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

[stopcrazypp]

For me the issue is, (and it's a minor one), why did they accurately label the 60 packs but not the 85 packs, and, more importantly, will other packs be accurately labeled going forward?

I answered this question about 2-3 times already, but keep getting ignored. The capacities were all announced before the production packs were designed. 85kWh pack came first and 60kWh was a modification of that one (and 40kWh a software limited 60kWh pack). I have more details in the comment train I quoted, but basically for 60kWh there are constraints in how many cells they can blank out and still maintain their battery longevity and charge/discharge power goals. It would be different if they chose to use different cells for the 60kWh pack (which might have been original plan that was cancelled when people overwhelmingly chose the 85kWh and they knew they would cancel the 40kWh pack).

I find it weird how people have to always assign malicious intentions but completely forget the history of what happened. Long story short: Battery capacities announced late-2011, the Model S was produced in June 2012 with 85kWh as the main pack, 60kWh came half a year later in January 2013 (40kWh was cancelled April 2013). The decisions made on what to do in the production version likely came far later than when they announced the 60kWh and other battery capacities in late 2011 (and it did not make sense to change the number).

I say this especially because they didn't even have the 40kWh developed yet up to the point they cancelled it and if you look at the 60kWh pack (which has cells blanked out), I think it is very obvious Tesla did not design the pack in a systemic way for all the capacities from the start.

My comment below:

The "marketer" or "marketeer" theory assumes that they had designed all the packs already in 2011 and then decided to underrate the 60kWh pack and overrate the 85kWh just to give the larger pack some marketing boost. I don't think the time-line supports that theory. Rather they announced the capacities and then designed the packs to get about the same capacity as announced (the only pack that might have been designed already beforehand was the 85kWh as the primarily design).

 

[smac]

Its such a bizarre thing, Tesla would not have been hurt in the slightest if they called the 85 an 80. Nobody is comparing its battery capacity to anyone else's. The only thing it did was push some people who were on the fence between the two packs to go to the 85. Which I guess makes Tesla a bit more money, but it doesn't seem worth the effort.

The other subtle thing is it helped justify the base price of the car to an extent. I clearly remember press around the time trying to use the 25 kWh difference to value how much Tesla were paying per kWh

 

[scaesare]

Hmm. So the difference between 100% and 90% is only 0.1 V? That makes 90% daily charging not look so great. I thought the difference was greater, like 0.15 V.

Remember, the entire "usable" voltage range of a Li-ion cell is only about 1V (i.e. from ~3.2V to 4.2V), so even thought it's not necessarily a strict linear curve, a 0.1v change for every 10% SoC is about right.

 

[JRP3]

I answered this question about 2-3 times already, but keep getting ignored. The capacities were all announced before the production packs were designed. 85kWh pack came first and 60kWh was a modification of that one (and 40kWh a software limited 60kWh pack).

I speculated something similar as well earlier in the thread, I'm just not sure it's the definitive answer, and if Tesla should have changed the designation of the 85 when they discovered they weren't getting near 85kWh from the cells. I would have thought Tesla might have tested some actual cells before committing to a pack size.

 

[apacheguy]

Remember, the entire "usable" voltage range of a Li-ion cell is only about 1V (i.e. from ~3.2V to 4.2V), so even thought it's not necessarily a strict linear curve, a 0.1v change for every 10% SoC is about right.

It should not be linear at the top end. Voltage should drop sharply from 100% to 90% and then even out below 90%.

The UI supercharge voltages are not the settled cell voltages. I'll have tl go through and make a chart of actual SoC vs cell voltages, since the UI supercharger numbers are higher than actual.

He was reporting settled cell voltages.

 

[wk057]

He was reporting settled cell voltages.

That's not how the post reads. Current has nothing to do with settled cell voltages.

My measured data... ( for current < 20A )
from Tesla UI power meter

For example, no-charging/discharging 80% on the dash in my car and my wife's is 3.95V +/- 0.02V. But, for example. during supercharger the cell voltages read at 3.95V when the pack is at ~55% SoC.

5% on my P85D dash is 3.37V. A recent supercharge to 98% left my cells at 4.15V after a few minutes, with during charging voltages at 4.2V.

90% I don't seem to have in the notes I have handy (I'm not at home) but it was around 4.05V.

 

[apacheguy]

Ah, those numbers make more sense. I misinterpreted pupik's data.

 

[smac]

The "marketer" or "marketeer" theory assumes that they had designed all the packs already in 2011 and then decided to underrate the 60kWh pack and overrate the 85kWh just to give the larger pack some marketing boost. I don't think the time-line supports that theory. Rather they announced the capacities and then designed the packs to get about the same capacity as announced (the only pack that might have been designed already beforehand was the 85kWh as the primarily design).

I've always suspected the original intent was a 14 x fully populated module pack. (so something around 70kWh). The hump of the extra 2 modules always seemed a strange design decision if for no other reason than transportation volume, and vehicle packaging freedom.

Maybe at the time they hadn't dialed in the efficiency to hit range requirements (which was saying it was a 300 mile car) or couldn't get the performance, so added the two extra modules.

 

[wk057]

I've always suspected the original intent was a 14 x fully populated module pack. (so something around 70kWh). The hump of the extra 2 modules always seemed a strange design decision if for no other reason than transportation volume, and vehicle packaging freedom.

Maybe at the time they hadn't dialed in the efficiency to hit range requirements (which was saying it was a 300 mile car) or couldn't get the performance, so added the two extra modules.

The front hump in the battery with the oddball module upside down on top of the 15th did strike me as a little strange. 15 modules would have made sense (since the vertical space with the 16th module is the odd thing to me, not so much the 15th spot) which would be about 75 real kWh, 71 kWh usable, or about 245 rated miles in a theoretical S75 with a nominal pack voltage of ~324V, charged ~378V.

