EVE 280Ah Lifepo4

[nebster]

I suspect these are Frey cells? (Aka Fortune, Overkill solar, etc). This is an interesting point. I wonder what role volume to

Indeed.

The EVE 280's have a much higher ratio of volume to surface area and lower C-rate. This may or may not be part of why EVE recommends compression. I would be curious to know whether other similar form factor aluminum cells (like CATL 202Ah, or ETC 277Ah) recommend compressions or 'fixture' and if their datasheets are any more clear on the method and the logic.

They definitely have a much higher energy density, so it makes sense that maybe they are pushing the mechanical envelope harder. Maybe there is less room to expand in there.

I may or may not be way off, but I have the impression that the bulge is the result of high state of charge more than c-rate. Can anyone confirm or correct my understanding on this point?

I don’t know the answer to your question, but I would argue we should not take them to ultra-high SOC either.

But, what I really meant was, I don’t know if expansion per se is a huge issue in terms of lifecycle, even if it turns out to have a small deleterious effect. I think most people are going to get so much life out of these that a little bit shaved off might not be worth optimizing for.

Then again, expansion might be a big deal if it causes the terminals to undergo mechanical stress vis a vis the bus bars. I would not want those to be moving around.

 

[Dzl]

Nah, our bulbs are brighter than EVE's.
I would be happy if someone could prove me wrong with my thinking....but with a detailed explanation

I would look at it the other way. I would be happier if you are right, and there is no reason to worry about compression, but I would say the burden of proof falls on us if we go against manufacturer recommendations.

 

[Dzl]

I don’t know the answer to your question, but I would argue we should not take them to ultra-high SOC either.

Good point, I wonder how the equation would change if cells never exceed 90% SOC

But, what I really meant was, I don’t know if expansion per se is a huge issue in terms of lifecycle, even if it turns out to have a small deleterious effect. I think most people are going to get so much life out of these that a little bit shaved off might not be worth optimizing for.

Then again, expansion might be a big deal if it causes the terminals to undergo mechanical stress vis a vis the bus bars. I would not want those to be moving around.

I basically agree with you here, on all points. Though If we take EVE's word for it (and I see no reason not to, other than that there are a lot of unknown variables in there model), the difference is 2500 cycles vs 3500 cycles or a non-fixture cycle life of 71% of the cycle life with fixture. But in my opinion there are waaaay too many unknowns to know whether those numbers apply to our use-case or not. Or to know how a middle case of fixture but no, or little compression would compare to the two scenarios they tested.

 

[Gazoo]

I sent an email to EVE and asked for an explanation. Hopefully they will reply and play nice.

 

[sremick]

I sent an email to EVE and asked for an explanation. Hopefully they will reply and play nice.

My experience talking with EVE is they don't want to talk to you, even to provide basic technical info, and will dismiss you and tell you to talk to the place you bought them from.

 

[Gazoo]

My experience talking with EVE is they don't want to talk to you, even to provide basic technical info, and will dismiss you and tell you to talk to the place you bought them from.

That's why I said "hopefully they will reply and play nice".

Maybe my experience will be a positive one. Doesn't hurt to try and gotta start somewhere.

 

[BiduleOhm]

This seems to imply that you are saying it is ok to apply compression on the narrow side? I remember reading somewhere that you DO NOT want to apply compression on the narrow side only the wide side. Unfortunately I cannot find the source at the moment, but something about the way the pouch is constructed and you do not want to apply pressure to the pouch seams. I apologize if I misinterpreted your statement.

No, on the biggest side of the cell:

Not that: -->[ cell ]<--

             |
             V
But that: [ cell ]
             ^
             |

I would say that makes sense but only if the cell bulges and contracts which as you noted they are known to do under a high state of charge. It's the amount of force that EVE notes in their specs that is throwing me off. I simply do not understand what the difference is between applying the force they state to apply, or applying enough force to the cells to ensure they don't bulge. I am going to do the latter.

I guess they performed multiple tests with varying amount of force and found 300 kgf gives the best results.

I may or may not be way off, but I have the impression that the bulge is the result of high state of charge more than c-rate. Can anyone confirm or correct my understanding on this point?

That's correct.

Good point, I wonder how the equation would change if cells never exceed 90% SOC

Educated guess tells me it's more or less linear with the voltage, if that's correct then staying out of the knee would make a big difference.

 

[Gazoo]

I guess they performed multiple tests with varying amount of force and found 300 kgf gives the best results.

So do you know how much force this equates to in pounds? Not very good at math here. Thanks.

 

[Gazoo]

I sent an email to EVE and asked for an explanation. Hopefully they will reply and play nice.

EVE hasn't replied. I will of course update if I receive an answer. I wonder if this is their North America division:

Home | EVE Energy North America

ICR, INR, NMC, LFP, primary, rechargeable, lithium ion, lithium ion phosphate, lithium manganese dioxide, lithium thionyl chloride, CR, ER, SPC, PLM module, battery, pack, rack, system, PCB, PCBA, PCM, BMS, wire harness, sensors, liquid cooling, container, CCCV, cut-off, continuous charge...

www.evebatteryusa.com

I might contact them and see what they have to say.

