I charged [in parallel] my cells to 3.65 volts and after 24 hours they are 3.335, is this normal?

[Deleted member 9967]

Ok so I finally got my new cells after the others were found to be bad.
I series charged them to 3.65 volts. I then lined them up in parallel and charged them up to 3.65 volts each to top balance them.
I then let them rest for 24 hours and the cells are 3.335 volts each now.
Is this normal?
Thank you.

EDIT: They are 280 Ah lifepo cells in case you need to know.

 

[Supervstech]

Explain exactly how you charged them and where you measured the 3.65V
3.5 is the normal drift back voltage of an open cell... 3.35 doesn’t sound like they achieved 3.65V yet.

 

[Cdkipp]

Yes. In my experience that is normal.

 

[cinergi]

Depends on the cell. My EVE's rest at 3.5xx and my Lishen's rest at 3.4xx .. After 4 weeks the Lishen's are 3.37. So 3.35 sounds low for having just been top-balanced to 3.65. Sounds like you didn't actually hit 3.65 (measured by a multimeter at the cell terminals with very little current coming from the power supply)

 

[Deleted member 9967]

Thank you

Yes. In my experience that is normal.

for reading what I typed and replying to me.

 

[Deleted member 9967]

Depends on the cell. My EVE's rest at 3.5xx and my Lishen's rest at 3.4xx .. After 4 weeks the Lishen's are 3.37. So 3.35 sounds low for having just been top-balanced to 3.65. Sounds like you didn't actually hit 3.65 (measured by a multimeter at the cell terminals with very little current coming from the power supply)

Interesting. Thank you

 

[Flux]

I am in the process of top balancing and there is for a difference in charging voltage at the terminals and amps as well. My power supply is not very high end so this could be expected.

I am not sure what the downfalls might be of series charging them before doing an actual top balance, but this could be some of the issue.

I would unhook the cells from parallel and check each cells voltage to see if they are truly balancing. if one is low you may want to charge that one individually to a state similar to the others and then do a top balance.

Did you check the individual cell voltages before series charging?

Check each individual cell voltage, charge separately if one or more is lagging.

I keep rereading the top balancing how to here just to keep it in my mind.

 

[cinergi]

I am in the process of top balancing and there is for a difference in charging voltage at the terminals and amps as well. My power supply is not very high end so this could be expected.

I am not sure what the downfalls might be of series charging them before doing an actual top balance, but this could be some of the issue.

I would unhook the cells from parallel and check each cells voltage to see if they are truly balancing. if one is low you may want to charge that one individually to a state similar to the others and then do a top balance.

Did you check the individual cell voltages before series charging?

Check each individual cell voltage, charge separately if one or more is lagging.

When top balancing check the voltage at the terminals vs what the power supply says. You many need to increase power supply voltage slightly to get the actual 3.65 at the terminals. My power supply reads 0.5 volts higher than the voltage at the terminals.

I keep rereading the top balancing how to here just to keep it in my mind.

Please don't ever do this. Either be more patient (the voltage WILL equalize) or get bigger cables, use ring terminals instead of alligator clips, etc. There are *so many stories* here of people damaging their cells by doing this. Measure & set the voltage output of the power supply while it's disconnected and don't touch it again, no matter what.

 

[dr.diesel]

Depending on how you paralleled them, meaning how robust the buss bars were, you might have reached 3.65v on the side that was connected to the charger and much less at the other end. Meaning a good portion of the 3.65v charge leveled out across the cells.

