Tesla's 85 kWh rating needs an asterisk (up to 81 kWh, with up to ~77 kWh usable)

[stopcrazypp]

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.

That is not how lithium ion battery charging works. Look at a CC-CV curve of a 4.35V cell and a 4.2V cell for example (note where the voltage stops):

Then look at discharge curves (note where the voltage starts):

 

[kennybobby]

The charging voltage may be held at or slightly above 4.2 in order for current to flow, but i doubt tesla would allow any cells to remain at 4.2 very long.

There is a chart of brick voltages after a 100% charge by LolaChampCar in his CAN-Logging thread.

 

[Johan]

Quantum: dude, if you don't know that "nominal voltage" is a mathematical construct, a sort of average voltage during a full discharge cycle that can be used to calculate energy storage capacity of a battery cell, you really shouldn't be arguing with wk057, jpet, JRP3, stopcrazyppl and other people with intimate knowledge and understanding of Tesla/Panasonic cells.

Let's get this perfectly clear: yes, in order to charge a battery one must apply a voltage delta, to make current flow in to the battery. At 100% SOC that charging current will be slightly above 4.2V. Keep increasing it and the cell starts degrading rapidly with a real risk of exploding (this is how Panasonic has defined 100% SOC). As you disconnect the charger and start drawing current you are definitely going to see 4.2V from the battery cell (unless you start drawing heavily in which case you'll experience voltage sag, which is another phenomenon).

 

[snooper77]

@wk57: How about you summarize your key findings so far in a few bullet points in your first post?

That way people will be less likely to miss your key findings (and thus won't re-iterate claims that you have already debuked), and you'll also find it easier to rebut if they still do by simply referring them to the bullet list.

 

[lolachampcar]

attachment.php
Hopefully the animation part works when linked. This should help with the battery voltage dropping BS which JRP has pointed out.

If not, its mid way down the page here
Chassis CAN Logging To ASCII Text Plus Graphing - Page 5

 

[CO2CLEAN]

attachment.php
Hopefully the animation part works when linked. This should help with the battery voltage dropping BS which JRP has pointed out.

If not, its mid way down the page here
Chassis CAN Logging To ASCII Text Plus Graphing - Page 5

Works like a charm! Great animation that clearly shows what is happening.

 

[brec]

... its mid way down the page here
Chassis CAN Logging To ASCII Text Plus Graphing - Page 5

Off-topic and thus I hope not worthy of public replies, but I don't know where else to post this to make it useful:

The number of posts per page varies by user from 5 to 500 depending on Settings::General Settings::Thread Display Options::Number of Posts to Show Per Page. It is unfortunate that page titles (as displayed in links such as the one quoted) include the page number. If the link is to a specific post, no harm; but if it's indeed to a page of posts it may be less useful than intended.

 

[dsm363]

mod note: the posts were being reviewed, not ignored so making accusations of being ignored by volunteer moderators not helpful. moved to
snippiness

 

[OddB]

mod note: the posts were being reviewed, not ignored so making accusations of being ignored by volunteer moderators not helpful. moved to
snippiness

Fair enough. .. But you should have left wk057 's comment about why he had left his own thread....
And why not remove Quantum's comments that are clearly pure trolling ?

 

[dsm363]

Fair enough. .. But you should have left wk057 's comment about why he had left his own thread....
And why not remove Quantum's comments that are clearly pure trolling ?

Some people leave threads often but come back. A lot of posts were swept up in it. He also quotes Quantum`which contains language that was complained about so that post was moved as well.

 

[lolachampcar]

sorry brec.... didn't know that.
I really need to learn how to reference a specific post instead of referencing a page.

 

[dsm363]

sorry brec.... didn't know that.
I really need to learn how to reference a specific post instead of referencing a page.

Click on the number of the post. For example your post above is post 391
Tesla's 85 kWh rating needs an asterisk (up to 81 kWh, with up to ~77 kWh usable) - Page 40

you click on the number and then copy and paste the URL from your browser.

- - - Updated - - -

Was the post you were talking about #48?

Chassis CAN Logging To ASCII Text Plus Graphing - Page 5

 

[wk057]

mod note: the posts were being reviewed, not ignored so making accusations of being ignored by volunteer moderators not helpful. moved to
snippiness

Thanks.

To set the record straight (since this post kind of reads like I was being unfair to the volunteers here, since context is lost) within 10 minutes of me reporting the post in question I received a PM from a moderator about it. The PM was about how they thought it was interesting that I'm reporting rude posts here on TMC, but that I've left certain things up on the little mini-forum that I started back when I was banned from TMC (and for the record, had essentially closed to registrations soon after and haven't touched since... it was quite dead). Fair point I suppose, but I hadn't gotten around to officially killing off the dead forum yet. So, my report was certainly seen by a moderator, and instead the moderator took the time to write me a PM about something someone posted on my dead forum months ago vs simply dealing with the post I reported. Knowing the report was seen, but not acted upon over 12 hours later, and given the PM I received, I made the assumption that my report was being ignored.

