Posted February 14, 20223 yr Greetings, I'm trying to figure out BSL 6.4kWh battery settings on an Axpert MKS II 5K off-grid system for cycling in the mid-SOC range of 95% to 15% (80% DOD). The battery datasheet states Voltage at end of Discharge: 47-48V Recommended Charge Voltage: 55V The BSL 6.4kWh user manual on the Victron Energy site has these settings for the Quattro 48/5000/70 inverter/charger. VE Configure Inverter Tab DC input low shut-down: 48.00V DC input low restart: 52.00V DC input low pre-alarm: 49.00V SOC low shut-down: 10% VE Configure Charger Tab Absorption Voltage: 55.00V Float Voltage: 54.80 Charge Curve: Fixed Absorption Time: 1 hour However, from the General LiFePO4 (LFP) Voltage to SOC charts/tables, 54.80V (float) to 48.00V (LVD) is approximately SOC 99.5% to 9.5% (90% DOD). For the mid-SOC range between 95% (3.363Vpc, 53.80V) and 15% (3.150Vpc, 50.40V), I want to try out the following Axpert settings: 26 - Bulk charging voltage - 54.00V 27 - Float charging voltage - 53.80V 29 - Low DC cut-off voltage - 50.40V 32 - Bulk charging time - 60 minutes BSL Bull battery users, what are your views regarding these voltage settings? Should I instead consider 90% to 10% SOC range i.e. 53.60V (3.350Vpc) float and 48.00V (3.000Vpc) LVD?
February 15, 20223 yr 12 hours ago, Kilowatt Power said: I want to try out the following Axpert settings: 26 - Bulk charging voltage - 54.00V 27 - Float charging voltage - 53.80V 29 - Low DC cut-off voltage - 50.40V 32 - Bulk charging time - 60 minutes Be aware that the Axperts have the nuisance of the back-to-grid voltage being 2.0 V above the low DC cutoff voltage (undocumented). Your proposed float voltage is very close to the bulk charge voltage, which is not good for battery life. But you may be more interested in load shedding preparedness.
February 15, 20223 yr Author 12 hours ago, Coulomb said: Be aware that the Axperts have the nuisance of the back-to-grid voltage being 2.0 V above the low DC cutoff voltage (undocumented). Hi Coulomb, the installation is completely off-grid with solar only charging. Do settings 12 (back to utility) and 13 (back to battery) matter in this case?
February 15, 20223 yr Author 12 hours ago, Coulomb said: Your proposed float voltage is very close to the bulk charge voltage, which is not good for battery life Noted. I'll use the float voltage stated in the Victron manual (54.80) as the absorption voltage then keep float voltage at 53.80 26 - Bulk charging voltage - 54.80V 27 - Float charging voltage - 53.80V 29 - Low DC cut-off voltage - 50.40V 32 - Bulk charging time - 60 minutes
February 17, 20223 yr On 2022/02/16 at 3:36 AM, Kilowatt Power said: I'll use the float voltage stated in the Victron manual (54.80) as the absorption voltage then keep float voltage at 53.80 It's the time spent at high cell voltages that reduces life, not the difference between the absorb and float settings. So I would reduce the float voltage, rather than raise the bulk/absorb voltage.
February 17, 20223 yr Author 11 hours ago, Coulomb said: It's the time spent at high cell voltages that reduces life, not the difference between the absorb and float settings Thanks for spelling this out. It's now perfectly clear and understandable. Edited February 17, 20223 yr by Kilowatt Power
February 17, 20223 yr Author On 2022/02/15 at 8:30 PM, Kilowatt Power said: Do settings 12 (back to utility) and 13 (back to battery) really matter in an off-grid situation? The site will not be connected to grid in the foreseeable future.
February 18, 20223 yr On 2022/02/16 at 3:30 AM, Kilowatt Power said: the installation is completely off-grid with solar only charging. Do settings 12 (back to utility) and 13 (back to battery) matter in this case? Oops, I missed that post. No, those settings are for "back to grid" and "back to battery from grid". Since you have no grid, you will presumably use the "utility first" output source priority, meaning that if and when generator voltage is present, you will want to use it to power the loads and possibly charge the battery.
February 18, 20223 yr Author 1 hour ago, Coulomb said: meaning that if and when generator voltage is present, you will want to use it to power the loads and possibly charge the battery Thanks. There's a 15 kVA DG set at site which has more or less been decommissioned since the 9.6kWp solar array fills up the 3 x BSL 6.4 kWh batteries in about 2 hours. We have more than sufficient sun at the equator 😉
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