stopcrazypp
Well-Known Member
The way they put it does not make sense. The rated cell capacity should be higher than the 85kWh pack capacity, esp. given the Tesla limits both the top and lower end of the charge cycle.
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The way they put it does not make sense. The rated cell capacity should be higher than the 85kWh pack capacity, esp. given the Tesla limits both the top and lower end of the charge cycle.
I've pulled over 81kWh out of my standalone pack in testing already and I could have pulled more (voltages were still safe) but I didn't want to fully discharge the pack. I figured 5% SoC was low enough. No idea where they got their 80kWh "actual" number...
palmer_md
Member
These guys are far more conservative on their estimates for Tesla than I am. It seems they were paid to write this report by someone wanting to compete with Tesla. Like when I had my house appraised once by a buyer for my home and once by the seller. Very different results. Great information on what exists today, but their projections are what seem to be lacking. My estimates are much closer to what I've seen DaveT write in his megaposts and newsletter.
Well, the Model S doesn't allow a full discharge on the pack for a variety of reasons. 5-6% safety margin seems reasonable.
In my standalone setup I have no such restrictions, so I could use the full capacity if I wanted to, but I think I'll stick with the same methodology as when it is in the Model S to help with longevity.
JRP3
Hyperactive Member
I assume by "actual" what they mean is "allowed". A 3.25 ah cell at 3.7V is 12.025Wh x 7104 = 85,425.6Wh
This makes sense. They obviously are writing against Tesla, however. "Actual" to me implies that this is what the battery is actually capable of... which in there case dsying 80kWh is incorrect. Something like "Permitted" or even "Available" would be more accurate and less biased against the pack.
To what voltage did you take your pack down that you are calling "5%"? Panasonic uses 4.2 (403.2 pack) as the top and 2.5 (240 pack) as the cell bottom in their testing/data sheets, just curious what you are using...
Using 4.2 @ 3.25A-hr is the 'available' if 3.25 is the correct value, times 7104 is about 97 kWh. Allow margin at top and bottom and you have an 85 kWh pack. Of course the pack label indicates 85kWh, 400 VDC which implies a lower capacity cell than the reported 3.25 A-hr.
Using 4.2 @ 3.25A-hr is the 'available' if 3.25 is the correct value, times 7104 is about 97 kWh. Allow margin at top and bottom and you have an 85 kWh pack. Of course the pack label indicates 85kWh, 400 VDC which implies a lower capacity cell than the reported 3.25 A-hr.
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You use the nominal voltage (3.7V) when determining the capacity not the maximum rated voltage.
Highlight the "Available upon purchase..." parts and copy-paste into Notepad to read under them. Lots of juicy information there.
$218 per kWh sounds interesting. Not sure what he means by 150kW EV powertrain costing more than 150kW ICE?
Tesla's IGBT cost for the PEM in the Roadster was less than $1,500 due again to the method of using multiple individual devices, like in the battery. Additional electronics doubled this, and the cost of the casing, cables and materials probably put it around $4,500. Motors are inexpensive, consisting primarily of wound copper, which is normally done by machine.
The Model S drivetrain is extremely well optimised, using less components and less control electronics. It probably costs under $6,000 to manufacture, including the electric motor.
This report smells of "what automakers want to hear"...
$218 per kWh sounds interesting. Not sure what he means by 150kW EV powertrain costing more than 150kW ICE?
Tesla's IGBT cost for the PEM in the Roadster was less than $1,500 due again to the method of using multiple individual devices, like in the battery. Additional electronics doubled this, and the cost of the casing, cables and materials probably put it around $4,500. Motors are inexpensive, consisting primarily of wound copper, which is normally done by machine.
The Model S drivetrain is extremely well optimised, using less components and less control electronics. It probably costs under $6,000 to manufacture, including the electric motor.
This report smells of "what automakers want to hear"...
JRP3
Hyperactive Member
Neat trick.
Tesla is charging less than $5K for the front drivetrain in the SD. Of course it is smaller than the standard RWD drivetrain.
Indeed, and what I'd expect from AAB.
stopcrazypp
Well-Known Member
The problem is all of Panasonic's NCA cells are 3.6V nominal, not 3.7V (there may be some third parties that claim 3.7V, but all of Panasonic's official datasheets say 3.6V).
A 3.35 Ah cell would work out (3.6V*3.35Ah*7104 = 85674.24Wh) and fit with an existing cell (the NCR18650B). So I suspect their numbers are wrong.
No maybe that's what YOU do, but i monitor voltage, current and time during charging and discharging to determine capacity. Then i can integrate the current-time curve to determine the cell capacity in A-hr, and i can multiply that times the voltage to determine the energy content of the cell in kWh. No percentages, SOC, ranges, miles, or # of turtles showing, just the basic measurements doing it the same way Panasonic does...
I think rlang59 was using the "royal" you, in that he was stating that's what is standard in the industry, what will be stated on a datasheet, etc...
Here's an example: PANASONIC NCR18650 DATASHEET
JRP3
Hyperactive Member
Tesla is a third party, and they are the ones rating the pack. They may feel that each cell sees a low enough average C rate that the nominal voltage ends up being a bit higher than the rating from Panasonic. We also don't know what Panasonic is rating the specific Tesla cells at. Of course AAB could be wrong too.
lolachampcar
Well-Known Member
Tesla removing the safety features and having slightly tweaked chemistry (assumption on my part) for automotive use may give them better capacity than the commercial cell when used for a specific automotive application.
The panny nca data sheets say 3.65V nom
it is a 3.3Ah cell
pack is over 85kw but you can only pull about 80kw out (in the car). This is "brick insurance"
stopcrazypp
Well-Known Member
The third parties I'm referring to are less-than-honest sellers who wish to inflate their numbers and thus say it is 3.7V.
The Panasonic numbers are rated at 0.2C (~670mA, in 85kWh equivalent to 17kW discharge):
http://www.batteryspace.com/prod-specs/8678_specification.pdf
From Tesla's blog, at 55 mph, the Model S uses about 15kW of power, so it's about the same.
http://www.teslamotors.com/de_AT/blog/model-s-efficiency-and-range
Even at 200mA (~0.06C) discharge (5kW discharge for 85kWh pack), the boost in voltage is not enough for a 0.1V increase:
http://lygte-info.dk/pic/Batteries2...asonic NCR18650B 3400mAh (Green)-Capacity.png
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