 

[smac]

The front hump in the battery with the oddball module upside down on top of the 15th did strike me as a little strange. 15 modules would have made sense (since the vertical space with the 16th module is the odd thing to me, not so much the 15th spot) which would be about 75 real kWh, 71 kWh usable, or about 245 rated miles in a theoretical S75 with a nominal pack voltage of ~324V, charged ~378V.

Good point I forgot the 15th was directly underneath the 16th!

I wonder what the 2 cycle EPA range of this theoretical 75 pack would have been, as certainly the delays in launch pushed them into the stricter testing regime. Probably very close to the magic 300 miles, as Tesla claimed 320 miles under EPA 2 cycle for the Model S with the 81kWh pack.

Model S Efficiency and Range | Tesla Motors

 

[pupik]

My measurement is ok. My english is bad :redface: sorry
Note that standard differences between the cells are 0.01-0.02V for settled cells < 95% SOC
for current 0 - 20A is decrease only 0 - 0.02V per cell
standard current for parking car is only 0 - 0.6A

for settled cells = current < 0.6A

100% = 4.16 - 4.19V
90% = 4.06 - 4.08V
70% = 3.85 - 3.87V

min. tolerance +/- 0.01V temperature today here is 8-10C !

so, I think optimum for long life is charging max. 80% better 75%
not forget that these are special Panasonic/Tesla cells and still isn't data sheet
and not forget Tesla warranty is 8 years

 

[jpet]

70% = 4.85 - 4.87V

You might want to quickly correct this into 3.85 - 3.87V. :wink:

 

[MsElectric]

So are we going to create one of these threads now also for the 90 kWh battery pack? :crying:

 

[lolachampcar]

Why, did they get that one wrong too?

 

[MsElectric]

Why, did they get that one wrong too?

Motortrend tested it and they reported it is exactly 90 kWh :tongue:

All specs now have an "As tested by Motortrend" footnote :wink:

 

[jpet]

Why, did they get that one wrong too?

Let me guess, it has 6% more capacity than ours, so 81 kWh X 1.06 = 86 kWh

- - - Updated - - -

Here's an educated guess...

7104 X 3.2 Ah X 3.6V = 81.838 kWh
7104 X 3.4 Ah X 3.6V = 86.953 kWh

 

[wk057]

As said in my first post in this thread, I haven't been able to check any data on 90's just yet. Soon I think, but not yet.

But the P90D is rated at 270 miles, and P85D at 253 miles, which points to about 82 kWh usable from an 86 kWh pack.

Showing my work:
81 kWh real capacity - 4 kWh protection = 77kWh usable ("85")
77000 Wh / 253 miles = 304.35 Wh/mi.
304.35 * 270 = 82.17 kWh
82.17 + 4 = 86.17 kWh real 90 pack capacity

But, if it were in fact 90 kWh with 86 kWh usable, that'd be ~282 miles of rated range for the P90D. So either the 90 pack is over specified or the P90D is ~5% less efficient than the P85D... which uses the same motors... and same inverter... and same everything else. Seems overstated is more likely.

This is just speculation based on some pretty reasonable assumptions... so I can't say definitely yes or no to it being wrong until I get some real data.

 

[jayx]

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.

Maybe there is some misinterpretation, but it’s not exactly like going from 90% to 80% and back to 90% equals 0.1 cycle worth of wear, which would mean ten times 0.1 cycles = 1 full cycle. And it makes big difference if it’s partial cycle. Jpet linked (post #366) document which clearly says wear is much smaller if you do cycles 60% compare to 100%, I can add another one which reveal pretty awesome results – over 100000 short cycles and cells were not dead yet!: http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA515369 I know it’s for completely different and old battery, but I think basics apply to all Li-Ion batteries, and new ones should be even better.

By the way, as 85kWh pack has just been discontinued and everyone is wondering what’s the true capacity of 70 & 90kWh packs, I think wk can get some preliminary capacity data from battery BMS via CAN logging.

 

[dirkhh]

Let me guess, it has 6% more capacity than ours, so 81 kWh X 1.06 = 86 kWh

- - - Updated - - -

Here's an educated guess...

7104 X 3.2 Ah X 3.6V = 81.838 kWh
7104 X 3.4 Ah X 3.6V = 86.953 kWh

That is OUTSTANDING news. Because while it is hard to round 81kWh to 85kWh, it's very easy to explain that you are rounding 86kWh to 90kWh

Which once again proves that Tesla is monitoring this forum very closely!

:-D

 

[stopcrazypp]

I've always suspected the original intent was a 14 x fully populated module pack. (so something around 70kWh). The hump of the extra 2 modules always seemed a strange design decision if for no other reason than transportation volume, and vehicle packaging freedom.

Maybe at the time they hadn't dialed in the efficiency to hit range requirements (which was saying it was a 300 mile car) or couldn't get the performance, so added the two extra modules.

That might be true also.

Anyways, given how the pack is designed, it seems they applied some "just in time" design (basically designing as they go along) to fit with the range promises way back in 2009. The packs do not have a signature of something that was designed at once. There are a lot of bizarre design decisions that do not make sense if everything was designed at one go.

The other one I pointed out was the decision to blank out cells while also using less modules in the 60kWh. This ruins both module commonality AND also pack production commonality (which is why I never guessed they would do that). If it was designed at the start, I see no reason why not to set the break points in capacity such that blanking cells would not be necessary.

Anyways it does not seem like they had all the packs designed already in 2011 and then had the marketers have their go at it. Rather it seems like they took their promised range numbers (which were already approaching 3 years old already) and gave rough estimates of kWh needed to achieve it (in 5kWh increments) taking into account weight. Then designed the packs to fit along with that roughly.