Cheap 4-life
My body is 2.63 trillion volts, .07v per cell
Is there any spacers/insulators between your cells other than the blue 3d printed spacers that go across the top and bottom?
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Compress or not, flexible busbar or not
- Thread starter Cheap 4-life
- Start date
Cheap 4-life
My body is 2.63 trillion volts, .07v per cell
In response to #1; there is advantages known like reduced swelling in high amp demand situations. Disadvantage is loosening busbars/nuts/screws have been noticed when using solid busbars due to swelling/expansion contraction that is uncontrollable which is why welding the busbars to the cells is preferred and often done when compression is used.
#2 yes the manufacturers recommend it but I’d assume that recommendation really only matters for high amperage draw situations when there’s severe swelling possible. It’s been logically proven by Will and Offgridgarage that compression doesn’t matter for cycle life for solar storage.
#3 yes proper compression won’t hurt the cells at all if using flexible busbars are used. With compression and solid busbars the nuts/screws can constantly loosen and need retighten due to uncontrollable expansion and contraction. I’m not make that up. Several users have reported this.he flexible busbars you are using add a lot more resistance to the battery bank. How many amps are they rated for? Also then the bms balance wires would have to be attached to the cell terminals because you can’t tap those type of flexible busbars for the balance wires
Not sure you are referring to these laminated busbars but these are extremely flexible: https://www.aliexpress.com/item/3256803043965156.html
Cheap 4-life
My body is 2.63 trillion volts, .07v per cell
Are those black spacers hard plastic?
Cheap 4-life
My body is 2.63 trillion volts, .07v per cell
They dont look very flexible. Looks like just a bend in a solid busbar. So they are flexible? Ok that’s another option. Thanks for confirming that.
Cheap 4-life
My body is 2.63 trillion volts, .07v per cell
So then your busbars/nuts would loosen (if it is possible) with your compression and no space between the 3d printed parts. How long has this setup been supplying power to loads? How many amps has been going into/out of them?
Those flexible busbars are empirically infinitely better than my solid busbars in my build. I used to have problems with varying cell resistance requiring loosening and re-tightening my solid busbars (some of which became nearly impossible to remove due to expansion). Ever since installing those flexible ones, I've had zero problems. Details are in the latest posts of my build thread (in my sig).
The ones that @rhino mentioned above are the ones I'm using. Quite flexible.
Cheap 4-life
My body is 2.63 trillion volts, .07v per cell
We’re your cells compressed?
They're in a spring-based compression setup.
Cheap 4-life
My body is 2.63 trillion volts, .07v per cell
Reading thru your build now. You still using chargery bms?
No, I dropped Chargery due to so many problems. I'm using Orion now. Happy to answer off-topic questions in that thread.
Nobodybusiness
Solar Sponge.
All I can tell you is mine are setup like Andy’s and I have never had one swell yet. Some are 18 months old. YMMV..
Worried about cable stiffness? Think diagonally. The the short red ones are 2/0. You don’t want them straight, but with a bow. When you crimp the second lug on put the bow into cable to lock in the shape and make it more flexible in that range. Remember to keep the lugs rotated on the same plane, they won’t twist easily after crimping. You want to use fine strand cable like Windy Nation welding cable or the most flexible but more expensive Ancore brand cable. I’ve found found that Ancore or Selterm are the best lugs for the job and crimp down the tight with my dies( nice crisp hex corners). Just before crimping I do a very light polish on the inside of the lug to remove oxides of the tin surface or copper. Use 320 or finer Emory on a wood dowel, steel wool or Scotch bright. The idea is just to knock down only the high spots, remove oxides but not scratch it or remove the thin tin plate. A #2 is plenty for most needs but nothing beats the low resistance of a solid, tin plated copper buss bar(supplied).
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Easy to cut, about .045” thick.
Large Silicone Heat Resistant Mat 78.7” x 15.7”, Nonslip Silicone Mats for Kitchen Counter, Countertop Protector, Nonstick Waterproof Craft Mat Table Placemat, Translucent-White https://a.co/d/bvgNWK7
Yay! I actually saved my notes in case I wanted to build more.
Material List for:
Eight Cell Compression Module
(lithium "Squeeze Box")
Fits most 272/320 Ah Prismatic LiFePO4 cells with allowance for .045" silicone
spacers sheets on wide battery surfaces (9 places).
