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Favor Low SoC or Small Cycles?
- Thread starter Drinyth
- Start date
All AC charging (home charging) is so ”slow” that there isnt any win in reducing the charging power for the battery longevity.
At max AC charging, 11kW it is only 0.15C or so.
I'd say there's a win for battery longevity when charging at a higher amperage. Used in conjunction with Scheduled Departure, this would allow the battery to sit at a lower SoC for longer, and thus reduces the average SoC and calendar degradation.
AAKEE,
Things get confusing fast here. Could you give a summary of your oppinion on the following (not looking for practical just pure battery):
For daily use what should the ideal state of charge range be? 20/30. 10/30 20/90(T recc).
What charger/rate should we use(tesla home charger 24048A or 110v)? Slow or fast?
Always prep the car(takes up to 40 mins)?
Any adjustments for say Ontario weather vs Alabama?
Thank you in advance.
Things get confusing fast here. Could you give a summary of your oppinion on the following (not looking for practical just pure battery):
For daily use what should the ideal state of charge range be? 20/30. 10/30 20/90(T recc).
What charger/rate should we use(tesla home charger 24048A or 110v)? Slow or fast?
Always prep the car(takes up to 40 mins)?
Any adjustments for say Ontario weather vs Alabama?
Thank you in advance.
The smaller the depth of discharge is, the better.
The lower the SOC is, the better.
This will be more of a theoretical discussion. There is a not a big difference between 30% to 20% and 30% to 10%. Both will give very low degradation.
-30-10% will give lower calendar aging, if the charging is done late so the car will spend the night at low SOC.
-30-20% has a smaller depth of discharge, so it will possibly give slightly lower cyclic aging
There should not need to be a choice of 30-10% vs 30-20%. If 30-20% was possible to use (10% depth of discharge) there would be an option of using 20-10% also.
This would take the advantage from what I wrote about both choices about.
You can se that there is not big differences between 30 and 20 and 10% at normal temperatures. Blue line at these points.
Below we can se that cycling at very low SOC gives the longest life.
In the chart we should compare cycles with the same load ( C ). In the car charging home and driving is about 0.05 to 0.25C so the cycles marked 4C can be disregarded.
Except the high load 4C cycles, its always better with lower SOC range during cycles.
(10-20% was better than 0-10% at 4C).
This chart does not show NCA Chemistry, but it is good at clearly showing different SOC ranges.
Noye that 0-10% and 10-20% have an average cyclcle number before loosing 10% SOC (end of yellow band) at 6000 FCE cycles compared to 60-70% that averages about 1500 FCE cycles.
The principle is that the lower the cycle range is placed, the less degradation.
20-90% will give much more degradation, so it should only be used when the range is needed if low degradation is the goal.
For the battery life due to charging power, we can not set a home charging rate that is high enough to start reducing battery life due to the charging power.
The highest possible we have in europe is 11kW charging power (three pases of 230V and 16A) That is the limit of the on board AC charger.
Reducing charging power will not save or increase the battery life.
This means that *Any home charging power* will cause very low /about the same cycling losses. You can select whatever charging power you want at home, or i limited by the net limitations.
What @STS-134 wrote/meant is that if we use the “charging late technique”, charging as late as possible, we can set the charging to start later which in turn gives shorter time at high SOC as the car continue to be at lower SOC until the charging starts.
This is only valid when using the charge late technique. Thats the reason I didnt mention this in my first answer.
If the charging is started at arrival at home so the car will be parked a long time with the charge finished a high charging power gives the opposite result, the car will be at a higher average SOC increasing the calendar aging.
It is not always needed.
In summer, not needed.
If it in a varmed garage, not needed.
If you charge late, not needed.
If the car is outside at sub freezing, was not recently charged and was not driven the latest hours it can be good.
But the car itself heat the battery when the driving is started so the battery will only spend very little time at low temps.
I do not always precondition if it is outside and has cold soaked. Each winter I do several Drives which was not pre planned somI start the preheating with the app when I decide to go or start taking clothes on.
Still, my car has very low degradation.
Probably not from the principles above but if yoy describe the climate or difference I’ll give it a try.
Ok, I get it now...albeit quite a few reads later. Thanks.
Bottom line if one cares to max out battery life above anything else... Keep battery SoC on the low end as much as possible(incl late charging).
