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Best way to compress cells in packs

cypher2001

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Jul 20, 2020
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Just looking for everyones best ideas to compress cells. I know Will used pipe clamps. Is that still the best method?
 
Photo's are worth a 1000 words right.
I used the Big Irwin Hand Clamps and squeezed them hand tight after making sure everything was square & flush.

My 175AH packs, 8 cells in straight series. (Thin-Wide cells, so straight 8S config = 10"x10-1/2")
The Plywood allowed enough space to wrap the Upper & Lower parts of these cells with Fibra Tape.
175AH-being squeezed A.jpg 175AH-being squeezed B.jpg 175AH-Bound Pack.jpg

My 280AH packs, 8 cells in series "Block Format".
They were clamped identically. Only two wraps of Fibratape used.
As seen above and here, orange Pull Strings are in place to help pull a pack or segment out if required.

cell-bundling.jpg Box With 280AH-cells (A).jpg

Once the packs are in their boxes, which is snug to begin with (advantage of building them myself to spec) they cells have nowhere to expand so they will remain as they are, well unless they break apart 3/4" ply, urethane glue & a heap load of pocket screws.

Hope that Helps, Good Luck
Steve
 
I'm going to use hose clamps and wood planks at each end


Cells, BMS and Hose clamps still in the post.
 
I'm not sure this is the best way -- but I located the following metal zip ties.. They were cheap and putting 3 inline allowed me to get around a 4S 120AH pack. This seems like it could work for any size battery and its cheaper than hose clamps.


They seemed to hold pretty well. the issue was getting good compression with them when they were installed. I ended up have 2 wood end pieces and getting the sizing right and sliding the wood down. Its got good compression and its holding. If necessary, I can also undo this -- but it will be some work.

IMG_1888.jpegIMG_1889.jpeg
 
Its been a few days and just want to report that the method above is still holding tight. I'm going to replicate this for next pack as it seems to work well.
 
Do you have a compression force spec for the cells? If not, ballpark 15 in-lb. Which is a not much.
 
No, I do not see that specd in the spec sheet. :(

The whole idea in my opinion is to keep the cells from expanding. What you have is fine. If you notice the cells are not snug when you discharge them, then tighten up the rods so they are snug and be done with it. That's what I am going to do and I will most likely use the same method you did. Threaded rods and plywood are cheap and will do the job perfectly. The only thing I might do different is have my cells at a lower SOC before I clamp them. They tend to expand slightly with a higher SOC. Also from what I have read, charging with high C rates can cause some swelling as well. But it's normal.

The reasons for clamping is to reduce stress on the terminals and extend the battery life. You have accomplished both with your clamped cells.
 
MATERIALS TIP:

Don't use Particle Board, MDF or composites. These can absorb moisture/humidity over time, 'some' also have chemicals (glues etc) which can interact with metals, in particular with aluminium. Ever see Melamine Shelves buckle after a few months with weight on them ?

Plywood is much more stable and even better if sealed with Polyurathane (water based is perfect, dries in 2 hours). Aluminium, Thick ABS plastic and some others are also really good BUT IF USING METAL be sure to put a non-metallic, non-conductive liner between the cells & the metal "plate" used. Always ensure the cells make no contact with anything conductive.

As per Gazoo, I also recommend that when compressing the cells, that it be done with them at a lower charge 50% is likely the optimal median... When cells are full 3.55V+ they do tend to bloat a bit (normal). This is more pronounced with the Aluminium Cased "blue" cells.
 
What happens if a BMS fails and one or more cells are overcharged like this? The main reason I ask if I am putting together a pack and as a newbie, am a little concerned that with this waterproof enclosure and the fit extremely tightly in the case (edge to edge exactly when closed (see pic) I want to make sure I'm not making a possible bomb with this setup when the case is closed if there was an unexpected issue with swelling.
 

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LFP does not explode or catch fire like some other Lithium Based chemistries. You can puncture the cells and they will still produce power as they are failing (smoke). IF they overcharge, they can puff up and even pop and spew their guts out BUT thaa is extreme. I have not heard of a BMS failing and this happening, I doubt it happens often or commonly as we would all hear about it and fast too !

Dangerous vs. Safe batteries, Explosion and fire test! - YouTube
 
Thanks, I will sleep better - as a newbie I want to be careful with everything I am doing.
 
What happens if a BMS fails and one or more cells are overcharged like this? The main reason I ask if I am putting together a pack and as a newbie, am a little concerned that with this waterproof enclosure and the fit extremely tightly in the case (edge to edge exactly when closed (see pic) I want to make sure I'm not making a possible bomb with this setup when the case is closed if there was an unexpected issue with swelling.

This just happened to another member. The cell didn't bloat until they removed the compression and I would say the bloating of that cell was severe.


It's still to be determined what happened here. But the point is there was no smoke or fire. This has also happened to a few others.....no smoke or fire.
 
Well done, I like this. What is that between the cells? Looks like masonite maybe
I am not sure what the material is, this is the "pegboard" material they sell at the hardware store (I just had some). The idea is that in the remote possibility that the plastic wrapping got damage the Al casings would not connect (as I think it is possible the casing is one of the battery terminals).
 
As @SteveS mentioned those kind of wood products swell with moisture and do not insulate as well as plastic. Not my choice to put between my cells
My system is inside a house so no worries at this point. Eventually this may be upgraded.
 
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