Since I was mistaken (post in question needed more moderator peer review), my apologies. Additionally, I've gone ahead and removed my entire little mini-forum. Instead skie.net will just have links to and info about my projects, my important threads here, etc. Hopefully there will be no more contention about the site now.

 

[lolachampcar]

Yes
Perfect. Thanks DSM.

 

[supratachophobia]

I have a question for wk and others that have been involved in these battery tests. What does the optimum life of a Tesla battery look like? Basically daily charging/discharging threshold? Going by Tesla's suggestion, daily charging to between 50 and 90% is as much as they will say. And they give no mention to the effects of running a battery down to a certain percent.

I understand their motivation. They don't want owners to worry about it and most likely the effects on the battery are a matter of only single digit percentages. They seem to have built fairly robust technology and systems into the car to make that a reality. But assuming that the owner is willing to assume a minor amount of inconvenience (both by worrying about how much to charge and how much to use of that charge), what is the absolute best practice on how to treat your Tesla battery?

 

[smac]

what is the absolute best practice on how to treat your Tesla battery?

In short there is none.

The 100% best source for a guidance would be Tesla, and they offer none explicitly other than keep it under 90%.

FWIW I charge mine to 80% in general, but then I fully intend handing it back and getting another.

One thing I will say is I set mine to a full 100% trip, and I forgot to unset it there once, next day I went out to my car and found it sat fully charged. At that point I had a minor moment of "regret" for the pack. But hey it will be going back to them long before range degradation is my problem....

... besides I don't feel too bad, it's their choice if they wont make it clear what the optimum is and leave charging to some customer determined slider, and won't force it to reset after a "trip button", just to avoid range averaging on the spec sheet like the Leaf

 

[jpet]

They don't want owners to worry about it and most likely the effects on the battery are a matter of only single digit percentages.

Personally I do not believe the effects to be single digit percentages but it depends on your time horizon and milage. In any case, I use the research that's available on Li-Ion cell degradation and I apply the conclusions to my daily charging / discharging habits. It is very easy if you only need around 30 to 40% of the pack capacity per day.

I have posted a link to a quite interesting research paper on the effect of DoD on the degradation of Panasonic Li-Ion cells in this thread a couple of days ago.

Here's another link to a Battery University page you might want to read very carefully:
How to Prolong Lithium-based Batteries - Battery University

Note that the Tesla battery is kept in a better shape since it is temperature controlled by the BMS but I do not believe Tesla has created some sort of "Super Cells" that are much better than anything else out there. Tesla cells will degrade and die like any other Li-Ion cells.

I'm trying to find out at what SoC % the cells resting voltage is 3.92V. I am without my car since December 21st because I was rear-ended. As soon as I have my car back, I will use a CAN bus logger to find out the best SoC to charge the car to. I'm currently using 70%.

Why 3.92V? "Charging to 3.92V/cell appears to provide the best compromise in terms of maximum longevity, but this reduces the capacity to only about 60 percent."

 

[supratachophobia]

In short there is none.

The 100% best source for a guidance would be Tesla, and they offer none explicitly other than keep it under 90%.

FWIW I charge mine to 80% in general, but then I fully intend handing it back and getting another.

One thing I will say is I set mine to a full 100% trip, and I forgot to unset it there once, next day I went out to my car and found it sat fully charged. At that point I had a minor moment of "regret" for the pack. But hey it will be going back to them long before range degradation is my problem....

... besides I don't feel too bad, it's their choice if they wont make it clear what the optimum is and leave charging to some customer determined slider, and won't force it to reset after a "trip button", just to avoid range averaging on the spec sheet like the Leaf

Do you think lower discharge levels adversely affect the battery? In other words, charge to 80% knowing you'll use it down to 30% or charge to 60% knowing you'll use it down to 10%.

 

[jpet]

Do you think lower discharge levels adversely affect the battery? In other words, charge to 80% knowing you'll use it down to 30% or charge to 60% knowing you'll use it down to 10%.

You can find the answer on page 94 of the research document I posted a link to in this thread a couple of days ago. There is almost no difference between cycling between 80 -> 30 vs 60 -> 10. But, since your car will have better performance when cycling at higher voltages + you will have a greater buffer available in case you need some extra range at the end of the day, I would cycle in the 80 -> 30 region.

Here's the chart from the research:

Note that DoD is the inverse of SoC so 10 to 70 DoD = 90 to 30 Soc and 40 to 100 DoD = 60 to 0 SoC.

By the way, in your example you have another option available and that is to cycle between 70% and 20%. That's the option I would personally choose since 70% will be closer to the optimum of 3.92V and you will also stay closer to the mid-point of the 3.6V nominal voltage of the cell.

 

[apacheguy]

@jpet - If you deeply cycle your pack a few times to give the range algo more data, does your rated range go up? I've found that it does not and that it possibly goes down. We have similar charge habits. I see you charge to 70%. I regularly charge to 80%.