Compression requirements for "green" LiFePo4 cells

Battery & Chargers
1

I have a qty of Dave’s older OEM “green” cells that I’m finally looking to build some battery packs with. One will be 25s1p (for my old 2002 GEM) and others will be 4s4p for 12V RV applications. Hence my need to “re-configure” the cell pack banding as originally shipped.

I’ve found a few different references to the “requirement” for compression banding, but also seen lot’s of builds in which there seemed to be minimal attention paid to that… at least in comparison to the the OEM versions. So my question to Inwo / the community is… how critical has compression banding turned out to be in real world usage? And how have others accomplished this short of the uber-expensive steel banding tools that I’ve seen used on a couple of builds?

Just to add a bit more info regarding my application model, I’m looking at light duty GEM cart application (no need to go over 20 MPH, small grades, and just a few miles of range), and for the solar/RV packs I’m assuming max current 100A in/out at any given time.

I’m guessing that the tendency for these cells to swell is dependent upon the magnitude of current flows and voltage range used, so please comment if you have any guidelines to suggest safe operating parameters when banding not required? And feel free to extend the discussion to other LiFePo4 cells… as there are lot’s of Chinese options now and I’m guessing they might have some of the same issues?

Thanks to everyone on this forum for making it such a interesting read!

2

I used a rachet cargo strap to hold them in place while I fitted top and bottom bands from sections of “cut to your own length” screw drive hose clamp . It worked ok, I’d be curious to hear if someone came up with something better.

3

I used Band It clamp sets to secure the cells when the light weight bands failed. Then used more Band It sets to secure the packs to the frame under the seat. Seems to work well.

4

How did you get the initial compression with the band it clamps?

5

Didn’t think of that jrjava, something like this I assume?

image
image1224×522 158 KB

I’m sure not as much pressure as the OEM bands… but again I’m not really sure how big of an issue this swelling problem is… there seems to be a lot of LiFePo4 plastic cased batteries being sold.

I know inwo has built some large banks (fork lifts,etc) with his green cells “in the early days”, I’m wondering how they have held up?

The Band-it stuff is nice and seems like the way to go if making many LiFe batteries, but north of a $300 investment to make the first one.

6

My cells weren’t swelling. I had used putty knives to slip the original bands off/on to replace bad batteries and they weren’t extremely tight to begin with. Just lined them up, kept the end plates on and used an electric driver to tighten clamps till they “sounded right” when I strummed them.