Home Depot 2' X 4' plywood Sheets, Radiata Pine 1/2"(.480) & 3/4"(.725) thick:
1pc Bottom 3/4" X 7" X 29-1/8"*
2pcs Sides 1/2" X 9" X 29-1/8"*
4pcs Ends 3/4" X 7"* X 8-5/16" (2per end)
2pcs Thrust plate 3/4"X 6-15/16" X 8-1/8"*
*Denotes surface grain direction. Doubled thrust plate has the only vertical grain.
Ends sit on bottom and between sides.
1 pc Spring, 634.6 LB @ .56" deflection
from MSC (mscdirect.com) PN 07661879.
1pc 3/8-16 four pronged Flange nut
1pc 3/8-16 X 3" Bolt, zinc plate (not stainless! it may bend)
1pc 3/8 fender washer, 2pcs 3/8-16 nuts
Grease for threads and washer surface.
Teks sharp point lath screws #8x1-1/4" to align while gluing.
Clamp up assembly squarely before gluing. Drill tight clearance holes through first side
and pre-drill small hole for threads.
Titebond 3 glue, re-coat edges after a few minutes soak in before assembly.
When done, protect with Minwax Helmsman Urethane 3 coats.
Sand between coats, warning very DUSTY!
"Large Silicone Heat Resistant Mat 78.7" X 15.7" (Amazon) (enough for two modules if smart).
Lightly spread a dusting of flower on sides of silicone to help it slide down between batteries,
You’re not picking anything apart, but making valid assumptions. That braided jumper looks cool, carries lot of current but has a major flaw of “cold flowing” and requires periodic re torquing, hence it’s got to go. I think another reason people are going away ring connectors/balance leads at the terminal is again, cold flow of that little soft crimp connector and it getting chewed up by the conical,spiral bottom of the flange nut. I replace all the supplied nuts with smooth flat bottom flange nuts. The ring connectors I use are Sopoby brand on Amazon. I discovered that they are actually brass, not copper (despite the description). They are much harder than copper and don’t cold flow. They are less conducive(only ever pull 4 amps) stiffer, easier to break with bending, harder to crimp and remain tight. Because of this I remove the heat shrink, crimp(if it’s a small wire, double it over) solder and use a clear flexible shrink tube with label printed number inside it. The combination of the hard ring terminal and flat bottom nuts seams to never move once torqued. I may even try a Belleville washer in the future if there’s enough thread.
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Cheap 4-life
My body is 2.63 trillion volts, .07v per cell
Like Andy’s meaning that you are using solid busbars and have roughly a 1/4” of space between your cells?
S Davis
Solar Addict
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- Sep 25, 2021
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If you are that worried about it go diagonal and use 1/0 DLO cable, it is very flexible and has a minimum bend radius of 4x it’s diameter. This actually makes things go easier not having to assemble for top balance and reconfigure after.
As for compression it is a no brainer especially for a mobile application, the cells have a lot of mass and will want to move which would put more stress on the terminals than the minimal expansion of the cells when using springs.
The way I understand the damage from expansion and contraction is when the pouches expand and contract with no compression the pouch layers can separate, by using compression the pouches have a flat surface to push against when expanding keeping the pressure constant across the face of the cell.
On my EVE LF280N without compression they are rated 2500 cycles @1c with compression they are rated at 3500 cycles. That is not a small drop in performance. With the newer EVE LF280K they don’t even rate the cells without compression.
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Two questions, where the heck are you getting the DLO cable and what kind of diagonal jumpers are those?
Cheap 4-life
My body is 2.63 trillion volts, .07v per cell
ATM I’m going to use flexible laminated busbars to prevent the busbars loosening. That should prevent the bms from thinking the resistance of the cells is different than actual. Will also compress the cells to prevent them from delaminating, most likely without using springs. Unless someone can recommend a spring because I’m not intelligent enough to figure out what spring I need..
question about compressing with threaded rod, will all the cells have the same amount of compression applied to them? Is the difference negligible from the middle cell to the end cell?
question about compressing with threaded rod, will all the cells have the same amount of compression applied to them? Is the difference negligible from the middle cell to the end cell?
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Thanks for the info on the flexible busbars and cable!
I would use something like these. Four threaded rods and four of these valve springs are in the right ballpark for the EVE 280 cells, so if yours have similar requirements, the same should work well. The pressures within the pack should be similar.
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