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I charge to 80% regularly and my apparent loss of rated range is greater than 3% with 10,000 miles. My last road trip in which I cycled the pack < 10% -> 100% 3 times in succession resulting in losing an additional mile. Not sure how to explain this.
Thank you, excellent lecture, but have a look here. Notice a couple of things; first off, he's referring specifically to the type of battery which Tesla uses. Second, there is absolutely no rollover at 4.25v. Do you think that Tesla has 100% charge set to -above- this level? Certainly not.
So we deduce:
- It is not harmful to charge to 100%, as long as the pack doesn't overheat, and there are protections against that. (coolant loop, heat pump, overtemp protection)
- In hot climates it's more difficult to get max life out of the pack, but again with protections there shouldn't be significant impact.
- It is better to -not- charge every day, as that is adding charge/discharge cycles to the pack, which directly affects lifetime. Run the pack down to whatever you're comfortable with, whether it's 40%, 10%, or 0% and then charge it up. Always charge up before a storm though.
I realize that 90% charge has been Gospel around here for a long time, but who are you going to believe, the Owner';s Manual, or your own lying eyes?
This is false. 1 cycle is one cycle, whether or not it is a partial cycle or not makes little to no difference. 1 cycle is equal to draining the full capacity out of the cell and replenishing full capacity. So if yoy drive from 90% to 80% and charge to 90% thats 0.1 cycles worth of wear. Same with regen, which contributes towards this total also.
The best resting state is 50% +/- 10% at 50 to 60F or so. But resting at 80 or 90% is not much different as long as thr pack temp is kept reasonable.
stopcrazypp
Well-Known Member
You are talking about something different. He is talking about charging to 100% SOC (4.2V cell voltage for Model S) and letting the car sit there (potentially at high temperatures too). Every single battery expert will say that is one of the worst things you can do for battery longevity. We are not talking about simply charging to 100% SOC (and then using it up almost immediately).
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jpet
Jan P.
DoD is a key factor in degradation so it is definitely better to charge your car whenever you can.
"A connected Model S is a happy Model S."
Here's some research material you might want to read on the subject:
http://repository.osakafu-u.ac.jp/dspace/bitstream/10466/14150/1/2014900048.pdf
He is talking about charging a battery up to given voltage points and then discharging it, as the point of his work was to exercise the battery. But nothing about this says that storing it for a reasonable time (say, 2 weeks) at 100% will impair longevity. Tesla has enough sense to not set 100% to a level which will impact life of the pack. (der)
(Must I also say that of course the pack won't stay at 100%, due to Ri, not to mention draws from the car? Hopefully we all know better)
Yes it's best to long-term store LIon batteries at 60% or so charge. (and to never let it freeze discharged) But most ppl drive their car almost every day, so energy transfer is taking place. But this doesn't mean that you should only ever charge your car to max 60%.
Believe it, or not. Idc. And I am not here to bicker with wk057 as he always wants.
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stopcrazypp
Well-Known Member
I thought Tesla set 100% at a lower voltage too (as they did with the Roadster), but found out long ago this is not the case. The Model S charging peaks at 402-403V. With 96 in series, that is 4.2V. So the Model S does charge to "true" 100%.
Although Tesla cells are not the same, for the similar NCR18650B, storing at 4.2V at 25C means you lose 1.6% of your capacity a month. At 50C you lose 20% in a month.
http://batterybro.com/blogs/18650-w.../77975750-how-to-store-18650-batteries-safely
Edit: dug for irrecoverable losses:
3-4% loss over 18 months stored at 100%SOC at 23C (Eagle-Picher cells).
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20030112621.pdf
More NASA data at 50% SOC storage (SAFT cells):
https://batteryworkshop.msfc.nasa.gov/presentations/Stor_Char_LiIon_Batt_KBugga.pdf
Compare this to the 5% we are wringing our hands over in this thread.
I would say that is significant.
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JRP3
Hyperactive Member
Time spent at 100% charge definitely matters. And 100% on the Model S is in fact 100% charged. 4.2V with about a 75mA cut off in the CV stage. This is pretty much filled to the brim for these cells. 0% USoC is really about 5% SoC due to the anti-brick/DoD safety buffer.
lol?
