LiFePO4 battery bank not charging completely

[JoeyB]

So I've got 2 chinese LiFePO4 batteries in our van. Specifically 2x 100Ah LiFePo4 EWT batteries connected in parallel, made with ifr26650 cells.

It seems they will not charge above 13.25v anymore. I did over discharge them 2 times below 10v. The BMS has a low voltage cut off of 8v. I did not realize it was configured this low when I bought them initially I was a bit more of a noob then I am now. I am unsure what voltage they got to.

Typically I meticulously checking the voltage but I mistakenly left our inverter on over some cloudy days and ran the power down in the middle of the night.

I have also noticed in my victron charge history that the batteries would have a low voltage of 0-8v every day but I knew that the batteries were not dead, each morning we still had power. I connected to the charger from my phone and watched for about 10 minutes and found that sometimes when the charging voltage peaked at 14.6v it would trigger the BMS to go into a protective state and disconnect the batteries for a moment. When this happened the voltage would drop down to 0-8v for a few seconds before reconnecting and resuming charging.

I changed our charge parameters to be 14.2v and this stopped happening. I never seem to get above 13.5v charging no matter what anymore. Earlier I disabled the charger and it was at 13.4v. Almost immediately it dropped down to 13.26v. There was a light load on the batteries but it seems they are never getting fully charged, float hasn't been reached in days. I also read that balancing doesn't happen unless 13.6v is reached and it never seems to make it there.

What can I do to remedy this? Are they shot? Should I try to discharge the 2 batteries completely and then charge them up individually, then reconnect them?

I have a 5.5A wall charger for LiFePO4 batteries. I have a multimeter and I have a battery monitor that I could use to check capacity.

I have two other 100Ah LiFePO4 which are new that I'd like to parallel together and create a 400Ah bank if these are not damaged. I've only really been using them for the past 2 months and until the past 4 weeks they have not been discharged below 20%.

 

[Fred S]

Do you mean the bank "never" goes above 13.5, or do you mean that it quickly settles to 13.5v or below, after charging is complete? I have a used 24v lifepo4 pack, and I can charge it up to any max voltage I want but it will quickly settle back to 26.5v (equivalent to 13.25v for you). This is not necessarily bad - while discharging, the pack stays in the 26.0 to 26.4 range for a long time (showing the famous flat discharge curve for lifepo4).

As far as separating your two batteries to check and see if one is significantly worse the the other, that's a good idea. Does each one have a bms, or is there one bms for the paralleled pair?

As far as paralleling the old pack with a newer pack, opinions will vary. *Personally*, I'd charge them up separately, then connect them in parallel and check the amperage transferring between them. Most likely it will be very low. If so, when they stabilize, which won't take long, check the resting voltage. If it is the same or better than your old pack, I wouldn't lose any sleep over leaving them paralleled. Others may have different suggestions. Good luck!

 

[JoeyB]

Do you mean the bank "never" goes above 13.5, or do you mean that it quickly settles to 13.5v or below, after charging is complete? I have a used 24v lifepo4 pack, and I can charge it up to any max voltage I want but it will quickly settle back to 26.5v (equivalent to 13.25v for you). This is not necessarily bad - while discharging, the pack stays in the 26.0 to 26.4 range for a long time (showing the famous flat discharge curve for lifepo4).

As far as separating your two batteries to check and see if one is significantly worse the the other, that's a good idea. Does each one have a bms, or is there one bms for the paralleled pair?

As far as paralleling the old pack with a newer pack, opinions will vary. *Personally*, I'd charge them up separately, then connect them in parallel and check the amperage transferring between them. Most likely it will be very low. If so, when they stabilize, which won't take long, check the resting voltage. If it is the same or better than your old pack, I wouldn't lose any sleep over leaving them paralleled. Others may have different suggestions. Good luck!

It's as though charging never completes. My charger used to switch off after a couple/few hours and flip back on every few minutes as my fridge/freezer/fan pulls power but this never seems to happen anymore. I will have 14-25A coming in for 4-5 hours most days and my fridge/freezer pulls 4A max and my fan pulls 5A max (usually less as I don't run it on high) so I should still be charging at 10-14A.

If I turn the charger off and see what the voltage settles to, it will almost always go to around 13.25v immediately, which may be expected from what you're saying I just did not think it was.

I have attached a screenshot of my victron history for example. It never leaves bulk charging it seems.


Each battery has its own BMS

 

[Fred S]

If you have fixed the "overdischarge" issue, then you could switch over to the new batteries and see if the charging behavior continues (i.e. not charging all the way to 14.2v). If so, then suspect your charger.

So you have bulk and absorption set to 14.2v? Float should be set to not run at all, if possible, or at least set to something lower, like 13.2.

 

[JoeyB]

If you have fixed the "overdischarge" issue, then you could switch over to the new batteries and see if the charging behavior continues (i.e. not charging all the way to 14.2v). If so, then suspect your charger.

So you have bulk and absorption set to 14.2v? Float should be set to not run at all, if possible, or at least set to something lower, like 13.2.

