I just procured two pieces of 24volts 200Amphr LiFePO4 batteries for my 24 volts solar system that includes a Midnite solar classic 200 charge controller and an Outback VFX3024E inverter. I will be connecting the two batteries in parallel for a resultant nominal voltage of 24 volts. I understand that the "float" aspect of the charging algorithm is not necessary for LiFePO4 batteries. How do I set the charging parameters on the Midnite classic charge controller?
The charging is very specific to the batteries that you have and their internal BMS.
Best is to contact the battery manufacturer to ask them about how to set it up for charging.
Also look at this
http://www.midniteftp.com/support/kb/faq.php?id=75
Larry
I'm running Classic-200 with 1190AH / 30.4kWh of LFP (Bank 1) and 428AH of Heavy Lead (bank-2).
My bank is 3x 24V/280AH & 2x 24V/175AH.
Each pack has a Chargery BMS8T-300, with 300A DCC (Solid State Contactor) and a QNBBM-8S Active Balancer.
LFP NOTE:
It does not require or use Equalization or Desulphation. Not Applicable.
CC (Constant Current) can charge to 90-92% at which time CV (Constant Voltage) comes into play as the current accepted decreases.
FLOAT is viewed as CV because it will reduce as required, allowing for the cells to top-off and balance out.
My Classic-200 LFP profile is below:
QuoteAll equipment MUST BE Voltage Corrected & Calibrated (VERY IMPORTANT).
Divide Values X2 for 12V. Multiply X2 for 48V.
Absorb: 28.2 for 15 minutes (3.525vpc) (some call this boost)
Equalize: OFF
Float 27.9V (3.4875vpc)
MIn Volts: 22.0 (2.750vpc)
Max Volts: 28.7 (3.5875vpc)
Rebulk Voltage: 27.7 (3.4625vpc)
End Amps: 14A (*1)
(*1): End Amps is calculated from the Highest AH Battery Pack in a Bank. IE: 200AH X 0.05 = 10A 280AH X 0.05 = 14A.
NB: Victron Forum discussion says EndAmps = TailCurrent
This get's the bank charged to full with high amps (Constant Current) and then float (Constant Voltage) tops off so the cells are on average between 3.475-3.500. I am running 7/24/365 so float is used up by the Inverter + provides whatever the packs will take to top off.
** Coulumbic Efficiency for LFP is 99%
I do NOT get HVD disconnects and typically in float by 12-1 pm on a sunny day, and all packs fill to 100% without stress or issues, by the time it's all done, all the cells are typically between 6-12mv apart pending on the pack. I allow for 20mv differential.
Some/Many will tell you to charge to 29.2V (3.650Vpc) which is "idiocy" as that is the TOP of the Max Voltage Limit which are 2.500Vpc for O% SOC and 3.650Vpc MAX Full. This WILL trigger runner cells that will force the BMS to HVD Disconnect when cells reach 3.650 ahead of the others.
LFP Nominal Voltage is 3.200, Working Voltage is 3.000-3.400Vpc.
LFP knees are 2.850 and below and 3.550 and above which only represents 5% of total capacity. This is typically reserved out for maximized cycles & lifespan.
Cells charged to 3.650 and fully saturated will settle to 3.550-3.500Vpc within one hour of charge stopping, this is NORMAL.
I'd paste my BMS settings in here BUT this software will not take a pasted table... nor a pasted image, ugh...
Hope it helps, Good Luck.