Is this normal bulging for a prismatic lifepo

[Stevesie]

Just wondering if this bulging is normal for new prismatics. The gap is about 1.25mm. Bit sad I didn't get 4 cells from the same batch :-( Cheers.

 

[jonescg]

Who did you buy them from? If you got them through a local distributor I'm sure they will provide some support and advice. As long as the sag is within reason, it might not be an issue.

 

[Stevesie]

They came from one of the Australian dealers, who got back to me today and said it's normal. I'll give 'em a load test when the pack is all set up.

Cheers.

 

[dogman dan]

Well, I know Jack about prismatics, but puffing when new sounds wrong to me. Might be quite normal by cycle 100 though.

 

[Stevesie]

Cheers dogman. It seems wrong to me too, but I also know very little about them. If the dealer says it's ok I guess that's what I have to trust.

 

[Ypedal]

yeah.. they bulge.... i've had LiMn metal can 20ah cells, 10ah lifepo4, 12ah lifepo4, when warm they bulge a bit more than when cold ( chemistry is great eh ) but all that is " normal" to a point.. do keep the straps and maintain the pressure imo.. best to keep them compressed.

heck.. lipo pouches puff ( swell ) too and they keep on ticking...

tic .. tic tic.. boom ?.. oh.. bad joke.

 

[amberwolf]

AFAIK for all those particular kind of large-Ah prismatics, in the plastic box cases, changes in swelling at various states of charge is perfectly normal. It's why normally they use the strapping around them, with stiff end plates, to press them all together harder.

 

[Stevesie]

Thanks folks, I'll assume all is well then! I'm going to strap some some solid end plates on to constrain the outer cells properly.

Such a treat being able to move the pack around without risking a hernia as was the case with the lump o lead.

 

[amberwolf]

Also, if you want really tight packing straps, don't use the crimp ones like in the pic--use the ones with the metal or plastic loops, as you can pull those as tight as you like, with nothing under them to stretch the strap away from the thing you're strapping.

You can get them free most anyplace that gets a lot of freight--at least some things they receive will have them on there, and you can ask to salvage them when they toss the shipping bits out. Poke around my ammocan RC LiPo pack thread and my CrazyBike2 thread and my Fusin 1000W review thread for some pics of those things.

 

[Stevesie]

Thanks Amberwolf. I was thinking about some using some webbing strap sewn to a S/S turnbuckle.

 

[amberwolf]

You can also use the really big SS hose clamps, like the ones used to clamp ventilation ducts to exhaust or intake ports in A/C systems. Just have to be careful where you put the connection/screwclamp, so it doens't catch on anything. I find these for next to nothing at garage sales and thrift stores sometimes.

 

[Stevesie]

Cheers for the tip. I live in a coastal/rural area so it's all about boats here, hard to find big A/C hose clamps like that, but rigging turnbuckles are pretty easy to come by.

 

[dogman dan]

I definitely see how they could start bulging after even one or two cycles. I just thought it odd that they would come that way.

Bigger pouches, or stack of pouches, makes sense they'd start bulging some at some point. I had a mental picture of them having to swell a LOT to bend the box, and stretch the straps though.

IR would tell all no doubt. Or a capacity test.

 

[Stevesie]

The dealer charged them before he sent them, so maybe that's got something to do with it. Cheers.

 

[dnmun]

.

 

[amberwolf]

Bigger pouches, or stack of pouches, makes sense they'd start bulging some at some point. I had a mental picture of them having to swell a LOT to bend the box, and stretch the straps though.

It's fairly softish plastic. A little stiffness from teh ribs in it, but not all that much, vs the pressure it could build inside. Been a while since I saw the pics over on DIY Electric Car of a disassembled one, but IIRC there aren't actually separate pouches inside, but rather just a lot of layers for what amounts to a single pouch, and the plastic casing is the "pouch". There is a pressure release vent on the top between the terminals on the ones I have, under a sticker.

 

[dogman dan]

Makes sense, the flat sides of the box would not be that strong.

I guess I just pictured enough space inside the box for the normal swelling that would happen. But that would make no sense if there wasn't pouches inside to seal the air out. Since no pouches, they'd have to pack the box tighter of course. Then it would swell a bit when charged.