32x Fortune 100AH Cells in a 48v Config

[Lt.Dan]

Hey guys, I'm diving in to make my first LFP battery, after extensive reading and studying, I'm preparing to start design. I manage a Laser/Waterjet Shop and plan on building my box from some .080" Aluminum and forming it to a box to fit all 32 cells. I plan on also using the Overkill fab 48v BMS with the Bluetooth capability.

My first question I have on here though, is my bus bar configuration. I've gotten the cells and BMS from Overkills website and plan on using it to design my battery bank and box. Can anyone confirm I am doing this right? I first set up cells in parallel to make 16x 3.2v Batteries at 200ah, then with long bus bars, I connect them in Series along with bus bars on the far left side to bridge all 4 packs together. Making my top right my main Negative and my bottom right my main Positive?

Let me know if there is something I'm forgetting, Or possibly a better arrangement of cells/bus bar configuration.

Thanks!
Daniel

 

[snoobler]

I presume you're looking for a 2P16S configuration.

I can't make your description fit with the image. What I see are 4X 2P4S batteries joined at one end (left) and open at the other. I don't see any way how your terminals can be as described.



If you move the bus bar from the X to the circled terminals, I believe that gets you there.

 

[Lt.Dan]

I presume you're looking for a 2P16S configuration.

I can't make your description fit with the image. What I see are 4X 2P4S batteries joined at one end (left) and open at the other. I don't see any way how your terminals can be as described.

View attachment 33889

If you move the bus bar from the X to the circled terminals, I believe that gets you there.

You are totally right, I do need to move that bus bar. This is why I asked!

Thank you! I'll update this thread with more progress.

 

[snoobler]

Also, given that you have two bus bars joining the 2P cells in series horizontally, it makes me feel good to have double bus bars on the 3 interconnects that series the cells vertically - essentially just two bus bars stacked in that position. That way you have 2 bus bars making every series connection.

 

[Lt.Dan]

I plan on laser cutting the bus bars myself more than likely, but am having a hard time determining thickness of the copper bar. Should I do 1/8" on the parallel connections, then 3/16" or even 1/4" on the 3 interconnect bars?

 

[snoobler]

See the link to the awg chart in my signature. It gives you a mm^2 value for each gauge. I'm in the process of sizing my bus bars, and am leaning towards .75w x .125t That's about 60mm^2. Right in between 1/0 and 2/0. My peak power is 10kW @ 48V, so current will be just a touch over 200A. That will give me about 2% voltage drop over the length of the bus bar.

 

[Lt.Dan]

I'm limited to the BMS at 100a at 48v, so it sounds like I can go a little more conservative and step the thickness down a bit. Say .080" on the parallel strings and .125" on the interconnect bars. Maybe I'll just make it all 125" to make it easy... I can always stack some if I go with a larger bms in the future as well...

 

[snoobler]

Issue for me is the custom nature of these bus bars... cost of copper bar, etc.... ouch. ;(

 

[Lt.Dan]

I hear you, thankfully I can laser cut them for free, but copper sheet is down right outrageous! Lol

 

[snoobler]

Yeah, that's what I mean. I'll be ordering "strips" from McMaster-Carr. I have a friend with a mill. I need 21 holes 1.135" apart in a 23.5" strip of copper...

 

[Lt.Dan]

How does this look? I figured why stack them when I can just cut them to any desired shape??

 

[snoobler]

Very nice.

Why stack them? Might be easier to just work with one thickness and one size doubling up where necessary.

Custom pieces will save copper though.

I would still double up in these locations to keep your series string resistance consistent between cells:



I've been driven to 1/6" stock. I was looking at nearly $800 in copper.

 

[Lt.Dan]

I can fit all the bus bars on a 12"x12" sheet of 1/8" Copper and can fit some extra small ones to. I will definitely double up where I can.

Also @snoobler I'd be happy to help if you need some bars laser cut, just let me know the dimensions.

 

[Pooroldplowboy]

Have you tried Metals Depot.com? A 12" by 12" square of 3/16" copper is $230.00. And a 12" by 12" square of 1/4" in copper is $281.67. 1/8 " is $176.44. I have used them in the past and their service was great. Everything exactly as stated and fast UPS shipping.

 

[Lt.Dan]

Have you tried Metals Depot.com? A 12" by 12" square of 3/16" copper is $230.00. And a 12" by 12" square of 1/4" in copper is $281.67. 1/8 " is $176.44. I have used them in the past and their service was great. Everything exactly as stated and fast UPS shipping.

Mcmaster is much much cheaper than that. And they ship next day to me for very very cheap.

This ship has sailed though, and I actually am putting together a group buy for bus bars. See the link in my sig.