Top Balancing So Slow

[Vanhandler]

I have 12 Eve 280AH Grade A brand new cells from Amy. The resting voltage of them was around 3.29 and each cell was within about .001 of each other. great.

After realizing I didn't purchase additional bus bars, I could only top balance six of the cells in parallel at a time. no problem.

I compressed the cells using 4 threaded rods and a plastic cutting board - cut in two - as end plates.

I attached my 10A bench power supply after setting the voltage to 3.65 and I was off to the races! I noticed the PS was pushing only around 5A and 16/17 watts which I thought was strange but left it. After about 24 hours, the cells were had only charged up to about 3.31v. This was going to take forever! After reading some of the forums, they suggested using a thicker gauge wire from the PS and using ring terminals. Great. I used 10 awg wire and ring terminals. I set my PS to 3.65 and connected my ring terminals to the paralleled cells. Now my PS went from C.C. to C.V, the voltage was reading around 3.47, amps were at 10.33 and my wattage was 35.84! amazing- it worked! this will take half as long. wrong.

I started documenting the progress and this is where I am at:

48 hours ago my battery cells were reading 3.327 and my PS was at 3.47v/10.33A/35.84W
Now my cells are at 3.367 and my PU reads 3.51v/10.32a/36.22w.

so in 48 hours, my cells have charged .04 volts.
at this rate, it will take me another 14 days to charge to 3.65v.

What am i doing wrong?

thanks in advance.

 

[BenQ]

Put them in series with a BMS and charge them up to 3.6 if you can limit your parameters in the scc then disconnect all batteries, put them in parallel and then top balance.

 

[acdoctor]

You are probably aware that the voltage is only linear in the middle. 80% of capacity is from 3 to 3.4 volts. I did not experience the large voltage difference from PS to cells. Should be about 20 hours per cell from 30% to 100%. You can series them with bms to about 3.5 volts depending on how they behave in upper curve. Then parallel the very top. You can charge 4 times as fast with same PS at 14.0 volts.

 

[S Davis]

I did my LF280s in parallel batches of four, I have done four so far and each one took between 65-70 hours each with the cheep 10amp power supply and upgraded 4 gauge leads. People need to read the top balance sticky at the top of this section and have some patience.

 

[Horsefly]

You are not doing anything wrong @Vanhandler. You can try some of the shortcuts @BenQ and @S Davis have suggested, as those are fine too. But what you are already doing works. You just have to be patient. Once the cells get up to 3.4V, it will accelerate and you will be up to 3.65V before you know it.

Just don't get impatient and try to turn up the voltage on the PS. NEVER change the PS voltage while it is connected to the cells. Resist the temptation.