JRP3
Hyperactive Member
Maybe we both read different graphs, but till now I just did not seen any graph where the Tesla cell discharge significantly more than 3100mAh.
Looks like about 3300mAh to me
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Maybe we both read different graphs, but till now I just did not seen any graph where the Tesla cell discharge significantly more than 3100mAh.
This. Anyone can throw a cell on a test bench, and come to a conclusion. Few are hacking into and diagnosing complex systems like wk. Voicing your opinion has little to with credibility.Not everyone has the time or ability to read and keep up with the rapid pace of wk057's projects and tinkering, but he has described all the instrumentation and methods in various posts while dismantling a couple of tesla battery packs, designing and installing a huge solar array grid on his house, including wiring up all the connections, controllers and other equipment necessary to use the packs to store the solar energy and power-up his house and charge his teslas completely from that system.
And he didn't die of electrical shock or burn down his house or car, and he still has all his fingers and toes.
Oh yeah and in his free time he reverse engineered the CAN busses used by tesla so he could read the actual brick voltages, pack currents, motor torque and power, and all the diagnostic screen info, and described how all that was done in another thread.
Like i said it's difficult to keep up, but he has plenty of validity and credibility amoung the technical crowd. His knowledge, skills and abilities have been demonstrated numerous times--nobody practiced in the art of electrical engineering would doubt his results.
Finally, on Flathill I agree with the other posters - tone it down bud. On the other hand, I understand his frustration. This thread has been a good example of a failure in this forum (not due to the mods) - We have posters like ... MukeBur who clearly have nothing substantial to add continuing to post - while wk has been driven from the thread, and he is one of the few who SHOULD continue to contribute.
Don't get me wrong - I know wk is very sharp and capable of understanding how to make the argument he's trying to make - it just wasn't complete and he got a little ahead of himself in terms of technical understanding - but I know he's sharp enough to get it. He is also a revolutionary / whistle-blower personality type - which I also respect.
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This post is a perfect example of why the technical minded, wk, myself, other... will always be driven from further posting - and threads that have the potential to make sound technical conclusions will continue to be rare on this forum.
Right. Even if okashira is right, if I guess at 25kW average highway cruising draw, then I get approximately 1A per cell, plus or minus depending on pack voltage, etc. So even his data says that under normal usage you'll never get 85kWh out of the pack.
...and that still doesn't explain the difference between 60 and 85. Although I don't believe EPA vs EPA is true at all for 70 vs 90.
Look at test conditions. That is 1A discharge at the slowest one. You aren't going to get the nameplate capacity of any cell at 1A discharge. That test was what I referred to before, where he wasn't trying to get max capacity. To do that most testers use a 0.2A load (he suggested even lower up thread).
For reference, the EPA UDDS cycle is 19.6mph average speed and Model S gets 320+ miles on it, so 16+ hours of discharge, probably 17+ hours if looking at nameplate (AKA C/16 to C/17 discharge). That nicely works out roughly to 0.2A for the cells in question.
One thing I noted in looking at the NCR18650B: although Panasonic dos not list a power (in watt-hours) spec for their cells [...]
Thus, for this cell, the power density per gram is 243/1,000=.243 Wh/g. And given the cell weighs 48.5g, we can determine the power would compute to 0.243*48.5=11.8 Wh.
I would be careful on that. The weight specifies the max cell weight. And if you see the little (1), (2), (3) footnotes that the test conditions may not be the same on the different numbers.Thus, for this cell, the power density per gram is 243/1,000=.243 Wh/g. And given the cell weighs 48.5g, we can determine the power would compute to 0.243*48.5=11.8 Wh. Thus, we can reasonably extrapolate that these cells have a manufacturer nameplate rating of 11.8Wh,
I would be careful on that. The weight specifies the max cell weight. And if you see the little (1), (2), (3) footnotes that the test conditions may not be the same on the different numbers.
