First Top Balance- One Bad Cell?

Solar4me22

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Greetings- I purchased 16 280Ah LiFePO4 batteries from a vendor on AliExpress last March and a week ago started preparing them for a 48v solar system. The initial voltage of the batteries measured 3.16v for each cell. After watching Will Prowse's YouTube video on how to top balance new batteries I purchased a 30v 10a power supply from Walmart.com and started charging all 16 of the batteries in parallel. It didn't take long to realize it was going to take forever so I divided the batteries into packs of 4 and charged them in series with a 12v 10a automotive charger up to around 3.35v. I then charged each 4 battery pack in parallel with the 10a power supply until they reached 3.65v. One pack seemed like it didn't want to charge past 3.35v and I noticed one of the cells was a bit lower voltage than the other 3. I removed the low cell and replaced it with another cell and finished top balancing the pack up to 3.65v. When charging the last pack of 4 cells it didn't want to charge beyond 3.35v. Again the same low cell was the culprit so I removed it and top balanced the other 3 to 3.65v. I tried charging the low voltage cell for several hours. The power supply seemed to be working hard because the cooling fan was staying on most of the time and the voltage would not exceed 3.35v. I didn't want to burn up the power supply so I shut it down.

Should I order another 3.2v 280Ah battery or is it possible that there is some other way to save it? -Best regards S4m22
 
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time2roll

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I would politely explain the issue to the seller and see if a partial (or full) credit might be given on the replacement.
If that cell has been charging alone for 28+ hours without the easily achieved results of the others... I assume it is defective.
 

RCinFLA

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Do you know how many times posters have claimed that their cells will not charge above 3.35v?

Between 50% and 90% state of charge is the most voltage flat portion of LFP capacity curve.

Between using a CC/CV power supply that starts to cut back current when it gets within 0.1v to 0.2v of CV limit and too much cable wire resistance it will seem that cell is stuck in that voltage range.
 
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WindWizard

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I would hook up the potentially defective Cell to the charger by itself and monitor the amount of current going into the Cell keeping the voltage fixed at 3.65 volts and make sure that the Cell does not get warm. I would see how much current is going into the Cell and make sure that it does not exceed 280 amps. It may be a Cell that is depleted and needs more charge.
 

Solar4me22

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I would politely explain the issue to the seller and see if a partial (or full) credit might be given on the replacement.
If that cell has been charging alone for 28+ hours without the easily achieved results of the others... I assume it is defective.
Thanks, I contacted the seller today but I don't have much confidence that they will offer a solution since they don't sell the 280Ah cells anymore. I'l probably buy one from a US seller. I don't want to wait 6 weeks to get one from China.
 

Solar4me22

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Do you know how many times posters have claimed that their cells will not charge above 3.35v?

Between 50% and 90% state of charge is the most voltage flat portion of LFP capacity curve.

Between using a CC/CV power supply that starts to cut back current when it gets within 0.1v to 0.2v of CV limit and too much cable wire resistance it will seem that cell is stuck in that voltage range.
Thanks for the insight regarding the charging curve. I noticed that once a cell exceeds 3.40v it will finish charging much more rapidly. The cell in question was on the power supply all day and didn't even gain .01v of charge. I might try it again for a few hours. I just don't want to risk overheating my power supply.
 

Solar4me22

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I would hook up the potentially defective Cell to the charger by itself and monitor the amount of current going into the Cell keeping the voltage fixed at 3.65 volts and make sure that the Cell does not get warm. I would see how much current is going into the Cell and make sure that it does not exceed 280 amps. It may be a Cell that is depleted and needs more charge.
My power supply usually only charges around 5 amps when set at 3.65 volts so I don't have to worry about exceeding 280 amps. When touching the multimeter to the alligator clips of the charging wires they measure around .02v higher than the battery terminals. The charging wires don't feel hot and the battery case doesn't feel warm. I've got it charging now and will post my results. Thanks for the advice!
 

time2roll

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At 5 amps the PS will have no issues. Set it outside if concerned but I would give it 48 hours.
 

