Charger Fault or Battery Fault?

[williaty]

I just purchased 4 280Ah LiFePO4 cells. I'm trying to top balance them by the method favored by this forum. I have a Volteq HY3030EX power supply that I'm using to charge/balance the batteries. A year or two ago, I lent the power supply to someone who ignored my warnings about what not to do with it and broke the current limiting function of the power supply so now it only limits itself to its max rated output of 30A. The 4 cells all arrived at 3.200V +/- 10mV. I made buss bars using 1"x1/8" aluminum strap that I had in the scrap bin to put all 4 cells in parallel. I set the charger to output 3.400V measured by my Fluke 87V multimeter.

The results are... weird. I have previous experience with commercially made LiFePO4 batteries but not individual cells. In bringing those commercially made batteries (Battleborn and SOK) to 100% SoC before assembling them into banks, each battery sucked up the max current the charger could output before dropping to 0 current very abruptly when they were full. There was no slowly tapering current like you'd see with a FLA battery. These cells, when hooked to the charger, only drew 14.5 amps. Even weirder, current in would sag slightly when the cooling fan in the power supply turned on and rebound slightly when it turned off (this is the part that makes me consider a power supply problem). After about 5 hours of charging, the current into the cells has dropped to 4.5A. It appears to be exhibiting a long, slow tapering off of current like a FLA battery (which is what makes me consider a cell problem).

Any ideas to help me sort out what isn't working as expected?

 

[MPRanger]

First I recommend giving the lendee the "You break it you buy it" speech.

Second, MAYBE Will will post a short equipment I use video again? Here is his old incomplete version. Yes, He leaves out bench top tools like those pictured in some videos. Workbench stuff gets overlooked, IMHO but watch this video.

 

[mikefitz]

If a commercially built battery abruptly stops charging it may be because the BMS is hitting voltage limits, and/or the charger is set to high charge voltages.

With your cell balancing and a 3.4 voltage power supply, tapering is expected as the driving voltage is low. I suggest increasing to 3.5 and 3.6 volts in stages as the current falls off.
Ensure the power supply is set to the voltage before connecting to the cells and connect using heavy duty cables and terminations.

Since its possible the power supply is partially faulty monitor the cell voltage with your meter and don't leave unattended.

If you cannot rely on the power supply, consider connecting the cells in series with a bms connected and charge as a 12v battery. By monitoring cell voltages and manually loading the 'high' cell with a suitable load for a brief period (car headlight bulb) its possible to balance the cells within an an acceptable delta.

Mike

 

[williaty]

Well, I'm plugging along....

Spent all of yesterday and all of today with the charger outputting about 4.5A. Oddly, when I disconnect it to leave for errands, when I get back home and reconnect it it'll jump up to about 9A for a little while before sagging back down to 4.5A. Cell voltage has climbed to about 3.280V. Looking at a random chart, that's ~55% SoC. 4x280Ah=1120Ah. 45% of that (remaining to charge) is 504Ah. At 4.5A, that's 112 hours. I'm getting about 10 hours of attended time a day where I can sit in the same room while they charge, so that's only 11 more days of charging before I can move up to the 3.5V and 3.6V steps...

It's tempting to buy a 30V 10A charger off Amazon just to try to cut that in half... it's also tempting to just put them into 4S configuration, attach the BMS and say the hell with it and charge them from the solar array, which will probably top them off in less than a day.