Is it ok to top balance LiFeP04 cells if solar system won't be assembled for a month or two?

[NorthTown2022]

Just received 16 280ah grade A EVE cells which are all sitting at about 3.29Voc. It will be a month or two before I have my panels and inverter wired in.

I was told not to bother with a top balance, to just hook them up in parallel and let them sit for a week or so before building my battery. Thoughts?

I purchased the 10A Longwei power supply and have the time. Would it be ok to top balance if cells will be sitting for a month or two at a full SOC?

 

[gonmag8]

I am in a similar situation, cells arrived but rest of the system isn't ready. I am choosing to not top balance until I am ready for using then as I think the cell life degrades quicker at high soc, unless you have a way to discharge the pack after top balance ?

 

[NorthTown2022]

I am in a similar situation, cells arrived but rest of the system isn't ready. I am choosing to not top balance until I am ready for using then as I think the cell life degrades quicker at high soc, unless you have a way to discharge the pack after top balance ?

Kind of what I was thinking as well and I don't have a way to discharge at the moment. Perhaps putting them in Parallel until I'm ready would be the safest bet.

 

[John Frum]

Kind of what I was thinking as well and I don't have a way to discharge at the moment. Perhaps putting them in Parallel until I'm ready would be the safest bet.

Don't put them in parallel.
Put a number on each cell and make a note on your computer of the voltage of each cell.
Consider the next month or 2 a self discharge test.
Check the voltage again and compare the results.
This is a good test to run on the cells before you make them into a battery.
If you get one or more cells that leak like a sieve it will inform your subsequent actions.
Where did you purchase these cells?
Where they advertised as brand new?
Where they advertised as grade A?

 

[NorthTown2022]

Don't put them in parallel.
Put a number on each cell and make a note on your computer of the voltage of each cell.
Consider the next month or 2 a self discharge test.
Check the voltage again and compare the results.
This is a good test to run on the cells before you make them into a battery.
If you get one or more cells that leak like a sieve it will inform your subsequent actions.
Where did you purchase these cells?
Where they advertised as brand new?
Where they advertised as grade A?

Yes brand new grade A, purchased them from Amy at Docan! What you said about numbering and monitoring for problematic cells sounds like a great idea. Thank you.

 

[A.Justice]

I would top balance the cells, disconnect them, and then follow @smoothJoey 's instructions and check the voltages every few days to see if they stay the same, or at least very close.

 

[NorthTown2022]

I would top balance the cells, disconnect them, and then follow @smoothJoey 's instructions and check the voltages every few days to see if they stay the same, or at least very close.

There is something I like about this, just not sure about cell degradation, I suppose a month or two at full SOC would only have negligeable effect?

The Label attached to all cells reads the same, 3.29V. Just numbered and measured all the cells with a fluke meter, one is at 3.290 seven are at 3.291 and the other 8 are 3.292. I just received them yesterday and delivery took 45 days so im assuming they not lost much voltage in that month and a half++

 

[Maitake]

Yes brand new grade A, purchased them from Amy at Docan! What you said about numbering and monitoring for problematic cells sounds like a great idea. Thank you.

Pretty sure Docan cells failed the EV testing at EVE. Doesn't mean they won't do what you need, but after researching it all I chose to buy new cells with test data for a few $ more.
The one reason I didn't go with the gray market cells is some of them have been failed for self discharging too fast. This is a PITA in a series pack and potentially more dangerous.
Good news is you have time to test and rid yourself of any leakers.

 

[NorthTown2022]

Pretty sure Docan cells failed the EV testing at EVE.

Really hope this is not accurate!!

 

[NorthTown2022]

Pretty sure Docan cells failed the EV testing at EVE. Doesn't mean they won't do what you need, but after researching it all I chose to buy new cells with test data for a few $ more.
The one reason I didn't go with the gray market cells is some of them have been failed for self discharging too fast. This is a PITA in a series pack and potentially more dangerous.
Good news is you have time to test and rid yourself of any leakers.

Maitake, when you said EV are you referring to Electric Vehicle? Where do you purchase your batteries with test data?

 

[A.Justice]

A month or two should be fine, but if you wanted to be on the extra safe side you could discharge them slightly while still in parallel. Really, if they're all pretty close and voltage (and SOC) you probably don't need to top balance them right now, and can just wait till you assemble the pack.

 

[Hedges]

But people get impatient when balancing, and for now OP has all the time in the world.
Depending on equipment available, now could be the time for balancing, self-discharge testing, capacity testing, or ...


