A strange thing occurred with Felicity's battery
- Thread starter ahmadsb
- Start date
DIYrich
Solar Wizard
A single cell may have run high (above 3.65v). Reduce your amps while charging until the battery is charged full without disconnect.
Is 30 amps considered high as a charging current?
What did you mean without discounted.. did you mean the BMS cable?
Steve_S
Offgrid Cabineer, N.E. Ontario, Canada
A few simple things:
- LFP batteries can take 0.5C Charge Rate. So a "typical" 100AH Battery can output 1C (100A) for 1 Hour and take 0.5C (50A) max for 2 hours to charge. See product Labels with regards to Amperage Output & Input. It depends on the cells used inside.
- LFP has TWO Voltage Ranges like other chemistries.
-- The Allowable Range (2.500 - 3.650) Volts per cell, this is the safe range where no harm is caused.
-- The Working Range which is (3.000-3.400) which delivers the actual rated AH of the battery pack. Nominal Voltage of 3.200 (50%).
-- Most use the range of 2.850-3.475 volts without issues. SEE CHART BELOW:
Next the Charging Profile MUST be Moderate !!!
Over / Under driving the cells within the battery pack will trigger the BMS (Battery Management System) to cut off as its job to to protect the cells and keep them within the Allowable Safe voltages.
You do NOT mention what equipment you are using (Solar Controller/Inverter etc) so here is a Moderate Profile settings that you should use. This sets voltages etc to operate and provide you with 100% of the capacity.
(*1): End Amps is calculated: (100AH X 0.05 = 5A or 280AH X 0.05 = 14A.
EndAmps = TailCurrent
Coulumbic Efficiency / Battery Status Meter Efficiency for LFP = 99%.
This gets the bank charged to full with high amps (Constant Current Constant Voltage) and then float (Constant Voltage, Variable Current) tops off so the cells are at 3.437Vpc. I
! Do Not forget to adjust for Voltage Offsets between Actual Voltage @ Battery Terminal & at Solar Controller.
BMS With Active Balancing should be set to start Active Balancing at 3.420V or possibly lower to 3.410 so that the cells can balance out at the top and not affect the charging process.
Very Special NOTE: Floating & Saturating to 3.437vpc, accounts for the Voltage Settling post Charge of any kind which actually brings the cells to just below 3.400Vpc.
EDIT - July 7 2022.
Voltage Corrected & Calibrated (VERY IMPORTANT)
- Midnite Solar Classics SCC's can be programmed for OFFSETS.
- Not all are capable so to adjust values it will have to be in charging values AS WELL as your Inverter/Charger.
- Even 0.1 Volt offset Can & Will affect operations
The simplest Way
Use 2 or 3 Decimal Accurate DVOM/DMM.
While SCC is Charging, Measure the Real Voltage coming out of the SCC and write it down, Same for the Inverter/Charger @ its BATT Terminal.
When Batts are in a + Charge (NOT when Discharging) measure the Voltage @ its/their Battery Terminal Lugs.
There WILL be some variances but there is always some Line Loss between these devices, Most important is what is going into the BATT.
Check your notes from each test. That Differential in Voltage must be Compensated for !
Take that Voltage Offset and apply it to the SCC, either an Offset Function or by the Charge Settings
IE, Assume SCC to Batt Terminal is 0.1V and you are Charging, Bulk/Absorb/Float Adjust the values UP. IE If Absorbing @ 27.6V increase that to 27.7V to compensate and the other Values as well. DO NOT FORGET to do the same for Low Voltage Disconnect !
The Inverter Needs two values;
The Charging Voltage offset applied as Above You got that value in your tests above. With SCC Charging.
Low Voltage Disconnect. MUST BE Measured when No SCC Charging is happening and the inverter is drawing from BATT only. It will be different than when SCC is charging the batts. Use that to adjust for Low Volt Disconnect ! Or you may get a Late Disconnect @ Low Volts making the disconnect lower than you set. NOT A GOOD THING !
Hope it Helps, Good Luck.
- LFP batteries can take 0.5C Charge Rate. So a "typical" 100AH Battery can output 1C (100A) for 1 Hour and take 0.5C (50A) max for 2 hours to charge. See product Labels with regards to Amperage Output & Input. It depends on the cells used inside.
