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Top Balancing LiFePo4's, out after 5 days in service. My situation and some questions

Tomco

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Dec 3, 2020
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Ok, so i may have compromised my balancing because of the way i did it (I'll explain a little later).
I recently put into service 32x 272aH Lishen cells setup as a 2P16S configuration. The cells all arrived reading approx 3.37x volts, i parallel connected all 32 and connected my CV CC charger and set it to 3.63V. The pack took ~35amps for around 12 days.

From day 12 the current started to gradually drop, on day 14 the current dropped to ~0.5A, i raised the voltage to 3.65 and it took another 8 hours or so to come down to 0.3A which is when i disconnected. I then let the pack sit in parallel (with no charge applied) overnight. When i removed all the links in the morning every cell measured to within 0.004 volts of each other. I then started to assemble the 2P16S pack, and this is where i may have stuffed things up, i assembled the pack over two days, i got 9 pairs connected in series late on the first day then finished connecting the other 7 pairs the next day (is this is where i ruined my efforts in a good balance ??)

The pack went into service 5 days ago and is connected to a Chargery 16S BMS. When first connected the biggest V difference between cells was ~22mV, over the last five days this has gradually increased to over 130mV, I believe balancing is active as i have current in the balance leads when the yellow dashes are indicating on the display of the chargery. My MPP Solar charge settings are set to 55.4V bulk and 55.4V float. Today the diff of the two worst cells was 220mV (3.598v.......3.337v), this was while charging (<4A going into the cells), as soon as the sun went down and i was drawing from the cells the discrepancy dropped back to just under 100mV.

Do i need to perform another Top Balance and get the 2P16S connections done quicker after i remove the parallel balance links ?
The High cells are around the 11/12/13/14 cells

One other thing i must mention is my rookie error: When i first connected the Chargery BMS i connected it back to front (not in regards to polarity), what I did was connect cell monitoring wire for cell 1+ and cell 1- to cell 16 (ie I made the cell with the main positive connection as cell 1 and the cell with the main neg connection as cell 16), i had this connected and plugged into the BMS for around 10 minutes before realizing my error (note at this point the display was showing all sorts of strange voltages and the BMS case was getting, almost, too hot to touch, but not quite), Have i fried my BMS even though i'am seeing current on the leads that are indicating 'balancing in progress' ? Because it seems that no effective balancing is happening.

Any advice would be appreciated.
 
The Chargery has different modes and voltage thresholds that can be set up to control when it balances .... How do you have these set?

I'm kinda surprised you didn't smoke the BMS .... but, if it seems like it is working it probably is.
 
i Have 'balance active' discharge/charge and storage all set to on, balance to 8mV and balance at >3.4 cell voltage. Yes i thought i did destroy the BMS (and maybe i have) however current is flowing on the leads that should be balancing according to my tong tester.
Ive decided to parallel up all 32 cells and top balance again. Its now drawing 4.5Amps at 3.65V so not long to go to complete the top balance..... ill then re assemble back into 2p16S over a couple oh hours (instead of a couple of days) and see how they perform.
 
i Have 'balance active' discharge/charge and storage all set to on, balance to 8mV and balance at >3.4 cell voltage. Yes i thought i did destroy the BMS (and maybe i have) however current is flowing on the leads that should be balancing according to my tong tester.
Try lowering that voltage threshold down to something like 3.2 for a while .... it may give you more balance time. I'd probably also move that 8 mv up .... no need to balance that tight.
 
I'll try both of those suggestions. the other thing ill mention is when i did lower the voltage 'start balancing' setpoint down the BMS would want to balance a heap of cells at the same time (thinking about it thats probably due to my 8mV setting), when this happened the BMS would balance for ~30seconds and then shutdown for ~3.5 minutes (and it would do this constantly), i emailed Jason from Chargery about this and he said its temperature related, 55degrees C is the heatsink temp cut out inside the BMS (Jason did mention that they are in the process of making one with a fan for this very reason).
As mentioned earlier I'm doing a 're top balance' and will check the integrity of all terminations.
 
It wasn't your top balance. You have something else going on. I'd start by making sure your cell terminals and bus bars are clean and deoxidized. Make sure all your cell connections are properly torqued.

My Chargery (when I used it) didn't have problems keeping my EVE 280's balanced. Setting the voltage threshold lower won't help. It's already balancing. You do not want balancing to happen below ~3.4 volts -- you're outside the knee at that point.

Can you cross-reference the chargery cell readings (all 16 of them) with a meter and find out your minimum and maximum offset from reality? The Chargery readings aren't very accurate. Definitely do not set the chargery to balance within 8mv. It's not capable of that level of accuracy. This could be the culprit, too. Set it to 20 or 30. This is why we need to check all cell readings against a meter to see how accurate your particular unit is, which will inform more proper numbers for balancing.
 
Lowering that balance voltage can help ..... if you have some cells that are higher than the others pretty much all the way thru the charge cycle. You will have to keep an eye on the BMS to determine if that is the case .... or do they only separate above a certain voltage level. It will give the Chargery longer to get them bled off. I would only do this on a temporary basis and then return the setting to normal.

Are you powering the BMS from the external power port? Powering it from the balance leads can cause the voltage readings to be somewhat inaccurate. Compare the cell voltages with a DVM as cinergi suggested.

Another thing that could help in that regard is to blow some air across the BMS case. Getting rid of more of that heat should allow the Chargery to increase the amount of time it is balancing.
I'm not really a fan of putting a fan in the BMS, however. I wish they would just do better passive balancing.

I agree with cinergi it is very possible you have a problems with some of your connections. You may correct that inadvertently if you have them in parallel again and then return to normal. Maybe clean the bus bars with some emery cloth or very fine sandpaper then some alcohol or acetone ... and put some noalox on them or similar.

When I put my pack I didn't even top balance them in parallel. I used an adjustable power supply and when the cells go to the knee I lowered the charge current to only a couple of amps. By the time the pack got fully charged the cells were nicely balanced and have stayed that way so far. If they get out of balance I will probably do that again.
 
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