Maximum and minimum charging and discharging for Lifepo4 battery

[Daham]

What is the maximum safe and practical voltage to use for charging and minimum voltage for discharging. At present i am using 28.0 volt for maximum charging and 24 volts for minimum. After a few hours the PV voltage went down even though the sun is shining very brightly. However when connected to extra load the PV will shoot up again. I found the the battery holds very little charge. I am using 24Volts 150AH lifepo4 battery. Any comments very much appreciated.

 

[nosys70]

check SOC chart , but all lthis is personal preferences (or needs), usually SOC charts are for one cell, so you need to multiply for a battery (by 8 for a 24V battery)

28V is ok, (while a bit on the low side, you can get a bit higher , closer to 29) , the 100% charge voltage is usually 3.65 that makes 8x 3.65= 29.2
you can even go higher but most people dont like to push the batteries to high because they want them to last as long as possible.
for the lower limit, that is even more debatable.
the absolute limit is about 2.0V (so 8x2=16V) but there is no chance a BMS will allow that. It will be closer to 2.5V (so multiply by 8, it makes 20V).
even that is considered very low, since the graph shows the useful range stop about 3.0V, after the curve dive very fast.
So you have to manage your settings to get the most of you battery, without hitting the limit of the BMS.
It depends also how you charge the battery, slow or fast. slow is better.

 

[Daham]

check SOC chart , but all lthis is personal preferences (or needs), usually SOC charts are for one cell, so you need to multiply for a battery (by 8 for a 24V battery)

28V is ok, (while a bit on the low side, you can get a bit higher , closer to 29) , the 100% charge voltage is usually 3.65 that makes 8x 3.65= 29.2
you can even go higher but most people dont like to push the batteries to high because they want them to last as long as possible.
for the lower limit, that is even more debatable.
the absolute limit is about 2.0V (so 8x2=16V) but there is no chance a BMS will allow that. It will be closer to 2.5V (so multiply by 8, it makes 20V).
even that is considered very low, since the graph shows the useful range stop about 3.0V, after the curve dive very fast.
So you have to manage your settings to get the most of you battery, without hitting the limit of the BMS.
It depends also how you charge the battery, slow or fast. slow is better.

Thanks for the clearification

 

[tictag]

It can be tricky for Lithium-ion because the charge/discharge curve is so very flat. I would definitely recommend querying the exact performance curves from your battery manufacturer e.g. 29V might well be 90% SoC for one battery, but 100% for another. Lead-acid is a lot easier to judge SoC from terminal voltage.

But yes, the typical values are:

• 3.65V (4-cell: 14.6V, 8-cell: 29.2V) = 100% SoC
• 3.00V (4-cell: 12V, 8-cell: 24V) = 0% SoC

 

[scott harris]

When doing a capacity test I accidentally charged a 280AH cell to 3.98 volts. Did I do any permanent damage? There was no bloating.