Nice find! Just a quick comment though: Wh is a measure of energy, not power (that would be W) :wink:
I would be careful on that. The weight specifies the max cell weight. And if you see the little (1), (2), (3) footnotes that the test conditions may not be the same on the different numbers.
Manufacturers will not post an official nameplate Wh. They will give nominal voltage and nameplate capacity in mAh. You have to do the math yourself. For the cell in question, the official capacity is "3350 mAh", but everywhere it will be advertised at "3400mAh".
Not a full capacity test. Test conditions:From the linked review below, it looks like the BE cell was tested at about 10.5 Wh of total energy discharge:
Comparing Panasonic 18650 BD vs. Panasonic 18650 BE 18650 Battery | BATTERY BRO
I agree with your point, I just say that you have be careful in extrapolating from energy density figures when the test data and conditions may not be the same between the two specs. Simple multiplication of nominal voltage and capacity is typically how "nameplate capacity" is figured.Derp on my end... thanks. Corrected.
My point is that the rating may very well be based of what the manufacturer provides. That same spec sheet for the B lists 3350mAh @3.6Vnom as well, which equates out to > 12Wh per cell... so it may be premature to assume that these cells are would have an industry accepted rating substantially less than what Tesla specs them to be to comprise their pack.
I would be careful on that. The weight specifies the max cell weight. And if you see the little (1), (2), (3) footnotes that the test conditions may not be the same on the different numbers.
Energy density based on bare cell dimensions
I agree with your point, I just say that you have be careful in extrapolating from energy density figures when the test data and conditions may not be the same between the two specs. Simple multiplication of nominal voltage and capacity is typically how "nameplate capacity" is figured.
Maybe this is true for charge current, but definitely not for discharge, esp. when we are talking about single percentage differences being significant (we are disputing a 5% overall difference in this case). The IR losses at least partially are going to be what contributes to this (edit: mAh capacity also changes even more significantly)....
Charge: 0.3-0.5C with cut-off current C/50
Discharge: 0.2C
and this can be translated as you don't get significantly better capacity/energy if you set even lower testing currents.
Not a full capacity test. Test conditions:
Charge end at 4.16 V (vs 4.2V)
20 or 25 degrees Celcius ambient temperature (difference between 20C and 25C gave a 5% difference in the NCR18650B, although the claim is less than that for NCR18650BE)
.61 ampere discharge current (vs 0.2A or even 0.05A suggested by okashira)
2.5 volt cut-off point when the discharge ends
2.5A charge rate (Panasonic is rated 0.909A)
Kelvin testing is 4-wire, not 2-wire.
A good time measuring device is also needed in addition to the current sense and voltage measurement.
The panasonic data sheet above would also correctly be interpreted as nominal 3200Ah x 3.6V = 11.52 Wh, times 7104 gives 81.84 kWh.
So... I went looking for a the datasheet for teh NCR18650BE, after okashira pointed out the likelihood that those are the cells (or very similar) that Tesla is using. Despite their being readily available for other Panasonic NCR18650 variants, I cannot find an authoritative datasheet on the BE anywhere, whech may be telling in and of itself.
One thing I noted in looking at the NCR18650B: although Panasonic dos not list a power (in watt-hours) spec for their cells, they do list the following:
- Gravimetric energy density (in Wh/kg)
- The weight of the cell
For example:
View attachment 111090
Thus, for this cell, the energy density per gram is 243/1,000=.243 Wh/g. And given the cell weighs 48.5g, we can determine the energy would compute to 0.243*48.5=11.8 Wh. Thus, we can reasonably extrapolate that these cells have a manufacturer nameplate rating of 11.8Wh,
A Tesla 85 pack with 7,104 of these cells would have a manufacturers rating of 83,827Kw/h. That rounds to 84 for whole numbers, or 85 for the nearest "5".
Given that the NCR18650BE undoubtedly has slightly different chemistry from the NCR18650B, I don't think it's outside the realm of reason to suggest that Panasonic themselves rate the cells such that the pack logically rounds to 85KW/h.
Anybody find a datasheet for the BE??