MisterSandals
Participation Medalist
This does not make sense. If you're top balancing (presumably in parallel), how could the voltage of any cell be different?
Just as odd, how does one top balance (presumably to 3.65V) without changing settings?
One cell always higher
- Thread starter larrylwill
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Just as odd, how does one top balance (presumably to 3.65V) without changing settings?
Pictures would help. It sounds like it might be working correctly, but either you don't have it connected correctly, or you don't understand how it is supposed to work.
chrisski
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We’ll see what the OP says, but I top balanced my cells individually. During one, the charger got bumped. I forget what my final voltage was, but it was in excess of 3.8 volts.
MisterSandals
Participation Medalist
I read back further and yes, jmsol was doing it individually.
jmsol not the OP so that further added to the confusion.
Ampster
Renewable Energy Hobbyist
He said he individually top balanced them not parallel top balanced them. Apparently there may have been some inconsistency on he process that allowed one cell to go higher. Just my guess.
Done is done. No real damage. If you want to match the others at 3.4 then take it down to 3.35 and run it up again.
I would just put it in service and expect all to be fine.
Your cell is not damaged at 3.67V. However, if the others were all individually charged to 3.4V, that is not enough for a balance. Close, but not quite. You need to be at about 3.5V per cell. You could probably get away with 3.45V. IMHO, there isn't much reason to go higher than 3.5V, but most people top balance to 3.65V
Individually charging cells is also a poor way to balance. The issue is that you aren't just trying to get them to the same voltage, but getting them to the same energy. You can charge to 3.5V, then either disconnect immediately, or let it absorb for a bit as the current drops. Either way, it is still charged "to 3.5V" but letting it absorb as current drops is preferable and will result in less of a voltage drop after the battery sits for a while. And if you do this individually instead of all in parallel, it is almost impossible to do it identically for all cells.
But you might get "good enough" results by charging them individually. If you are happy with a capacity test afterwards, then fine. But I expect that by both charging individually, and by balancing to a low voltage, you could do a lot better.
larrylwill
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Its been a year since I and installed my 280 amp 4s Lifepo4 battery and 150A BMS. I also installed a Renogy 60A DctoDc. I have a blutooth phone monitor. I never drove many miles for a trip untill last week. I drove about 1100 miles. I noticed the following. The battery cells start withen 20mv of each other. As I drove I watched the balance rise up to 164ma. The voltages were. Temp= 24c, V diff=0.164, Cell1=3.453, Cell2=3.399, Cell3=3.560, Cell4=3.542. Bms Cell OverVoltage was set to 3.65, Pack Over Voltage was set to 14.4v. On the return trip I set the BMS Cell OverVoltage to 3.4 andPack Overvoltage to 13.8v Readings an hour later were Temp= 21.7 Total Voltage= 13.8v, Voltage Diff=0.173, Cell1=3.422, Cell2= 3.477, Cell3=3.508, Cell4=3.597. While driving the battery Amp out drops to 0v after it is fully charged, the only thing running on the Lithium battery is the Fridge which draws about 5.5 amps when running. I also have solar which when the sun was out kep the battery drain at 0v most of the time. After stopping or living off the battery and solar for a couple of days the balance eventually comes back down to 20-40mv.
Question: Does this look normal?
If not what should I do?
Question: Does this look normal?
If not what should I do?
Last edited:
Could manually pull some charge out of the top cells with a resistor or boost the low cells with a power supply. This can be done while the battery is in service. Or add an active balancer. Either way it still take some time for improvement.
larrylwill
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A hieltec active booster is only $18 I think i will buy one.
thanks
thanks
Did you do a top balance when you first bought the cells? What is the balance start voltage set to in the BMS? Set your cell over voltage back to 3.65 or higher and pack overvoltage to 14.7 or higher to give balancing a chance to work before the BMS cuts out. What voltage is the Renogy DCDC set to. It must be set lower than the pack overvoltage and cell overvoltage (x4) or the BMS will cut out before balancing happens.
An active balancer balances cells if they are damaged or if there is something wrong with them. I recommend against that route unless you set everything correctly and a cell is still acting up. Pack overvoltage of 14.4 is too low. Your charger is almost certainly charging higher than that and tripping the disconnect. The disconnect should never happen. You always whan the charger to reach its voltage (probably 14.6v with the Renogy) and stay there long enough to balance.
I would suggest breaking it apart and doing a proper top balance, then review your charger and bms settings. Balancing cannot happen below about 3.5v per cell. So you at least need the BMS let them get that high.
An active balancer balances cells if they are damaged or if there is something wrong with them. I recommend against that route unless you set everything correctly and a cell is still acting up. Pack overvoltage of 14.4 is too low. Your charger is almost certainly charging higher than that and tripping the disconnect. The disconnect should never happen. You always whan the charger to reach its voltage (probably 14.6v with the Renogy) and stay there long enough to balance.
I would suggest breaking it apart and doing a proper top balance, then review your charger and bms settings. Balancing cannot happen below about 3.5v per cell. So you at least need the BMS let them get that high.
larrylwill
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Yes top balanced when I installed them. I set the BMS to 14.6 and the Renalgy to Lifepo4. However when I charge with a 10A battery charger set to Lifepo4 which I did today. This is what I got when the BMS kicked out.
3.523, 3.441, 3.590, 3.597 This as after I tightened all connections. So after a few hours and the charger shut down, I have
3.336, 3.326, 3.337, 3.336
Do you still think I should top balance again?
3.523, 3.441, 3.590, 3.597 This as after I tightened all connections. So after a few hours and the charger shut down, I have
3.336, 3.326, 3.337, 3.336
Do you still think I should top balance again?
On_The_Road
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