EVE 304 Cells from 18650batterystore & zke-40 testing.

[Alkaline]

OP did you contact 18650 what did they say?

 

[Alkaline]

My problem with your tests, how do you know your equipment is accurate to the margin you're trying to test to?

What makes you think your setup is capable of doing 100% accurate tests and that you are doing the tests properly?

Its the zke-40 tester many of use, I'm quite certain people have said its almost as good as high dollar ones. Still the ZKE tester produced much better results than the inverter because the 303 has some strange graph its not going down like usual cells instead it seems to be slanted.

 

[Checkthisout]

I dunno. It would seem like accurate testing would require overcharge and then going down to below comfort level.

And then look at the ending voltage.

How does the factory test them?

 

[Alkaline]

This voltage curve is very strange, the cell that is dropping; he tested to 306 AH on the zke at 30 amp discharge, but RCinFLA called it, said it was a bad cell before he tested with his inverter.

 

[Sam Cho TX]

You will have a tough time keeping them in balance if you run a near full discharge, more than about 230 AH DoD. Absolute max discharge will be limited to ballpark of 280 AH, after which you will need to do some significant rebalancing. Only as strong as weakest link. Greater load current may make things worse.

You have two really poor cells from the data you attached, 304.1 and 303. Only 305 comes close to looking like a 304 AH cell.

View attachment 143243

can you explain a bit about the 303 cell you said has some graphite problem, this was the cell that tested poorly when I tested it with a BMS and inverter. I'm still puzzle how you were able to figure this out before I did my test.


It tested to 306 AH when I tested at 30 amps with the zke, but very poorly when with the jbd 150 bms and 62 amps.


I think I'm done with grade B, this is just not worth the savings, you basically have to buy 1 extra cell as a stand by, at that point you are the same price as the EV grade.

 

[Sam Cho TX]

OP did you contact 18650 what did they say?

I sent them an email, will try to call tomorrow, but if I have to pay to ship back and get a 20% restocking fee I'm just not going to bother and just take the loss and move.

I'm planning on buying 64 cells for a large 48v bank, I also have luyuan 304 matched and batched genuine on order 4 to try out.

 

[Bud Martin]

I sent them an email, will try to call tomorrow, but if I have to pay to ship back and get a 20% restocking fee I'm just not going to bother and just take the loss and move.

I'm planning on buying 64 cells for a large 48v bank, I also have luyuan 304 matched and batched genuine on order 4 to try out.

Also sent them the link to this thread.

 

[upnorthandpersonal]

I dunno. It would seem like accurate testing would require overcharge and then going down to below comfort level.

And then look at the ending voltage.

How does the factory test them?

No, as per standard testing for LiFePO4: charge to 3.65V and saturate (tail current), discharge until the voltage drops to 2.5V. Discharge rate: 0.2C.

 

[RCinFLA]

When you use a sinewave inverter for a test load you have to be sure the voltage and current measurement instruments are okay with some 2x AC line frequency ripple due to the DC input current profile from the sinewave inverter.

The 2x AC line frequency peak to peak current from a sinewave inverter DC input will be up to nearly twice the average DC current which can cause some battery performance variance compared to a pure constant DC current.

Battery monitors have a low pass filter in the range of 1 to 2 Hz to average out the 120 Hz ripple from 60 Hz sinewave inverter.

The input capacitors on inverter DC input have little impact on filtering the 2x line freq ripple current. They are for filtering the high frequency PWM switching currents. Only at very low inverter load power with low DC average current do they reduce the 2x line frequency ripple current.

You would need several Farads with very low ESR resistance supercaps on inverter DC input to have an impact on inverter DC input 2x AC line freq ripple current.

 

[RCinFLA]

I sent them an email, will try to call tomorrow, but if I have to pay to ship back and get a 20% restocking fee I'm just not going to bother and just take the loss and move.

I'm planning on buying 64 cells for a large 48v bank, I also have luyuan 304 matched and batched genuine on order 4 to try out.

Hard lesson on the crap shoot of grade B cells. As Forest Gump said, 'Like a box of chocolates.'

 

[Kornbread]

Greater than 80% discharged.,

You mentioned earlier about one of the cells not being cycled enough and that capacity might increase with the number of cycles; can these be easy cycles or does the cell/cells need to sustain a certain charge/discharge rate for a certain length of time and number of cycles?