Solar4me22

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For some reason the questionable cell charged up to 3.65v! Hallelujah! Perhaps it just needed some time away from the rest of the cells. Now I can connect all 16 cells in parallel and perform a final top balance. Next on the agenda is to shop for a BMS to use in conjunction with my FLEXmax 80. Many thanks to all who offered their suggestions! This forum is awesome!
 

Substrate

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Edit: Ooops - I see you got it! Whew. Good thing.

I guess a further consideration for the notebook now with my response just before yours...

I would assemble your bank, put on the bms, and see if the system pulls rated capacity, keeping an eye on that suspect cell. I'm assuming you are using a bms, unless you are going commando.

At the risk of starting a propeller-head thread which belongs elsewhere, I always advise those to be very careful when using very low C charging currents that typically fall into the range of where "tail currrent" is stopped, regardless of voltage. Yes, you should stop at your desired voltage. But if your current is too low to begin with, you may *never* reach that desired voltage. Except ...

Ie, it is quite possible to charge a cell at 3.45v, and reach full capacity when 0.025C of so-called "tail current" is reached. The cell is fully charged! Trying to push that cell voltage to 3.6v, under such low current, can be signifying a voltage raised not from charging, but from secondary reactions of overcharge.

Trying to top-balance based on secondary-reaction overcharge from dinky currents can be misleading.

So not trying to hijack the thread, but just saying to assemble your system, attach bms, and see if it pulls full capacity, rather than rely on voltage-based assumptions alone.
 

WindWizard

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Next on the agenda is to shop for a BMS to use in conjunction with my FLEXmax 80.
I have two of the Flexmax 80's and they work very well for me. I am using two of the Overkill Solar BMS's and they are highly recommended. I love the bluetooth range and the phone app is awesome. They have a no-fault guarantee which means that if you do something stupid and burn it up then no problem, Steve will send you another or give your money back. This makes them a must buy.

The good thing about the Overkill is that you can look at all 16 Cells and see at a glance on your phone if there is an issue. I can sit on my couch in the living room and monitor the Cells down in the cellar and not have to even walk a step.
 

Solar4me22

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I have two of the Flexmax 80's and they work very well for me. I am using two of the Overkill Solar BMS's and they are highly recommended. I love the bluetooth range and the phone app is awesome. They have a no-fault guarantee which means that if you do something stupid and burn it up then no problem, Steve will send you another or give your money back. This makes them a must buy.

The good thing about the Overkill is that you can look at all 16 Cells and see at a glance on your phone if there is an issue. I can sit on my couch in the living room and monitor the Cells down in the cellar and not have to even walk a step.
Thanks WindWizard, I'll probably buy one of the Overkill Solar BMS units. Being able to monitor each cell and change charging parameters remotely with a phone is a great feature!
 

WindWizard

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Thanks WindWizard, I'll probably buy one of the Overkill Solar BMS units. Being able to monitor each cell and change charging parameters remotely with a phone is a great feature!
The thing that gets me is the Outback FM80's. They are a nice charge controller but they make you pay extra to do some of the basic things like remote monitoring. That is what makes the Overkill BMS so awesome. They send you the remote monitoring and software for the cost of the BMS. I wish the Outback company would do the same. It really bothers me that you purchase something and then they nickel and dime you to get it so you can use it comfortably. I have to walk down into the Cellar to change any of the parameters of the FM80 but I just can not see spending a bunch of more money to do it.
 

Solar4me22

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I just ordered an Overkill 16 cell BMS with the 24" wires. I like the fact that it'll handle 100 amps so that adds a margin of safety for my system. I 'll be using the 48v bank to power a 240v submersible well pump with a Matrix 5000w 240v UPS inverter. I've also thought about bypassing the battery bank on sunny days by powering the well pump directly from a 3600w 240v grid tie inverter if it can handle the the pump's starting amperage. That way it would save my battery bank from large current loads. 3600 divided by 240 = 15 amps so the grid tie inverter might not be able to handle it.
 

WindWizard

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Now I am confused. You have an APC Matrix 5000 watt UPS that has two lead acid cells in it and 15Kw of LFP cells and an Outback FM80 Charge Controller and now you are talking about a grid tie inverter? You have not mentioned about Solar Panels yet. The Matrix Inverter that I found requires 208 volts AC for an input. Grid tie inverters are typically used for selling power back to your electric company and are not usually used for powering pumps or other equipment.
 

