Resting voltage for LifePo4

Dasler

10 µW
Joined
Dec 7, 2018
Messages
5
Hello,

Just wondering if is normal for the Battery after it get fully charged to 3.6V to drop down to about 3.3V 3.35V in about 1 hour.

the battery charged to full capacity according to the charger just over 17,000mah

As I do have some smaller Lifepo4 that hold the voltage much better.

Thanks.
 
Dasler said:
Hello,

Just wondering if is normal for the Battery after it get fully charged to 3.6V to drop down to about 3.3V 3.35V in about 1 hour.

the battery charged to full capacity according to the charger just over 17,000mah

As I do have some smaller Lifepo4 that hold the voltage much better.

Thanks.

That's perfectly normal for Lifepo4
 
They are new cells.

Should I slow charge them at around 0.500mah a few times to see if they hold a little higher than 3.34V

After charge they all dropped to about 3.34V

Edit-update
So I put one back on the charger at 0.500Mah and it took 160mah to get to 3.6V
I disconnected it and this are some voltages I took with time.
12:24pm 3.6V
12:50pm 3.51V
12:57pm 3.50v

I left for work so not sure if it got any lower.
 
Dasler said:
They are new cells.

New new, or new to you new?

I ask because "new old stock" that has sat around a long time can have the same issues that cells in-use for some time do. If they sat around fully charged or fully discharged (or worse) all that time, too, then that also negatively affects their behavior, capacity, internal resistance, etc.


If they are "generic" cells, like most of the cheap Chinese stuff, then those are often poor (or no) quality control, and have significant variations from cell to cell even within a "batch".

If they are from a reseller, they can also be from many different batches, so perform differently. (or they can even be recovered cells (taken out of scrapped packs, and thus of completely unknown quality/properties), or "seconds", stuff that didn't pass the QC of the manufacturer and were supposed to be scrapped but isntead were resold )
 
My LiFePo4 pack has a BMS that balances/bleeds the pouches to 3,5V for longer life. Charging/resting at 3,65V only increases the Ah's slightly but decreases pack life. So are you sure your BMS isn't just bleeding the cells to prolong battery life?
 
amberwolf said:
Dasler said:
They are new cells.

New new, or new to you new?

I ask because "new old stock" that has sat around a long time can have the same issues that cells in-use for some time do. If they sat around fully charged or fully discharged (or worse) all that time, too, then that also negatively affects their behavior, capacity, internal resistance, etc.


If they are "generic" cells, like most of the cheap Chinese stuff, then those are often poor (or no) quality control, and have significant variations from cell to cell even within a "batch".

If they are from a reseller, they can also be from many different batches, so perform differently. (or they can even be recovered cells (taken out of scrapped packs, and thus of completely unknown quality/properties), or "seconds", stuff that didn't pass the QC of the manufacturer and were supposed to be scrapped but isntead were resold )

New, New with a build date November 20 according to label.
I ordered from Ali App. Directly from Headway
They are Headway Cell their new 17 Ah cells.
The same cell is today reading 3.42V so after the slow charge is holding a little higher than before.
Is on the garage the garage is about 65-70F at night.
So would this be considered abnormal behavior? to drop from 3.6 to 3.4 by itself?


SlowCo said:
My LiFePo4 pack has a BMS that balances/bleeds the pouches to 3,5V for longer life. Charging/resting at 3,65V only increases the Ah's slightly but decreases pack life. So are you sure your BMS isn't just bleeding the cells to prolong battery life?

I have the cell unassembled at the moment.
I charged them one by one they all reached the 3.6- 3.63V and then they dropped to about 3.3xV
After a slow recharge it seem that they are holding better at around 3.4xV

I would send a message to the manufacturer and see.
 
They replied the nominal voltage is 3.2V.

So I guess. Is normal according to Headway
 
Nominal (3,2V) isn't fully charged (3,65V).
You would expect that a fully charged single cell (not connected to anything, you have disconnected the charger I presume?) will hold it's voltage. No matter what that is. So if you charged to 3,5V it should hold that voltage when not connected. And 3,65v when charged to that. Self discharge that quickly from name brand, new cells is very strange...
 
LiFeP04 chemistry cells always settle somewhere in the 3.4x range. They never maintain the charge termination Voltage. I have Zippy LiFeP04 packs, PWN Real Force brand, 100 Ah packs, Thunderpower 100 Ah packs, numerous brands of E-bike packs and have had other brands. They all settle to 3.4x no matter whether charged to 3.5VPC or up to 3.65VPC. It's just the nature of the chemistry. You'll get all your capacity from about 3.35VPC under load down to about 3.0VPC under load. Beyond that, there is very little capacity left. That's one of the beauties of this chemistry. Very little Voltage drop over the full capacity of the cell.
 
SlowCo said:
Nominal (3,2V) isn't fully charged (3,65V).
You would expect that a fully charged single cell (not connected to anything, you have disconnected the charger I presume?) will hold it's voltage. No matter what that is. So if you charged to 3,5V it should hold that voltage when not connected. And 3,65v when charged to that. Self discharge that quickly from name brand, new cells is very strange...

yes, I disconnected the charger completely from the cells while the cells were resting.
I charged 1 by 1. No multi board or anything like that.
I was wondering as I have another no name Chinese lifepo4 and they were holding voltage pretty much spot on.

I did a slow charge to 1 cell and it took about 90mah to reach 3.6V from about 3.3xV so not sure what that means.
If it was a normal cell from 3.6v to 3.3xV it would be a huge difference in mah I think not sure.



BVH said:
LiFeP04 chemistry cells always settle somewhere in the 3.4x range. They never maintain the charge termination Voltage. I have Zippy LiFeP04 packs, PWN Real Force brand, 100 Ah packs, Thunderpower 100 Ah packs, numerous brands of E-bike packs and have had other brands. They all settle to 3.4x no matter whether charged to 3.5VPC or up to 3.65VPC. It's just the nature of the chemistry. You'll get all your capacity from about 3.35VPC under load down to about 3.0VPC under load. Beyond that, there is very little capacity left. That's one of the beauties of this chemistry. Very little Voltage drop over the full capacity of the cell.

hmm so it seem they vary from brand to brand that weird.
I did have now some sitting at the 3.4xV range

I guess I let them sit for about two days and then do a cycle, discharge charge and see if they provide about 17Ah
 
I charged my A123 20ah to 3.45 - 3.50v as two 12s for 24s. They will settle above around 3.4v or above. Plus I just bulk charge. I do have a una9plus + thru the sense wire charger. But never need. No bms 1,380 cycles 5yr old
 
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