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maartenvt avatar image

Charging a 12V Lifepo4 battery. Who has the key to this mystical knowledge?

I have bought a lifepo4 12.8V 40Ah battery from an unknown but experienced manufacturer for a small project, that was not too expensive to wake the kraken and dragon of my spouse.

It came at 13,33V and looked very tame.

I charged it with a blue smart ip65 12/15 charger on lithium configuration and low current (4A) instead of 15A to wake it up softly.

The manufacturer prescribes a CCCV load profile with cut off voltages of 14,6v high to 10V low. But Victron thinks that 10V is too low. They told me to cut off at 12,5V. And load with 14,2V.

I think Victron uses a more conservative load profile. Maybe to protect the battery from unballanced cells in these high limits? Is that right? Or does that have another reason? Lifepo4 is lifepo4 right?

The first charging got to 14,2V for a little while, but then very quickly started ballancing at 13.5V. Is that normal?

So now the battery is 13,5V... Which is good I guess for storing the battery? When I look at a voltage chart of 12V Lifepo4, that is about 90%SOC? I have enough capacity to do what I want, so that's ok.

But I need to calibrate an Aili battery monitor (I know it might be rubbish but I want a little experiment). So when the battery is 100%, I have to tell the monitor by pushing a button that it's 100%SOC. But how do I know whether the battery is completely charged at 100%? On the voltage charts of lifepo4 I see that 13,5V is not 100%, but the smart charger brings the voltage automatically to 13.5V, and I don't want to start messing with the configurated values...

I also have a smart battery sense, a smart battery protect on load side, a battery protect on charge side, and an mppt 75/15 for a solar module when I install everything. Some are new, some were of a previous AGM project (that's why the chargers are 15A, instead of 10A which would be preferable for a 40Ah battery). But without a shunt, these victron appliances can't determine the SOC, so they can't help me either, although they all blink very willingly.

Any suggestions to educate me on this and protect my precious investment from my erratic ignorance, and help me to set this battery monitor please?

Would it calibrate itself when the battery reaches full capacity again? Even when the voltage drops again to 13,5 V?

BMV Battery MonitorLithium Batterybattery chargingBlue Smart Chargerbattery capacity
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2 Answers
alan avatar image
alan answered ·

This is another great link full of details

https://marinehowto.com/lifepo4-batteries-on-boats/

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marc-de-montreal avatar image
marc-de-montreal answered ·

hi,

your battery have a bms and will balance your cells only near the top voltage.. if the cells are very unbalanced, that will take a while for the first time (may take days) but with usage, if you don’t avoid the top voltage, the batt will balance a bit each time.. 10v look bms the voltage battery disconnect and you don’t want that happen when pluged to your controller.. below 12v the voltage drop rapidly, and for your battery lifetime cycles, a good idea is to avoid it.. let you batt at full a while (1 day minimum) to balance it..

for the mystical knowledge, go to see https://batteryuniversity.com/ section lithium

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