Senbury LiFepo4 cells 280ah

shavermcspud said:

So my overnight work has been postponed so Ive made it home with enough sunlight to reinstall the pack.
Id left the pack this morning connected in parallel but removed the power supply and charge leads so any microvoltage differences would hopefully level out across the pack
Its been 12 hours since i removed the charger and I've just checked each cell manually, disconnected from the parallel group with a multimeter each cell read dead on 3.64v not quite 3.65 but the power supply had stopped outputting current and read battery voltage as 3.65v this morning with 0 amps being drawn so I considered this balanced.

I've re assembled the pack in to 16s in a different order to last time with no load or charger attached and after an hour or so this is what the chargery bms shows.

View attachment 22183
Ive already got cell 9 climbing above the rest Is this normal?

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Climbing above the rest or settling less quickly? If you balanced to 3.64, it would appear all cells are settling as would be expected.

upnorthandpersonal said:

Keep in mind that you can overcharge a cell even if it doesn't go over 3.6V. A low C rate at 3.5V or so will overcharge a cell if kept too long.
Notice in the graph below that at a low charge rate, you get to 99% capacity at 3.5V compared to the other rates of charge.

Also, check this document: https://files.ev-power.eu/inc/_auto88/_info/Doc/GWL-Power-Cell-Damage-OverCharge.pdf

In this document the reason for balancing cell per cell individually is also discussed.

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@shavermcspud
This is key. Here is the official spec sheet from EVE
Study the discharge curve closely. I have two packs at 16s2p for the past few months and noticed that anything above or below 3.387 and 3.28 the voltage delta between the cells start the grow from under 10mv up to 40-50mv. The bulk of the the cell capacity is in that range, 3.28 to 3.387, I know crazy. I tried multiple times trying to eke out more power by uppping the charge but my BMS at the time would overheat and was not up to the task trying to keep the cells within 20mv. Wasn’t worth the risk since you are at the knee for very little value.

As for the cell voltages bouncing around, increasing with nothing connected, etc I would disconnect the bms and measure by hand. Sounds like you have a bum bms or bad wiring (I had a 16t that was off by 150-200mv)

Just found this, don't know if it was posted already but it pertains to the eve cells

No.15 said:

Just found this, don't know if it was posted already but it pertains to the eve cells

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Yes, posted before. The latest version of that doc is here on the site in resources:
https://diysolarforum.com/resources...-product-specification-version-e-2019-7-5.15/

Firstly, thanks to all your recommendations.

Secondly, I put the pack in to service last night, after the parallel balance at 3.65v
My night load is quite high at 780w
I woke up to see all the cells within 50mv of each other and an SOC of 42% on the bms and 44% on the inverter
Id set my charge voltage to 54.5 volts to be on the safe side, and the pack charged up just fine within 4 hours.
Got home from work and all cells are showing just fine and no higher than 3.35 volts and within 60mv of each other.

I will let them run again overnight this evening and report back.

shavermcspud said:

Firstly, thanks to all your recommendations.

Secondly, I put the pack in to service last night, after the parallel balance at 3.65v
My night load is quite high at 780w
I woke up to see all the cells within 50mv of each other and an SOC of 42% on the bms and 44% on the inverter
Id set my charge voltage to 54.5 volts to be on the safe side, and the pack charged up just fine within 4 hours.
Got home from work and all cells are showing just fine and no higher than 3.35 volts and within 60mv of each other.

I will let them run again overnight this evening and report back.

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Glad to hear

shavermcspud said:

Firstly, thanks to all your recommendations.

Secondly, I put the pack in to service last night, after the parallel balance at 3.65v
My night load is quite high at 780w
I woke up to see all the cells within 50mv of each other and an SOC of 42% on the bms and 44% on the inverter
Id set my charge voltage to 54.5 volts to be on the safe side, and the pack charged up just fine within 4 hours.
Got home from work and all cells are showing just fine and no higher than 3.35 volts and within 60mv of each other.

I will let them run again overnight this evening and report back.

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I would double check with a MM to confirm values as you are investigating. I found my Chargery to be a little off on the cell voltage reading. Also you SOC may not be accurate so I would also base your research on pack voltage. I would bet your true cell delta is lower when you measure each cell by hand vs the Chargery (my experience).

A little update.

Today the batteries charged up to 100% again and stayed within voltage tolerances and we're now on another discharge cycle and all seems to be ok. I've still got the massively bloated cell from the first set of 16s cells from senbury and these went through exactly the same treatment so I'm convinced i had a duff cell from day one there. Not much I can do i guess and the risk of buying from China with little to no customer support once your money has been taken.

Another update.

Things seem to be just as id wanted.
The pack now discharges down to 20% and recharges to 80% during the day, all cell voltages are good and very close. Ive completed four cycles so far without issue.

As a side note my other 16s cell pack with the bloated battery also now seems to be working fine after a second rebalance, evern the expanded cell still seems to have the same capacity before it expanded. A discharge test show 283AH with the damaged cell. not sure of the long term effect on the cell but it seems to be working fine.

shavermcspud said:

Another update.

Things seem to be just as id wanted.
The pack now discharges down to 20% and recharges to 80% during the day, all cell voltages are good and very close. Ive completed four cycles so far without issue.

As a side note my other 16s cell pack with the bloated battery also now seems to be working fine after a second rebalance, evern the expanded cell still seems to have the same capacity before it expanded. A discharge test show 283AH with the damaged cell. not sure of the long term effect on the cell but it seems to be working fine.

