I think you misunderstood that part (but really nice post otherwise BTW ), the +/- 1 mm is just a manufacturing tolerance, the expansion will be around 0.5 mm between 30 and 100 % no matter what.
The typical cell will be 71.5 mm @ 30 % and 72 mm @ 100 % but for example you can have a cell that is 70.8 mm @ 30 % then it'll be 71.3 mm @ 100 %.
I guess the datasheet should have been clearer and said 71.5 mm +/- 1 mm @ 30 % and +0.5 mm @ 100%. But I think we're quite lucky with what we have, I've seen datasheets much worse than that...
well I did a test and carefully measure the expension of an EVE brand new cell from 50% to 100% SOC...this was NOT in a fixture, just free standing.I think you misunderstood that part (but really nice post otherwise BTW ), the +/- 1 mm is just a manufacturing tolerance, the expansion will be around 0.5 mm between 30 and 100 % no matter what.
The typical cell will be 71.5 mm @ 30 % and 72 mm @ 100 % but for example you can have a cell that is 70.8 mm @ 30 % then it'll be 71.3 mm @ 100 %.
I guess the datasheet should have been clearer and said 71.5 mm +/- 1 mm @ 30 % and +0.5 mm @ 100%. But I think we're quite lucky with what we have, I've seen datasheets much worse than that...
That's consistent with my results too, but I budgeted for .5mm in my spring selection and fixture design.No, my expansion under compression is less then 0.5mm per cell on average.
An arrangement like that could definitely work. I considered doing something like that, but abandoned the idea as I felt springs in compression with rods was just going to be simpler for my use.New member here. I’ve been reading a lot about cell compression using springs. All the packs I’ve seen are using the springs on the outside pushing the end supports toward the cells using four springs. Am I right at assuming these springs should compress at 165 lbs to achieve the 12 psi goal.
Could I use four springs to pull the end supports together using threaded rod with eyelets on the end? I recently salvaged the seat springs out of my old Toyota. I found they started to stretch at about 160 lbs. I’m not an engineer, what do you think? 4S 280 ah cells
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Thanks 100 Proof, I’ve got eight springs out of the two seats. I thought I’d give it a try since the springs were free. I’ll use 1/4” eyelets with 3/4” plywood ends. I’ll post pictures after the build.An arrangement like that could definitely work. I considered doing something like that, but abandoned the idea as I felt springs in compression with rods was just going to be simpler for my use.
If you can, try to hang 165 pounds off of one of your springs and then measure its extension. Use that same extension measurement to dial in your force.Thanks 100 Proof, I’ve got eight springs out of the two seats. I thought I’d give it a try since the springs were free. I’ll use 1/4” eyelets with 3/4” plywood ends. I’ll post pictures after the build.
That’s exactly what I did. I put a hook into a ceiling stud, hooked the spring to it, made a loop with a rope and stepped into the loop. I weigh 170 lbs and had all my weight on the spring. Reached up with some calipers and measured the length of the spring. I figured, close enough!If you can, try to hang 165 pounds off of one of your springs and then measure its extension. Use that same extension measurement to dial in your force.
Did anybody do compression on a larger bank of e.g. 8S4P cells? I mostly saw builds of only low-cell units but may have missed a pic or two. If somebody did it, do you compress all cells with one and the same mechanism or is there an advantage to compressing each (4P or even 2x4=8P) parallel stack by itself? I imagine so but it might not be very practical or nice looking when doing it with springs. So that's why I'm also interested in knowing if there is a final verdict on the spring vs foam issue ...?
Definitely a very nice setup cinergy! Unfortunately I do not have space for a 2x16 setup like that and will need to do a 4x8, complicating things a little... Also, I am a little surprised to notice the springs compressed to just about 100%, am I seeing that right?Mine is two compression structures of 16 cells each. Just have to account for X cells times 0.5mm of variance when sizing your spring.
Cinergi's 28 kWh / 4 kW Solar / 10 kW inverter RV build
I've completed the last revision the battery before I head to Kanas next week (in theory) to pick up the new RV and install this (at their facility with their assistance WRT any welding or physical work beyond my capabilities). The previous revision had a few spots that were +40F under 120 amps...diysolarforum.com
Definitely a very nice setup cinergy! Unfortunately I do not have space for a 2x16 setup like that and will need to do a 4x8, complicating things a little... Also, I am a little surprised to notice the springs compressed to just about 100%, am I seeing that right?
I went through the whole compression thread, and I have a question:
Each cell is supposed to expand 0.5mm which makes it at least 2mm for a pack of 4 cells. Now these 0.5mm go in some direction, one cell pushes the other a little bit further.
In your installations: like this one I see 4 cells connected by a solid copper bar.
Where does the movement go here? My theory is that there must be a lot of strain on the rods where the solid bar is screwed on. So after a few (hundred) movements, the rods might become lose or might push something inside the cell.
Sorry for my ignorance, but I just received my cells 3 days ago and I wonder how this all works.
Wow, that is a lot.well I did a test and carefully measure the expension of an EVE brand new cell from 50% to 100% SOC...this was NOT in a fixture, just free standing.
The answer is that I measured an expansion of .762mm so that is much less than what I thought it would be however it is certainly more than 0.5mm... so an 8cell fixture would need at least 0.24" of room.
I wonder if the 0.5 expansion is when the cell is compressed with the 300kgf???