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Best practice for 300kgf ‘fixture’ 280Ah cells

<--- Very, very new to this.

Since it seems like most of the issues are the cells expanding after/during charging, how about putting the cells in the smallest battery box they will fit in and filling the box 90% of the way up the cells with an epoxy such as west systems 105. You could leave a slight gap between cells (I read somewhere it is possible for these cells to slightly leak to the case?) to ensure no movement is possible in any direction other then to stud side. Of course this would making changing a single cell pretty much impossible - Could apply a PVA and hope replacement cell is exact. Balancing would have to be done with a flexible cable.
 
PVA as in PVA glue? it retracts quite a lot while drying so it's far from ideal.

It's not only about replacing a cell, but for example checking the nuts are still thight on the busbars, or replacing a broken balancing wire, or anything else.
 
PVA as in PVA glue? it retracts quite a lot while drying so it's far from ideal.

It's not only about replacing a cell, but for example checking the nuts are still thight on the busbars, or replacing a broken balancing wire, or anything else.
I said fill it 90% of the way or so, leave the terminals exposed. PVA release argent, If the cells do not deform, in theory you could pull them out after it cures.
 
I said fill it 90% of the way or so, leave the terminals exposed. PVA release argent, If the cells do not deform, in theory you could pull them out after it cures.

"Draft angle"?

Pictures of cells show wavy sides, a reentrant shape, so pulling them could be extremely difficult. Unless you apply force and wait for the filling to flow.

How do you plan to grip them?

1611585075296.png

1611585124673.png
 
If a new cell has to be inserted into an existing pack, you would want to redo the top balancing process to get them aligned.
Good to know if a cell fails a few years down the road the others could be saved. I didn't think just top balancing would correct for this, figured to many minor changes over time. Good to know.
 
The other thing to do for a failed cell is remove it, change voltage settings, and operate with one fewer cell.
Not for a 12V pack, but for a 48V pack.
That assumes the BMS can work with 15s instead of 16s - anybody know which could?

With lithium, because a BMS is required and provides balancing as well as monitoring, it is probably OK to replace a cell. Issue is going to be finding compatible model several years from now.

For lead-acid, there is normally no BMS and equalization is done occasionally by overcharging the pack, letting better cells bubble in overcharged condition while putting more current into a weak cell (which also probably has more self discharge.) Not necessarily the best thing to do to better cells, but not as bad as leaving a weak cell discharged. We don't replace weak cell with a new one because it would have greater imbalance. (Maybe a LA BMS could deal with that, and would reduce degradation of cells. But would need to build pack out of 2V cells, not 6V or 12V with inaccessible busbars.)

Sunny Island (supports LA, NiCd, Lithium with BMS) allows nominal 48V battery from 42V (minus 3 cells) to 52V (plus 2 cells).
 
My only experience with mixing cells is lead-acid and has proven to not be a smart/cost effective way to do things. So since I am doing a 4S 12V setup using Lishen 272AH cells, if one goes it more then likely they will go in the trash or sold online and replacing the pack.
That being said my Epoxy idea might not be terrible but probably will result in an I shouldn't have done that as some point. Was just a thought.
Having 2 kids in Diapers right now is proven pretty much impossible to have any sort of fabrication time. Threaded rod idea is probably the best but cant help but think of getting deflection in the middle even if using C channel.
 
Threaded rod idea is probably the best but cant help but think of getting deflection in the middle even if using C channel.

My 0.6" plywood, without C channel deflected a little, but not much. I've added 1" 14 gauge box bar and and I moved the top and bottom closer to the center instead of at the very bottom and top and I believe I have virtually 0 deflection now. This stuff is meant to handle thousands of pounds in a 12" run and I'm applying 350 in a 9" run, so ...

(Check out my build thread, towards the end, in the sig below if you wanna see it)
 
Updated to show my top balancing compression fixture. It is basically a dry run of the real compression fixtures. I will reuse the metal bits, but will use higher quality plywood for the end caps and add a bottom to the setup.

Dead End.

View attachment 34379

Rubber isolators installed. I have a slide these are going to mount to, so I can pull the batteries out the door of the van, making it easier to load and unload them.

View attachment 34380

Sprung end. I was near 50% SOC so I set the preload for 75 kg. Not cutting the rods until I make the two, 4 cell compression frames.

View attachment 34381

I think cinergi is seeing as much as .9mm deflection in his test setup ..... since you started at 50% .... have you measured how much difference in pressure you will see if you get 4.5mm deflection both directions on your pressure sensor?
 
Dzi,

I have been looking for a flexible battery bus bar solution and you have provided some great ideas.

The 71mm CALB bus bars made for the CALB CA180 cells look like the best solution to me and they appear to be able fit the EVE 280 cells (holes are a bit oversized however for M6). However, no one seems to sell the CALB bus bars separately from the CALB cells. Anyone know where you can get these?

See my post here: https://diysolarforum.com/threads/w...raided-interconnects.15826/page-2#post-194128
 
I think cinergi is seeing as much as .9mm deflection in his test setup ..... since you started at 50% .... have you measured how much difference in pressure you will see if you get 4.5mm deflection both directions on your pressure sensor?
Yes. I need to calculate that. I was thinking I had to be able to deal with 3mm of deflection. This makes it a lot easier to deal with. Basically I can just charge to 100% SOC then set the spring preload for the max compression force I want. I can probably remove some the Belleville Disc Washers. I have 12 in series in order to be able to handle 3mm of movement and still stay within +/- 4 PSI of the target 12 PSI.

I bet I can reduce the range to 10 to 14 PSI if I only need to handle 1 mm of travel.
 
OK, new figures.

Assuming 0.9mm is the travel I need to handle from 0 to 100% SOC.

I am using 5/16" x 18 TPI threads. 18 TPI is 0.056" per turn. Convert that to mm and I get 1.4224mm per turn or 1 mm = 70% of a turn. I am going to call this 2/3 of a turn since I am not a human protractor.

I retested with a total of 10 Belleville washers in series <><><><><>.

Test procedure used:
  • Run nuts until finger tight (not as tight as humanly possible, just snug). Reading ~ 1 - 2 kg on cell.
  • Rotate nut one full turn. Force measured = 56.8 kg:
  • Rotate nut an additional 2/3 of a turn. Force measured = 90 kg
Results of doing this.

W10_1_Turn.jpg

57 kg per threaded rod x 4 rods = 228 kg total = 502 lb which results in 9 PSI
90 kg per threaded rod x 4 rods = 360 kg total = 794 lb which results in 14 PSI.

The means the compression range from 0% to 100% SOC will be 9 PSI to 14 PSI (11.5 PSI +/- 2.5 PSI). I am willing to declare victory.

Here is how I am going to use this information.
  • Charge all cells to 100% SOC.
  • Assemble compression fixture with 4 threaded rods, 10 Belleville disc springs in series and double nuts on each threaded rod.
  • Tighten all primary nuts finger tight.
  • Tighten each primary nut an additional 1-2/3 turns. I suggest doing this in stages, working diagonally across the cell to ensure even tightening.
  • Tighten secondary (jam) nuts against primary nuts so they won't vibrate loose. Feel free to use locktite if you want, just don't get any locktite on the Belleville disc spring washers. I am going to skip using locktite myself. If corrosion is a possibility you might want to consider lubricating the Belleville disc springs since they need to be free to move against each other.
 
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