 

[upnorthandpersonal]

Someone check it this is correct, but:

300 kgf == 2942 Newtons == 661 lb

 

[Dzl]

Someone check it this is correct, but:

300 kgf == 2942 Newtons == 661 lb

If this is accurate, and the broad side of an EVE cell is roughly 17.36cm x 20.48cm (355.53 cm^2 or 55.11 in^2). Would this equate to roughly 12PSI (or 0.844 kg/cm^2)?

 

[BiduleOhm]

Someone check it this is correct, but:

300 kgf == 2942 Newtons == 661 lb

That's correct

If this is accurate, and the broad side of an EVE cell is roughly 17.36cm x 20.48cm (355.53 cm^2 or 55.11 in^2). Would this equate to roughly 12PSI (or 0.844 kg/cm^2)?

That's correct too

 

[Gazoo]

Thanks very much for answering my question. But wow! Seems to me that much force would crush these cells. Maybe the aluminum casing is thicker than I think it is. I am still going to stick with my plan and do what I can to keep the cells from bulging. My charge and discharge rates will be much less than 1C. Charge rate maybe around 20 amps and discharge rate around 100 amps at most with a 24 volt pack.

 

[Dzl]

Thanks very much for answering my question. But wow! Seems to me that much force would crush these cells.

Does seem like potentially a lot of force doesn't it. Whether the force was measured when the cells are near 'full' or 'empty' seems like it would make some difference.

Nothing wrong with your intended method, other than potentially shorter cycle life of roughly 25% at most. On the plus side you wont accidentally crush your cells and with conservative charge/discharge rates and 95-10 or or 90-20 bandwidth cycle life might be long enough not to even worry about.

 

[Gazoo]

I sent an email to EVE and asked for an explanation. Hopefully they will reply and play nice.

Sales at EVE has forwarded my email to another division. Still hoping for an answer.

 

[Steve_S]

Sales at EVE has forwarded my email to another division. Still hoping for an answer.

Understand something.... You are wasting your time !
EVE, Calb, Sinoploy, - ALL OF THEM will NOT deal with Joe Shmoe End User ! Unless you are a company who is looking to contract buy in bulk, they won;t waste time on you or anyone else. They always point you back to your contact, the vendor. They are not staffed for dealing with "users", they are staffed to deal with corporate sales and volumes.

It is unfortunate and some people may be all up & angry about that but it's no different than anywhere else. Do you call FORD Corporate when your F-150 breaks, or do you goto the garage / dealer to get fixed. Do you call LG Head Office when your LED TV packs it in ?

 

[sremick]

It is unfortunate and some people may be all up & angry about that but it's no different than anywhere else. Do you call FORD Corporate when your F-150 breaks, or do you goto the garage / dealer to get fixed. Do you call LG Head Office when your LED TV packs it in ?

I think the problem here is when someone needs detailed technical info... there isn't an authorized/licensed, certified, trained, etc "EVE Dealership" with all the inside scoop. A more-accurate analogy would be if you have a technical question about your Onkyo AVR, but when you call Onkyo they refuse to talk to you and instead refer you to contact Wal-Mart where you bought it from for "tech support". But of course when you call Wal-mart all you get are min-wage highschoolers who only know how to work the cash register, since they're just in the market to resell stuff and don't have any inside technical knowledge of any of the stuff they sell from countless different brands.

If I go to a Subaru "Dealership", they are certified and trained by Subaru, and have access to all the inside technical documentation, have a dedicated service and tech-support department alongside their sales dept, and are specifically tasked by Subaru to provide the full level of tech support and are empowered with everything they need to do so. And they aren't doing the same for Ford, Toyota, Nissan, Honda, etc... they are just Subaru.

So EVE is trying to treat the channel like it's car dealerships, when it's really like Wal-marts, Target and the Dollar Store. So the end user is left SOL.

 

[Gazoo]

Understand something.... You are wasting your time !
EVE, Calb, Sinoploy, - ALL OF THEM will NOT deal with Joe Shmoe End User ! Unless you are a company who is looking to contract buy in bulk, they won;t waste time on you or anyone else. They always point you back to your contact, the vendor. They are not staffed for dealing with "users", they are staffed to deal with corporate sales and volumes.

It is unfortunate and some people may be all up & angry about that but it's no different than anywhere else. Do you call FORD Corporate when your F-150 breaks, or do you goto the garage / dealer to get fixed. Do you call LG Head Office when your LED TV packs it in ?

Thank you for your very enlightening and informative post... I had a feeling you would come along to make a comment since you had a bad experience with EVE when you were communicating with them. But it's all good and it's my time to waste. In fact my reply to you is taking as much of my time as it took for me to shoot off an e-mail to EVE.

Whatever the end result of my inquiry is I will not be angry. If EVE answers my question, then great, If they don't that's ok too. It doesn't hurt to try does it?

I have gone to the top a couple of times and had good results. In fact it's not at all uncommon. People do it all the time if they are not satisfied with general customer support. But yeah this is different since I am simply looking for information and I totally get what you are saying. And I will say it to you one more time....it doesn't hurt to try.

 

[nebster]

Also, if more people try, it might send a message.

 

[Dzl]

Also, if more people try, it might send a message.

Or at least possibly see the need to revise and clarify the language in their documentation when they get around to the next revision.