Charge to the lowest state you can for what you need...lowest being 50%(without having to watch the percentage constantly.
Charge smaller drops(Prob why the manual states to always keep car plugged in, so that cars may recharge after a short drive.
Winters in Canada, pre heat if possible but not necessary unless super cold. Above freezing dont worry too much about pre-heating.
Of course range and dynamic breaking would be impacted in some of the scenarios but to each his/her/he/she it's own.
Of course as I read this I am topping off to 100% from 30% at work because ....its free
Due to the work charger I may kill the battery early. I cant resist free charging , so I like ot run it low and leave work with full juice. Most days I only get to about 90% due to the slow 30A 240V(USS ONLY 198V) CHARGER So far I have driven my car about 2500 miles since purchased last month and I paid about 20 bucs in Energy.
AAKEE:
Just want to say thanks for your patience and helpful answers!
Just want to say thanks for your patience and helpful answers!
I have a personal experience with my cell phone becoming noticeably hot at a lower SoC. At or below 5% SoC, which probably equates to a cell voltage of 2.7V or less, a thermal runaway can happen. I'm not sure if the Tesla BMS has a built in protection or buffer to protect the battery pack. I hope to get some expert advice to understand the Tesla's BMS capabilities?
No, thermal runaway does happen at low SOC.
Thermal runaway happens above a high temperature if the cell is heated, but not with very low SOC*.
The regulations for Dangerous goods in air for shipping lithium batteries stipulate that the SOC must be 30% or lower, for increasing the safety in exactly that matter.
The Internal resistance is higher at low SOC so for the same usage, the battery self heating from use increases the temperature slightly more at low SOC. I often have my cell phone at low SOC, and when not using it it doesnt have a elevated temp at all.
In most cases, a warm cellular comes from that it was used for a longer period, heated from a combination of the battery “self hesting” + CPU usage + screen lamp.
Tesla has a complete thermal management.
As you probably understand from the earlier part of this post, there is no risk for thermal runaway at low SOC.
But Teslas thermal management can cool or heat the pack within any need in the envelope.
For supercharging at the V3/250kW chargers, a preconditioning means heating the battery to 48C befor the car is connected. At the start of the charging, the battery is still heated until the cells reach 56-58C, then the system cools the pack to keep that temperature throughout the charging session.
*) To totally kill a possible evolving myth about thermal runaway at low SOC, This research can be read. I have read numerous research report. This is just the first hit, I didnt read it that thorough, as I already know from other reports. But i did loan a few pictures…
This is how a thermal runaway looks like (vertical red temp line at time about 148 minutes). Does not happen at low SOC.
This is the same test with 0% SOC:
= more or less nothing.
This is the termal runaway temperature for different SOC’s.
Note that 0% is not in the chart, even if it also was tested as the 30/50/80/100% was.
If anything, low SOC is also safer for thermal runaway and reduces the risk of a dangerous fire if the battery get damaged.
This is how the cells looked after a heating session to thermal runaway:
If you are about to have an terrible accident you might wanna be on the low SOC side.
I mean from a practical standpoint low SOC cuts degradation by half right.
In my case 250 miles base model 3 range 5% vs 10% is literally a 12.5 mile difference in which the grand scheme of things doesn’t even matter lol
In my case 250 miles base model 3 range 5% vs 10% is literally a 12.5 mile difference in which the grand scheme of things doesn’t even matter lol
We all have to decide how to charge from our own preferences. As long as anyone do not charge to 80% because she/he thinks that it will give the lowest degradation I’m happy.
It might also be a question of thinking ”like I use to do”. When refuelling the ICE car, we mostly fill it up completely.
But when making coffee in the coffee maker we perhaps only make what is needed, with a margin?
Or when withdrawing money in the ATM we mostly only withdraw whats needed in the near future, and not all the money on that account (unless all = whats needed
).The industry standard for lithium ion batteries is that they are consumed when reaching 20% degradation (80% capacity). The reason is that below 80% capacity the degradation is not as predictable. In some cases the ”straight” predictable degradation continues but in some cases it dives steep.
An EV car might be less demanding in some cases, but I would not buy a used EV with a battery that lost 20% or more. I would see to it that I had the margin not to reach 20% during my ownership. In some years we probably will start to see used EV’s with tired batteries, and at that time we probably would not like to sit with a car that can not be sold.
