Retail batteries, how do they do it?

[deeuubee]

I'm about to build my first LiFEPO4 pack.
I keep reading about the need to build and compress the pack.
It seems to add a lot of bulk to the pack.
How do the ready made companies (SOK, Amperetime, Battle Born) compress their packs in such a small housing?

 

[denpmt]

I've also been wondering about this. Recalling a couple of Will's tear down videos of these batteries, I've never noticed any compression. Perhaps I missed it?

 

[blutow]

I'm about to build my first LiFEPO4 pack.
I keep reading about the need to build and compress the pack.
It seems to add a lot of bulk to the pack.
How do the ready made companies (SOK, Amperetime, Battle Born) compress their packs in such a small housing?

Battleborn doesn't use prismatic cells where compression is an option/recommendation.

I think the whole compression thing is somewhat of a hand-wringing exercise. It might be a good idea to do it, but "need" is up for debate. For the larger packs (280Ah for example), the spec sheet says compression will extend life and I don't doubt that, but it's not mandated. I think the retail battery companies are just playing the numbers. They have probably determined that the cost of designing and producing a case that optimally compresses cells is greater than the possibility of more warranty claims or poor customer satisfaction costs in the future. Also, they will probably sell more batteries if the case is smaller and lighter.

I also think the compression is less critical for the smaller prismatic cells many of these manufacturers use. Some of cell spec sheets don't say anything about compression. You'll also find that the manufacturers state that the batteries can be installed in any orientation even though it seems that it's optimal for the cells to be operated with terminals facing up. Again, it's a numbers game for the retail folks, they are trying to optimize sales and profits and that doesn't always align with optimizing battery performance and longevity.

The nature of these forums is that everyone is debating and overthinking everything. It's part of the fun of a DIY hobby. Does it really matter whether the cells are compresses at x lbs of force vs. y and whether you use springs or compression washers? Probably not enough to matter for most of us, but it's an interesting thing to debate.

I built boxes with compression, but mostly because I want everything clamped down tight for my van install. More about safety rather than battery longevity or performance.

 

[deeuubee]

I whole heartedly agree with what you said. I've managed large industrial LA and Ni-Cad battery rooms and never dealt with compression.
Being new to LiFEPO4, I want to know everything there is before making a decision.

I guess it's like building everything else.
Plan out what you would like to have, and then decide how anal you want the build to be.

 

[wholybee]

I suppose part of it is that compression will prevent or hide bulging cells, which could be a warranty claim even if they still work perfectly. In a sealed case where the cells are not visible, that becomes less of an issue. Nor does it matter if the battery lasts as long as the warranty before any issues related to not compressing arise.

 

[Forbisher]

I'm about to build my first LiFEPO4 pack.
I keep reading about the need to build and compress the pack.
It seems to add a lot of bulk to the pack.
How do the ready made companies (SOK, Amperetime, Battle Born) compress their packs in such a small housing?

Battle Born 100Ah uses 120 stainless steel cylinderical cells so i guess every cell has compression.
SOK etc are not compressed.
I just saw 8 50Ah prismatics in a Victron battery so tightly packed (and glued?) into a plastic box that they could not be removed so they would be sort of compressed.

 

[RStone13]

Wills videos say space between cells to prevent overheating. How do you do that and compress at the same time?

 

[Gazoo]

Wills videos say space between cells to prevent overheating. How do you do that and compress at the same time?

Did Will measure the temperature of the cells charging and discharging at 1C rates? From what I have seen the cells don't overheat if compressed. One other thing to note is too much compression can reduce cycles according to EVE.

 

[Rocketman]

Space between cells vs compression. I think that is an either/or design question.

If you are running at high C-rates - constantly charging & discharging- then I think heat is the larger problem- so the cells should be spaced. The cells will last longer.

If charging at low rates, low discharge rates, heat is not a problem- then the cells will last even longer if they are compressed.

For me - I plan on making my box tight to the cells - when they are at a low charge state - and call that “enough” compression.

Good luck with your decision.

