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280AH cells not charging above 3.3v?

Cvantwout1

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Oct 30, 2020
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Hey guys,

I recently received a set of 4 varicore 280AH LiFePO4 cells, but after charging with an icharger 306b, it keeps telling me the batter is full at 3.3V. What am I doing wrong here? Are these cells grade B and hence not going up to 3.6V?

Thank you in advance!
 
I don't know anything about that charger ... but .... my bet would be on a setup or charger problem.

Have you checked the voltage with a DVM while charging?
 
Thanks Bob, very well could be. I set the termination voltage to 3.6v and the charger was showing a charge voltage of 3.55 - 3.6, but the DVM i have never read teh terminals being above 3.33 on the terminals of the cells
 
Maybe a connection problem .... were you using alligator clips?
 
Sound like you are top balancing these cells in parallel, confirm?
How much amperage can the charger deliver?
What charge voltage have you configured?
What gauge are the charge leads?

Most new cells come aproximately half full which means you need to put 560 amp hours into those cells.
The charge curve for lifepo4 is very flat so the voltage won't rise until the cells are almost full.
 
Correct, I am top balancing in parallel.
The charger can deliver up to 30 amps and I set it to 20A, but I was only getting 3.6A at the end before it told me it was full. At o At one point, it was able to deliver about 9A, but it gradually decreased.
Charge voltage is 3.6V
The charge leads from the charger are 12AWG, but I used strips of copper in place of bus bars to connect the cells, so its on the thinner side than ideal. maybe 1/32 or 1/16 of an inch thick
 
Since there is a difference between what the charger thinks it is supplying and the voltage getting to the cells .... either the charge leads are causing a voltage drop or the charger isn't providing the correct voltage.
 
Patience is important.
I use a TekPower 1540 which can output 40A. Takes about 14 hours to go from 2.50 to 3.600 starting with 40A Constant Current for an EVE 280AH cell. That drops to Constant Voltage around 30A and seems to sit FOREVER between 3.20 until it tickles 3.40 then the rest from there to 3.65 is quicker. This is doing a SINGLE CELL AT A TIME. If you are going 2 or more cells in Parallel then it will take that much longer.

Remember the main power curve is from 3.000 to 3.400. Voltage drop is quick from 3.00V, it's the cliff fall. From 3.400 it's Climbing the cliff as the end is a steep curve as well. These "ENDS" actually only represent less than 10% of total gross capacity and most folks reserve this off anyways to prolong lifecycles and maximize cell life.

AN IMPORTANT TIP !
When charging the cells and once they reach 3.400+ EAGLE EYE THE CHARGER !
As the cells start to fill up, their impedance & resistance changes and the amps taken, starts to drop as it should.
At this point recheck VOLTAGE at the Charger Terminals and at the CELL Terminals, you will see a difference in voltage between the two, this is expected.
As the amperage taken drops, the voltage will start to align between the charger & cell. THERE'S THE GOTCHA !
Watch Carefully, because this is where things can go pear shaped.
You need to be careful because the voltage will slowly climb up at this point and can exceed 3.65V quite quickly and you will have to fine tune the charger output to ensure you do not cross 3.65V.
* It is NOT a crisis if you stay below 3.800. Above 3.8V the damage potential begins, by 4.0V there is harm and that is VERY QUICK !
Even if charged to 3.8V, once charge is removed the cells always settle and will typically settle around 3.500 +/-0.050 within 2 hours of charge. If allowed to sit static, they will ultimately settle closer to 3.45 +/- a tiny bit and this is fine as that is the top of the power curve.
THIS IS NORMAL FOR LFP !