- LFP has TWO Voltage Ranges like other chemistries.
-- The Allowable Range (2.500 - 3.650) Volts per cell, this is the safe range where no harm is caused.
-- The Working Range which is (3.000-3.400) which delivers the actual rated AH of the battery pack. Nominal Voltage of 3.200 (50%).
-- Most use the range of 2.850-3.475 volts without issues. SEE CHART BELOW:
Next the Charging Profile MUST be Moderate !!!
Over / Under driving the cells within the battery pack will trigger the BMS (Battery Management System) to cut off as its job to to protect the cells and keep them within the Allowable Safe voltages.
You do NOT mention what equipment you are using (Solar Controller/Inverter etc) so here is a Moderate Profile settings that you should use. This sets voltages etc to operate and provide you with 100% of the capacity.
| SETTING | V per cell | 12V | 24V | 48V | notes |
| Bulk / Absorb: (boost) | 3.437 | 13.74 | 27.5 | 55.0 | Absorb < 60min Transitions to Float |
| Equalize: | 0 | NOT for Lithium Based Batteries | |||
| Float | 3.425 | 13.70 | 27.4 | 54.8 | allows cells to balance internally |
| Min Volts: | 2.650 | 10.6 | 21.2 | 42.4 | Never allow to drop too low. Safe Buffer |
| Max Volts: | 3.575 | 14.3 | 28.6 | 57.2 | |
| Rebulk Voltage: | 3.200 | 12.8 | 25.6 | 51.2 | |
| End Amps / Tail-Current: | formula: 100AH X 0.05 = 5A |
EndAmps = TailCurrent
Coulumbic Efficiency / Battery Status Meter Efficiency for LFP = 99%.
This gets the bank charged to full with high amps (Constant Current Constant Voltage) and then float (Constant Voltage, Variable Current) tops off so the cells are at 3.437Vpc. I
! Do Not forget to adjust for Voltage Offsets between Actual Voltage @ Battery Terminal & at Solar Controller.
BMS With Active Balancing should be set to start Active Balancing at 3.420V or possibly lower to 3.410 so that the cells can balance out at the top and not affect the charging process.
Very Special NOTE: Floating & Saturating to 3.437vpc, accounts for the Voltage Settling post Charge of any kind which actually brings the cells to just below 3.400Vpc.
EDIT - July 7 2022.
Voltage Corrected & Calibrated (VERY IMPORTANT)- Midnite Solar Classics SCC's can be programmed for OFFSETS.
- Not all are capable so to adjust values it will have to be in charging values AS WELL as your Inverter/Charger.
- Even 0.1 Volt offset Can & Will affect operations
The simplest Way
Use 2 or 3 Decimal Accurate DVOM/DMM.
While SCC is Charging, Measure the Real Voltage coming out of the SCC and write it down, Same for the Inverter/Charger @ its BATT Terminal.
When Batts are in a + Charge (NOT when Discharging) measure the Voltage @ its/their Battery Terminal Lugs.
There WILL be some variances but there is always some Line Loss between these devices, Most important is what is going into the BATT.
Check your notes from each test. That Differential in Voltage must be Compensated for !
Take that Voltage Offset and apply it to the SCC, either an Offset Function or by the Charge Settings
IE, Assume SCC to Batt Terminal is 0.1V and you are Charging, Bulk/Absorb/Float Adjust the values UP. IE If Absorbing @ 27.6V increase that to 27.7V to compensate and the other Values as well. DO NOT FORGET to do the same for Low Voltage Disconnect !
The Inverter Needs two values;
The Charging Voltage offset applied as Above You got that value in your tests above. With SCC Charging.
Low Voltage Disconnect. MUST BE Measured when No SCC Charging is happening and the inverter is drawing from BATT only. It will be different than when SCC is charging the batts. Use that to adjust for Low Volt Disconnect ! Or you may get a Late Disconnect @ Low Volts making the disconnect lower than you set. NOT A GOOD THING !
Hope it Helps, Good Luck.
DIYrich
Solar Wizard
0.5c is way too fast to balance really out of balanced cells. once a bns cutout i had to drop to 0.05c to get a rack battery to balance. It took overnight to fully charge.
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