulu very close to the rate in Phoenix.

I'd be more inclined to steepen the heat-induced curve by doubling every 5 or 8 degrees but assume "normal" is a lower percentage of the total loss per year. The cycling losses would, then, represent a larger percentage of the total loss and the sum total loss rate would be more linear.
I agree that it isn't really the right direction, but that is what I found. I don't think steepening the curve will help, because I couldn't make the numbers work even with the original factors--I had to make the battery aging factors somewhat lower in order to get the numbers to work properly. The ratios weren't too far off, since normalizing on "Normal" produced:

Phoenix - 1.5
Normal - 1.0
Boston - 0.83

That number is really kind of a side alley, since the model currently works quite well with numbers that are at least fairly reasonable.

As I said before, if anyone wants to play with the spreadsheet, just PM me. I have an almost perfect fit to Nissan's data (including TickTock). I am going to try adding a few other factors I think may be important (solar loading, percent of time spent at high SOC, perhaps DOD), then need data to calibrate it (and test it). Unfortunately, I no longer trust the Gid meter as a proxy for usable range. Only a range test will suffice, although going to VLBW and then extrapolating would certainly be acceptable. My next task is to set up the spreadsheet so I can just plug in some number and the predicted range will pop out for comparison with the measured range.
Last edited by Stoaty on Tue Oct 16, 2012 6:01 pm, edited 1 time in total.
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ENIAC
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Re: Battery Aging Model

Mon Oct 15, 2012 8:34 pm

I found this study which looked at parking lot temperatures in Phoenix at various times of the year. They measured temperatures in June of 149 deg F (figure 2a). BTW, measurements are taken at 8 feet above the surface.
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Re: Battery Aging Model

Mon Oct 15, 2012 10:02 pm

Weatherman wrote:I'm not sure that's the appropriate direction to take, since it makes the heat-induced degradation rate in Honolulu very close to the rate in Phoenix.
Hopefully, we will learn more about the state of Hawaii Leafs soon. It's been surprisingly quiet on the islands. The low average annual mileage could be an ameliorating factor:
Hawai'i drivers ranked near the bottom in per capita miles driven, averaging 7,907 miles per person per year, according to data from the Bureau of Transportation Statistics.
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abasile wrote:I would expect the LEAF's battery temperature to be somewhat less dependent on solar loading than the Prius battery. The Prius vents its battery pack via the passenger cabin, which in full sun can be far hotter than the outside ambient temperature. The LEAF's battery, under the car, would more closely track the temperature of the pavement below, which might not be too much higher than ambient if it is parked in the same spot all day, particularly with other cars around.
I left my Leaf out in the sun on a hot day once. The sheet metal on the roof was at about 130 F. The battery container was a few degrees warmer compared to what I would see when the Leaf was parked in a shade. Additionally, the battery was about two degrees warmer on side facing the sun.

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ksnogas2112
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Re: Battery Aging Model

Tue Oct 16, 2012 7:39 am

Weatherman wrote:I would agree that solar loading doesn't seem to be a big issue with the LEAF battery (something Nissan got right in the design?). Over the past summer, even with the heatshield in the windshield, cabin temps in my car got up around 110F and held that high most of the day. But, with outside air temps in the lower to mid 90s, I never saw seven bars on my battery's temperature gauge.

However, the real difference between a high 6 TB and a low 7 TB is slight. I found that with the windows up at 100*+ air temp this summer the battery would hit 7 bars. This even happened when I parked in an abandoned bank drive thru that was in the shade all day. With the windows down so the cabin was the same temp as the air, the battery would stay at 6 TB even when the outside air temp was 110* with a 115*F heat index (i know that doesn't apply to the battery only the poor miserable humans).
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DaveinOlyWA
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Re: Battery Aging Model

Tue Oct 16, 2012 7:51 am

Stoaty wrote:
Weatherman wrote:I'm not sure that's the appropriate direction to take, since it makes the heat-induced degradation rate in Honolulu very close to the rate in Phoenix.

I'd be more inclined to steepen the heat-induced curve by doubling every 5 or 8 degrees but assume "normal" is a lower percentage of the total loss per year. The cycling losses would, then, represent a larger percentage of the total loss and the sum total loss rate would be more linear.
I agree that it isn't really the right direction, but that is what I found. I don't think steepening the curve will help, because I couldn't make the numbers work even with the original factors--I had to make the battery aging factors somewhat lower in order to get the numbers to work properly. The ratios weren't too far off, since normalizing on "Normal" produced:

Phoenix - 1.5
Normal - 1.0
Boston - 0.83

That number is really kind of a side alley, since the model currently works quite well with numbers that are at least fairly reasonable.

As I said before, if anyone wants to play with the spreadsheet, just PM me. I have an almost perfect fit to Nissan's data (including TickTock). I am going to try adding a few other factors I think may be important (solar loading, percent of time spent at high SOC, perhaps DOD), then need data to calibrate it (and test it). Unfortunately, I no longer trust the Gid meter as a proxy for usable range. Only a range test will suffice, although going to VLBW and then extrapolating would certainly be acceptable. My next task is to set up the spreadsheet so I can just plug in some number and the predicted range will pop out for comparison with the measured range.someones measured range.
i think temp loading should be formulated as a delta from a "normalized" point creating an exponential degradation formula from that point.

also something to consider is that in situations where higher rates of degradation are present, i think we need to also consider that it might affect cycling degradation as well, changing it from a near linear loss to one where the loss also accelerates based on mileage driven AND heat. iow; a double heat penalty.

this might account for small changes in temperature from FL and HA having less degradation than AZ. we all know that AZ may average out to only be slightly warmer than HA, but in reality its much more uncomfortable which is key since batteries react to heat very much the same way we do. they get sluggish when cold, they overheat (and may die) in extreme heat just like we do
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JPWhite
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Re: Battery Aging Model

Tue Oct 16, 2012 5:35 pm

ENIAC wrote: They measured temperatures in June of 149 deg F (figure 2a).
That's certainly enough to cook a battery. The body repair manual states that 140F is the max temp in a paint booth for any period of time. 149 is enough to do damage for sure.
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Stoaty
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Re: Battery Aging Model

Wed Oct 17, 2012 7:13 am

Update on progress on Battery Aging Model:

--cleaned up spreadsheets, added some color to make it clearer what goes together
--merged spreadsheets into one "Battery Aging Model" by moving "Leaf Climate Data" to its own tab in the Battery Aging Model. I don't want to deal with 2 spreadsheets, plus will need to access Battery Aging Factors
--scaled Battery Aging Factors to correspond with empirically derived aging factors from the model; this will allow predictions for any of the cities for which we have calculated aging factors

More work planned as time allows.

Currently, the spreadsheet is only available in .ods (Opendocument) format. Spreadsheets were created in OpenOffice (a free download). For some reason, one of the pre-merged spreadsheets would not save in Excel Format (says there are too many rows???). If someone wants to take a look at the spreadsheet and try to figure out what the problem is, you are welcome. Perhaps I formatted an entire column so the Excel format thinks there are a lot more rows than there are (there are about 135)?
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