I was doing "sets" and that is so tedious and not practical for me in my situation. I chose to use an alternate method to accelerate the process and make it workable for me. Cell Topping and then Parallel Set Topping.
1- Charge each cell to 3.65V at maximum Amps possible till Amps received is <2.0A (not much gain waiting till it drops to less)
2- Allow cell to settle on it's own, while charging other cells.
3- Once final cell is charged, let it sit NO LESS than 2 hours to properly settle out.
* Other cells will have continued to settle and will likely be static around 3.450 +/- 0.020. This is OK.
4- Then set all cells in Parallel and reapply charge at High Amp to 3.65V and wait till Amps Taken drops to <4A *this is collective for all the cells so it's perfectly fine.
5- Once the Parallel Set is done, remove charge and allow to settle at least 1 hour. The cells will likely be around 3.500 to 3.550 or so. Each cell WILL match that voltage. If allowed to sit in Parallel, even for a few days, the cells will continue to settle to close to 3.450 +/-. It is normal.

You can now assemble your battery pack with fully topped Cells.

SEE HERE:
General LiFePO4 (LFP) Voltage to SOC charts/tables 12/24/48V | DIY Solar Power Forum (diysolarforum.com)
 
Thanks Bob, very well could be. I set the termination voltage to 3.6v and the charger was showing a charge voltage of 3.55 - 3.6, but the DVM i have never read teh terminals being above 3.33 on the terminals of the cells
Check your Icharger X8 manual. If i am not mistaken in the charge setup interface, there is a "charge end current" settings field which is at default 10%. From what i remember. What this does is it terminates the charge cycle when your charge amperage reaches 10 percent of your set charge current. Double check this, i think you can change the default "10" percent down to "1" percent. Change it, lower your charge end current percentage and let me know what happens. 10 percent of the 20 you set is around 2 amps, you said you were getting around 3 amps before the charge cycle ended...so i am relatively certain your problem lays there (end charge current setting). Let me know.
 
Thank you all! This was partially an issue with the bus bars and I believe partially the charge current setting. After charging the cells individually, I was able to get them up to 3.55 (when the charger was set to 3.6 - this is where the 10% charge end current setting is kicking in). I've swapped out the bus bar for 12 awg and not am now top balancing the cells the last of the way. I was expecting some settling of the voltage, but it drains pretty quick. After letting the cell I charge to 3.55 sit for 48 hours, it dropped to 3.45. Is this a normal amount of settling?
 
I charged my 8 in parallel to 3.64 v. I took them apart and they settled some but not that much. I was then told to leave together. So I put them back together and topped them off. I left them together for a few days. Don't know if this helped but I now have cells that are very close. I don't have a bms on it yet but I charge it with my 40 p power supply set at 14.5 v. I watch the cells. Going to try and configure bms today.

Also I ran my house on the pack for 3:50 min yesterday. Its at 76% and all the cells are 3.330
 
You need to be careful because the voltage will slowly climb up at this point and can exceed 3.65V quite quickly and you will have to fine tune the charger output to ensure you do not cross 3.65V.
Let me know if this makes sense. I measure the open circuit voltage with a multimeter on the power supply and adjust the open circuit voltage to 3.650v. When I connect the power supply to the cell the voltage drops considerably on the display and amps are maxed. I should be able to basically ignore it now, correct? As the cell approaches 3.650 the current should drop to 0 as that is the state I had adjusted the power supply to in the first place (3.650v and 0 amps)
 
On my power supply I was able to. But I sat there and watched it like a hawk. Now that I know it will go to the set voltage.
 
An LFP cell once at 3.650 will still absorb more amperage and even drop to 2A. Of course it varies a bit with cell size obviously. They do not have to be pushed deep there is no gain and it's lost during the normal settling process over the following 4 hours after charge finishes.

On the charger, it is prudent to verify the voltage at the output terminals on the charger & at the cell terminals as the cells are reaching the target volatge. LFP can goto 3.8-3.9V without damage if it happens once/twice but from 3.60-4.00 happens VERY FAST if the charger is not dialed in and "verified" at the intended target voltage. Junking a Cell is no fun and makes for lot's of Bad Language ! I Know !!
 
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