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Re: The 40KWH Battery Topic

Posted: Fri Sep 11, 2020 3:37 pm
by DougWantsALeaf
The newer chemistry doesn't seem to be as affected moderate temperatures (20 - 30C). As we can't see actual SoH, hard to tell for certain.

Re: The 40KWH Battery Topic

Posted: Fri Sep 11, 2020 3:55 pm
by cwerdna
jmurtagh13 wrote:
Fri Sep 11, 2020 3:17 pm
My understanding is that EV's with battery thermal management don't start cooling until the batteries reach around 110 degrees.
Totally untrue, at least for my Bolt.

See https://www.chevybolt.org/threads/batte ... ost-512173. Also look at the pink lines at https://www.chevybolt.org/threads/best- ... dcfc.32809. In the 1st graph, he hits 34 C and then the battery starts getting cooler for the rest of the charge. I've made some other comments about Bolt TMS before like at https://www.mynissanleaf.com/viewtopic. ... 99#p564799 and viewtopic.php?p=561008#p561008. In the latter case, no, it wasn't past 110 F.

Here are some temp conversions:
27 C = 80.6 F
31 C = 87.8 F
34 C = 93.2 F
43.3 C = 110 F

BTW, at viewtopic.php?p=565246#p565246, I have a video of what Bolt's thermal management sounds like on full (e.g. when it kicks on during DC FCing or the moment when you plug in and the battery's hot). If the battery's not that hot, the noises are much softer (e.g. fan only or fan w/compressor running slowly or cycling on/off at low speeds).

Re: The 40KWH Battery Topic

Posted: Fri Sep 11, 2020 5:31 pm
by jmurtagh13

If you keep the car in a poorly ventilated garage, consider instead leaving it outside during the hot months when ambient is less than your garage. You are otherwise managing the car wisely, but battery temp is THE issue with these cars. The more you can do for the LEAF battery, the longer it lasts. My 2013 LEAF still has 11.5 battery capacity bars but I start fretting when the temp bars goes over 5. That is unfortunately what it takes to get long(er) life from these cars.
I do keep the car outside which is much cooler than the garage. I do agree that if i could keep the temperature year round at 70 deg. that would extend the life of the battery. My hope was that Nissan had made significant progress in battery temperature resilience, that the 80 - 85 deg. battery temperature would not greatly decrease the battery's life compared to 70 or lower. Also my understanding is that charging at a high temperature does the most damage. I almost always charge at or below 80 deg during the summer and then lower than 70 during the other months. I do think my temperature ranges are comparable to the EVs that have TMSs

Re: The 40KWH Battery Topic

Posted: Fri Sep 11, 2020 5:49 pm
by cwerdna
jmurtagh13 wrote:
Fri Sep 11, 2020 5:31 pm
Also my understanding is that charging at a high temperature does the most damage.
I don't think that's correct at all. I pointed to https://www.nec.com/en/global/techrep/j ... 120112.pdf when I was trying to educate Powersurge at viewtopic.php?p=508974#p508974. Page 3, section 3.1 makes no mention of charging.

Table 3 at https://batteryuniversity.com/learn/art ... _batteries talks about capacity remaining after storage at 40% vs 100% SoC at various temps. Ditto for table 2 of https://batteryuniversity.com/learn/art ... _batteries.

See my examples at https://www.mynissanleaf.com/viewtopic. ... 69#p496269. https://www.mynissanleaf.com/viewtopic. ... 95#p473995 is in Phoenix and has the same build month as me. I'm still at 11 bars now with SOH around 79.xx% in a hotter part of the SF Bay Area. That guy lost his 4th bar (at 8 bars) in late 2016.

L2 charging does heat the battery by a few degrees F, so yeah, it's better to start off charging when it's cooler so that the battery doesn't get as hot. DC FCing can really heat up the battery, esp. multiple ones in a day.

https://web.archive.org/web/20170717073 ... hp?t=22134 got his 30 kWh Leaf to a battery temp of 137 F.

Re: The 40KWH Battery Topic

Posted: Fri Sep 11, 2020 6:00 pm
by SageBrush
jmurtagh13 wrote:
Fri Sep 11, 2020 5:31 pm
Also my understanding is that charging at a high temperature does the most damage.
Definitely something to avoid if possible

Other than not garage-ing (which you do not do), the only other advice I can offer is to be OCD about not parking on hot tarmac. I have convinced my wife to walk 10 minutes to her gym so that she can park in the shade ;)

Lucky for the LEAF, she views it as an opportunity to add to her 'steps' counter

Re: The 40KWH Battery Topic

Posted: Fri Sep 11, 2020 6:14 pm
by lorenfb
jmurtagh13 wrote:
Fri Sep 11, 2020 11:04 am
Image

22,186 Miles 30 months old. Last month's drop .12%, SOH 90.60

Charge only with level2 to a max of 65%. Charge early morning when it's cooler and the battery get's a chance to cool some. I don't drive aggressively so the battery temp stays below 85 deg most of the time, never above 90 deg. I feel like a I really baby the battery, yet the BMS shows about the same as others who have many more miles and do DC charging. I'm into ebikes and do the same by only charging to 65-70% and that definitely makes those batteries last a lot longer. I'm just not sure I believe the BMS, I guess more time will tell.
Based on your 2.5 year Hx graphic, increasing over time, Hx appears to be the ratio of the present battery resistance to the initial battery
resistance as a percent. This appears to be opposite to Leaf 1, where Hx measures the ratio of battery conductance over time as a percent,
and decreases over time as the battery degrades. Initially, Leaf 2 Hx appeared to move randomly, but your graphic lends insight to Hx
being a percentage value for increasing battery resistance over time.