I am using the default Victron profile for LiFePo4. It doesn't actually let me set a bulk voltage, it says absorption is 14.2v (I think this also sets the bulk voltage to 14.2v) and float is set to 13.4v I believe (possibly 13.5v or 13.6v -- unfortunately I don't have my phone on me at the moment to double check).

Also my Victron history, logged that yesterday my bank reached absorption for the first time in 3 weeks at 14.2v a couple hours. Maybe a good sign?

Right now I have removed the old 2 batteries, have my fridge hooked up to a drop cable from the house, and I am charging them individually with a 5A wall charger to see what they reach. At 13.5v right now -- and the charger is charging at 13.6v

A few minutes after disconnecting them I checked both voltages and they were both settled at 13.38v

I am trying to balance the 4 batteries before connecting all 4 together tonight if it goes well. I also noticed a noob mistake I made in my electrical system today, my positive and negative bus bars have washers on them.
Instead of layering the connections bus bar > terminal for device > washer > lock washer > nut I was doing bus bar > washer > terminal for device > lock washer > nut on ALL of my connections on both bus bars. From what I understand, these washers could've added a bit of resistance to all connections. I am wondering if this could be a part of the issue.

 

[JoeyB]

Got all 4 batteries within 3% of each other (specifically: 13.39v, 13.40v, 13.55v, 13.65v -- rough state of charge range 98-100%). I connected 13.55v and 13.65v in parallel, letting it sit until there are no amps transferring between them. Then I will parallel it with the 13.4v and 13.39v battery.

 

[Fred S]

The washers probably didn't hurt anything, since amps are low (I assume) and you uniformly made all the connections the same way. But it was good to correct it.

Are you sure you're getting enough solar each day to fully charge the batteries? I hope the new pack works out, good luck!

 

[JoeyB]

Eh, sometimes I power an electric kettle that pulls roughly 68A but I don't know if that is considered "low".

I am fairly certain. The only things powered all day are my fan and fridge/freezer and recharging a phone.

My fridge/freezer pulls 4A when it's running the compressor which is about 1/3 the time. Roughly 31Ah a day. With my fan usage I'd estimate I use 36Ah. Totalling 64Ah or 768Wh.

I am installing a battery meter soon. That will let me see a more accurate figure of what I'm pulling per day

 

[OnTheRoadAgain]

I know this was almost a year ago....but I'm encountering a similar situation with "brand new Grade A" (supposedly) cells I just received.

They flat refuse to charge past about 13.5v no matter what. I've tried two different power supplies.

Did yours begin to lose voltage as they got near 13.5v ? Mine would charge to about 3.377v per cell (13.5v total) then peak out and begin losing voltage. Like a brick wall. I'm beginning to believe these "Brand New Grade A" cells batteries I received are a fraud.
I think they are VERY used cells masquerading as "brand new Grade A". Total fraud UNLESS I get some amazing breakthrough all of a sudden.

The perplexing thing is that I did a thorough internal resistance check on each cell (the long way) and they all were good. They did seem new.
Yet, I cannot get them past 3.377v per cell.

Glad I found this thread because it's the ONLY one I've found that seems to have encountered the same issue I'm having.

 

[JeepDaddy]

How many threads are you going to dig up from the dead for the same issue?

https://diysolarforum.com/threads/g...ell-drifts-0-08v-would-you-accept-this.14887/

 

[OnTheRoadAgain]

as many as it takes to figure out the problem?
I am hoping the OP might respond with his unique end result of his situation

If you don't mind
thanks

 

[JeepDaddy]

The common approach to keeping forums organized is:

One Thread, one Topic.
One Topic, one Thread.

 

[SolarDavidguy]

I am using the default Victron profile for LiFePo4. It doesn't actually let me set a bulk voltage, it says absorption is 14.2v (I think this also sets the bulk voltage to 14.2v) and float is set to 13.4v I believe (possibly 13.5v or 13.6v -- unfortunately I don't have my phone on me at the moment to double check).

Also my Victron history, logged that yesterday my bank reached absorption for the first time in 3 weeks at 14.2v a couple hours. Maybe a good sign?

Right now I have removed the old 2 batteries, have my fridge hooked up to a drop cable from the house, and I am charging them individually with a 5A wall charger to see what they reach. At 13.5v right now -- and the charger is charging at 13.6v

A few minutes after disconnecting them I checked both voltages and they were both settled at 13.38v

I am trying to balance the 4 batteries before connecting all 4 together tonight if it goes well. I also noticed a noob mistake I made in my electrical system today, my positive and negative bus bars have washers on them.
Instead of layering the connections bus bar > terminal for device > washer > lock washer > nut I was doing bus bar > washer > terminal for device > lock washer > nut on ALL of my connections on both bus bars. From what I understand, these washers could've added a bit of resistance to all connections. I am wondering if this could be a part of the issue.

if your float is 13.4v you wont get battery to charge past that figure. Float is what charger will maintain it at....