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Top balance with used cells. Can i overcharge/damage a cell with low capacity?

narmenia

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I am trying to do a top balance with 4 used sinopoly 100ah cells.
If i apply 3.6v to the paralleled pack would i risk overcharging the cell with the lowest capacity first?
 
No ..... just make sure you adjust the power supply before connecting it to the parallel pack and then don't touch it again.

Cells with higher capacity will take more current to get to 3.6 V and lower capacity cells will take less current .... but all will come to 3.6 V and the current from the power supply will taper off to zero.
 
No ..... just make sure you adjust the power supply before connecting it to the parallel pack and then don't touch it again.

Cells with higher capacity will take more current to get to 3.6 V and lower capacity cells will take less current .... but all will come to 3.6 V and the current from the power supply will taper off to zero.
Once the pack reaches 3.6 volts i disconnect the charger then let it sit for an hour. Correct?
Then check voltage if voltage is above 3.5v the pack should be balanced. Right?
 
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Once the pack reaches 3.6 volts i disconnect the charger then let it sit for an hour. Correct?
Then check voltage if voltage is above 3.5v the pack should be balanced. Right?
After fully charged, I would let it sit overnight still connected in parallel but with power removed.
 
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Once the pack reaches 3.6 volts i disconnect the charger then let it sit for an hour. Correct?
Then check voltage if voltage is above 3.5v the pack should be balanced. Right?
The higher your voltage, the better matched voltage levels reflect proper balance, but they settle-down do quickly from 3.6 or 3.65V that unless you have equipment to measure from all cells at the same instant, it’s exceeding difficult to measure voltages way up in the charge knee where they are meaningful.

As already stated, leaving a parallel-balanced pack connected overnight after charging, or even 24 or 48 hours is the safest way to assure charge balance continues and all cells settle to an identical voltage.

You can even let settle overnight and then recharge to 3.6 or 3.65V the next day.

With each cycle, overall state of charge increases and balance improves.

Once you see the approximate same settling voltages the next morning, you know that the incremental charge you are adding every morning is just enough to offset overnight leakage (self-discharge).

It’s really a question of how much time you have and how much of a perfectionist you are (but only one hour after the the first balance cycle is insufficient).
 
The higher your voltage, the better matched voltage levels reflect proper balance, but they settle-down do quickly from 3.6 or 3.65V that unless you have equipment to measure from all cells at the same instant, it’s exceeding difficult to measure voltages way up in the charge knee where they are meaningful.

As already stated, leaving a parallel-balanced pack connected overnight after charging, or even 24 or 48 hours is the safest way to assure charge balance continues and all cells settle to an identical voltage.

You can even let settle overnight and then recharge to 3.6 or 3.65V the next day.

With each cycle, overall state of charge increases and balance improves.

Once you see the approximate same settling voltages the next morning, you know that the incremental charge you are adding every morning is just enough to offset overnight leakage (self-discharge).

It’s really a question of how much time you have and how much of a perfectionist you are (but only one hour after the the first balance cycle is insufficient).
charging at 3.6v is kind of slow when the voltage reaches around 3.570v.
it take ages to reach 3.6.

is it safe to do 3.65v?
Let the voltage reach 3.63X then just continue charging?
till the amp reading is almost 0?
or should i disconnect once the voltage goes above 3.6v?
 
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charging at 3.6v is kind of slow when the voltage reaches around 3.570v.
it take ages to reach 3.6.

is it safe to do 3.65v?
Let the voltage reach 3.63X then just continue charging? till the amps go below 1.0?
or should i disconnect once the voltage goes above 3.6v?
3.65V is safe, even 3.70V, but you’ve achieved most of what you!re aiming at if you reach 3.60V.

I assume you have a multimeter. As long as you are monitoring that, you can speed things up by increasing charge voltage and current.

What you want is for voltage increase rate on the cell to be easily manageable.

Even at 10.2A, I’m able to approach 3.650V at a rate of less than 1mV / second. This makes it easy to stop charging right at 3.65V.

The only word of caution is NEVER leave your charger unattended with voltage set above 3.6V - when the cell hits the knee at 3.4V, it can shoot up in a heartbeat so don’t take that risk unless you are attentively watching it.

It’s safe for the cell to charge at lower and lower current levels, but it slightly inflates stored charge in a manner that your actual charger is unable to copy.

The specification calls for charging to 3.65V with an 0.05C current cut-off (meaning cutting off the charger once current drops below 14A for a 280A cell).

So if you want to check how closely your cells capacity compares with specification, you actually want to charge at a current as close to 14A as you can (safely) manage...
 
I received 4 new cells of 150ah LiFePO4, and like i did with my other pack I charged the whole thing close to 14 volts. Then I top balanced each cell.

But I did a stupid thing, I put my charger at 4.60 instead of 3.60 volts. When I saw my mistake the cell was beginning to 'inflate' so I stopped everything, put them in series and put a 45 amps charge on it to try to 'deflate' it.
The cell did not deflate but it stopped inflate.

That was 3 days ago. I came home today and the cell was really big, it continue to inflate during the weekend.
I tried to take a picture of it, but the photo do not really show the actual size of the cell.


I ordered another cell from my Alibaba seller, but I need to know.

Is it safe to use that cell ? Is that cell still good ?
 
But I did a stupid thing, I put my charger at 4.60 instead of 3.60 volts. When I saw my mistake the cell was beginning to 'inflate' so I stopped everything, put them in series and put a 45 amps charge on it to try to 'deflate' it.
The cell did not deflate but it stopped inflate.

That was 3 days ago. I came home today and the cell was really big, it continue to inflate during the weekend.
I tried to take a picture of it, but the photo do not really show the actual size of the cell.


I ordered another cell from my Alibaba seller, but I need to know.

Is it safe to use that cell ? Is that cell still good ?
Did you mean you put them in series and applied a LOAD to the battery to deflate it?
Did you bring it way down to 3.2 or lower and it still expanded?

I would probably not use that cell. It would kill me to restart the 75 to 90 day wait again for shipping. :(
Best of luck.
 
Did you mean you put them in series and applied a LOAD to the battery to deflate it?
Did you bring it way down to 3.2 or lower and it still expanded?

I would probably not use that cell. It would kill me to restart the 75 to 90 day wait again for shipping. :(
Best of luck.
Yes when I saw that I made an error of voltage I put them in series and applied a load (the voltage was more then 15volts). After 5 or 6 minutes of load, the voltage was under 13.5 volts. So I figured that the expansion of the cell was stopped.
I removed the charge and let it sit in series for the week end.

The normal width of a cell is about 1'' but the cell that expanded is about 1.75'' (close to 2''). The expansion was not stopped for what I have seen.

When I saw that the cell expanded that much, I put the cell outside of the house ! I ordered a new one this morning. I will certainly ask my seller to send the new cell by plane...so only 2 weeks of wainting.
 
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