A123 20AHr Pouch Cell Battery Build & Info Thread

I guess I got lucky when I built my 2 6S packs with Agnius's kits in that I compressed them with wooden clamps and filament tape around hardboard. I used Silicone oven paper between the leaves and have had no puffing. I did have to replace one cell that charged way too fast so the charger had difficulty balancing. The replacement was on the end cell so it was fairly easy to undoo the alloy blocks and get the old cell out. It still has not puffed sitting free for several months. Dnmun has done this with Lipo's in his build threads so compression seems to help all prismatic type cells.
otherDoc
 
I just wraped with filament tape. I rode it down to 72v 17.5ah and the cells where close enough. So I rode around the block and the cells started running apart. One at 2.7. So knowing I can get 17ah out of this pack is great. Back to just taking out 12ah. 24s and the 9fet lyen is set at 30amps.
 
Ok, I did some asking around today. Without getting into details, it turns out an honest to goodness 10-15 psi of internal pressure is indeed a good target after the pack has relaxed from being compressed for banding, or whatever method one uses to keep the pressure on the cells. More pressure is OK, up to around 25 psi or so. There are many opinions on the importance of compression and how much is appropriate. It's probably safe to say that the field is still learning here. Because even distribution of electrolyte is important, be sure whatever pressure you apply is applied evenly. End plates need to be good and stiff (no bowing) and the pack should be as close to "square" as possible after relaxing. These attributes are probably more important that the exact amount of pressure applied. You'll want to use bands that won't stretch. We use stainless steel. Large hose clamps can work, but a band-it tool is probably the preferred method.
 
Ypedal said:
so 25 lbs pressure on the end plate.... not exactly 25 lbs per square inch of surface area.. :wink:
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No, it really is an honest to goodness 10 to 25 psi. More pressure than I realized at first. Sorry for the confusion....but it's been educational for me :oops:
 
So folks since a cell is 57 square inches in area that says that the A123 20 Ahr pouch cells want:
570 to 1425 lbs of compressive FORCE on the stack!

So that is a sack load of force. Going to take an endplate with quite a moment to preclude deflection.
eb9k, sure would be great if we could buy some factory endplates! Any chance of us mere peons getting access to "kit" so to speak, components?
 
PM sent.....
 
These are homemade packs and compression like that would be hard. I guess the best I could hope for is the compression I get from reinforced tape.
 
If my cells go pop when i squeeze them with the 1 tonne press, can you give me some new ones :wink:
 
Guys this compression thing with numbers is a huge, huge insight for us. We need to start to figure out how to get say 500# of compression on these cells. The stated correlation with puffing, increase in internal resistance, and loss of C rate is something we need to add to our designs.

Wrapping in filament tape alone won't provide even force distribution. Sad thing is the battery pack is going to get larger and heavier. Raaats the constant in "product development" raises it ugly head again. :evil: (It gets bigger, heavier, more expensive...)
 
compressing the pouches and keeping them like that is easy enough.... 10mm steel plate at each end and threaded rod to hold them together, 2 each long side and 1 in the middle of each short side should be more than enough... it's just a bit heavy :-(

2 x 3mm plates at each end separated 20mm or so (by something a bit lighter) should work pretty well too


the problem is keeping the pressure spread evenly over the cells, I bet compressing them unevenly is worse than no pressure at all!
 
I wander if this is specific to nanophosphate A123 cause say enerdel cells look like have little compression in their assembled pack and 370kg is a lot.
 
knighty said:
compressing the pouches and keeping them like that is easy enough.... 10mm steel plate at each end and threaded rod to hold them together, 2 each long side and 1 in the middle of each short side should be more than enough... it's just a bit heavy :-(

2 x 3mm plates at each end separated 20mm or so (by something a bit lighter) should work pretty well too


the problem is keeping the pressure spread evenly over the cells, I bet compressing them unevenly is worse than no pressure at all!
Click to expand...

I did not understand why pouch cells before and I really don't understand why now.

Would not the extra weight added by the stuff needed to compress them make them as heavy as cells in little cans ?

