WillemF

You can use a Lithium battery with no problem. The Axpert 3kW inverter assumes a 24V battery. You need to set the battery type to USER in the setup of the inverter (option 5) in the case of the Axpert King. You would also have to play around with options 26 and 27 (Bulk charging and float charging voltage) to suit your battery. Out of the factory, the charging regime of the inverter is optimised for lead acid battery, NOT for LiFePO4. My Bulk charging voltage is 27.2 and Floating voltage is 27.1. However, this depends on the exact battery you use. The big difference between lead acid batteries and Lithium is in stable voltage. Lead acid batteries love being fully charged at around 13V. The policy is then to charge the lead acid battery fully, and not run it down too low. With Lithium, the policy is very different. LiFePO4 patteries love being around 50% charged, so one would cycle the battery so that the output power available crosses 50% SOC every day. They do NOT like being charged to the absolute maximum or being totally discharged. Forget the rubbish that the sales people banter that one can discharge a Lithium battery from 100% down to 0%. Of course that IS true, one CAN do that, but this would shorten the life of the lithium battery to a fraction of its expected life span of at least 4000 charging cycles. I cycle the battery around 50% SOC. From that you can decide how much power you require from the Lithium battery, probably using between 50% to 80% of the total battery capacity with each charge cycle. My battery is built up from cells and battery management hardware. If you use a Pylontech or similar pre-built battery the charge/discharge parameters would be handled by the battery software using the dedicated communications link between inverter and battery. However, this is a much more expensive approach.

I have been following this forum for some time and still have a question that has probably been extensively dealt with but I cannot find such a complete discussion. So please bear with me. I run an Axpert king 3kW inverter (removable console) with solar panels giving 1.3 kW and a 24V 6.3 kWh LiFePo4 battery composed of an 8 serial 2 parallel arrangement of cells, supervised by a Daly bms. The Axpert main CPU version is 51.08, secondary CPU is v02. 00, SCC version 1.10. Our overnight household power usage is about 1.8 kWh. My problem is that the inverter is not set up for lithium batteries (unless pylontech) and the shallow charge curve. My approach to running the system is to charge up to 75% SOC and discharge to 25%. To achieve this I bulk charge to 27.3V and then float at 27.1V. My problem is that the Axpert charges at a slow rate (around 500W). On sunny days it eventually gives the full charge, but on cloudy days the low charge rate is problematic. However, if I set the bulk charge voltage to 27.6V then the charge rate increases to over 1kW which is what I would have expected in the first place. Our washing machine draws 2.2kW (only for 2 minutes) and when using that, the solar panels deliver close to their maximum capacity. So I am convinced there is not a panel efficiency problem. Now, I gather there has been a number of updates to the firmware of the Axpert King, done by Coulomb and some Australians. I need to understand whether a firmware reflash will solve my problem. I cannot find a systematic description of what issues were addressed in these firmware changes and whether they could alleviate my problem. I regularly download logs from the Axpert to a memory stick using a USB OTG cable. I have managed to decode most of the information in the log files. Apologies for such noob questions, but I suppose one needs to start somewhere. Any information about useful links for addressing the above issue will be very much appreciated. Kind regards, willemf

Hi King users, I have had a 3KW King installed for 2 months now. I have it in SBU mode and it works flawlessly as far as I can see. I use 2 x 8 LiFePO4 batteries with a separate battery management system to give me around 5.6 KWh at 24V. The battery type is set as "user". I have 1300W of solar input, so it is a reasonably small system. The solar panels only deliver about 900W max at this time of year, but this is due to the solar azimuth during Jul/Aug. I use around 4.5 kWh/day and batteries are fully charged around 13h00 on a sunny day. The only gripe that I have is that the SOC calculations are obviously not for LiFePO4 batteries (maybe applying to lead acid or glass lead acid cells?). Consequently, when the battery voltage drops below 3.15V/cell, it gives a low voltage warning. Extremely irritating. Because of this I switched the warnings off. I download the inverter data using the USB port on the inverter and self-written software in R. Does anyone have an idea of how the SOC calculation is performed by this equipment? Is there any way to change it? Kind regards, wf