The 40KWH Battery Topic

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DougWantsALeaf said:
Congrats. The BMS taketh..but every once in a while giveth.

It certainly is a strange system that Nissan coded. Taking it away only to give it back, assuming we are looking at data that's actually useful and valid in the first place.

Still going up as of this AM. Will post again when the 3 month adjustment is complete.
 
danrjones said:
DougWantsALeaf said:
Congrats. The BMS taketh..but every once in a while giveth.

It certainly is a strange system that Nissan coded. Taking it away only to give it back, assuming we are looking at data that's actually useful and valid in the first place.

Still going up as of this AM. Will post again when the 3 month adjustment is complete.
Nothing real was taken away. The estimate changed, that's all.

SOC is an estimate. Accurate to a couple of percent at best, readout to 4 significant digits is misleading at best.
 
WetEV said:
danrjones said:
DougWantsALeaf said:
Congrats. The BMS taketh..but every once in a while giveth.

It certainly is a strange system that Nissan coded. Taking it away only to give it back, assuming we are looking at data that's actually useful and valid in the first place.

Still going up as of this AM. Will post again when the 3 month adjustment is complete.
Nothing real was taken away. The estimate changed, that's all.

Right!

WetEV said:
SOC is an estimate. Accurate to a couple of percent at best, readout to 4 significant digits is misleading at best.

All this preoccupation with very minor anecdotal changes in SOH/SOC has little value, and any inference results in a non sequitur.
 
WetEV said:
danrjones said:
DougWantsALeaf said:
Congrats. The BMS taketh..but every once in a while giveth.

It certainly is a strange system that Nissan coded. Taking it away only to give it back, assuming we are looking at data that's actually useful and valid in the first place.

Still going up as of this AM. Will post again when the 3 month adjustment is complete.
Nothing real was taken away. The estimate changed, that's all.

SOC is an estimate. Accurate to a couple of percent at best, readout to 4 significant digits is misleading at best.

I understand that, its Nissan's system I find wonky. Why bother to sit there day by day and nibble away at it then run a algorithm every 3 months to adjust up or down. The daily nibbles can contradict the algorithm and vice versa. Those daily nibbles seem a pointless maneuver if the 3 month adjustment is going to go and overrule them.
 
4D0J5F2l.png


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.
 
jmurtagh13 said:
the battery temp stays below 85 deg most of the time, never above 90 deg.
Ouch

If you can improve (decrease) the average battery temp it will last longer.
 
DougWantsALeaf said:
Nice graph. Have your miles been put on fairly consistently over the past 2 1/2 years?

Thanks.

Yes for the most part, this last month was a rare exception, we put on an additional 300 miles to our normal 700 a month.
 
SageBrush said:
jmurtagh13 said:
the battery temp stays below 85 deg most of the time, never above 90 deg.
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.
 
jmurtagh13 said:
SageBrush said:
jmurtagh13 said:
the battery temp stays below 85 deg most of the time, never above 90 deg.
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

I can only speak about my Tesla -- temp management is waay lower than 110F. You can watch youtube videos by Bjorn Nyland when he monitors pack temps after supercharging. IIRC the battery is cooled down into the 80s F immediately after DC charging but the car is still being driven, and once the car is parked the battery is cooled into the 70s F within an hour or two. That is the pack chemistry of the Model 3, which I gather prefers life at a warmer temperature than prior Tesla cell chemistries.

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.
 
jmurtagh13 said:
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/battery-conditioning.33279/#post-512173. Also look at the pink lines at https://www.chevybolt.org/threads/best-charging-curve-ive-seen-yet-from-a-100kw-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.php?p=564799#p564799 and https://mynissanleaf.com/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 https://mynissanleaf.com/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).
 
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
 
jmurtagh13 said:
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/journal/g12/n01/pdf/120112.pdf when I was trying to educate Powersurge at https://mynissanleaf.com/viewtopic.php?p=508974#p508974. Page 3, section 3.1 makes no mention of charging.

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

See my examples at https://www.mynissanleaf.com/viewtopic.php?p=496269#p496269. https://www.mynissanleaf.com/viewtopic.php?p=473995#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/20170717073322/https://mynissanleaf.com/viewtopic.php?t=22134 got his 30 kWh Leaf to a battery temp of 137 F.
 
jmurtagh13 said:
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
 
jmurtagh13 said:
4D0J5F2l.png


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.
 
jmurtagh13 said:
4D0J5F2l.png


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!
 
lorenfb said:
jmurtagh13 said:
4D0J5F2l.png


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
 
SageBrush said:
jmurtagh13 said:
SageBrush said:
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.php?f=17&t=27677#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.
 
cwerdna said:
jmurtagh13 said:
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.
 
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