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Where did you read manufacturers saying this?
I can't find it now. I thought it was in the Thundersky Instruction Manual (2007030222 seems to be in the name of the PDF file). But when I read page 37 of that document, it seems to say that swelling should not happen in normal use.

I'm talking about slight swelling, a few millimeters of extra width, which gentle clamping will fix. A post that seems to agree that gentle clamping is good for cells:

http://www.aeva.asn.au/forums/forum_posts.asp?TID=1903&PID=23996#23996
 

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I don't agree that is what it is saying. It looks more like a device they have to apply a large amount of pressure to correct casing distortion issues. It is repeating exactly as previously said in this thread that swelling is due to damage to the cells.
 
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My cases are distorted for sure from the heat generated but the pack within is also swollen and will not go back flat. Now that the cells have been sitting awhile the fattest one will be cut open too and the pack within will be checked. I think I will do a load test first because it is still holding a charge. The case would need to be heated up again and held under pressure until it cooled to get the case back to a more normal size if the internal packs are still flat. But squeezing the cell results in no change in swelling. I will check once again but use a much stronger form for squeezing. I think the fat one is just that. FAT.

Correct. No cells swell under normal use of charge and discharge. Period.
 

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It looks more like a device they have to apply a large amount of pressure to correct casing distortion issues. It is repeating exactly as previously said in this thread that swelling is due to damage to the cells.
Well, I can't disagree with you there. What I was trying to say is that my recollection is that "the manufacturers" (I can't remember if it was TS only or SE only or both of them) indicated that swelling is common, not serious, however mild pressure is recommended to prevent this anyway. I thought that this document is one of the places that I formed this opinion. I agree that after all, this document does not support my recollection.

Two quick observations:
Why do both Thunder Sky / Winston and Sky Energy / CALB supply clamping hardware if it should not be necessary in normal use?

Why would TS make a device for clamping swelled cells, if swelling implies that the cells are damaged? Well, I suppose it makes sense in a laboratory situation, where they would presumably push cells to their limits and beyond, and attempt to quantify the amount of damage done, and whether that damage is reversed with clamping.


The other thing is that we did observe some of our cells swelling enough to be visible to the naked eye. (See below for details.) We had probably done things like 6C continuous tests down to about 2.5 VPC, which at the time we thought of as acceptable treatment. I'm now coming to the conclusion that perhaps 6C continuous discharge is bad for the cells; even though we recorded a maximum temperature of 52°C (126°F), they may have gotten a lot hotter inside.

Possibly, charging at over 3C is also bad for cells. After all, the manufacturers do specify that limit. I guess we were hoping to get away with higher peak regen than 3C (at least for short bursts), although in our case that would be some 90 kW. I note that in the link below, Tesla argue that charging at higher than C/2 is detrimental. However, they are using a different chemistry in their cells.

Ok, I finally did a proper search (searching the images, in fact, using images.google.com), and I think this thread is what started the clamping habit:

Clamping is for real after all?

It all seems to be based on one comment on a photo, and that was about a cell that had ballooned like a blimp from overcharging. I don't suggest that everyone read all of the above thread, it's just for reference in case someone wants to delve deeply into this. The take-home message seems to be: high current charging is bad for cells, and makes them swell. Our Thunder Sky test cell seems to have taken this rather badly; it's not clear to me whether any of the Sky Energy cells (which we need for our MX-5 conversion) received the same treatment. I hope and suspect not.

In conclusion, I have to withdraw my assertion (that manufacturers consider swelling to be normal). My memory of why we routinely clamp our cells seems to have been faulty (unfortunately, not an unheard-of circumstance). My apologies.
 
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If I am not mistaken TS comes with end clamps with like 5 cells already clamped. I more assumed that the clamping is to hold them and not for keeping them from swelling. If they swell they swell clamped or not. But if they are clamped you just don't see it or they vent sooner. I can see that a case might sag a bit due to heating and just weight and time. But I highly doubt it. That is some tough plastic. But it will sag under excess heat. I think they should use different plastic. I will open my super fat cell to confirm that that pack within the cell is bloated too. If I find it is not then I will eat my words about that and try to squeeze my other one back to normal. But once the plastic is distorted I am quite sure you need heat and pressure the let it cool before it will return to normal. I don't think just squeezing it would do the trick. Swelling a cell results in lots of heat. That heat will distort the plastic without a doubt. When I removed that side piece the plastic is obviously distorted and no longer flat.

Pete :)
 
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I see no reason not to clamp nor a reason to clamp. If you are one of those that uses a BMS and takes the cells to the outer limits each and ever charge and discharge then I'd be in the camp of clamping the cells. It won't prevent damage but may keep hot cells from having the cases sag.

Pete :)
 

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I see no reason not to clamp nor a reason to clamp.
One very important reason to clamp is to prevent movement between cells that can put undue load on terminals... a nasty thing that you don't want to do, that is, if you are not using braided/flex interconnects.
 

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True, you do want them secure from load shift but a good fitting box can do just fine.
I dunno Pete, I'm not so sure that a good fitting box can offer the same tight, unitized battery that clamping can??. . . unless perhaps if the box was made to clamp???
 
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Clamping would be best but if you take care of your cells then a good stiff bok and good fit in the box should be fine.
 

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Why do both Thunder Sky / Winston and Sky Energy / CALB supply clamping hardware if it should not be necessary in normal use?
In case you overheat the cells due to high currents (3C) in hot summer temperatures, or due to severe overcharge? They can't assume everyone will use them within the prescribed limits.
I think someone here posted that Jack Rickard is no longer clamping cells, and is using the flexible webbing interconnects to avoid strain on the terminals. I know Jack has swelled some and used a clamp to compress them with some regain of capacity, but they are never the same. There would have to be voids where there is no solvent and electrolyte since the volume increased with swelling, and some solvent may have vented. My cells are only clamped with one of the small CALB clamps centered on the cells and they show no visible sign of swelling. All edges are tightly together. A couple were overcharged once to about 3.95V, but at low current. I would guess they don't swell under normal conditions unclamped, but sure wouldn't try it.:D They say clamp, I clamp with the hardware I was sent.
 
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