DIY 24s using little cells

[OhYou_]

Is there any best practices for cell layout? The best I came up with was Pic below. It's a 24s pack for a e-scooter.
I will be having a shop cut out separators out of fr4 don't worry

I'm worried about the middle batteries getting hot, the motor is rated for 8kw peak but I can push it to the limit of the cells for a couple seconds at probably 11kw.

 

[Supervstech]

Is there any best practices for cell layout? The best I came up with was Pic below. It's a 24s pack for a e-scooter.
I will be having a shop cut out separators out of fr4 don't worry

I'm worried about the middle batteries getting hot, the motor is rated for 8kw peak but I can push it to the limit of the cells for a couple seconds at probably 11kw.



View attachment 254297

Im not sure what im looking at.
Looks like 2 sets of 4p, with a 9S string beside it, surrounded by 7 loose cells...

What are you attempting?

 

[740GLE]

76-80v? Nice.

If your just looking for layout in a specific dimension? I’m guessing those installed bus bars are just temp configuration.

What’s the dimensions you’re trying to fit the cells into?

 

[Supervstech]

Ok, im understanding better now.
EXACT identical length busbars, is critical.
Make sure the cells are rated for the max output amps you are chasing.
24S 8kW is over 100A
Some cells can do 25C, but most are rated for around .2 or so...

 

[OhYou_]

Oh yes, the bus bars are from an old config, I started cutting them apart but realized I would not have enough so I will have to make or get a full matching set I guess.
These are designed for forklifts I think, they are rated for 3c continuous and 5c pulsed which I'm not sure what that means so I'm assuming it means peak. (i found a datasheet, 3c for 18min, 5c for 10 seconds)

Good point on bus bar length, I can accommodate that in this layout if I shove the three cells on each side together
The dimensions don't matter too much because I have to build a frame to put it on anyway.

 

[OhYou_]

I ended up just modeling it. This layout allows for the bms and motor controller to be integrated and all the bus bars are mostly the same length.
The shortest bar is 27mm post to post and the longest are 32.5mm. surely that wont be too bad right?
I'm thinking about making an aluminium enclosure, if so, then the motor controller can mount through the wall using a gasket so that the heat sink is outside the enclosure and the black plastic part is inside. I'm kind of concerned about thermals on the bms though.