 

[RCinFLA]

You mentioned earlier about one of the cells not being cycled enough and that capacity might increase with the number of cycles; can these be easy cycles or does the cell/cells need to sustain a certain charge/discharge rate for a certain length of time and number of cycles?

I gave a couple of possible reasons for cell 303 discharge curve, one of which was possible improvement with cycling. More likely is the anode was manufactured with thinner graphite paste printing yielding lower anode capacity.

The graphite paste printing of the anode on copper foil is only 6-8 mils thick so keeping tight distribution on print thickness is not easy.

There is a normal manufacturing tolerance to electrode printing, and it can be compensated with a few more or less cell lamination wraps. Negative anode graphite thickness has to be ratioed to match positive cathode LFP thickness, however. A thin print anode has to be matched up with thin print cathode for the layer wrap compensation to be effective.

All requires attention to details on process control during manufacturing.

 

[Checkthisout]

No, as per standard testing for LiFePO4: charge to 3.65V and saturate (tail current), discharge until the voltage drops to 2.5V. Discharge rate:

What if my load tester is off by .1 amps or there is outside interference or only discharge to 2.51 volts etc.

 

[RCinFLA]

What if my load tester is off by .1 amps or there is outside interference or only discharge to 2.51 volts etc.

AH calculations accuracy relies on accurate current measurements and accurate sample time increments. WH accuracy also needs accurate voltage increments measurements.

Every measurement has a tolerance variability on accuracy. When cumulating small time increments, any resolution rounding error can add up.

For testing cell capacity, you also have to be aware of temperature during testing. Below 10 degs C (50 degs F), the cell will deliver less capacity with greater cell impedance that increases in degradation the colder the cell is. You should record the ambient temperature during testing to ensure apples to apples comparison to any test results taken at another time.

 

[Alkaline]

Well seems like the old adage of coin toss with grade B is still at play here, too bad I thought 18650 had cracked the code, but looks like they are subject to the same realities as the rest.

Good for them for disclosing these are grade B upfront, however, guaranteeing pulling rated capacity is going to probably cause them more problems. Maybe they were good when tested in China, but by the time they arrived here not so good.

Either way, OP I see you are in Austin, I'm about 500 miles from you, I have the zke-40 as well so If you want me to test these for you and can meet half way or something I will be glad to compare.

As for me, grade A Rupi 280s it will be when I'm ready to build a pack for a 48v system.

 

[RCinFLA]

What if my load tester is off by .1 amps or there is outside interference or only discharge to 2.51 volts etc.

0.1 amps error in 30 amp discharge is 0.1A / 30 A = 0.33% error, not significant.

 

[RCinFLA]

Well seems like the old adage of coin toss with grade B is still at play here, too bad I thought 18650 had cracked the code, but looks like they are subject to the same realities as the rest.

At least they are telling you it is grade B.

Grade B means all bets are off.

'Second life' recycled cell's are one thing, but I don't think a manufacturer should dump their manufacturing yield garbage on the market. I believe in the long run it hurts their reputation as a quality manufacturer.

My experience in manufacturing is if you have a place to bury your poor process yield it does not get improved. It is part of a quality culture.

 

[Alkaline]

Well I'm actually more concerned about capacity tests, seems to be this is not the tell-all of cell. So a .2C discharge is going to be what should be done at a minimum.

 

[Checkthisout]

Well seems like the old adage of coin toss with grade B is still at play here, too bad I thought 18650 had cracked the code, but looks like they are subject to the same realities as the rest.

Good for them for disclosing these are grade B upfront, however, guaranteeing pulling rated capacity is going to probably cause them more problems. Maybe they were good when tested in China, but by the time they arrived here not so good.

Either way, OP I see you are in Austin, I'm about 500 miles from you, I have the zke-40 as well so If you want me to test these for you and can meet half way or something I will be glad to compare.

As for me, grade A Rupi 280s it will be when I'm ready to build a pack for a 48v system.

I need some education.

Does the factory load-test the battery and then put a stamp or code on there telling what the battery pulled during that qc test?

 

[RCinFLA]

Well I'm actually more concerned about capacity tests, seems to be this is not the tell-all of cell. So a .2C discharge is going to be what should be done at a minimum.

0.2 to 0.4 C(A) is a good range with reasonable load test on cell.

I wish I could convince folks with zke-40A tester to program in some 5 minute rest periods sequences during the discharge cycle. Observing the cell voltage slump from rested no-load voltage to loaded voltage after about 3 minutes into load gives info on cell impedance.