Compress or not, flexible busbar or not
- Thread starter Cheap 4-life
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Cheap 4-life
My body is 2.63 trillion volts, .07v per cell
I suppose most of these Lifepo4 prismatic cells with aluminum cases have similar expansion thru SOC. So looking at how EV batteries are made imo could give good insight on how to DIY a battery..
yes as I have mentioned in previous posts if I was able to have welded busbars then a light compression (like Lifepower4 server rack batteries implemented) with strapping or similar would imo be fine because the busbars could not loosen with expansion as is recently being reported. And there has never been reports of terminals breaking from stress, they flex.. flexible busbars are the next best thing to welded busbars to hopefully stop busbar loosening..
Yes that’s kinda my point. They even leave room for these good Gafang cells to expand. However there might be a plastic piece vertically down the center of the cells. In that last video it can be seen which wouldn’t allow the bubble shape expansion to happen as much...
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That really wasn't the point of my post. The point of my post was that cell interconnect testing was done at max BMS capacity using 4ga wire which is highly flexible.
42OhmsPA
What's in a title?
Has anyone that has issues with buss bars loosening ever try a NordLock washer?
I used them under extreme heat and vibration in my GTI stroker build when everything short of trying safety wire failed. 2 piece locking design, I'd bet they would never loosen.
Combine them with a distorted thread locknut and you'd never have to worry, in my opinion. Obviously you'd use some thread locker on the studs.
I used them under extreme heat and vibration in my GTI stroker build when everything short of trying safety wire failed. 2 piece locking design, I'd bet they would never loosen.
Combine them with a distorted thread locknut and you'd never have to worry, in my opinion. Obviously you'd use some thread locker on the studs.
Cheap 4-life
My body is 2.63 trillion volts, .07v per cell
I think 4awg wire is only good for like 80amps conservatively. Yeah if that’s all you charge with at 12v 4awg busbars would work
Cheap 4-life
My body is 2.63 trillion volts, .07v per cell
The nuts or screws for the cell busbars should be torqued. I’m not sure how much the washers and nuts your saying about would influence that torque. The busbars slide under the proper amount of torque due to not being able to torque a lot because of aluminum studs or threads.. it’s not really the nuts or screws loosening as much from my understanding of what I read.. but laminated flexible busbars and wire busbars have been shown to stop the sliding or loosening or whatever it’s called
The wire is only 4 inches long so it handles much more than 80 amps. As was indicated in the linked post this entire battery configuration was tested at 150amps while obtaining temperature readings on the wires and terminals with MINIMAL rise of cell interconnect wire temperatures using 4ga.
Again this setup has been in use for over 10,000 miles of real world testing in a class B RV.
I downloaded and read the LF280K datasheet. It says mostly the same thing as the LF230 datasheet (except, of course, some of the numbers are different). The interesting part is that the LF230 datasheet goes into a bit more detail about how the cells are cycled in the fixture and what the results are.
Cheap 4-life
My body is 2.63 trillion volts, .07v per cell
Can you link the 280 data sheet please
42OhmsPA
What's in a title?
The Newest Specification Sheets of EVE Cells
EVE has updated their specification sheets in July, the new version ones are more detailed, adding more information, such as the information about clamp. I sent them in the attachment, hope it is helpful for you.
diysolarforum.com
Now THAT is a proper datasheet. Someone needs to get that April 2022 datasheet into the Resource Section here - I can only find the outdated datasheet from March 2021.
So now I finally see all the pictures you guys are referring to.
And I also see the new specification for 300kgf +/-20kgf which formalized the inputs we were provided n Eve through back channel in 2021.
6000 cycles to 80% capacity @ 25C and 2500 cycles to 80% capacity @ 45C is unchanged
The fact they now detail that cells should be clamped to 300kgf when at ~40% SOC is great.
Section 6.2 makes clear the pressure limits we were discussing (stay under 500kgf to avoid the formation of internal defects) and I can finally see table 6.3.2 indicating tye battery expansion force at BOL and EOL.
But I don’t see anything anywhere indicating Eve suggest the use of a rigid enclosure for a battery.