No wonder the A123m1 cells pop out like they do when overcharged ? They are so tight already ?
 
agniusm said:
I wander if this is specific to nanophosphate A123 cause say enerdel cells look like have little compression in their assembled pack and 370kg is a lot.
Click to expand...

Actually the EnerDel package essentially has no compression of the pouches. The cells are held in place by the edges in the plastic frames and have a thin spongy compliant sheet next to them. It offers no appreciable pressure on the cell. The thru bolts can't compress the cells because they tighten on the plastic.

I have also tested these type of mixed oxide (whatever they are) cells by themselves lying on the bench without compression at high C-rates without any swelling. In one case up to about 25C.

I know the A123 cells require compression. We used them on the first Lightning bike. Great care was taken to design the containers to get the proper compression. Unfortunately I don't recall the number. But I do think wb9k is confused w/r/t pressure and force.
 
Well, if I'm confused at this point, so are the company's assembly specs and every engineer in the building responsible for them.
 
Did anyone buy one of the 7S3P modules from victpower? http://endless-sphere.com/forums/viewtopic.php?f=14&t=39320
I notice they only have two steel bands for compression but the end plates are quite thick therefore spreading the force evenly over the cells.

There were also some much longer modules too 28S3P,

I tried to follow the band compression method with my build, the stainless steel cable ties I used have loosened slightly with vibration. I should have used the proper Band-it st/steel strap.

I also tried a nylon band strapping tool but it was difficult to attain good tension with a small diameter (under 500mm) loop of band.

The Band-it system seems the most accessible method but it is very expensive for a roll of stainless steel band, I picked up a used tensioning tool of ebay
https://www.youtube.com/watch?v=69JhQDmJALA
 
etriker said:
I did not understand why pouch cells before and I really don't understand why now.

Would not the extra weight added by the stuff needed to compress them make them as heavy as cells in little cans ?

No wonder the A123m1 cells pop out like they do when overcharged ? They are so tight already ?
Click to expand...

Prismatic modules weigh more, but still have higher energy density per volume.

The cans are tight inside, and get tighter when a cell heats up, so they are more-or-less self-compressing. The cans have a safety vent scored into the + end of the can. They are designed to crack open with a few atm. of internal pressure in the can. They are meant to vent before pressure is sufficient to cause something more violent.
 
flexy said:
Did anyone buy one of the 7S3P modules from victpower? https://www.youtube.com/watch?v=69JhQDmJALA
I notice they only have two steel bands for compression but the end plates are quite thick therefore spreading the force evenly over the cells.

There were also some much longer modules too 28S3P,

I tried to follow the band compression method with my build, the stainless steel cable ties I used have loosened slightly with vibration. I should have used the proper Band-it st/steel strap.

I also tried a nylon band strapping tool but it was difficult to attain good tension with a small diameter (under 500mm) loop of band.

The Band-it system seems the most accessible method but it is very expensive for a roll of stainless steel band, I picked up a used tensioning tool of ebay
https://www.youtube.com/watch?v=69JhQDmJALA
Click to expand...

Got a pic of the 7S3P? Sounds like a Fisker module.
 
wb9k said:
Well, if I'm confused at this point, so are the company's assembly specs and every engineer in the building responsible for them.
Click to expand...

This leads me to believe there is still confusion.

wb9k said:
OK, well mech stuff is not my forte. Apparently the verbiage comes from the air pressure driving the stack compressor, not the actual measurement of psi in the stack. My bad. So what's the proper verbiage...10 lbs of end-to-end pressure?
Click to expand...

_10 lbs of end-to-end pressure?_ You say. 10 lbs is a measure of force, not pressure. Pressure is measured in pounds per square inch. Force is measured in pounds. See the difference?
 
999zip999 said:
If there is that much presure it's just going to pop out the sides.
Click to expand...

Only if you abuse the cell. Even then, there is room at the margins of the cell for some gas to go to before the pouch vents.

If you don't compress, the electrode stack develops uneven heating due to uneven distribution of electrolyte--even with "normal" use conditions. Hot spots result, which in turn results in gas generation and further delamination of the electrodes, and it just escalates from there. This is what we are trying to prevent with the pressure.
 
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