accidentally charged cells to 3.8v while top balancing, would they be damaged?

[bordenov]

I had my charger set to 3.6v but coming into the third week of top balancing I decided to up the voltage since my cells were barely charging (like .001v a day if that.)

I read here and there that the absolute max a lifepo4 could be charged to was 4.2v and so thought setting the charger to 3.8v shouldn't hurt anything but I'm not sure after reading around here. I left them overnight after thinking I should probably set it back to 3.6 before I slept but didn't get out of bed to do so and so found them in an overcharged state this morning.

I'm dropping the voltage the only way I can which is with LED puck lights but now I'm worried I damaged them. I have them compressed and they haven't bulged or anything. Thanks for any input.

 

[FilterGuy]

It's not good for the cells, but it is not a big deal. You are probably OK

 

[Warpspeed]

I agree, should be o/k.

 

[rodrick]

are you using the leads that came with the charger if so try making some heavy 10 gage wire leads you may get better results use ring lugs on the leads also set the charger before hooking up the cell don’t make adjustments while charging

 

[Will Prowse]

Is there any noticable bulging?

Will probably be ok, but inspect each cell.

 

[Bud Martin]

What kind of charger are you using?
Are you using large wire gauge, 10AWG or larger, between cell and the charger?
What is the cell Ah rating?

 

[curiouscarbon]

Any adjustment to the voltage setting needs to be done while the battery is disconnected ?

I think the short period of time above 3.65 Volts (this is the normal max voltage for LiFePO4 chemistry as far as I know) should be ok.

If there is no swelling, then the likelihood of permanent damage is low. Be careful going forward to adjust charge voltage before connecting battery, and to stay below 3.65 Volt and all should be good.

Wishing you good luck!

 

[FilterGuy]

To everyone who might read this thread: Patience is the most important thing to have when you are top-balancing. Set your power supply to the target top balance voltage and leave it there. Keep in mind that with a 10A power supply you are using around 35W to charge cells that might have over 5000Wh of capacity..... it is going to take a long time and during most of that time, it will seem like nothing is happening. Then, when things start happening, they happen fast.

You might see several millivolts difference between the power supply and the cells. This is normal. Don't raise the voltage of the supply.
You can speed things up with larger wires between the power supply and the cells, but don't raise the voltage of the supply.


If you have not read it yet, please review this resource:

Top Balancing LiFePo4 Cells using a low cost benchtop power supply.

To get the paper, click on the orange at the top of this page. This is a tutorial with detailed steps on how I top-balance my LiFePO4 Cells using a low-cost benchtop power supply. To get the tutorial, click on the orange "Download" button...

diysolarforum.com

 

[Steve_S]

Patience in an impatient world.
How many reach for the Instant Rice because 20 minutes to cook proper rice is too long ?

 

[RCinFLA]

Electrolyte is fairly stable to 4.3v.
LFP positive cathode electrode has strong lattice so it can take some overcharging.
Graphite negative anode electrode is stuffed with lithium-ions at maximum graphite negative electrode expansion (about 11% in graphite volume).

There will be a bit more cracking of SEI protective layer around graphite granules due to greater graphite expansion. This occurs to some degree every time a cell is fully recharged and is part of normal cell aging.

SEI is grown during charging and its purpose is to keep electrons in graphite electrode from escaping into surrounding electrolyte, chemically combining with lithium ions coming into graphite during charge cycle and electrons from escaping into electrolyte which chemically decomposes electrolyte.

The cell will be a bit more vulnerable to electron escape degradation described above until SEI cracks are regrown on subsequent recharging cycles.
The regrowth of SEI does consume a small amount of free lithium and electrolyte which reduces cell capacity a small amount.

Probably not desirable to subject cell to high recharging current, >0.1-0.2 C(A) rate, until it has had a couple of lower rate recharge cycles to regrow any excessive cracking in SEI protective layer due to the overcharge.

 

[Brett V]

Electrolyte is fairly stable to 4.3v.
LFP cathode has strong lattice so it can take some overcharging.
Graphite is stuffed with lithium-ions at maximum graphite negative electrode expansion (about 11% in graphite volume).

There will be a bit more cracking of SEI protective layer around graphite granules due to greater graphite expansion. This occurs to some degree every time a cell is fully recharged and is part of normal cell aging.

SEI is grown during charging and its purpose is to keep electrons in graphite electrode from escaping into surrounding electrolyte, chemically combining with lithium ions coming into graphite during charge cycle and electrons from escaping into electrolyte which chemically decomposes electrolyte.

The cell will be a bit more vulnerable to electron escape degradation described above until SEI cracks are regrown on subsequent recharging cycles.
The regrowth of SEI does consume a small amount of free lithium and electrolyte which reduces cell capacity a small amount.

Probably not desirable to subject cell to high recharging current, >0.1-0.2 C(A) rate, until it has had a couple of lower rate recharge cycles to regrow any excessive cracking in SEI protective layer due to the overcharge.

That's what I was going to say..LOL

 

[bordenov]

are you using the leads that came with the charger if so try making some heavy 10 gage wire leads you may get better results use ring lugs on the leads also set the charger before hooking up the cell don’t make adjustments while charging

I used 8awg.

