How do electric Vehicles use Li-ion batteries

Thread Starter

Jwrede

Joined Mar 11, 2021
15
How exactly are electric vehicles able to use Li-ion as their main power source, the 21700 e.g. has a maximum discharge rate of 35A while tesla motors draw up to 800A (very short research, might be wrong)
 

Ian0

Joined Aug 7, 2020
3,268
It requires that all the cells, and the connections between them, have identical voltages and identical resistances.
 

Thread Starter

Jwrede

Joined Mar 11, 2021
15
It requires that all the cells, and the connections between them, have identical voltages and identical resistances.
okay so let's say I have a motor that requires 100A, how many 21700 cells would I need and how do I have to connect them?
 

Ian0

Joined Aug 7, 2020
3,268
okay so let's say I have a motor that requires 100A, how many 21700 cells would I need and how do I have to connect them?
First, you need to know the motor voltage, and then it's a question of how long it requires 100A for before the batteries go flat.
 

Thread Starter

Jwrede

Joined Mar 11, 2021
15
First, you need to know the motor voltage, and then it's a question of how long it requires 100A for before the batteries go flat.
Lets take for example a 4 drone motors where each motor requires a constant supply of 25A and around 15V, how would you power that with only Li-ion batteries?
 

Ian0

Joined Aug 7, 2020
3,268
So, 15V would require four or five cells in series.
You need 100A for 10 minutes, which is 16.67Ah (100x10/60)
So you need to find, a cell or a number of cells in parallel which have a total capacity of 16.7Ah, AND have a peak current capacity of 100A
so two in parallel 8.4Ah capacity/50A peak, or three in parallel 5.6Ah capacity/33A peak etc.
 

BobTPH

Joined Jun 5, 2013
3,682
Batteries in parallel add their currents. So if you need 100A and a cell can supply 25A it would require 4 in parallel.

Batteries in series add their voltages, so, if you need 12V and have 4V cells, you need 3 in series.

You can the combine batteries in parallel and series to get any multiple of the single cell voltage and current.

Bob
 

Thread Starter

Jwrede

Joined Mar 11, 2021
15
So, 15V would require four or five cells in series.
You need 100A for 10 minutes, which is 16.67Ah (100x10/60)
So you need to find, a cell or a number of cells in parallel which have a total capacity of 16.7Ah, AND have a peak current capacity of 100A
so two in parallel 8.4Ah capacity/50A peak, or three in parallel 5.6Ah capacity/33A peak etc.
I'm sorry if I understood you incorrectly, all my knowledge about electricity is very surface level, but if I understand you correctly the answer to my original question (which was probably wrongly stated) is that the maximum discharge rate of a battery pack depends on the amount of batteries put in parallel, so if I have two Li-ion battery with a maximum discharge rate of 35A and put them in parallel I could supply a motor that draws 70A at ~3.3V? Please correct me if I'm wrong, as I said I have almost zero knowledge about actual physics, I have more of a Forum / Video knowledge :D
 

Thread Starter

Jwrede

Joined Mar 11, 2021
15
Batteries in parallel add their currents. So if you need 100A and a cell can supply 25A it would require 4 in parallel.

Batteries in series add their voltages, so, if you need 12V and have 4V cells, you need 3 in series.

You can the combine batteries in parallel and series to get any multiple of the single cell voltage and current.

Bob
Ahh thanks alot, that was the answer I'm hoping for!
 

Ian0

Joined Aug 7, 2020
3,268
There are TWO ratings for each cell, its capacity and its maximum current. You may exceed neither.
The cell can be designed for a high capacity but a low maximum current, or vice versa.
 

Audioguru again

Joined Oct 21, 2019
3,543
My electric model airplanes can float high in a thermal or gradually glide down for an unpowered but controlled smooth landing when their battery is almost dead but drones suddenly crash.
 

shortbus

Joined Sep 30, 2009
8,817
My electric model airplanes can float high in a thermal or gradually glide down for an unpowered but controlled smooth landing when their battery is almost dead but drones suddenly crash.
That's because the drones "wings"(propellers) stop working. But the planes wings work as long as there is forward motion.
 
Take the Nissan Leaf as an example. The early versions use a 96-Series 2-Parallel configuration (96S2P) comprised of 192 cells total. this can be viewed as 2 parallel stacks of 96 cells in series. Each of the individual NMC Li-ion pouch cells has a nominal 3.7V at 33aH rating. The total voltage of each stack is then 96 x 3.7V = 355.2V with a 33aH rating. The two stacks in parallel then provide a complete battery pack that's 355V at 66aH providing 23,443 kWh of energy ( 355.2V x 66aH ). This is a simplistic way to view the Gen 1 Leaf battery pack. In reality the pack is divided up into 48 modules arranged as 2S2P each. Each module is internally wired to create in effect one large 7.4V at 66aH cell. Treated as such the math works out the same, (48 x 7.4) x 66aH = 23,443 kWh
 

Thread Starter

Jwrede

Joined Mar 11, 2021
15
Take the Nissan Leaf as an example. The early versions use a 96-Series 2-Parallel configuration (96S2P) comprised of 192 cells total. this can be viewed as 2 parallel stacks of 96 cells in series. Each of the individual NMC Li-ion pouch cells has a nominal 3.7V at 33aH rating. The total voltage of each stack is then 96 x 3.7V = 355.2V with a 33aH rating. The two stacks in parallel then provide a complete battery pack that's 355V at 66aH providing 23,443 kWh of energy ( 355.2V x 66aH ). This is a simplistic way to view the Gen 1 Leaf battery pack. In reality the pack is divided up into 48 modules arranged as 2S2P each. Each module is internally wired to create in effect one large 7.4V at 66aH cell. Treated as such the math works out the same, (48 x 7.4) x 66aH = 23,443 kWh
Thanks man, that's a great example, I think I got it now!
 

MrAl

Joined Jun 17, 2014
8,479
My electric model airplanes can float high in a thermal or gradually glide down for an unpowered but controlled smooth landing when their battery is almost dead but drones suddenly crash.
From what i read now some of them return to the starting point and land when their battery becomes low. Never used one myself though. Did use gas powered planes long time ago, those things are nuts the speed at which then can go.
 
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