EVE280 high C rates anyone?

[cinergi]

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!

 

[Supervstech]

We’re they top or bottom balanced?

 

[cinergi]

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!

 

[Luthj]

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?

 

[cinergi]

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.

 

[snoobler]

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.

 

[Luthj]

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??

 

[Dzl]

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

 

[cinergi]

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.

 

[cinergi]

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.

 

[Luthj]

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.

 

[cinergi]

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.

 

[Luthj]

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.

 

[snoobler]

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.

 

[cinergi]

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.

 

[snoobler]

Have you confirmed with another source that the current is correct?

 

[cinergi]

Have you confirmed with another source that the current is correct?

Two shunts and my meter and math (constant load of a portable heater).

 

[cinergi]

Time lapse:

 

[snoobler]

Ah. All you had to say was you're using a Victron battery monitor.

 

[Luthj]

Hmm, not ideal that's for sure. Is 10% lower capacity a deal breaker for your application?

 

[cinergi]

Hmm, not ideal that's for sure. Is 10% lower capacity a deal breaker for your application?

I may learn to accept it ... I'm going to create a 2p16s battery so I'm going to have "fun" matching up the cells properly...

Some of this exercise is just validating what the vendor is selling. If they're selling 280 and I can't squeeze anything more than 270 out of them, that's a problem.

 

[Honuz]

I may learn to accept it ... I'm going to create a 2p16s battery so I'm going to have "fun" matching up the cells properly...

Some of this exercise is just validating what the vendor is selling. If they're selling 280 and I can't squeeze anything more than 270 out of them, that's a problem.

Perhaps the problem is that those specifications, are for grade A cells from Eve.... and perhaps those ( the one we are buying) are not following those specifications aka not grade A, reason they are sold at this discount.

 

[Ampster]

I can't squeeze anything more than 270 out of them, that's a problem.

You may want to manage your expectations. I sized my pack under the assumption that I would only use 80 percent of the packs capacity. That comes out to be 224 Ahrs. I have been exercising my pack for the past three months with no issues. During the past 20 days with colder weather and more use of my Forced Air Unit fan I have tested that assumption and it seems to be a reasonable assumption that is a practical constraint. My cells are in an unheated garage and the temperature log tells me that they never went below 48 degrees Fahrenheit during the past 30 days.

Overall at an average cost of $120 per kWh I knew that only using 80 percent of the capacity these cells were actually costing me $150 per kWh. To me that is still a very good price compared to CALBs purchased locally at $300 to $400 per kWh.

 

[Dzl]

Perhaps the problem is that those specifications, are for grade A cells from Eve.... and perhaps those ( the one we are buying) are not following those specifications aka not grade A, reason they are sold at this discount.

I think you are most likely right.

But the issue is that the resellers (most of them at least) represent them as meeting manufacturer specifications (and some of them outright represent them as grade A, or claim to capacity test all cells individually). A few folks on the forum have really latched on to the (in my opinion unsupported and unlikely) claim that these are grade A cells, I think this is misleading to new members and newbies and leads to unrealistic expectations about cell quality and about the level of opacity and integrity of the market.

Almost weekly there are questions in the beginner section along the lines of "I bought matched grade A EVE cells from a trusted seller, do I still need a BMS or can I just use a charge controller" or "I bought well matched grade A EVE cells, do I still need to balance?"

If a cell does not meet its capacity specification (or any other specification), it is not a grade A cell, that doesn't necessarily make it a bad cell or a bad value (it could still be a great value), but it should be accurately and honestly represented by the seller (and if a seller misrepresents a cell, we should acknowledge that, not amplify the misrepresentation).

The funny thing about the grey market for raw cells is we know there are tons of B grade cells that get offloaded to the grey market to be sold at a discount, and most grey market cells are selling at deeply discounted prices, yet somehow nobody is selling or buying B grade cells..

 

[Ampster]

The funny thing about the grey market for raw cells is we know there are tons of B grade cells

Despite protestations to the contrary I have assumed I was getting B grade cells. They have been a good value to me.