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You can charge them higher, but the return is basically nothing at the expense of instantly damaging the cell. The capacity difference betwen a 4.2V/75mA cut and 4.35V/75mA cut is something like 0.08Wh at best (off the top of my head, don't hold me to that). And occasionally the cells explode when doing this, so, that's a drawback to longevity. If it does survive, capacity is immediately degraded by almost as much as the extra capacity that was initially packed in. So, I wouldn't consider anything above 4.2V as safe or usable.
This paper, written by Panasonic employees, presents lifecycle information on NCA cells:
Development of High Power and Long Life Lithium Secondary Batteries
They are cycling between 3.6 volts and 4.05 volts. I leave it to you all to sort out what that means for the Tesla packs. Of course, these aren't exactly Tesla's cells.
Development of High Power and Long Life Lithium Secondary Batteries
They are cycling between 3.6 volts and 4.05 volts. I leave it to you all to sort out what that means for the Tesla packs. Of course, these aren't exactly Tesla's cells.
Yeah, you can see that at 3,000 charge cycles, the degradation at 2C charge! and discharge is just over 10%. Even at 150 miles a charge cycle conservatively, that's 450,000 miles. Of course, our cars actually discharge at 3-5C, and never charge at 2C. I don't know the effects of the DC-IR increase, I'm assuming that is dropping the available power in pack or increasing it? I don't know which direction, it isn't clear.
JRP3
Hyperactive Member
I wasn't thinking of anything above 4.3. Just looking at some NCA discharge curves made me think 4.25-.430 might be a true 100%, but as you say not much to be gained up there. Examples comparing NCA to modified NCA:
The Model S averages well under 1C discharge in normal driving. IR will increase with the life of the battery, which limits the peak power available.
But yeah, I expect these battery packs to last for a very long time in the Model S with very little degradation, especially following the basics for longevity. No sitting for extended periods at > 90% or < 10%, no sitting for extended periods at high temperatures, etc.
stop and JRP, please understand: The Panasonic 18650 cell's nominal voltage, that is its fully-charged voltage, is 3.6v. When ppl talk about 4.2v and above, that is actually charging voltage. When charging is removed, 4.2v is no longer applied. (Do I have to acknowledge that Tesla's cells aren't quite Panasonic's?)
Better LIon battery chargers always have sophisticated charging algos toward the end of a cycle to trickle the pack, of course Tesla being no exception. These algos are specifically intended to top off and allow balancing of the pack with the clear intent of maximizing its lifetime of use. If you do not charge to 100% at least occasionally, you may not be triggering the balancing logic. I say 'may not' because I think it's likely but I haven't absolutely confirmed that.
I should also observe, if you watch the lecture in its entirety it could cast serious doubt on the longevity of the 90kWh pack.
Better LIon battery chargers always have sophisticated charging algos toward the end of a cycle to trickle the pack, of course Tesla being no exception. These algos are specifically intended to top off and allow balancing of the pack with the clear intent of maximizing its lifetime of use. If you do not charge to 100% at least occasionally, you may not be triggering the balancing logic. I say 'may not' because I think it's likely but I haven't absolutely confirmed that.
I should also observe, if you watch the lecture in its entirety it could cast serious doubt on the longevity of the 90kWh pack.
*shrugs* In my testing basically anything above 4.2V causes immediate and measurable degradation that far outweighs the value of the one-time minor capacity gain. Do this a few times and you'll have degraded the cell literally 10-20x faster than charging to 4.2V.
Well... without a few full charge cycles, it is unlikely your pack is balanced enough and the BMS is calibrated correctly to know your actual degradation. That means discharging below, say, 20 miles of range, and then doing a full range charge. Supercharging might not help in this process, possibly doing it at a lower amperage works better. And possibly more than once. Then you get both a balanced pack and a BMS that is calibrated correctly.
Now, is it worth doing that to see the display say 252 or 255 instead of 248? Probably not.
You're going to gave to stop with the misinformation at some point. Not sure what you base this claim on, but sharged to 4.2V, with a low cut amperage (normal), the cell will remain at or near 4.2V once charging is done. They don't reach 3.6V until around 50% SoC. Nominal is just the average voltage over the entire SoC range, which happens to work out to ~50% SoC. The cells don't just drop to 3.6V when you're done charging them.
Based on that battery lecture I was watched, wasn't the best storage method 50%-ish at 30 degrees F?
Edit: 1:08:00, batteries stored at 20% charge (estimated 3.5v) in 1999, and then tested in 2013, had no degradation. Now he didn't mention at what temp they were stored.
Also, it should be noted that I think Tesla hired that guy. So he probably does know what he is talking about.
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