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One cell charging to fast

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agillis

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Oct 23, 2020
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I built my own 48v pack with 16 of those big blue 280AH LiFePo4 cells from a reputable battery company in china. They came well packed and look like new A cells with a manufacture date of a few months ago. I check all the voltages on the cells and they matched with a difference of a few hundredths of a volt. I wired them all in parallel and left them for a few hours for good luck.

I then put them in series using a Daly Smart BMS (250A) as the manager.

I tried to charge the cells for the first time with a Victron Quattro.

The Quattro ran for a few hours and showed it was charging the pack at around 100 amps.

Then the Daly Smart BMS shut down charging with a high cell voltage error.

I check and just one cell was at 3.65v while the rest are around 3.3v.

I turned off the Quattro and the BMS is very quickly lowering the cell voltage on the high cell.

Is this a bad cell?
 
agillis said:
I built my own 48v pack with 16 of those big blue 280AH LiFePo4 cells from a reputable battery company in china. They came well packed and look like new A cells with a manufacture date of a few months ago. I check all the voltages on the cells and they matched with a difference of a few hundredths of a volt. I wired them all in parallel and left them for a few hours for good luck.

I then put them in series using a Daly Smart BMS (250A) as the manager.

I tried to charge the cells for the first time with a Victron Quattro.

The Quattro ran for a few hours and showed it was charging the pack at around 100 amps.

Then the Daly Smart BMS shut down charging with a high cell voltage error.

I check and just one cell was at 3.65v while the rest are around 3.3v.

I turned off the Quattro and the BMS is very quickly lowering the cell voltage on the high cell.

Is this a bad cell?
Click to expand...
Don't know if it is bad but do your process was faulty. You should have top balanced them slowly with a regulated power supply at about 10 amps until all of the cells came up to 3.65, could
have taken a week with the cells connected in parallel.
 
agillis said:
They came well packed and look like new A cells with a manufacture date of a few months ago.
Click to expand...
So just to be clear are they EVE or Lishen cells? And how do you know they were manufactured a few months ago? Who did you buy them from?

As Mex Rider mentioned, the cells should be parallel top balanced. The cell terminals and busbars need to be lightly sanded before doing anything.

Voltage is not a good indicator of SOC. It's very possible the cells all arrived at different SOC's even the voltages were the same. If you look at the flat part for the curves of these cells you will see what I mean.

What I would do is drain the high cell down to match the voltage of the other cells. Then parallel top balance them.
 
I did sand the terminals. But I didn't top balance the cells.

Gazoo said:
So just to be clear are they EVE or Lishen cells?
Click to expand...
I don't know about those two types. This is what I got.

www.aliexpress.com

517.0US $ 45% OFF|4pcs Liitokala 3.2v 280ah Lifepo4 Battery Diy 12v 280ah Rechargeable Battery Pack For E-scooter Rv Solar Energy Storage System - Battery Packs - AliExpress

Smarter Shopping, Better Living! Aliexpress.com
www.aliexpress.com www.aliexpress.com

Gazoo said:
And how do you know they were manufactured a few months ago?
Click to expand...
Because they told me :)

Gazoo said:
What I would do is drain the high cell down to match the voltage of the other cells. Then parallel top balance them.
Click to expand...
I'll try that. My BMS has already leveled the cells down to equal voltage.

As you mentioned top balancing can take time. In my case 16 x 280ah cells charged from 0 charge at 10 amps would take about 125 hours (of course they are not a zero charge so it will be less, but still that a long time)

Should I try chagrining the full pack at 48v but only 10 amps with the BMS attached?
In this doc it says that is possible and a faster way to get the cells close to 3.65v.

diysolarforum.com

Top Balancing LiFePo4 Cells using a low cost benchtop power supply.

To get the paper, click on the orange at the top of this page. This is a tutorial with detailed steps on how I top-balance my LiFePO4 Cells using a low-cost benchtop power supply. To get the tutorial, click on the orange "Download" button...
diysolarforum.com diysolarforum.com
 
agillis said:
Should I try chagrining the full pack at 48v but only 10 amps with the BMS attached?
In this doc it says that is possible and a faster way to get the cells close to 3.65v.
Click to expand...
You could try that first. But charging at 10 amps could exceed the balancing current of the BMS. And I don't know anything about the Daly BMS.
 
The short answer is you need to parallel top-balance them. You've shaved off most of the time by doing a series charge until the first cell disconnected. Now you need to top balance them. The BMS will take too long to do it for you and the Daly will constantly disconnect the battery.
 
I too had 1 runner... so i pulled the series pack apart, verified terminals and buss bars had NO burs. Then parallel connected, hooked up to charger and topped them all up to 3.4x let them sit. Connected in series again, attached bms, pulled a discharge on the pack with inverter and gun, they all dropped down hit LVD and then recharged them up again in series config. watched the charging action every hour, All topped off to 3.4x again without any runners.
 
Just know that parallel charging to 3.4x is really really at the edge of being able to successfully top balance. Chance of success is low. You need 3.5x - 3.65
 
I have the same issue with my 32650 from batteryhookup configured 15s4p. I'm using one of those smart BMS with the phone app and for some reason, cell#6 charges to 3.65 while the rest is @ 3.4+v.

After putting some load, cell#6 would discharge to the same voltage as the rest of the cells, around 3.3 - 3.35. But as soon as I charge the pack, I would see Cell#6 run away from the rest. Any ideas?
 
so what fixed it for me was to charge / discharge them, finding the cell that is too low, and using a lower amp charger to charge only that cell up to the rest level. then charge discharge and it would match the rest. I'm starting to test again, had about 2 out of town for work. I have 2 - 4 cell packs im working on
 
Thanks, I'll keep cycling them since it balances every time I discharge the pack and see if it will eventually correct it self.
 
I have the same issue.. I havent top balanced them as I am charging to 3.35v. I am planning to bottom balance. I have tried to charge the 16s2p cells to 3.65 two times but in both times one or other cells go beyond 3.65 while others are at 3.4. I wonder if this is manufacturing defect of eve cells.. I asked both chargery and eve and they are blaming each other. :( cells came brand new from factory with test details and every cells has same voltage and impedance. I noticed the impedances changes everytime during charge, discharge cycles.
 
maharzan said:
all ev forums suggest a bottom balance.. :) i m using it in my ev.
Click to expand...
From your description your cells are not top balanced or bottom balanced.
Its not surprising that one cell gets to 3.65 before the others.
I'm not familiar with Chargery BMS but doesn't it have a balance function which is trying to top balance your pack?
 
I am far from an expert on the LIfePo batteries, but my experience and listening to others here, top balancing is the key. I have discharged them, charged them back up, topping them all up to same level, then discharging again. I keep cycling them to the top, single cell topping off if necessary , then discharging them again. Charge backup. My 1st pack is topping off as should now. Staring same process on 2nd pack.

start with a parallel balance first, then do the above and they should come in.
 
smoothJoey said:
From your description your cells are not top balanced or bottom balanced.
Its not surprising that one cell gets to 3.65 before the others.
I'm not familiar with Chargery BMS but doesn't it have a balance function which is trying to top balance your pack?
Click to expand...
It does but it takes forever and it didnt stop at 3.65v but kept pushing to 4v even though its set to cut off at 3.65v. maybe i have to add a relay too. I just have the charger and bms. The current gets to 4A but that one cell keeps going up. I had to manually disconnect before damaging the cell. I might keep all the cells in parallel and top balance perhaps and see if that fixes it. Its a huge pack though, 48v 210Ah, might take over a week.
 
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