Solar4me22

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I bought the Matrix 5000 used several years ago. My particular unit is wired for 240v single phase ac input. I had it in my garage attached to a 48v bank of FLA batteries to use during power outages. It can be powered on manually without any ac input voltage. I charged the 48 volt battery bank with a forklift charger for several years until the batteries expired and I scrapped them. The Matrix is designed to charge AGM batteries so it didn't do a very good job of charging my 48v bank of 6v FLA batteries.

I plan on using the Matrix temporarily for an off grid application until I can find a deal on a more efficient inverter with 240v output. The cooling fans run continuously which reduces its efficiency. I'll only use the Matrix intermittently to run the well pump. I currently have around 4200 watts of solar panels to install at that location. Ten of of the panels are commercial size and if I remember correctly they're 37v and around 280 watts per panel. Six of the panels are the smaller size 37v and around 240w per panel. I plan on buying more panels after I get the existing system installed.

I bought the grid tie inverter used and was thinking of experimenting with it by energizing its control board with a battery and a small inverter so it senses ac input voltage. I haven't read the manual but assumed that during a utility power outage it will continue to produce ac power as long as its receiving dc input voltage from a solar array. I was going to experiment with it to see if I could use it as an inverter to run loads that are within its watt rating.
 

WindWizard

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The FM80 works well with three solar panels in series. You could put two in series and have a 2s8p panel array which should work nicely. As long as the voltages are similar then they should play together.

I have a Magnum mspae-4448 48volts inverter which does an awesome job of powering whatever I throw at it. It is a bit on the spendy side at $2000. I wanted something that had the split phase so I could use it to replace the grid.

You may be able to use your grid tie inverter if you can figure out how to make it turn on without connected to the grid. The Matrix I am not sure how you will connect that to what you have.
 

Capt Bill

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Greetings- I purchased 16 280Ah LiFePO4 batteries from a vendor on AliExpress last March and a week ago started preparing them for a 48v solar system. The initial voltage of the batteries measured 3.16v for each cell. After watching Will Prowse's YouTube video on how to top balance new batteries I purchased a 30v 10a power supply from Walmart.com and started charging all 16 of the batteries in parallel. It didn't take long to realize it was going to take forever so I divided the batteries into packs of 4 and charged them in series with a 12v 10a automotive charger up to around 3.35v. I then charged each 4 battery pack in parallel with the 10a power supply until they reached 3.65v. One pack seemed like it didn't want to charge past 3.35v and I noticed one of the cells was a bit lower voltage than the other 3. I removed the low cell and replaced it with another cell and finished top balancing the pack up to 3.65v. When charging the last pack of 4 cells it didn't want to charge beyond 3.35v. Again the same low cell was the culprit so I removed it and top balanced the other 3 to 3.65v. I tried charging the low voltage cell for several hours. The power supply seemed to be working hard because the cooling fan was staying on most of the time and the voltage would not exceed 3.35v. I didn't want to burn up the power supply so I shut it down.

Should I order another 3.2v 280Ah battery or is it possible that there is some other way to save it? -Best regards S4m22
I had a time suck learning curve problem like that (took awhile to figure it out) ... on one of 8 x EVE 280Ah Cells. ... That Cell also proved to be low in Ahs, which I documented by pictures from my BMS, and it was replaced by the seller Xuba (via another sea freight ride). Maybe the vendor will replace it. IMO: Those kind of below par cells will mess up your whole battery Ahs, plus your BMS Balancing operation. I like testing the full charge and discharge cycle, to see all those cells balanced at all voltages via my BMS info., ... to confirm what just purchased. I just turn off solar in, and run my house, and turn more on, then charge back up. Also: My Thoughts when ordering 16 + cells: I personally think it is a good idea to order two extra cells, for such roll of dices that might show up sooner or later. Last Thought to Share: . To beat sea freight shipment times, DocanPower's Texas Warehouse is an option that has taken just 5 days after order arriving to my door in California for about 20% more than my earlier orders from China, and I like the quality of LiFePO4s I received. Their website says 4 battery minimum on orders, but I once got in an order for just two 280Ah LiFePO4s by dialoging and asking for that option, which cost me a smallish add on fee.
 
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