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105AH DIY Battery cell overvolt

db73

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Joined
Feb 9, 2021
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5
Hi
I’ve made my own 105AH lifepo4 battery to be used to run a fridge in my vehicle and has been working well.

Just notice 2 cells seem to be running away from the others which has been triggering the single cell over voltage alarm and turning off the charger.

Should I be concerned and what can cause this?

IMG_0584.png
 
Did you do top balance before putting the pack to work?
Sure did and a capacity test plus a few cycles and had been working flawlessly
 
Sure did and a capacity test plus a few cycles and had been working flawlessly
Great.
Did you recheck all the connections on each cell?
Do you have Volt meter to verify the Voltage readings.
If all the above are OK, I would swap the cell locations to see if the readings will follow or not.
 
Great.
Did you recheck all the connections on each cell?
Do you have Volt meter to verify the Voltage readings.
If all the above are OK, I would swap the cell locations to see if the readings will follow or not.
Errr no

I have since sealed it all up in a nice ABS battery box.

May have to bust it open and do some checking
 
Should I be concerned and what can cause this?
What isn't your BMS set to cutoff at 3.65V per cell? 3.7V will damage LiFePO4 cells.

Can you post your settings?

Charging at .43C is pretty aggressive. ( 45.33A/ 105Ah)
Charging at a lower rate often results in more even absorption and gives the balance functionality more time to work.
 
Cell over volt should never be over 3650 for LiFePO4
3500 for release is inconveniently low... 3620 plenty conservative.

3000 for under voltage release is also pretty far from cutoff. Its safe but you will be frustrated that you cannot charge until you somehow get cells up to your 3000 value.

Why do you not enter 105Ah as your capacity? Are you trying to be more clever than the engineers that design this stuff?
 
DD2FD7EF-0055-468E-A8D4-685E0B385590.jpeg4E66C39E-A594-40AB-B312-941704E0BA76.jpegCell over volt should never be over 3650 for LiFePO4
3500 for release is inconveniently low... 3620 plenty conservative.

3000 for under voltage release is also pretty far from cutoff. Its safe but you will be frustrated that you cannot charge until you somehow get cells up to your 3000 value.

Why do you not enter 105Ah as your capacity? Are you trying to be more clever than the engineers that design this stuff?
I guess this is what happens when you Google solutions.

My problem is/was I don’t actually know the manufacturer of the cells. They were gifted to me from a new retail slimline battery that got torn down for reverse engineering.

Not sure why the capacity is set to that. Don’t remember doing that and definitely not trying to outsmart anyone.

My formal training is in Vehicle Body Building so still learning.

Edit - I think the Total cycle capacity should have set to 93AH because that’s what the capacity test proved
 
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I guess this is what happens when you Google solutions.
Did you google "lithium ion" or LiFePO4 (also a lithium ion but a different/specific chemistry)?

Your new settings look reasonable except for your 70% and 30% cap voltages.

Have you seen this?
LFP Voltage Chart.jpg
 
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