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Re: Early Capacity Losses-Was(Lost a bar...down to 11)

Posted: Sun Aug 19, 2012 12:36 pm
by surfingslovak
edatoakrun wrote:And clearly, there is a correlation of capacity bar loss with both time and miles driven, whatever adjective you use to describe it.

If bar loss was not correlated to these factors, and an entirely random event, then the entire field of your graph would have equal distribution.
...

Both of these factors might be expected show far greater correlations in cooler climates. Even more so, if they are restated as time from delivery, and number of charge cycles. But in Phoenix, both of these individual factors are themselves probably reflecting (in varying amounts) a much "strong"(er) correlation, to exposure to high battery temperatures.
Good points, if you recall I evaluated a small but geographically dispersed sample three months ago. I used Gid counts, because none of these folks have lost any capacity bars at the time. While I realize that Gids do not equal permanent degradation, they do represent a capacity reading, and I hope that if nothing else they can be used as a proxy for capacity degradation. That said, the sample showed very clear correlation to average ambient at the place of residence (around 70%) and weak correlation to vehicle age and miles driven. This was suprising, since it was previosly believed that cycling losses, and by extension mileage, will play a pivotal role.

When I saw how much larger the dependence on ambient temperature was when compared to the other two factors, I rang my private alarm bell, and let a few people know about it. Unfortunately, they did not see or want to believe the significance of the data they were looking at. It was difficult to argue otherwise given the sample size and the type of data used (Gids).

I would not be at all surprised to see stronger correlation to mileage than my original sample implied, if you restricted yourself to a particular locale (hot or cold), just like what Stoaty's plot showed. This is my personal opinion, but I do not believe that what we see in Phoenix is in any way abnormal, we are just seeing it sooner due to elevated ambient temps. It seems to be accepted practice to cycle batteries in a temperature controlled chamber to accelerate aging and get test results sooner than it would take at normal room temperature.Image

Re: Early Capacity Losses-Was(Lost a bar...down to 11)

Posted: Sun Aug 19, 2012 2:07 pm
by Stoaty
I analyzed the Leafs in Texas that lost a capacity bar, but didn't find a correlation with monthly mileage and rate of capacity (correlation coefficient = 0.013). Perhaps this was due to there being too few Leafs in the sample with a few outliers, or maybe the climate varies enough between the various cities to allow for a meaningful comparison. Interestingly, the average rate of capacity loss was 1.2% per month, similar to the average 1.3% per month seen in the Phoenix metro area sample (latter not previously reported, I believe).

Data below:

Image

Graph below:

Image

Re: Early Capacity Losses-Was(Lost a bar...down to 11)

Posted: Sun Aug 19, 2012 6:35 pm
by Stoaty
Guidelines for purchase or lease added to Wiki section on battery capacity:

"Guidelines suggested by Weatherman on whether the Leaf is likely to experience temperature related accelerated battery capacity loss in your area:

If you almost always see five bars or less on the battery temperature gage, and it only gets up to six bars a handful of times each summer... Don't worry about it.
If you see five bars or less during the winter half of the year, and fairly often see six bars during the summer half... You probably are going to see the loss claimed by Nissan (20% loss at 5 years and 30% loss at 10 years).
If seeing six bars is common for a large part of the year, and a seventh bar pops up occasionally during the summer months... Don't consider buying. Lease would be OK.
If you spend a large part of the summer with seven temperature bars or more showing... It's probably best to avoid the Leaf completely. Consider an EV with an active thermal management system or the Chevy Volt."

You can inquire on the forum how many battery temperature bars others who live in your area are typically seeing.

Re: Early Capacity Losses-Was(Lost a bar...down to 11)

Posted: Sun Aug 19, 2012 6:40 pm
by thankyouOB
Stoaty wrote:Guidelines for purchase or lease added to Wiki section on battery capacity:

"Guidelines suggested by Weatherman on whether the Leaf is likely to experience temperature related accelerated battery capacity loss in your area:

If you almost always see five bars or less on the battery temperature gage, and it only gets up to six bars a handful of times each summer... Don't worry about it.
If you see five bars or less during the winter half of the year, and fairly often see six bars during the summer half... You probably are going to see the loss claimed by Nissan (20% loss at 5 years and 30% loss at 10 years).
If seeing six bars is common for a large part of the year, and a seventh bar pops up occasionally during the summer months... Don't consider buying. Lease would be OK.
If you spend a large part of the summer with seven temperature bars or more showing... It's probably best to avoid the Leaf completely. Consider an EV with an active thermal management system or the Chevy Volt."

You can inquire on the forum how many battery temperature bars others who live in your area are typically seeing.
i think 6 is fine.

Re: Early Capacity Losses-Was(Lost a bar...down to 11)

Posted: Sun Aug 19, 2012 7:27 pm
by Weatherman
thankyouOB wrote:i think 6 is fine.
There's, definitely, a lot of mischief that can hide in that sixth bar.

