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Discussion in 'Roadster: Technical' started by doug, Apr 4, 2009.
All about the Roadster battery (ESS)
Here is what I have learned from my research:
6831 cells - 69 parallel/99 series
18650/2,2Ah Li-ion cells (18 mm in diameter and 650 mm long)
450 kg/992 lb
A conventional 18650 cell weights ~45 gram. 45 g * 6831 cells = 307 kg
So "only" 300 kg out of 450 kg ESS are cells.
The most 18650 cells that I'm aware of have poor discharge rates (2C or less) and a poor cycle life (500 cycles or less). The Cycle life is probably extended due to the very good BMS and cooling/heating system but the discharge rate is a misery for me.
The Roadster motor generates 215kW peak at the output shaft. That means that the inverter pulls 575 Amp from the pack, even if we imagine a perfect situation where the 375 pack voltage won't drop (what it does in real life) and that there are no looses from the cells to the motor output shaft. That would be almost 4C for every cell. I guess that 5,5-6C is more realistic in real life.
We also know that each cell is double fused. This also sounds a little strange.
New battery pack page here:
structure for ess
Here are some pictures for ess .
There's supposed to be 9 bricks x 69 cells = 621 per sheet, 6,831 total.
However, its hard to know how precise the drawings were supposed to be, or if the artist couldn’t count … because influenced by a bit to much wine and 10 minutes to spare, I counted 627 cells in each sheet, giving 6 more than stated, and 6,897 total !
Maybe I should sober up and count again ...
What the illustrations show nicely is how densely the cells are packed and how the cooling system is plumbed in - details I've not seen before.
What is the actual chemistry?
Tesla Motors says Lithium-ion, but that's a generic category, isn't it?
Someone commented after an online article and claimed that Tesla Motors uses Lithium Cobalt oxide (LiCoO), but when I searched for those terms all I could find are Tesla's plans to recycle their batteries at a facility that can create LiCoO batteries from the remains of the ESS. Considering how plastics recycling works, there's no guarantee that the ESS is LiCoO just because you can recycle them into that.
Anyway, does anyone know what the actual chemistry is for the shipping Roadster ESS?
If you look at the safety sheet they are LiCoO2.
Did you notice the dotted line to a block marked "Internal Power Generator"? Serial hybrid...
Is the 53kWh figure correct ? Tesla's battery site page says 56kWh (Roadster Technology - Battery | Tesla Motors).
Was it 53kWh earlier & they have increased the capacity now ?
Actually I think the original specs said 56, then they changed it to 53.
I am not sure we got a 100% clear answer why the number moved around a bit. It may be that they derated the pack for longevity purposes, or switched cells.
I am not sure if they were 2400mah or 2200mah cells.
There were also some rumors that some roadsters might have had a lesser number of a higher capacity cells.
(Another rumors that a half dozen Roadsters could do 0-60 in 3.5s... But just unsubstantiated rumors...)
It's always been 56kwh.
ESS: 53kWh or 56kWh
(An earlier version of that document had said 56kwh then they edited/changed it to say 53...)
Well we know the roadster uses 2.2mah cells, and we know that there are 6831 of them. The rest is easy to figure out....
It might depend on what nominal voltage they use to calculate. 3.7V gets close to 56 kwh, 3.6V is around 54 kwh.
Absolutely. Both answers could be correct. It doesn't really matter unless you compare the roadster pack to a different EV using different criteria for calculating numbers.
Different chemistries have different nominal voltages, and different cells within the same chemistry can have more or less sag under the same current draw, which would also change nominal voltage and kwh's delivered. Tesla may have assumed 3.7V nominal at first and then seen more voltage sag than expected and recalculated with 3.6V.
Maybe, but in the end, who cares? As long as like comparisons are being made when comparing different packs, all will be well.
Well EVNow did ask the question.