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Best to charge to 60%?
- Thread starter Doug1000
- Start date
I know that Elon said 90% every day is "fine", BUT...that doesnt align with whats considered best practice for Lithium battery's in general for longest life. (nor can we believe 100% of everything Elon says).
Also..in case of major accident and (heaven forbid) battery fire? Pack catching fire at 50% or less will be a lot less energy than same pack going into flames at 90%. Total loss either way, but still...
Also..in case of major accident and (heaven forbid) battery fire? Pack catching fire at 50% or less will be a lot less energy than same pack going into flames at 90%. Total loss either way, but still...
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Could you elaborate a little more on the 50% being less volatile in the case of a fire rather than 90%. Do you have specific information on how this works?
Serious question, because I truly don't know and am curious if you are using reasonable assumption or If you had more detailed information on how SOC and a battery pack fire are related?
I know voltage doesn't change that much with Pack SOC, but not sure if that relates or not???
SageBrush
REJECT Fascism
Let's say you have a pile of logs, all the same.
Will you have a bigger fire with one log, or two ?
pepperoni
Member
He didn’t say it is less volatile. He said it has less stored energy, which I believe is rather obvious. EV fires are notoriously difficult to put out.
Abstract:
In order to further investigate the thermal runaway characteristics of 18650 lithium ion batteries and the related hazard, experiments of 18650 lithium ion batteries with different SOC (State of Charge), such as 50%SOC and 20%SOC under two initial pressures of 96kPa and 61kPa are conducted. The results show that the chemical reaction of 20%SOC batteries is weaker than that of 50%SOC batteries, leading to a lower peak temperature, less CO and CO 2 release, and less mass loss. Under 61kPa, the initial combustion time is longer, the reaction intensity is weaker, more CO and CO 2 release and less mass loss than that under 96kPa. The fire hazard of 50%SOC batteries is larger than that of 20%SOC batteries.
SageBrush
REJECT Fascism
liability to change rapidly and unpredictably, especially for the worse.
This is more the definition I had in mind, essentially the change rapidly, especially for the worse. In essence the ability for a pack fire to become worse based on SOC.
I do feel my M3P at 60% SoC is significantly weaker than at 90% SoC and it is even measured here: Tesla Performance Model 3 Dyno Testing At Various SOC
What I would like to know is whether M3LR and M3P power differs at SoC 50%. It does obviously differ at 100% SoC as this chart shows:
SageBrush
REJECT Fascism
Nope. The SOC will make a noticeable difference in the degradation.
The lower the SOC, the lower the degradation.
Staying low in SOC makes a clear difference in calendar aging. Low temperature over time is also good, but the ambient temp that set the battery average temp is hard to control for most people.
In this graphs the lowest blue line show about how much the battery will degrade from calendar aging in the first year. (25C 9.6 months).
If the average SOC is low the calendar aging can be for example about 2.5% at 30%.
If SOC instead averages 80-90% the calendar aging will be around 5%. Thats the double amount.
Calendar aging reduces with time (square root of time) so the low SOC car will have about half the calendar aging compared to car with high SOC.
Cyclic aging is much less, normally around 1% per year or less (Its easy to show this with a calculation).
The main degradation for the first five years or so comes from calendar aging, not the miles driven.
For cyclic aging, low SOC is also good (even if the cyclic degradation is smaller anyway)
The lower the SOC the lower the cyclic aging.
The smaller the cycles, the lower degradation. Charge often but not more then needed.
@nate704 is right, you need quite high SOC to get full power from a Tesla performance car. And quite high battery temp also.
For a regular LR its less pronounced because less power.
You need to make a choice between high power and low degradation if both is very important for you.
Calendar aging can be low if the car stands at low SOC during the night and if the charging is done late.
But if you only drive average miles each day, a high SOC in the morning do not end up in a low SOC in the evening.
If you drive little and could manage with only 55% (or down to 50%) instead of 60% there could be a clear reduction of the degradation.
Look at the knee between 55 and 60% in this graph:
The knee does actually have its sharp piint about 57-58% SOC but as the research tested only 55 and 60% they did draw a straight line between.
As the true SOC is higher than displayed due to the buffer you will have about 57% true SOC when 55% is displayed. In this case you will be below the knee and have reduced calendar aging.
One point: If charging higher than 55% and driving asap so the SOC is below 55% after the drive there will be no increased calendar aging.
I am now for half a year in a different country. I left the car at SoC 50% (sure connected in my garage to Tesla Connector) as that is the lowest valid SoC officially supported by Tesla.
I understand I can stop the charging to get to lower SoC than 50% but maybe there is some other battery technology catch for too low SoCs? The charts above do not test it in the far future years and on real Tesla batteries. Or at least they may test different generation of the battery than what I have.
Why do you not recommend 2% or 5% SoC instead of 30% SoC? I can maintain such SoC using Tesla API.
I feel as if there is really some technological catch. I may lose the 70% capacity warranty with hacking the SoC too low. Or I may just get a higher degradation still above 70% than with the official SoC 50%.
At the end of the day I find the 50% SoC degradation low enough so that I do not want to play with fire.
I park my car at 5-30% most nights.
I did leave it at ~30% during a three week trip to US. If It had been at 15% that day, I had left it there also.
50% is OK as it is below the “knee” in the calendar aging charts”.
As we talk charging target, 50% is the lowest setting and I guess 99% of the people do not have the possibility to use a lower setting than 50%.
I would be pleased to see a lower possible charge setting, the lower the low limit is, the better.
Also, in these threads it sometimes is a hard job (
) arguing against “90% is the best, Elon said so” and “I have been babying my battery at 80%…” Its easier to kill the myths one by one…Recommending a charging target of 2 or 5% would not result in a specially useable vehicle, and people probably would start the day with heavy range anxiety.
What I recommend (for the people that like to reduce the degradation) is having as low SOC as possible. You can charge to 70-100% and not have a noticable increased calendar aging if you drive the car shortly after the charging is done.
Using lowest possible charging target* and charging late is the key to low calendar aging.
*) Allow a personal margin to treat the range anxiety.
There is a lot of research with Panasonic NCA cells, like 18650 either exactly the same as tesla model S or very closely related. The sum of all research of NCA chemistry do paint a quite clear picture. There is not a very big difference between each research result. Because of this we can be quite sure that the cells in the cars behave in the same manner.
For Tesla + Panasonic, the main goal is most probably not to make a super cells much better than the best Panasonic NCA we can buy for > 20$ each. The goal is most probably to make the batteries cheaper.
A serious calendar aging test takes at least one year to perform, and a few months to write the report. All this after getting the battery cells in the hand. So we do not see reports of the newest technology until sone time has passed. The latest reports there is, is reflected in what I write.
As lithium batteries in general (NCA, NMC, NCO LFP) behave quite similar its not really probable that a new Tesla panasonic NCA (like 2170L or so) suddenly behaves completely different.
I often use the caviat “from the latest reports we can read” as we can not be sure that the latest batteries performs exactly like in the reports.
Until we know from future reports, assuming that the new ones is not too far away from the next newest might be a sound idea.
You can be quite sure that low SOC is safe.
There is no information in Teslas instructions that say to stay above 20% or so. They tell you to allow for 1% per day, so 14 days would need 14% at least.
They also say that other components can be damaged if the SOC goes so low that the HV battery shut down (to save itself from too low SOC). We know that the Low Volt battery ( lead acid type) is sensitive to low SOC.
There is a lot of battery research and more or less all reaearch tell us the same thing.