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Very happy to hear things are working out, any theories as to what you observed early on, did you change out any equipment? Do anything differently? Misinterpret anything the first time around?

Dzl said:

Very happy to hear things are working out, any theories as to what you observed early on, did you change out any equipment? Do anything differently? Misinterpret anything the first time around?

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I used the same kit, cables, power supply and voltages to balance the cells. I may have made an error along the way that went unnoticed by me but I can't be sure. I'm still convinced I had one duff cell from Senbury out of the 32 with the bloated cell but its my word against theirs and i cant prove it either way.

I am happy that things are now working as I had expected, I am literally off grid now having used no power from the grid since I put the pack back in use several days ago.

I can quite happily run all day on PV with my 26Kwp even in cloudy conditions, charge the car, run all the utilities the wife, children and I need and still get the batteries back up to my 80% charge level I've set, then by sun down currently around 7pm here in the UK run off the LFP pack all night well in to the next morning around 9.30am at arond 28% DoD until I'm producing enough PV to start the cycle again and this is just on the 16s at the moment, I am going to now finish off my initial plan which was 16s2p with all 32 cells, this way i hope I can use a 30% - 70% charge cycle to prolong the life of the pack beyond the spec'd 3000 cycles

Gazoo said:

Actually I didn't think of that. I will use letters. I have 8 cells coming and I think I can still remember that part of the alphabet..

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You could use a different alphabet to keep it interesting ...

So another update, it seems its the BMS that's at fault here, two of them. Ive also posted this in the BMS thread to see if anyone else if having the same issues.

I have been under the impression that my new EVE cells are appearing to charge themselves when in standby with no load connected or discharge applied making the pack delta v out.

I have 2x Chargery BMS 16t and both show exactly the same issue on the same pack.

Cells 9 shows over the rest of the pack voltage and cell 10 shows under the other cell voltages, not by much but if i charge the pack to 3.60v per cell its enough to trigger the cut off on cell 9 while the rest are still at 3.5v ish

So ive taken per cell measurements in place with a volt meter and every cell shows currently at 3.45v with the meter I have available, even cell 9 and 10 where as the BMS shows different values. (see bellow)

Ive stripped the pack down to individual cells and taken exactly the same reading at 3.45v on my volt meter..(it only goes to 2 decimal places.)
To make sure my meter wasn't playing up i used a quite expensive balance charger that supports 1-16s LiFepo4/lipo cells that I use for my hobby batteries to try and discharge cell 9 down to 3.45v and charge cell 10 up to 3.45v respectively, and my balancer immediately shows done on both cell 9 and 10 showing them to be exactly 3.45v each

Why do 2x chargery units both exhibit the same issue and has anyone else had this, im on firmware version 4.0
Ive tried two complete BMS units, 2x balance leads, Ive even swapped the displays but the reading is the same.

I appreciate were talking mV here but its enough to trip the BMS safety cut-off when trying to charge the pack.

Looking for a pattern(s), in post #52 it was cells 10 and 11, in post 60 it was cells 7 and 10.
Small sample size but all 3 of these involve cell in 10th position.
Has this been the same cell?
I wonder if swapping cells 1-8 with cells 9-16 would continue this pattern or move it to the other half of battery.

Just observing and musing.

MisterSandals said:

Looking for a pattern(s), in post #52 it was cells 10 and 11, in post 60 it was cells 7 and 10.
Small sample size but all 3 of these involve cell in 10th position.
Has this been the same cell?
I wonder if swapping cells 1-8 with cells 9-16 would continue this pattern or move it to the other half of battery.

Just observing and musing.

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The pack has been assembled and disassembled so many times now that they're all in different positions from last time but it does seem to be the issue shows anywhere after port 9 -11 on the BMS.

The only thing I havent changed out is the serial communication extension cable I made between the BMS unit itself and the display. but from my understanding this is just simple rs232 communication

im going to swap the cells over now and reports back.

shavermcspud said:

but it does seem to be the issue shows anywhere after port 9 -11 on the BMS.

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Its a little unfortunate you do not have cell histories but if they are randomized in the reassembly that helps.
When you get the unbalanced cells shown on the BMS, have you checked the cell voltages on the balance lead itself?
Unplug the lead from the BMS and check pin 1 vs pin 2, then pin 1 vs pin 3...pin 1 vs pin 16.
The incremental voltage as you progress is the cell voltage: pin 2 for cell 1, (pin 3 - pin 2) for cell 2,...(pin 17 - pin 16) for cell 16.

Before you can officially blame the BMS, you need to verify what is going in and that it is same as voltage at the cells themselves.

Ok ive just swapped cells 9 and 10 to position 1 and 2 in the pack and it shows the same issue.
Cell 9 up and cell 10 down

Im going to check the balance leads ends now and report back.

Ive checked on the plug end of the balance lead
and got the following.

Cell 9 3.34
Cell10 6.68
cell 11 10.02
cell 12 13.36
cell 13 16.70
cell 14 20.04
cell 15 23.38
cell 16 26.73

If my maths are correct that looks like each cell is 3.34v the BMS is not reading correctly

Do you have cell 9- tap/lead connected properly? Cells 9-16 use the 9- lead to measure voltage, while 1-8 use the 1- lead.

Luthj said:

Cells 9-16 use the 9- lead to measure voltage, while 1-8 use the 1- lead.

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Thanks, i did not know this. So does an 8s BMS have 18 leads then?