diy solar

diy solar

EVE280 high C rates anyone?

cinergi

1.21 Jigawatts
Joined
Aug 9, 2020
Messages
1,419
Is anyone charging or discharging their 280Ah EVE cells at or above 0.5C and observing 280Ah? I'm having a bear of a problem getting more than 250-260 out of some of them and I'm wondering if it's because I've been pushing 120 amps in and 220 amps out on occasion. Out of 36 cells, I've tested 22 and at least 6 of them are pulling my battery bank down well under 280Ah. I've individually tested 2 of those 6 with a tester at 10 amps and only got 250-260Ah out of them. One of them even intermittently stopped discharging at least twice during the test due to very high internal resistance.
TIA!
 
Top. If you want the full details of the method, I covered that in my build thread in this same forum. It's safe to assume they were properly top balanced (and the method reviewed by other members here). Thanks!
 
  • Like
Reactions: Dzl
How are you terminating your charge? What is your discharge voltage limit? Current at that limit? Its possible you are loosing a few percent at either end by terminating early.

Have you done a thermal survey to see if you are seeing higher resistance losses at one connection or bus bar?
 
How are you terminating your charge? What is your discharge voltage limit? Current at that limit? Its possible you are loosing a few percent at either end by terminating early.

Have you done a thermal survey to see if you are seeing higher resistance losses at one connection or bus bar?

Terminate at 2.5v on the lowest cell. Current is any of 0.1 to 0.8C. No thermal problems. This is my 4th run now at 0.1C with the lowest 4 cells replaced ... 4 hours until results.

Individual cell testing has yielded no more than 270Ah with 10 amps using a tester like this. One of the cells had intermittent high IR and didn't discharge for several minutes while connected to that tester.

Basically, I'm wondering if these cells can withstand high C rates. When testing with 0.1C or less (like the 10 amp tester above), they may show 280. But exposing them to high C's may have damaged them, even though they're spec'ed for 1C charge/discharge and their documented test method is 0.5C. I need to know if anyone has been pulling/pushing 0.5C with these.
 
Individual cell testing has yielded no more than 270Ah with 10 amps using a tester like this. One of the cells had intermittent high IR and didn't discharge for several minutes while connected to that tester.

The above is very confusing and not consistent with expectations. Intermittent high IR is almost exclusively tester or connection related. What do you mean "it didn't discharge for several minutes while connected to that tester"?

Did you test the IR of all of your cells? Did they meet spec?

High IR will act in a Peukert-like way, and you'll lose capacity. Even a SINGLE cell with high IR may cut the pack capacity short and trip the BMS.
 
Last edited:
In addition to snoobler's suggestions/questions.

What is your charge termination voltage and current? When the charge terminates, what is the voltage spread between cells?

Does your BMS calculate instant IR with changing current? If so, do you see significant variance between cells? At rates above 0.5C, interconnect resistance can be significant contributor to imblance.

That being said, you are testing cells individually. Are you seeing capacity loss compared to new? Did you do an initial test before commissioning??
 
That being said, you are testing cells individually. Are you seeing capacity loss compared to new? Did you do an initial test before commissioning??
If I have followed his progress correctly: these are new cells, and this is the initial testing.
See here
 
The above is very confusion and not consistent with expectations. Intermittent high IR is almost exclusively tester or connection related. What do you mean "it didn't discharge for several minutes while connected to that tester"?

Did you test the IR of all of your cells? Did they meet spec?

High IR will act in a Peukert-like way, and you'll lose capacity. Even a SINGLE cell with high IR may cut the pack capacity short and trip the BMS.

That one cell has some weird issue where it would discharge via the tester at 10 amps and 0.25ish ohms and then all of a sudden it would read 30 ohms and .13 amps ... and after a few minutes it would slowly begin ramping up again. Happened twice. Only on that cell. I'll repeat the test because that's incredibly crazy. I checked the connections during that time and all was well. I rebooted the tester - no change. I've only had that problem with that one cell. But I'll repeat it to be sure. At a later date.
 
In addition to snoobler's suggestions/questions.

What is your charge termination voltage and current? When the charge terminates, what is the voltage spread between cells?

Does your BMS calculate instant IR with changing current? If so, do you see significant variance between cells? At rates above 0.5C, interconnect resistance can be significant contributor to imblance.

That being said, you are testing cells individually. Are you seeing capacity loss compared to new? Did you do an initial test before commissioning??

Per above, 2.5v on the lowest cell = termination (amps was 30). Voltage spread was 550mv.

The BMS hasn't calculated instant IR (and it won't until I hit 20% of the current sensor's rating of 800 amps at least twice).

since the imbalance only ocurred at the end of the test (it was 10-20mv otherwise) and the imbalance wasn't corrected at the end of the test, it's not interconnect resistance.

I didn't do initial tests of individual cells before I built the pack. That would take literally 40 days.
 
In case you misread, I was asking for *charge termination criteria* not discharge. Just want to confirm we are on the same page.

With the odd cell that jumped up/down during discharge, that sounds like a bad connection. It could be internal to the cell, or it could be your gear. I have seen something similar happen with lead acid, where a crack in the internal bus to terminal connection looks good, but once it warms up the resistance goes crazy.

Your likely right, as I would expect interconnect issues to show a higher delta-V at that rate. Though I would confirm with a multimeter at several points.
 
Oh sorry, charge.. I top balanced all to 3.650

I've confirmed everything with my Klein, too.

I know everyone's trying to help me make sure I'm being thorough -- that's all been done in other threads already. I just need to know if anyone's using these 280's in high C-rate conditions ... My cell fail rate is higher than otherwise reported but I've not seen reports of users drawing 220 amps or charging at 120 amps ... so I'm trying to see if it's my bad luck or if these cells can't withstand the published C rates.
 
Sounds like you've done your due diligence. I am not implying your at fault, but experience has taught me to start with user error and work down.

I have not seen any other users report C rates that high with these cells. The highest I see is about 0.4C for any significant duration, and my average draw is around 0.02C.
 
Next time you're under a heavy load, manually measure battery voltage AT the terminals and AT the inverter/load. You may find some additional resistance in the components/wiring/bus bars.

If you're losing 0.1 or 0.2V across that connection, you'll have premature cut-off.
 
Capacity test #4 at 30 amps to ~2.6v just completed. Cell 7 - the one I just replace with an unused cell (charged obviously) was the low-ball with another very close behind it. 262 Ah. I took some time lapse and I'll post here once I compile it.

I don't think these cells are 280Ah.

I have a third cell on the previously mentioned tester. I expect 270 from it.

I may pull one of my high cells and test it on that tester, too.
 
Hmm, not ideal that's for sure. Is 10% lower capacity a deal breaker for your application?
 
Back
Top