Recommended Charge Profile for DIY LiFePO4 Batteries *Sticky Post*

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Will Prowse

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12V 4S LiFePO4 Battery w/ BMS:
  • Absorption: 14.5V
  • Float: 13.6V
  • Inverter Cut-off: 10.7V-12V (depending on size of load and voltage drop etc)

24V 8S LiFePO4 Battery w/ BMS
  • Absorption: 29V
  • Float: 27.2V
  • Inverter Cut-off: 21.4V-24V

48V 16S LiFePO4 Battery w/ BMS
  • Absorption: 58V
  • Float: 54.4V
  • Inverter Cut-off: 42.8V-48V
Individual 3.2V LiFePO4 Raw Cell (for individual cell capacity testing)
  • Absorption: 3.625V
  • Float: 3.4V
  • Low voltage disconnect for capacity testing: 2.5V

If you are using a BMS and wish to manually cycle up to 90% SOC:
  1. Do a discharge capacity test with a shunt. Record capacity in watt hours.
  2. Charge slowly up to 90% SOC (take capacity Wh figure and multiple by .9), and while charging, record the voltage right when it hits 90% SOC
  3. Set the absorption for all chargers in system to the voltage you recorded in step 2
5,000+ Charge Cycle Absorption Recommendation
If you want your LiFePO4 cells to last a long time, you can set your absorption to Victron's custom LiFePO4 charge profile recommendation:
  • 12V Battery: 14.1V
  • 24V Battery: 28.2V
  • 48V Battery: 56.4V
You can pull full capacity with the absorption figures above, but the charge rate will be reduced at high SOC.

If you are not using a BMS (not recommended, for advanced users only)
  1. Bottom balance the cells
  2. Charge the cells at a .2C rate
  3. The moment a cell hits 3.6V while charging, record the pack voltage
  4. Manually set absorption for all chargers to the voltage in the previous step

If you are using used LiFePO4 cells w/ varying internal resistance readings, charge up to 3.525V per cell (12v/24v/48v absorption: 14V, 28V and 56V).

This will be a sticky post. If you disagree with a figure above, please message me with evidence to substantiate your claim. If something is missing, let me know :D
 
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