Busbar thickness requirements for my build (23S3P | 96.6V 150A)

[Residents evil]

Hey fellas

I'm in the deep trying to finalize the theory of my project before jumping into purchases. My relevant parameters:
- Grin MAX45 KV12 + Statorade
- 150A battery limit (3P of Molicel P50B's)
- 200A phase limit
- 22" wheel fatbike


The motor simulator indicates that my top speed eats 66.6A from the battery, peaking at 150A during acceleration.
I don't think I'll be cruising at the top speed often, majority of the time I see 70% throttle to be enough.




Even at 70%, top speed requires 31.6A from the battery, peaking at 114.2A during acceleration.

I'm thinking of ordering bus bars to deal with these amperage values. I've devised a battery setup that fits my case, and managed to make a 2x cell width into the next set of batteries to provide more mm2 to carry all this current. Ignore the two rows with empty cells.


With 21700's, that's essentially 42mm2 width from group to group. I've used some random website calculators and I've been suggested 2.5mm thick for only 75A (my top speed @ 100% throttle with headroom), so I'd need 5mm thickness to carry the 150A of the peak...

However, the calculations between websites seem to vary wildly, with different sources stating different values for copper current capacity (from 0.8 up to 6 A/mm2).

Formula used: I = W x T x J
I = Amps capacity of busbar
W = Width of bar (mm)
T = Thickness of bar (mm)
J = Assumed current capacity of material (Copper)

Basically, do I really need this thick of a copper-nickel bus bar for my battery, or am I being completely insane because I'm missing an obvious detail of these calculations?! Wellgo's calculator states about $200 for 23S3P @ 2mm thick, I can expect to be more expensive for something that fits my specific needs (See image above), anybody knows about how much more for such customization?

Will not build the pack myself, will give to a reputable battery builder all the parts for the build instead.
Apologies if I'm breaking any forum rule. And yes, I've been using the search function extensively, this forum is a goldmine of information < 3

Some sources (No particular order):
1) Reddit post of different sizes and current capacity
2) Wellgo's page on busbars thickness and current rating
3) Busbar calculator 1
4) Busbar calculator 2
5) Ebikes.ca Motor Simulator with my parameters

Still don't have a build thread, want to finalize the research to then present the plan, get the final criticism, adapt and move forward.

 

[BlueSwordM]

Regarding the busbars, since you're using precut busbars with nickel weld points, I think 0.3-0.5mm copper thickness would be your best bet, since that would place it right in the optimal range:

Current Carrying Capability of Nickel Strips - Help Understanding

I'm simply trying to understand how to select nickel strip for my battery pack. Note that I'm just simply trying to understand the math here only and the concepts behind selecting nickel strips, and nothing more. I'm not suggesting anyone do anything unsafe. I'm building a 5S3P Li-Ion pack from...

endless-sphere.com

For reference, if you were to go with the original 2.0mm busbars, you'd be able to push... 135A/cell lmao.

Now, for your choice of cells, I think going with Reliance RS50s would be a much better choice than P50Bs. Lower voltage drop and tougher cells that last much longer in terms of cycle life.

 

[Residents evil]

I might be dense...
Let's say my controller requests those 150A, don't I have to have busbars that, from start to finish of the series, can carry 150A?
Between Parallel cells, 50A is enough, but between Series cells it must carry 150A, right?
If so, and using 1.2 for Copper's current capacity in the formula I = W x T x J = 42 x 0.5 x 1.2 = 25.2A, this would be my current capacity between each cells in series.
What am I thinking wrong here?

Reliance RS50s do seem to be better, thanks for the suggestion : )

 

[BlueSwordM]

I might be dense...
Let's say my controller requests those 150A, don't I have to have busbars that, from start to finish of the series, can carry 150A?
Between Parallel cells, 50A is enough, but between Series cells it must carry 150A, right?
If so, and using 1.2 for Copper's current capacity in the formula I = W x T x J = 42 x 0.5 x 1.2 = 25.2A, this would be my current capacity between each cells in series.
What am I thinking wrong here?

Yes, but that's why you at least have one series link per cell, not one series link per cell group.
Of course, that is made harder to do with your cell layout, but it is easily doable if you can just stack busbars.

 

[Residents evil]

Yes, but that's why you at least have one series link per cell, not one series link per cell group.
Of course, that is made harder to do with your cell layout, but it is easily doable if you can just stack busbars.

Considering my case, I can only do the width of 2 cells into the next group, so 42mm.
As such, I need to thicken the copper so as to be capable of carrying the 150A.

I got quoted $46 for the whole busbar set at 1mm thick, so I think I'll just go the safe route and triple that (I = 42 x 3 x 1.2 = 151.2 A) since the price point is low enough. Makes no sense (to me) to stack busbars when I can just increase copper thickness.

I want to make sure I can pump the 150A through the battery, and assuming the current capacity of copper is indeed 1.2 and not 0.8 (which would then require 4.5mm thick copper), 3mm will be enough.

 

[BlueSwordM]

Considering my case, I can only do the width of 2 cells into the next group, so 42mm.
As such, I need to thicken the copper so as to be capable of carrying the 150A.

I got quoted $46 for the whole busbar set at 1mm thick, so I think I'll just go the safe route and triple that (I = 42 x 3 x 1.2 = 151.2 A) since the price point is low enough. Makes no sense (to me) to stack busbars when I can just increase copper thickness.

I want to make sure I can pump the 150A through the battery, and assuming the current capacity of copper is indeed 1.2 and not 0.8 (which would then require 4.5mm thick copper), 3mm will be enough.

Good call. I didn't initially think the layout would be that much of a problemsince I'm so used to dealing with skateboard style packs.

Anyway, since you're dealing with a low of power per cell, also look into how you can improve thermal dissipation.