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Cells seem to have stopped increasing voltage when balancing

 

Since this group has provided me with the soundest advice I am coming back for some more, on a similarly related issue dealing with balancing my 16 Eve 3.2v 280 ah LifePo4 batteries. I purchased a dc power supply as advised. Charged the cells to 3.27, give or take, and then put the 16 cells in parallel. That was 10 days ago.? Put the dials at 3.7v and 3.52 ah. They are all now at 33.09v after 10 days, although the two end batteries are 3.10v. That is probably fine as it goes but here's the issue I need advice on: The batteries have not advanced from the 33.10/33.09 for over a day now. Every day before this the battery voltage would increase only a few tenths of a volt, but there was a steady increase. However, with no increase in the last 24 hours I am wondering if they are topped out, despite what I'm reading and seeing from others that they should be balanced to at least 3.5v. Any ideas why they might be "stalled" or are they topped out? Should I just patiently wait a little longer to see what happens or does no change in the last 24 hours mean they are topped out and ready to go? Thanks for whatever ideas you have.
?
Peter
 

Peter,
?? No clue. I just did the math and based on your voltage and amp readings (12 watts coming in) and came up with 7 days. The last time I did this myself it was a week to 10 days. Longest I've heard of from one of my buddies was 2-3 weeks. It really depends on the SOC when you first parallel them. Will Prowse on You Tube has a couple of videos on this. Watch them and maybe he's got some insight.
Jerry



On October 12, 2024, at 8:37 AM, Peter Knowlton <pqknowlton@...> wrote:


Since this group has provided me with the soundest advice I am coming back for some more, on a similarly related issue dealing with balancing my 16 Eve 3.2v 280 ah LifePo4 batteries. I purchased a dc power supply as advised. Charged the cells to 3.27, give or take, and then put the 16 cells in parallel. That was 10 days ago.? Put the dials at 3.7v and 3.52 ah. They are all now at 33.09v after 10 days, although the two end batteries are 3.10v. That is probably fine as it goes but here's the issue I need advice on: The batteries have not advanced from the 33.10/33.09 for over a day now. Every day before this the battery voltage would increase only a few tenths of a volt, but there was a steady increase. However, with no increase in the last 24 hours I am wondering if they are topped out, despite what I'm reading and seeing from others that they should be balanced to at least 3.5v. Any ideas why they might be "stalled" or are they topped out? Should I just patiently wait a little longer to see what happens or does no change in the last 24 hours mean they are topped out and ready to go? Thanks for whatever ideas you have.
?
Peter
 

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You have 4,480 ah at 3.2 volts. Sounds like you are putting in 3.52 amps? If your batteries are at 50% SOC you need to put in 2,240 ah. At 3.52 amps it will take 636 hours or 24 days! Sit tight.?


Matt Foley

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On Oct 12, 2024, at 10:09?AM, shredderf16 <Shredderf16@...> wrote:

?

Peter,
?? No clue. I just did the math and based on your voltage and amp readings (12 watts coming in) and came up with 7 days. The last time I did this myself it was a week to 10 days. Longest I've heard of from one of my buddies was 2-3 weeks. It really depends on the SOC when you first parallel them. Will Prowse on You Tube has a couple of videos on this. Watch them and maybe he's got some insight.
Jerry



On October 12, 2024, at 8:37 AM, Peter Knowlton <pqknowlton@...> wrote:


Since this group has provided me with the soundest advice I am coming back for some more, on a similarly related issue dealing with balancing my 16 Eve 3.2v 280 ah LifePo4 batteries. I purchased a dc power supply as advised. Charged the cells to 3.27, give or take, and then put the 16 cells in parallel. That was 10 days ago.? Put the dials at 3.7v and 3.52 ah. They are all now at 33.09v after 10 days, although the two end batteries are 3.10v. That is probably fine as it goes but here's the issue I need advice on: The batteries have not advanced from the 33.10/33.09 for over a day now. Every day before this the battery voltage would increase only a few tenths of a volt, but there was a steady increase. However, with no increase in the last 24 hours I am wondering if they are topped out, despite what I'm reading and seeing from others that they should be balanced to at least 3.5v. Any ideas why they might be "stalled" or are they topped out? Should I just patiently wait a little longer to see what happens or does no change in the last 24 hours mean they are topped out and ready to go? Thanks for whatever ideas you have.
?
Peter
 

Thanks. Will check out those you tubes. I started the balancing at 3.27v. Only because that was their voltage when I got them 3 years ago.

Peter


Sent via phone and big thumbs
 

After doing this balancing for about 10 days and still a long way from 3.65v , and doing some more research, I am wondering about splitting the 16 batteries up into groups of 4 and then charging them, with a 12v LifePo4 charger, to 3.55v, which will take about an hour or two for each group of 4, which are now at 3.310. Then top balancing them to 3.65v. From what I have read LiFePo4 batteries flatline and increase a tiny bit at a time, until they get close to the target voltage, 3.65v, and then the balancing happens a lot quicker. The batteries are at 3.310 now, and they were at 3.27v ten days ago. If charging them in groups of 4 to 3.55v and then putting the 16 back in parallel to balance to 3.65 is an acceptable method I will do it and it will save me a lot of time and accomplish the same thing. I hope. Whatever thoughts you have would be appreciated. Thanks in advance.

Peter


Sent via phone and big thumbs
 

It doesn't seem like that will speed things up.? The same amount of energy needs to go into the battery with either approach.? Sure, you'll see one four-pack get there more quickly.? But getting all sixteen cells full will not go more quickly.? It will go a bit more slowly due to the regrouping of cells (and self-discharge on four-packs not being charged).
?
I suspect you could use more power.? In the other thread, I suggested MeanWell's RSP-500-4.? Yes it costs more.? It's a spend-more or wait-longer tradeoff.? Not counting delivery time for the better charger.
?
Another possibility is that you have damaged-cell issues.? You may want to check for one or more cells being warmer than the others.? They could be 'sinking' current.? Although at the low level you're charging, you might not be able to tell the difference just by touching them.? At 100A the difference would be more obvious.
?
?
 