 

[bordenov]

To everyone who might read this thread: Patience is the most important thing to have when you are top-balancing. Set your power supply to the target top balance voltage and leave it there. Keep in mind that with a 10A power supply you are using around 35W to charge cells that might have over 5000Wh of capacity..... it is going to take a long time and during most of that time, it will seem like nothing is happening. Then, when things start happening, they happen fast.

You might see several millivolts difference between the power supply and the cells. This is normal. Don't raise the voltage of the supply.
You can speed things up with larger wires between the power supply and the cells, but don't raise the voltage of the supply.


If you have not read it yet, please review this resource:

Top Balancing LiFePo4 Cells using a low cost benchtop power supply.

To get the paper, click on the orange at the top of this page. This is a tutorial with detailed steps on how I top-balance my LiFePO4 Cells using a low-cost benchtop power supply. To get the tutorial, click on the orange "Download" button...

diysolarforum.com

what can happen if you raise the voltage while the batt is still connected?

 

[FilterGuy]

what can happen if you raise the voltage while the batt is still connected?

Exactly what happened to you. The voltage can quickly go from OK to too high. There are many threads on the forum where people got impatient and turned up the voltage and did not catch it in time. Everyone thinks they will watch closely and catch it.... but it is too easy to get distracted and cause problems.

 

[RCinFLA]

what can happen if you raise the voltage while the batt is still connected?

When the power supply is in current limit, raising the voltage knob has no effect until current drops out of current limit.

You have no indication of how high you turned up voltage so when battery finally does get near full charge and the current drops off, the power supply continues up to whatever the voltage you blindly cranked the knob up to. This is where overcharging happens.

Always set power supply voltage limit with no load on power supply.

Some power supplies have separate limit settings, but I would not trust them blindly. Check voltage with no load is most certain way.

Many power supplies begin to taper the current limit set value as they approach the voltage limit setting. This prematurely reduces constant current and prolongs the top off charging a bit. Nothing you can do about this as it a limitation of power supply (cheap) design.

A higher quality supply will hold the constant current right up to where voltage cap limit is reached.

 

[GooseF16]

I use a Radio Controlled Lipo/Life charger to top balance any battery basically.. there are several really good ones that go nice and slow with CV/CC in that mode needed, but also do a great job FLA and NMH. my favorite 8S unit is an i308 charger 8 chan, and a IDST k2 for 6S and under.. I have 2 of them, and can balance charge a huge pack, often times using the same balance leads.. or make up a spider web lead with clamps.. it does all the balancing for you. but I fly RC so I had the equipment I also fix drill packs with it by spot soldering the taps and balancing them when they get out of whack and wont trigger the BMS. fwiw.. the key to Lixx is having a constant voltage, constant current, and holding it spot on until the current flow basically stops. so its alot at first and painstakingly slow at the end.

 

[Warpspeed]

I know its usual to balance right up at the supposed absolute maximum safe voltage, and I have always wondered why.
Its not without some risk....

If you only plan to charge up to a lower and much safer voltage, why not balance at that voltage ?
Once the cells are installed and running, that is what your cell balancer is going to do anyway.

What I do these days, is charge the whole battery up to a very safe voltage, 3.45v in my case. Then manually either charge or discharge individual cells so they are all at as close to 3.45v as I can get. I repeat the process over a few days, as a discharge/recharge cycle does move the voltages around.
After a few days of this, and normal battery cycling each day, it can all get pretty close.

After that, your cell balancer should easily be able to keep it there.

 

[FilterGuy]

I know its usual to balance right up at the supposed absolute maximum safe voltage, and I have always wondered why.
Its not without some risk....

If you only plan to charge up to a lower and much safer voltage, why not balance at that voltage ?
Once the cells are installed and running, that is what your cell balancer is going to do anyway.

What I do these days, is charge the whole battery up to a very safe voltage, 3.45v in my case. Then manually either charge or discharge individual cells so they are all at as close to 3.45v as I can get. I repeat the process over a few days, as a discharge/recharge cycle does move the voltages around.
After a few days of this, and normal battery cycling each day, it can all get pretty close.

After that, your cell balancer should easily be able to keep it there.

I like to balance to a voltage slightly higher than my target charge voltage. This helps ensure the cells stay close as they approach the target charge voltage.

 

[curiouscarbon]

I like to balance to a voltage slightly higher than my target charge voltage. This helps ensure the cells stay close as they approach the target charge voltage.

same here.

i personally define the "high range" of LiFePO4 to be 3.40 Volts to 3.65 Volts.

in this range, especially more as it goes higher, a given Voltage Difference represents a smaller and smaller Capacity Difference.

i usually charge to 3.45 Volts per cell to 3.55 Volts per cell.

the voltage changing more for a smaller difference in capacity at the highest end (3.55 Volts to 3.65 Volts) implies that balancing is "more accurate"

as @RCinFLA has mentioned though, the voltage seen during charging is different than the voltage seen at rest due to overpotential "push", so the behavior of the LiFePO4 cells are somewhat complex to fully interpret.

good luck

 

[GooseF16]

a very very light load peels off the overcharge of the LIFE cells.. even a small wattage load
balancer can do that on a big bank relatively