Living in a average temperature zone, we have about 15-16% loss after 8 years but only 7.5-8% loss with the low SOC strategy.
Living in a warm climate, we might have reached or passed the 20% after eight years.
For myself, I often need a big part of the range. My job is 240 km away, and in wintertime it can be -30C or colder, making the cars range about 300km, when I drive home (parked outside, slow charhe so relatively cold battery). In these conditions its not safe to aim for arriving with 0%.
Driving to my mother in law, is > 250 km with no fast charger on the way. In winter I might arrive with 15-20%, and we usually need to drive around after arrival. Theres no chargers nearby so UMC 3kW is the best we can do.
Loosing 15% capacity is not an option. With my still good battery capacity it is possible to charge overnight so we can srive home the next day, taking a longer detour via a supercharger.
So for me the choice is easy, keep the capacity because I need it.
Thanks for bringing up the end of life capacity number for discussion. I totally agree with the known best practices in the battery industry that a level of battery degradation above 20% is considered the end of life. At that number, even when an EV owner has 90,000 mi (145,000 km) on the vehicle, it will be unsettling. At that point, assuming you're not plain old angry, you're genuinely disappointed with Tesla. Interestingly, however, Tesla would like you to keep driving until that degradation number hits the 30% mark. This is not a sustainable position. As the competition from other EV manufacturers heats up and the battery tech gets better really fast, Tesla would hopefully be thinking about this issue. Tesla should consider revisions to their battery warranty statement, adding a prudent limit (research guided) of Supercharging sessions as one of the important qualifying criteria, amongst other conditions. What are your thoughts about it?
E90alex
Active Member
Tesla is not in the business of replacing batteries for free. Thus they have set the warranty criteria so that the vast majority of cars will not reach the 30% degradation threshold by the time warranty runs out. If they lowered that threshold to 20% they would likely have to replace significantly more batteries.
zoomer0056
Active Member
Unless I am reading the wrong, Tesla battery warranty goes to 30% degradation. I saw this in the Tesla battery warranty found here: Vehicle Warranty | Tesla Support
30% is a fair number for warranty reasons.
I think Tesla have chosen a good number there.
But this is not the same as that the batteries work fine down to 30%. Its not improbable that the battery pack start to give fault codes and work bad before reaching 30% degradation.
As the branch standard is not chosen randomly and the research tests shows just that ”unpredictability” after 20%: in some cases they work fine with the same degradation per time or cycle and in some cases they “loose it” I would recommend to for own personal limits try to stay out of degradations above 20%.
When the warranty period is over it would be very vice to be on the right side of the 20%-mark.
The market (people) will probably learn in the coming years and I believe in the future we will see cars that no one would like to touch.
We still can get unlucky and get a BMS failure or water leak or something, but I’m sure Tesla did learn from the weak spots and makes more solid packs, making tje risk for other failures lower.
A battery with good health will never be a burden when selling the car.
I think Tesla have chosen a good number there.
But this is not the same as that the batteries work fine down to 30%. Its not improbable that the battery pack start to give fault codes and work bad before reaching 30% degradation.
As the branch standard is not chosen randomly and the research tests shows just that ”unpredictability” after 20%: in some cases they work fine with the same degradation per time or cycle and in some cases they “loose it” I would recommend to for own personal limits try to stay out of degradations above 20%.
When the warranty period is over it would be very vice to be on the right side of the 20%-mark.
The market (people) will probably learn in the coming years and I believe in the future we will see cars that no one would like to touch.
We still can get unlucky and get a BMS failure or water leak or something, but I’m sure Tesla did learn from the weak spots and makes more solid packs, making tje risk for other failures lower.
A battery with good health will never be a burden when selling the car.
SageBrush
REJECT Fascism
The Nissan LEAF experience does not confirm your guess -- quite the opposite. They have a veritable fleet of cars happily running around with degradation over 30%, and large numbers of cars with degradation over 50%.
The real issue is a few weak cells in the pack cutting off the range at low SoC. People who do not understand SoC and rely on the range estimators have the most confusion about practical range in these degraded cars but they run fine until they run out of range. Fine, as in they do not throw fault codes.
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