The 85 kWh A pack used different cells with slightly different chemistry. There is now some reason to believe that A packs had greater capacity given bluetinc's data. This is a reasonable inference.
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The 85 kWh A pack used different cells with slightly different chemistry. There is now some reason to believe that A packs had greater capacity given bluetinc's data. This is a reasonable inference.
I don't necesarily think I have a problem with that route. And yes, it can hit 265 miles of range as advertised. But Tesla doesn't need to fib or stretch the truth to make their car successful. It's real world performance sells the car on it's own merits, not what it can do on paper.
I suggest we follow up on the lead from bluetinc. The A packs seemed to have true 85 kWh capacity. That's the most reasonable suggestion thus far as to how Tesla derived 85 kWh. It used to be when the model was first introduced just not any longer. And, believe me folks, be happy you don't have an A pack.
Bangor Bob
Member
Even if A packs had 85kWh of capacity (which personally I don't believe), when the A pack was discontinued the specifications should have been updated. When ICE manufacturers bump up the compression on an engine between model years, the displacement specs (and power output specs) are updated. When they change the size of the fuel tank, that gets updated and the EPA range gets updated. Technical specifications are not marketing material. (Gaming the specs for marketing advantage has a long tradition, however).
This is a very disappointing situation. Their CTO and chief counsel should have strongly argued (and hopefully have, and kept records of it) for disclosing the proper spec. To not do so is a risk to the business. Risks to public companies are to be disclosed to shareholders. Shareholders should be PISSED, the trustworthiness of brand is being damaged (and not for the first time via misreported specs).
This is a very disappointing situation. Their CTO and chief counsel should have strongly argued (and hopefully have, and kept records of it) for disclosing the proper spec. To not do so is a risk to the business. Risks to public companies are to be disclosed to shareholders. Shareholders should be PISSED, the trustworthiness of brand is being damaged (and not for the first time via misreported specs).
@Bangor - Not disagreeing that Tesla should have updated the specs, just saying that the A pack explanation is the most compelling argument as to how Tesla came up with 85 kWh. There is solid evidence that available energy was > 77 kWh. Unless Tesla doubled the footprint of the bricking buffer, which I doubt.
Bangor Bob
Member
It appears there may be a couple applicable SAE standards, I'm not a member so don't have access to the actual documents.
Following the accepted industry standards tends to keep you clear of troubles such as this. There's one for motor power as well...
Following the accepted industry standards tends to keep you clear of troubles such as this. There's one for motor power as well...
Andyw2100
Well-Known Member
It seems to me you are giving quite a lot of weight to one report from one user of one A-pack. While I'm sure the source is credible and means well, I really think jumping to the conclusion that the A-pack actually had more kWh available than the current packs, based solely on this, is premature. There are a number of possibilities that could account for this. I am by no means an expert, but off the top of my head, here are a few:
--Tesla could have made changes in the software, and how trip energy usage is displayed.
--The car in question could have been malfunctioning, and not recording everything properly
--Tesla could may have been doing something funky with respect to working regen figures back into total kWh usage back then
--Tesla could have been displaying the anti-bricking reserve in energy used once energy used exceeded some figure, or displaying some portion of it every x kWh, such that by the time the figures shown were displayed, the entire anti-bricking reserve was being displayed
Sure, I'm pulling some of these out of thin-air, but not any more than others are pulling other theories out of other places. I'm sure TMC members more expert in this stuff can come up with other more reasonable possibilities for why bluetinc's data may appear as it does, but why that may not mean that the A-packs actually were higher capacity than current packs.
LargeHamCollider
Battery cells != scalable
Ahhh but have you tried charging to 4.35v and then discharging at a cell temp of 45 degrees Celsius at C/10 with 2 hour breaks at every 10% of soc discharged? I suspect that there is a way that one could get the 11.9Wh out of these cells but perhaps not, really this is just marketing, and unfortunately this is completely normal for marketing departments, they drive me nuts. My first rule of buying something is never ever ever ever ever trust a salesman.
Also NCR18650b is a family of cells with widely varying characteristics, there is no one cell that has THE properties of an NCR18650b.
Also NCR18650b is a family of cells with widely varying characteristics, there is no one cell that has THE properties of an NCR18650b.
It could also explain why Tesla insists on keeping A-pack drivers on an A-pack : because if they switched all wholesale there might be a risk that someone notices the range reduction which would have exposed the 'little' secret that >=B-packs have a lower capacity. I like this theory the best of all. Smoking gun would be to find the reason why they couldn't continue with the A-pack cells.
Generally there's a motive behind questionable marketing though. With KWH ratings the numbers means absolutely zip to 99% of the buying public. You could have called the cars 120kwh and it would have made no difference because that's not a term in the average person's vernacular. The juice isn't worth the squeeze. Tesla wouldn't intentionally mislead on a metric that basically nobody used to determine whether or not they were going to buy a Model S. If there's no reasonable reason to lie about something like this, and there isn't, then I tend to look at explanations that are more likely.
I floated the idea earlier that Tesla initially thought to go with an 85kwh pack and then eventually ended up with an 81kwh pack and several people have attempted to discredit that theory by saying that the battery has always had the same capacity. To be clear, I'm not suggesting that the pack has changed capacity during production. What I am suggesting is that way back in the early design phase Tesla set a mileage goal and determined that to reach their mileage goal they would need an 85kwh battery pack. In between rolling out the prototypes, naming the different models (40, 60 and 85) and then actually designing the car and it's electrical system, it was determined that they didn't need 85kwh to reach that mileage goal. Maybe they took some weight out of the car or the heavier pack didn't have as much as a drag on efficiency as they thought it might. Whatever the case may be, before the car went into production they determined that they didn't need a full 85kwh pack and instead went with what they needed to reach their goal. Were this the case, it would totally make sense for them not to rename the car. It would just muddy the waters and add needless confusion. Also people would suddenly perceive that they're getting less, despite the fact that the delivered product would perform exactly as advertised. I think this is what happened.