A FLIR infrared cam on your smartphone could easily show temperature differences during charging.
I have a small thing called FLIRONE PRO. Very efficient, very useful. Snaps into the USB-C gate on your phone.


On Monday, 14 October 2024 at 06:11:26 CEST, bobkart <couch45@...> wrote:


It doesn't seem like that will speed things up.? The same amount of energy needs to go into the battery with either approach.? Sure, you'll see one four-pack get there more quickly.? But getting all sixteen cells full will not go more quickly.? It will go a bit more slowly due to the regrouping of cells (and self-discharge on four-packs not being charged).
?
I suspect you could use more power.? In the other thread, I suggested MeanWell's RSP-500-4.? Yes it costs more.? It's a spend-more or wait-longer tradeoff.? Not counting delivery time for the better charger.
?
Another possibility is that you have damaged-cell issues.? You may want to check for one or more cells being warmer than the others.? They could be 'sinking' current.? Although at the low level you're charging, you might not be able to tell the difference just by touching them.? At 100A the difference would be more obvious.
?
?
 

Peter.
You're balancing a batch if cells identical to the ones I recently finished capacity testing, recharging, and balancing as my new pack.
My ThunderStruck chargers and related monitoring gear were already installed on the boat, so on my test/work bench at home, all I had to use to recharge each cell after drawing it down were a 300 watt variable voltage power supply, and a 12vdc, 30 amp Lipo charger.
My target pre-install balance voltage for each cell was 3.55v starting from just under 3.00v.
My work flow for each cell was to do a discharge test (end state of ~2.7v recovering to ~3.0v) and use the variable power supply to bring the cell up 3.2v or so while the next cell was being discharged.? As each cell completed that cycle, I connected it in parallel with the previous cell such that I had 4 cells at roughly the same 3.2v.? After the four cells had some time to balance to one another (checking each cell with a good multimeter), I reconnected them into 12v series and attached my 30amp, 12v Lipo charger.? The 30a charger pumped more watts per cell than my 300 watt variable power supply could.
Once the cells were just over my target voltage, I took the 4-pack apart and reconnected them in parallel once more.? The next 4 cells went the same way, then I had 8 cells in parallel at my target, and so on thru the 16 cells.
If you don't have access to a 30+amp charger running at 48+volts, and are limited as I was to a low-watts power supply, or a 12v 30amp charger, then grouping them into 12v packs can take less time.
Whether discharging or charging, these cells will sit at around 3 3vdc for most of the cycle.? The like all Lipo cells, the discharge curve is quite flat between about 15% SOC and 90% SOC.
It's important to closely monitor each cell individually while charging to avoid exceeding 3.65v.? Once they get to ~3.55v they can climb pretty quickly to max allowable.
The equipment you're using is different than mine, and it seems youbare starting from a higher SOC for each cell than I was in my process.? So you'll have to make appropriate adjustments.
Be safe; have fun!!
[-tv]
?
 

Thanks Bob. I will check that out.
 

Peter

By now I’m sure you have got your batteries charged but I will try to explain for others to maybe learn from.

For a battery to charge, the charger voltage must be higher than the battery voltage so that current will flow into the battery.

Usually, the larger the voltage difference, the larger the charging current. This is why most chargers that are set on 3.6 volts are connected to a battery that has 3.2 volts will only show enough voltage to reach the maximum current the charger can deliver at the immediate resistance of the battery (I wanted to say “current” instead of “immediate” but it would be confusing). This resistance in LFP batteries changes as the battery charge changes (and can be different between batteries). This is why we have to have smart battery chargers to keep changing the charge voltage as the battery voltage increases.

If the actual battery voltage while being charged is 3.20 the charger and or display might only show 3.30 (or similar), but as soon as you turn off the charger the battery voltage will drop back down to near actual voltage then after about an hour it should be actual “resting” voltage.

As the battery voltage goes up while charging, so does the charge voltage but the charge amps stays the same. Then when the actual battery is close enough to 3.6 volts, the charger display should stop on 3.6 volts and then as the battery is charged more, the charger lowers the charge amps, and when it gets down to 0.1 or 0.2 amps the battery is fully charged.

When charging a LFP battery from discharged, the charge voltage will be between 3.1 and 3.35 for a long, long time compared to before and after these voltages.
 
Edited

First, do not charge the cells to 3.7, especially at that low rate. Stop at 3.55 or 3.6 at most.?
Second, the math is the math. As others have pointed out, if you parallel all the cells, ?280ahx16=4.480ah at 3.2v nominal. If they were completely discharged, it would take 1,280 hours to recharge at 3.5a. Figure they were at 50%, it would take half that many hours, 640hrs.?
When I was doing this, I took a 30a, 12v charger and brought 12v nominal, 4 series, 4 parallel ? to 3.45v (roughly) per cell for a total of 13.8v, then paralleled them all and charged to 3.55. I hooked up the 12v charger without a BMS and let it go but had a timer on my phone to check it every hour or so and did not let it run overnight. ?Don’t do that, it’s risky!
Even doing it that way was 280ahX4=720/30=24hrs, though I think it only took about 12hrs, so presumably the cells were at about 50%.
No need to let them sit paralleled of you’re going to charge them, that’s just a waste of time unless that’s your only balancing strategy.?
I have also built some packs from used cells and just stuck them together at whatever state of charge they were at, but used a 4a active balancer and let it balance over time while using it.?

anton

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