Hello guys.
I'm a lurker on this forum but some people may know me from other EV related sites. I'm a EV enthusiast and I build my own EVs.
The Tesla is very interesting for me, especially the battery pack but I can't find any good information on that topic.
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)
375V/151Ah/53kWh
450 kg/992 lb
Liquid cooled/heated
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.
I'm using much bigger cells for my EVs. Here is a good cell for lower power applications:
It's available in many sizes. I just pick the size (Ah) I need and connect them into series to get the voltage I need. A member of this forum is the major distributer for this cells (and a lot of other EV stuff)
A 375V/160Ah pack out of this cells would weight 660 kg and cost $20.000 if purchased in low volumes.
The cells are LiFePO4 chemistry so they are safer, they have a 3C continuous and 10C peak rating and 8000 cycles if treated gently. 3000 cycles shouldn't be a problem.
For higher power applications I use these:
Each cell is 3,2V and 10Ah. A pack out of these cells would weight 530 kg but be more expensive.
I also use some brand new flat cells that can give 30C currents, have a very long life (10.000 cycles) and are very light. A pack out of those would weight 400 kg.
I wonder why Tesla bothered with thousands of those tiny laptop batteries that are not made for high power applications although there are alternatives available.
The engineers at Tesla have tested many cells, and I'm aware that they are very smart and experienced people, but I would just like to know why they have chosen this tiny cells. I believe that cost wasn't the only reason. Does anyone have more information?
Maybe I'm wrong with my calculation, don't hesitate to correct my mistakes
Greetings from Croatia!
Btw. What are these black boxes in this photo? There should be 11 "battery bricks" but there are more of these boxes in this photo. Is this the power electronics module?
I'm a lurker on this forum but some people may know me from other EV related sites. I'm a EV enthusiast and I build my own EVs.
The Tesla is very interesting for me, especially the battery pack but I can't find any good information on that topic.
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)
375V/151Ah/53kWh
450 kg/992 lb
Liquid cooled/heated
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.
I'm using much bigger cells for my EVs. Here is a good cell for lower power applications:
It's available in many sizes. I just pick the size (Ah) I need and connect them into series to get the voltage I need. A member of this forum is the major distributer for this cells (and a lot of other EV stuff)
A 375V/160Ah pack out of this cells would weight 660 kg and cost $20.000 if purchased in low volumes.
The cells are LiFePO4 chemistry so they are safer, they have a 3C continuous and 10C peak rating and 8000 cycles if treated gently. 3000 cycles shouldn't be a problem.
For higher power applications I use these:
Each cell is 3,2V and 10Ah. A pack out of these cells would weight 530 kg but be more expensive.
I also use some brand new flat cells that can give 30C currents, have a very long life (10.000 cycles) and are very light. A pack out of those would weight 400 kg.
I wonder why Tesla bothered with thousands of those tiny laptop batteries that are not made for high power applications although there are alternatives available.
The engineers at Tesla have tested many cells, and I'm aware that they are very smart and experienced people, but I would just like to know why they have chosen this tiny cells. I believe that cost wasn't the only reason. Does anyone have more information?
Maybe I'm wrong with my calculation, don't hesitate to correct my mistakes
Greetings from Croatia!
Btw. What are these black boxes in this photo? There should be 11 "battery bricks" but there are more of these boxes in this photo. Is this the power electronics module?