If you want 6000 cycles to 80% initial capacity, you must maintain pressure of between 280kgf and 320kgf through that cycle life.
It’s a real pity that Eve did not include a MOL specification for expansion force at reduction to 80# of initial capacity, but it’s certain to be below the 5000kgf they characterized after capacity has been reduced to 60% of initial capacity (which is apparently what Eve considers EOL).
Since Section 6.2 makes clear that internal defects will not firm until pressure reaches 5000kgf, you can safely assume that if you do elect to use a rigid enclosure which applies no more than 300kgf to cells that are fully-charged when new, you are unlikely to cause any interval defects through cycling all the way to 60% of initial capacity.
But no question that a clamping fixture maintaining between 280kgf and 320kgf is the safest solution to maximize the cycle life of your Eve 280K cells…
It says prepare the fixture:
And then says to put the cell in the fixture at 30%-40% SOC before cycling the cell:
The LF230 datasheet is much more clear about this. Neither of them say to do anything but put the cells in a rigid fixture.
Cheap 4-life
My body is 2.63 trillion volts, .07v per cell
I think if anything we all can for the most part agree that flexible busbars of some type should be used?
Cheap 4-life
My body is 2.63 trillion volts, .07v per cell
This specification in the data sheet is simply the kgf that the cells were compressed with at 30-40% SOC IN A RIGID FIXTURE.. meaning that the kgf goes up as SOC rises. Far more than 320kgf..
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Cheap 4-life
My body is 2.63 trillion volts, .07v per cell
I do still agree with this,, however this new data sheet sure is kinda implying that it’s not necessary to do anything else other than rigid. In that rigid fixture the cells were beat to hell, still showing the cell made it 4000 cycles and had 80% of original capacity left.. easily imo double that 4000 if DOD is only like 70% and c-rates are much less.. so my very vague uneducated estimate is 8000 cycles minimum for most home batteries in a rigid fixture like the data sheet and still have 80% or original capacity left.
But if I was to use a rigid fixture. How do I know if the battery is actually at 40% SOC with such a flat voltage? Actual capacity can vary so much and voltage barely changes if at all
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So you are interpreting this to mean that there are no springs in the fixture they are using and the initial clamping force of 380kgf to 320kf @ 40% SoC will be allowed to drop as much as it wants towards full discharge and increase as much as it wants towards full charge?
Looking over the datasheet a second time, it is true that they only speak about ‘bolts’ with no mention of springs and they only speak about the about the ‘initial’ clamping force of 300kgf.
So I agree that the ‘300kgf compression force of ‘EVE cycle method’ could correspond to 300jgf of force @ 40% SOC within a rigid fixture (with the ability to drop as much as it wants towards minimum SOC and increase as much as it wants towards high SOC…
But I’m still not convinced that there is any reason to suspect that using springs to maintain 300kgf on force +/-20kgf over the full charge/discharge cycle is going to result in reduced cycle life…
Eve datasheet says nothing about busbars.
If this new data means that rigid fixture can get used, rigid busbars may be OK.
If a sprinkler-calibrated 300kgf clamping fixture is being used that can allow for some expansion, flexible busbars are l likely preferable over rigid…
Agree. At 40% SOC, not 30%…
Cheap 4-life
My body is 2.63 trillion volts, .07v per cell
I’m saying no matter what the fixture is, flexible busbars are imo best to prevent the possibility of any bms issues or bad cell connections.. I thought that would be easily agreed with. There is several 280ah prismatic cell sellers that now supply flexible busbars instead of solid busbars.. yes with a rigid fixture there is less expansion but it’s only less, so flexible busbars are still a good choice
I don’t think you can conclude anything about the LF280K from the LF230K datasheet. Among other things, the LF230 may have one fewer fold in its pouch than the LF280 (how do the mechanical dimensions compare?),
You’ve got to apply a calibrated 280kgf to 320 kgf to cells charged to 40% anyway, so the only question to me is will you get lower cycle life with a rigid fixture calibrated to 300kgf @ 40% SOC, or will you get at least the same cycle life (and possibly higher) maintaining 280kgf to 320kgf throughout the full charge / discharge cycle?
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