New lifepo4 batteries very slow top balance

DIY
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1

Since a week i have 4 parallel lifepo4 batteries, 300a per unit. They are 16 cell, Chinese (delongtop) with their own BMS, connected to Cerbo.

I put it in charger only mode and it immediately charged from 55% to 99 and now it has been pushing the voltage from 53.5 to 57.2, taking 4 days already and only taking 1A in this phase.

Ma manufacturer specifies absorption voltage 57.6 and float 53.5-54.5 with 20 minutes absorption time.

I am going to use the batteries in a DESS setup, connected to the grid. Charging in cheap hours and using the battery in expensive hours.

So if I am correct: it needs to top balance every 1 or 2 weeks. Will that mean that every time it does, it takes 4 or 5 days to reach 100% charge /57.6v ? And that I cant use the battery as intended in the meanwhile?

2

There are many variables that affect this.

  1. What are the charger settings supplying charge to the batteries.
  2. How good is the quality of the cells / bms.
  3. Is the bms set up correctly.
  4. Is the bms capable of balancing to a suitable amount.
  5. Do the cells keep within acceptable limit, with normal use.
  6. Does normal use allow charge voltage to get to higher enough voltage to balance.
  7. If yes to 5+6, is a scheduled balance charge required.
  8. What you consider is an aceptable deviation in cell voltages.
  9. How often you want to top balance.
3

@ferdyvw

Most (many) life4po battery owners never reach 100%, check topics here, and it doesn’t matter.. 99% is even better for the battery then always want 100 % and have risk of cell over-voltage.

Cell balancing is only required above 50 mv cell voltage difference at +99 % SOC.

4

Thanks Frisianstar,

So knowing that the BMS limits current very much when reaching 99,% and 53,5v, it takes a long time to reach set absorption voltage 57,6%; what absorption and float voltage would you recommend? I am completely new in this and need some general direction to start while learning.

5

55.2 Volts is my absorbtion limit and also the 100% SOC value..most of the it hangs on 99% that’s ok for me.. I don’t like overcharged batteries anyway.

At 57.6volts the overvoltage protection kicks in! 16 cell battery, should be lower like 56.5 Volts.