I'm sure a lot of people will see six bars every summer afternoon and evening, but will it drop to five bars at night. It might even stay at six bars for 24-hours a day for a few days during the summer. Southern California coastal residents can correct me if I'm wrong, but it seems like that's pretty typical for that area. Anecdotal evidence suggest that, unless you rack up lots of miles in that environment, the battery's probably going to last as long as Nissan claims it's going to last. If that's fine with you, then good.

The real unknown is those of us who see six bars, 24-hours a day, for week, after week, after week (or, in the case of Florida, for month, after month, after month), but rarely if ever see a seventh bar. There is, essentially, no information, yet, as to what happens under those conditions. It might be ok. It might not. That's why I suggested lease-only for that third group.

We already know what happens if the infamous, seventh bar shows up a lot. I don't think there’s any question that if you are seeing seven bars a lot, the battery is degrading relatively quickly, and you have to decide if you can live with that.

Re: Early Capacity Losses-Was(Lost a bar...down to 11)

Posted: Sun Aug 19, 2012 8:00 pm
by vrwl
So far since I bought my car in June, I've consistently seen 6 bars and rarely seen a 7th bar and I'm right here in the same area as many of those people in Texas who have lost a bar, so I'll have to agree with Weatherman, there's a lot of mischief that can hide in that 6th bar. I'm not so sure 6 bars is fine.

Re: Early Capacity Losses-Was(Lost a bar...down to 11)

Posted: Sun Aug 19, 2012 9:32 pm
by neal77
I'm here in So Cal (inbetween LA and Disneyland) and I have seen 5 tb twice in the morning and the rest of the time has been 6tb. (i have had the car for 1 month now) I'm glad this 2 week heat wave is about over. I hope I will see more 5tb soon. So far I love this car and right now I am kinda sad to think I have to gvie it back in 38 months.

Neal

Re: Early Capacity Losses-Was(Lost a bar...down to 11)

Posted: Sun Aug 19, 2012 9:54 pm
by DaveEV
Weatherman wrote:I'm sure a lot of people will see six bars every summer afternoon and evening, but will it drop to five bars at night. It might even stay at six bars for 24-hours a day for a few days during the summer. Southern California coastal residents can correct me if I'm wrong, but it seems like that's pretty typical for that area.
My car hasn't seen 5 bars in probably 2 months - and then it was only briefly in the morning a couple times. It's probably been 3 months since the battery has held at 5 bars for any significant time.

I live about 4 miles from the ocean.
I work about 7-8 miles from the ocean.

I highly doubt anyone in San Diego has seen 5 bars much in the last 2 months unless they live within a mile of the ocean and park outside, or live further inland where it cools down more at night and they park outside at night.

Re: Early Capacity Losses-Was(Lost a bar...down to 11)

Posted: Mon Aug 20, 2012 6:48 am
by Pipcecil
Stoaty wrote:I analyzed the Leafs in Texas that lost a capacity bar, but didn't find a correlation with monthly mileage and rate of capacity (correlation coefficient = 0.013). Perhaps this was due to there being too few Leafs in the sample with a few outliers, or maybe the climate varies enough between the various cities to allow for a meaningful comparison. Interestingly, the average rate of capacity loss was 1.2% per month, similar to the average 1.3% per month seen in the Phoenix metro area sample (latter not previously reported, I believe).
I think you find it more difficult to analyze the Texas data. For example, Houston has a more average temperature being next to the coast, summers don't get as hot elsewhere, but don't get as cool either, getting more of a warm/hot coastal feel. Then when you look at people living in the urban areas of Dallas-Fort Worth/San Antonio/Austin you may get a more localized "heat island" effect versus those living in the surburbs that could see a more cooling since Texas cities are very spread out.

You may be able to get better results if you isolate climate types, i.e. Houston as a costal, DFW as plains, Austin/San Antonio as Hilly Plains (could be similar to DFW) and anywhere out west as Desert/Plains/Scrublands. But, you probably will run into low data at that point. Texas could see similar problems as California in interpreting results. You have nice cool coastal cities, cooler moutain places, and hot desert areas.

Re: Early Capacity Losses-Was(Lost a bar...down to 11)

Posted: Mon Aug 20, 2012 6:57 am
by ttweed
drees wrote:My car hasn't seen 5 bars in probably 2 months - and then it was only briefly in the morning a couple times. It's probably been 3 months since the battery has held at 5 bars for any significant time.

I live about 4 miles from the ocean.
I work about 7-8 miles from the ocean.

I highly doubt anyone in San Diego has seen 5 bars much in the last 2 months unless they live within a mile of the ocean and park outside, or live further inland where it cools down more at night and they park outside at night.
I live 3 blocks from the ocean in the coolest microclimate in SD and we have also spent the last several months at predominately 6 TBs. Never seen 7 yet, but 5 bars have not been seen on our car for some time now.

TT