 

[RStone13]

I'm just saying in many of Wills build videos he likes it when he sees there is a space between for air. And I was wondering how you compress and have air at the same time

 

[Johncfii]

I think the whole compression thing is somewhat of a hand-wringing exercise. It might be a good idea to do it, but "need" is up for debate. For the larger packs (280Ah for example), the spec sheet says compression will extend life and I don't doubt that, but it's not mandated.

The nature of these forums is that everyone is debating and overthinking everything. It's part of the fun of a DIY hobby. Does it really matter whether the cells are compresses at x lbs of force vs. y and whether you use springs or compression washers? Probably not enough to matter for most of us, but it's an interesting thing to debate.

Very much agree.

But a big part of my satisfaction as a DIY’er is when I can build it BETTER than the commercial equivalent, for significantly lower cost, without getting crazy about it. This is often possible because I don’t need to mark up raw materials, don’t have to pay for my labor, and don’t need a profit margin on the finished product.

Lower cost is good. Cheaper AND better is great! Cheaper, better, and knowing how repair it later is a home run.

 

[Gazoo]

I'm just saying in many of Wills build videos he likes it when he sees there is a space between for air. And I was wondering how you compress and have air at the same time

From what I know there is very little to no heat if charging at .5C rates or less. @cinergi has charged and discharged at 1C rates and heat was not a concern. I don't recall what his temps were but he posted it in his thread. And he has compressed his cells.

 

[cinergi]

From what I know there is very little to no heat if charging at .5C rates or less. @cinergi has charged and discharged at 1C rates and heat was not a concern. I don't recall what his temps were but he posted it in his thread. And he has compressed his cells.

220 amps discharge followed by 140 amps charge with 16 cells all clamped together (two rows of 8) and I had +10F temperature rise.

 

[Gazoo]

220 amps discharge followed by 140 amps charge with 16 cells all clamped together (two rows of 8) and I had +10F temperature rise.

Thanks for the clarification. For some reason I thought you did 1C rates. Maybe it was someone else.

 

[JoeHam]

And I was wondering how you compress and have air at the same time

Obviously you don’t.

The Fortune cells deliberately leave space between cells.

I couldn’t agree more that this is hand wringing. I have poorly cared for LiFePO4 cells that are over 5 years old with minimal degradation. And I can now buy twice the capacity for a much lower cost. Glad I didn’t know enough to stress over their care.

I have plenty of things to worry about in my life but cell compression is one thing off my plate ?

 

[cinergi]

Thanks for the clarification. For some reason I thought you did 1C rates. Maybe it was someone else.

Yeah max I can sustain is around 220 with my 2 5kva inverters. Now that I'm in a 2p16s config, I won't see more than 100 amps per cell discharge (and that's if I'm purposely abusing my system), 70 amps charge.

 

[cinergi]

WRT compression - EVE suggests it but not Lishen even though they're the same form factor. And now that I've first-hand handled both cells, I see why. The Lishen's are perfectly rectangular and don't have any wavy sides and they don't breathe like the EVE's do. These are much more physically solid.

 

[blutow]

WRT compression - EVE suggests it but not Lishen even though they're the same form factor. And now that I've first-hand handled both cells, I see why. The Lishen's are perfectly rectangular and don't have any wavy sides and they don't breathe like the EVE's do. These are much more physically solid.

lishen doesn't get specific about different cycle life based on compression like EVE, but they do mention it in their spec sheet under the cycle life test protocol. - "cells should be clamping during cycling". Ignoring the bad english, I think they are saying the cells should be clamped (compressed).

 

[blutow]

I've cycled my lishen packs (in fixtures) 20+ times and I can't can measure any noticeable difference in compression when charged or discharged. The overall pack length doesn't vary in the fixture. I have strips 1/16" thick neoprene tape between all cells and I assume it is taking up the small expansion/contraction that must be occurring. I have no concerns about heat or airflow. You have have to push these cells really hard to get any heat generation and a little air in between them isn't going to prevent that unless you are moving a bunch of air over them. If cells are inside a closed box, having a air space between the cells isn't going to make a significant difference in thermal loading or how heat is dissipated.

 

[Bob B]

So ..... EVE cells like to be compresssed ..... Lishen may have a leaking problem ... CATL is being recommended as a not buy buy some suppliers and some have scratched off or fake QR codes.

Are these aluminum cased prismatic cells having quality control problems in general?