Now with all that out of the way, where I do take issue is in the optional upgrade to the 90kwh pack. In that upgrade literature they specifically refer to an 85kwh pack and a 90kwh pack and if neither is actually that size and they're not explaining this, then that's a problem that's tough to explain simply because now people are making a purchase decision based on kwh and not advertised range as the 90 doesn't have advertised range.
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stopcrazypp
Well-Known Member
That one is a WIP (work in progress) so completely worthless at the moment for industry use and definitely not an "accepted" standard. The SAE electric motor power standard is also a WIP. It needs to at least be a published first edition before it can be used and relied on (after that there will also be continued revisions, but at least you have something basic first). As always, SAE is too late with their standards (just like with J1772 AC and DC/CCS).
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Skimmed the thread up to here from when I was last browsing. Lots of activity!
I'll note again that I did test cells from an A-pack as well as B and D packs. They're all the same.
There are ways to get the "Since Last Charge" meter to show pretty funky results. For example, if you reboot your 17" screen while going down a mountain your kWh used will be artificially higher since it wouldn't have subtracted the regen while it was rebooting. Lots of other ways to boost that, too. There's also a few ways to charge without that meter resetting, which actually can happen due to bugs in older firmwares too. If I were to guess, this is probably what happened with the pic up-thread showing ~79 kWh used.
Tesla's response to the news article is amusing. It would be nice if Tesla would release some actual data on the cells to try and prove me wrong vs just implying that I must have not tested them right. lol. I mean, if it's actually an 85 kWh pack and somehow all of the data points we have are wrong (seems unlikely, but hey, anything's possible right?) then it should be pretty simple for them to clear that up, right?
I'll note again that I did test cells from an A-pack as well as B and D packs. They're all the same.
There are ways to get the "Since Last Charge" meter to show pretty funky results. For example, if you reboot your 17" screen while going down a mountain your kWh used will be artificially higher since it wouldn't have subtracted the regen while it was rebooting. Lots of other ways to boost that, too. There's also a few ways to charge without that meter resetting, which actually can happen due to bugs in older firmwares too. If I were to guess, this is probably what happened with the pic up-thread showing ~79 kWh used.
Tesla's response to the news article is amusing. It would be nice if Tesla would release some actual data on the cells to try and prove me wrong vs just implying that I must have not tested them right. lol. I mean, if it's actually an 85 kWh pack and somehow all of the data points we have are wrong (seems unlikely, but hey, anything's possible right?) then it should be pretty simple for them to clear that up, right?
stopcrazypp
Well-Known Member
If for example someone on the internet said Nissan got their kWh rating wrong on their pack after doing their own tests, does anyone expect Nissan PR to respond any different (or any car company's PR department)? I'm not sure where the expectation comes that Tesla should do a point by point rebuttal (which would involve one of their engineers looking at the post).
I think the closest is for example claims about MPG not being matched. The response by company PR is always on the order of YMMV depending on conditions.
And the point made is a fair point: measured capacity does vary significantly (way more than the 5% claimed here) based on discharge rate and temperature as well as other many other factors not mentioned by the PR person (charge rate, current/voltage cut-off, calendar degradation, cycle degradation).
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Sorry I didn't read everything in this thread as it became so HUGE in such a short time.
But if the A B D packs are all the same, then my theory of increased mi/kWh over the years led to smaller battery pack sizes later is debunked.
But if the A B D packs are all the same, then my theory of increased mi/kWh over the years led to smaller battery pack sizes later is debunked.
I would go with that if every test didn't yield virtually the same result. I would also go with it if Tesla's own battery management system didn't report the pack as ~81 kWh +/- 0.5% in CAN logs from over a dozen vehicles from around the world that have been shared with or captured by me.
When every bit of evidence yields the same conclusion, at some point you just have to accept the fact that it's not an 85 kWh pack.
stopcrazypp
Well-Known Member
Did you control for cycle/calendar life degradation? Given you are using salvaged packs (and not taking brand new packs or cells from the factory) this will likely mean significant variance in the amount of miles and age of the cells you tested. This is further complicated by degradation being non-linear (rapid at the start and slows down later).
One way to account for this as best as possible is to cycle the newer cells so that they match the older ones before doing tests. This is still flawed (given original cycling conditions are unknown and degradation rate may not be the same between cells, which can introduce significant error), but a lot closer to a control.
Under the theory raised by others (A pack having more capacity than subsequent versions), it would match a result where a degraded A pack measures close to a newer B pack when tested at the same time. Otherwise in the case where both are came out of the factory with the same exact capacity, the older A pack should measure lower capacity based on degradation.
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I think Andy's response up thread, quoted below, with few mods in blue, is quite fitting answer to the above
Darn, these engineers better focus on stuff that really matters
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stopcrazypp
Well-Known Member
Are the dozen vehicles you got CAN logs from brand new vehicles? How much variance is there in age? I find it unlikely there be only a +/-0.5% variance in capacity simply based on aging. At least 1-2% loss should easily happen within one year (15k miles) at least from the PIA survey results.
If the CAN report is anything like the CAC in the roadster, it is not a true measure of battery capacity, but rather a rough estimate (and that one does change with conditions and software updates).
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JRP3
Hyperactive Member
I think this may be key. As I said, if when you drive your 85 off the lot the cells are capable of delivering close to 85kWh then it's a moot point. If it's 81-82 right off the lot then that's a bit more of an issue, though again if the car delivers range as advertised it could be argued that Tesla delivered you a more efficient vehicle.
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