diy solar

diy solar

Compress or not, flexible busbar or not

You could use springs to calibrate your bar clamps by putting the springs between two plates and then compressing them with the bar clamps. Record the torque required on the bar clamp screws in order to get you the desired clamping force (calculated from the spring constant). You could then clamp your cells in the fixture using the same torque on the clamps, then snug the nuts and release the clamps.
Related but different, you could use a second end-plate on on end and so with if like a car Jack positioned against a wall to apply pressure sideways until the second end plate has been pressed by the predetermined deflection to represent 300kfg (was about 1/4” in the case of my springs).

You can then hand-snug nuts on all the threaded rods (probably on the backside without springs ) to ‘lock in’ the 300kgf.
 
The way I would build a rigid fixture clamped to 300kgf would be to use half the treaded rod with springs so I could tighten exactly the correct deflection to apply 660kgf, then I would snugly tighten nuts into the other threaded rods without springs. Whether you want to loosen the nuts and remove the springs from the first set of rods or not is largely immaterial.

If the springs were left on some rods and not others then the pack could expand unevenly across its face
 
If the springs were left on some rods and not others then the pack could expand unevenly across its face
No, it could never expand.

But it could compress at lower SOC (from which it could again expand back to original position as charged, but not beyond.

The rods without springs form a stop (only expand from the elastic factor of the steel itself).
 
Related but different, you could use a second end-plate on on end and so with if like a car Jack positioned against a wall to apply pressure sideways until the second end plate has been pressed by the predetermined deflection to represent 300kfg (was about 1/4” in the case of my springs).

You can then hand-snug nuts on all the threaded rods (probably on the backside without springs ) to ‘lock in’ the 300kgf.

Only problem with this is trying to move the cells once all compressed together. Where it’s made it would have to stay so thevwall where it’s made would have to be strong enough to handle 660lbs of pressure and the extra room to set it up with a floor jack
 
Only problem with this is trying to move the cells once all compressed together. Where it’s made it would have to stay so thevwall where it’s made would have to be strong enough to handle 660lbs of pressure and the extra room to set it up with a floor jack
Precisely. I built my pack in place and it will only be moved through complete disassembly. It’s far, far easier to just clamp in place with springs and leave them in place.

If you are building multiple packs, you could have two holes for rod at each location, calibrate force using one set of rods with springs then secure non-spring loaded rods without springs into the second set of holes before removing the spring-loaded rods to calibrate force of the second pack etc…
 
Would require assembling and disassembling, but you'd get a great idea of what pressure the cells are seeing and how uniform it is.

There's also a nice calculator towards the bottom.
 
You could use springs to calibrate your bar clamps by putting the springs between two plates and then compressing them with the bar clamps. Record the torque required on the bar clamp screws in order to get you the desired clamping force (calculated from the spring constant). You could then clamp your cells in the fixture using the same torque on the clamps, then snug the nuts and release the clamps.
Torque doesn't equate to linear force? Unless you measure it.
 
Tie nuts to long bolts? Why because the threaded rod wasn’t long enough or what
Yes, 16 cells are over 45” long plus I needed another 4-5” per end to accommodate the endcaps, steel cross braces and springs.

I found 3” long tie nuts that allowed me to tighten 3” or 4” bolts into the tie nuts rather than tightening standard nuts onto the ends of the exposed tie rod. Because there is no exposed tie rod ends, it’s a bit cleaner (and shorter).
 
With 16 or 19 cells in a row, how would you apply 660lbs of force before tightening up the nuts for a rigid fixture. Would need some very long clamps and somehow incorporate a weight scale?
I’m planning on using springs and slowly tightening each one till they are at 50% deflection which is supposed to be 160lbs per spring.
I guess if a rigid fixture was wanted then the springs could be used and then measurements to the walls recorded then remove springs and retighten walls to that measurement..
Disappointed in your assumption, why not test the " supposed" by testing the springs under various compressed lenghts, for example at 50% deflection how much more deflection do you have before the force exceeds required design?
Remember spring force is not linear for compressed lenght, the first 1mm might equate to 10lb, but from half compression the next 1mm might equate to 50lb extra.
 
Right but doesn’t the data sheet imply pressure will not reach damage potential in a rigid fixture under normal usage..
I don’t think the small extra cost either way should sway the decision of a DIYer. Doing what best however to get more cycles might matter. That’s if the user wants the best life for the cells instead of simply thinking calendar aging will happen first..
Higher pressure thru the SOC might stop unwanted expansion that users are reporting when using springs and 300kgf. Remember your c-rates and charge cycles are low/not fast so you are not seeing as much expansion as two other users commenting on this thread that use springs.
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Yes cheaper. Have seen just strapping used. To allow some expansion instead of rigid fixture and still claiming 10k cycles..
If what you seem to be hoping / suggesting were true, you’ll need to explain to me why EVE didn’t clamp their fixture to 600kgf if not 1000.

Their spec for clamping force is not ‘>300kgf’, it’s 280kgf to 320kgf.

The idea that higher clamping force than 300kgf can extend cycle life is misguided.

EVE has shown you how you can get 6000 cycles to 80% of initial capacity by building a rigid structure.

Without having stated so explicitly, they have also suggested that you can safely use that structure to cycle a cell all the way to 60% of initial capacity without needing to worry about pressure when charging increasing past the point where it could start causing defects.

So I agree with the conclusion that EVE’s new datasheet gives the ‘all clear’ on using a rigid fixture (assembled according to their specifications).

It’s the idea that you are going to get fewer cycles in a fixture maintaining 280-320kgf throughout the full cycle that I find misplaced.

If anything, fully-depleted cells in a rigid structure will be under less pressure than fully-depleted cells in a constant 300kgf structure, so ‘expansion’ and internal deformation could be worse.

EVE suggested a constant 300kgf fixture was required for increased lifetime in 2021 and my read is that enough battery manufacturers complained about the added complexity and cost that would involve so EVE came out with all tjus additional detail showing constant force was but required to get the same cycle life.

This datasheet makes it clear how you can build a simple rigid fixture to achieve a full 6000 cycles to 80%.

But it include nothing to suggest tgat a constant 300kgf will deliver fewer than 6000 cycles to 80%.
 
If expansion continues thru the SOC as some are saying they are seeing with springs at 300kgf then that could be worse than a rigid fixture keeping that expansion from happening, is all I’m saying,
 
Remember spring force is not linear for compressed lenght
The whole point of springs is that they provide a linear force per displacement over their usable length. The last mm of useful distance will have essentially the same force as the first mm.
 
The whole point of springs is that they provide a linear force per displacement over their usable length. The last mm of useful distance will have essentially the same force as the first mm.
My mistake ☹ i should of looked at my own test results ?
 
Would this work for measuring clamp force?
Use ratchet straps around your plated cells with one of these in between. https://www.amazon.com/dp/B01F6IOWDG/ref=cm_sw_r_cp_awdb_imm_B5YEK54D0XV0C4RR4C8R Tighten the ratchet straps till you hit 300 kg then snug up your bolts.

Also this company sells a variety of pressure sensor pads.

I could be very wrong, but I don’t think those pads can withstand/sense 660lbs of force. I think they are for much less compression
 
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