No mention of BMS, which is required when charging or discharging in series.
"Connecting in parallel" won't accomplish anything. Charging in parallel could.

 

[brb58]

I top balanced my 280AH Eve cells and all 10 are within 0.02 V after 2 months.

 

[Maitake]

Really hope this is not accurate!!

If you have new cells and you don't have the EVE spreadsheet, and your supplier can't provide it, you have cells that failed the China Electric Vehicle certification and have been auctioned off to the "bulk" market. It doesn't mean they are not suitable for solar. Doesn't mean that they all are either.

 

[Maitake]

Maitake, when you said EV are you referring to Electric Vehicle? Where do you purchase your batteries with test data?

Yes Electric Vehicle. It's the main use for these cells. If they don't pass they can't be used for EV in china and are sold off cheap.
I bought at
18650batterystore dot com.
I don't actually have them yet, probably this week. USA stock too.
About $20/cell more than "D" brand delivered. For me cheap money to get EVE factory certification.
Two cell flaws will make you hate your pack. High leakage and very high IR.
You can test out both from "D" company. Might even get lucky and have them all be suitable. Dice roll.
Grey market cells are not "bad" many have success with them for solar, I just chose to spend a little more and fiddle a little less with the battery portion of my project.

 

[JoeHam]

I cannot see any benefits to top balancing them now and storing them at a full SOC for two months.

 

[A.Justice]

I cannot see any benefits to top balancing them now and storing them at a full SOC for two months.

The benefit would be testing the cells before they go into service. 2 months would be enough time to charge, discharge, and check resting voltages at a high SOC, and a low SOC.

I should have been more clear, It looks like I was trying to say there was a benefit in LEAVING them charged up, which there isn't.

 

[A.Justice]

I have experience with both legitimate grade A, EV cells, and grade "B" cells.

The only perceptible difference was performance during high (over 3c) discharge rates. The A grade cells were put into a relatively high-powered scooter, and can push 1-4c all day, without much voltage sag, and all tested about 1-3% over capacity, even after sitting in a warehouse for a few years. The balancer on the BMS, as far as I know, has never needed to be switched on, the cells stay perfectly in balance under huge loads.

My B grade, or "reject" cells tested over rated capacity, had 0 swelling, and perform flawlessly in a backup ESS. At rates over 1c (which I never achieve outside of testing), the voltage can start to deviate slightly, but the balancer on the BMS is able to keep up. My system is designed to be operated around .5c, so it's really not an issue at all. I sleep with my ESS about 5 feet from my family, if that says anything about how I feel about my cells.

Unless you KNOW you got grade A cells (test reports that match S/N's, QR codes, and paid 2x as much), than you have "reject" cells. BUT there's nothing inherently wrong with them, most people on here are using "B" cells for their builds and either don't know it, or aren't too concerned about it because they can be just as safe, and offer similar performance to "A" grade cells.

I would argue that there should be different categories of cells, rather than just grades. You could have a grade "B" EV cell, still meet all the performance specs for a solar setup. Would that make it grade "A" for a solar application? I think so.

 

[John Frum]

@NorthTown2022 I suggest you spend the next 4 to 6 weeks getting out of the crab bucket.
Learn what a top balance does, why its important and how to do it and all the other battery commissioning steps correctly.
IMHO commissioning a battery is where most of the pain in this journey occurs.
I've seen a horrifying number of folks destroy or hobble all their cells before they even get to use them.
I would be glad to help you get through this choke point.
The fact that you proposed leaving your cells in parallel for a couple of months suggests you could use some pointers.

 

[NorthTown2022]

@NorthTown2022 I suggest you spend the next 4 to 6 weeks getting out of the crab bucket.
Learn what a top balance does, why its important and how to do it correctly.
IMHO commissioning a battery is where most of the tears and teeth gnashing occurs.
I've seen a horrifying number of folks destroy or hobble all their cells before they even get to use them.
I would be glad to help you get through this choke point.
The fact that you proposed leaving your cells in parralel for a couple of months suggests you could use some pointers.

Lol at the crab bucket. I'm pretty new to solar as you can tell and would greatly appreciate your assistance, thank you for the offer! I joined here a couple of months ago and spend every free minute I get (which is somewhat limited) trying to learn everything I can. Perhaps a little too much jumping around between components of my build.
I do believe I understand what a top balance does, why its important and slowly becoming more confident of the balance.
For now I've got a Fluke DVM, 10A Longwei power supply, 200A 20s JBD BMS. Also have a YR1035 internal resistance tester on route (wont see it until end of June) to work with.