Re: The 40KWH Battery Topic

Posted: Fri Sep 11, 2020 7:34 pm
by DaveinOlyWA
jmurtagh13 wrote:
Fri Sep 11, 2020 11:04 am
Image

22,186 Miles 30 months old. Last month's drop .12%, SOH 90.60

Charge only with level2 to a max of 65%. Charge early morning when it's cooler and the battery get's a chance to cool some. I don't drive aggressively so the battery temp stays below 85 deg most of the time, never above 90 deg. I feel like a I really baby the battery, yet the BMS shows about the same as others who have many more miles and do DC charging. I'm into ebikes and do the same by only charging to 65-70% and that definitely makes those batteries last a lot longer. I'm just not sure I believe the BMS, I guess more time will tell.
Time is your biggest degrader but also I am impressed that you have several intervals ranging from a month to over 6 weeks when you lost less than .1% .03% in 5 weeks? HOLY MOLY, that is killing the curve!

Re: The 40KWH Battery Topic

Posted: Fri Sep 11, 2020 7:39 pm
by DaveinOlyWA
lorenfb wrote:
Fri Sep 11, 2020 6:14 pm
jmurtagh13 wrote:
Fri Sep 11, 2020 11:04 am
Image

22,186 Miles 30 months old. Last month's drop .12%, SOH 90.60

Charge only with level2 to a max of 65%. Charge early morning when it's cooler and the battery get's a chance to cool some. I don't drive aggressively so the battery temp stays below 85 deg most of the time, never above 90 deg. I feel like a I really baby the battery, yet the BMS shows about the same as others who have many more miles and do DC charging. I'm into ebikes and do the same by only charging to 65-70% and that definitely makes those batteries last a lot longer. I'm just not sure I believe the BMS, I guess more time will tell.
Based on your 2.5 year Hx graphic, increasing over time, Hx appears to be the ratio of the present battery resistance to the initial battery
resistance as a percent. This appears to be opposite to Leaf 1, where Hx measures the ratio of battery conductance over time as a percent,
and decreases over time as the battery degrades. Initially, Leaf 2 Hx appeared to move randomly, but your graphic lends insight to Hx
being a percentage value for increasing battery resistance over time.
Interesting theory but there are a handful that would seem to counter that. The 40 likely to lose the first bar is only in the high 90's. Not sure what Hx history was previously. He has piled on the miles quite rapidly though. IIRC, he is averaging well over 20,000 miles a year

Re: The 40KWH Battery Topic

Posted: Sat Sep 12, 2020 6:26 am
by WetEV
SageBrush wrote:
Fri Sep 11, 2020 3:27 pm
jmurtagh13 wrote:
Fri Sep 11, 2020 3:17 pm
SageBrush wrote:
Fri Sep 11, 2020 11:59 am

Ouch

If you can improve (decrease) the average battery temp it will last longer.
That would be hard to do in Atlanta's summers. By the time the charging starts about 3:00am the battery is down to between 75 and 80. and that is just during the hottest 4 months of the year. The other 8 months it's 70 or below. I really thought that those temperatures were reasonable. My understanding is that EV's with battery thermal management don't start cooling until the batteries reach around 110 degrees.
Reasonable for driving -- sure.
Reasonable for degradation -- No
No?

A battery is a sack full of chemical reactions. The ways that batteries work and the ways that batteries degrade are all chemical reactions. Chemical reactions often follow this:

https://en.wikipedia.org/wiki/Arrhenius_equation

For every roughly 10C or 18F warmer, the lifespan of a battery halves. In Atlanta, your battery will have a shorter life than in Seattle, and that would be true for both an actively cooled battery such as a Bolt or Tesla or a passively cooled battery such as a LEAF. Yes, the actively cool battery is better, but not that much better.

https://www.mynissanleaf.com/viewtopic. ... 77#p547072

Perhaps 5% better. Which might be unreasonable if you have very high standards. Or might be unreasonable if you get a commission for referrals, as Tesla owners get.

The difference will depend a lot on things hard to model. And for the actual use. A car driven long distances at high speeds, for example, will not have happy batteries with passive cooling. Especially in a very hot place.

Re: The 40KWH Battery Topic

Posted: Sat Sep 12, 2020 6:35 am
by WetEV
cwerdna wrote:
Fri Sep 11, 2020 5:49 pm
jmurtagh13 wrote:
Fri Sep 11, 2020 5:31 pm
Also my understanding is that charging at a high temperature does the most damage.
I don't think that's correct at all.
I agree. Charging temperature being low is more likely to be problematic, due to the issue of Li plating. I doubt if Atlanta gets cold enough for long enough to worry.

Best charging practice is to finish the charge right before departure, to minimize the time at high SOC.