 

[Deleted member 9967]

Each cell has been tested many times for voltage.
They all went to 3.65 like I said.
They are all at 3.335 like I said.
Not sure how I could say they were at those voltages unless I tested them. But whatever.
Thanks for the comments to those who answered my question. [

Dhasper} ​

 

[spongie]

Each cell has been tested many times for voltage.
They all went to 3.65 like I said.
They are all at 3.335 like I said.
Not sure how I could say they were at those voltages unless I tested them. But whatever.
Thanks for the comments to those who answered my question. [

Dhasper} ​

my 16s/280ah bank took 8 days for all the cells to reach 3.65v then i configured them to series and immediately the bms was showing 3.35 -/+ .05 on each cell, and that happened when i top balanced my both banks of batteries . im still puzzled but i just let them be

 

[Deleted member 9967]

my 16s/280ah bank took 8 days for all the cells to reach 3.65v then i configured them to series and immediately the bms was showing 3.35 -/+ .05 on each cell, and that happened when i top balanced my both banks of batteries . im still puzzled but i just let them be

Thanks Spongie

 

[Brian_B]

It could be the absorption current cut off. If it is too high, then the cells would not have had time to balance out. Just a thought.

 

[Deleted member 9967]

It could be the absorption current cut off. If it is too high, then the cells would not have had time to balance out. Just a thought.

After three charges in a row? Um ok. Thanks.

 

[spongie]

understood, but since Ive done that initial balance they seem to be fine, when the charger goes to FLOAT, the BMS shows each of the 32 batteries in both banks relatively close. the actual figures in bank one last evening were 3.538 3.532 3.526 3.539 3.531 and so on. however by sundown they all came down to 3.37 -/+.05 with a SOC of 98% this morning just before dawn the SOC was 65% and the volts were about 3.31 -/+.05 . so imho the system lives at about 3.25 to 3.39 however when being charged it goes up to the mid 3.5s but doesn't stay there, as soon as the charging stop they drop right back to 3.3ish

 

[curiouscarbon]

sounds normal, but i’m using different cells.

my frey/fortune/overkill 100Ah LiFePO4 cells are sitting at 3.378 right now before dawn. 4S pack. 3.5V/cell absorb. 3.375V/cell float.

hope this helps

 

[Deleted member 9967]

understood, but since Ive done that initial balance they seem to be fine, when the charger goes to FLOAT, the BMS shows each of the 32 batteries in both banks relatively close. the actual figures in bank one last evening were 3.538 3.532 3.526 3.539 3.531 and so on. however by sundown they all came down to 3.37 -/+.05 with a SOC of 98% this morning just before dawn the SOC was 65% and the volts were about 3.31 -/+.05 . so imho the system lives at about 3.25 to 3.39 however when being charged it goes up to the mid 3.5s but doesn't stay there, as soon as the charging stop they drop right back to 3.3ish

I think just charging them to 3.37 is not the same as going to 3.65. By going to 3.65 I believe they become saturated even though they come back down to 3.37.
So getting them up to 3.65 is a form of saturating the cells with amperage goodness.

However, just charging them to 3.3ish as you say. Will certainly get them fullish. But not saturated.
Which is fine with me as I don't plan to charge them fully any more anyhow.

 

[jtvt]

understood, but since Ive done that initial balance they seem to be fine, when the charger goes to FLOAT, the BMS shows each of the 32 batteries in both banks relatively close. the actual figures in bank one last evening were 3.538 3.532 3.526 3.539 3.531 and so on. however by sundown they all came down to 3.37 -/+.05 with a SOC of 98% this morning just before dawn the SOC was 65% and the volts were about 3.31 -/+.05 . so imho the system lives at about 3.25 to 3.39 however when being charged it goes up to the mid 3.5s but doesn't stay there, as soon as the charging stop they drop right back to 3.3ish

Sounds like my two 16s banks. Charging brings them up into the 3.5 range. I'm using absorb setting at 56.6 which is 56.4 at the battery. After charging they settle to 3.3 ish. They always have a load from inverter, charge controllers, etc plus a small amount of phantom.

So far, it looks like capacity is as expected. So all is good.

For top balance, I used a bms and a solar charge controller to speed up the process and then put a 60a power supply on them at 3.65 until 0 amps which was overnight. I did each string separately. I had to wait a few days on some battery cables before hooking them up and IIRC, they settled into the 3.3 range by then.

 

[GSXR1000]

did you charge them to 3.6 and wait for the current goto zero... I would only charge in parallel for this step.. never change in series without a bms.. if one cell is at a higher state of charge then it will over volt before you hit 14.4 pack voltage