I have AC500 with one B300S and I’m experiencing problems with SOC. For example, sometimes the system charges (from solar) with 500W for an hour, but SOC stays almost unchanged. Then later, SOC suddenly jumps up to 100% or so. The BMS is v1022.09
Would like to update the BMS to the latest version, which was mentioned here:
The serial number is AC5002241000496080
Please push me the latest version, thank you!
Hi @southside, Thank you for getting in touch with us.
We have pushed the new BMS firmware for you. Please upgrade the firmware tomorrow. Please do not load any device when upgrading it.
Please update each battery one by one, connecting only one B300S battery at a time.
After that, please try to complete the cycle of discharge and charge to correct the SOC. The problem will be resolved.
Please follow the steps below to recalibrate it:
You can click this link for reference.
Please let us know if it does help.
Thank you for pushing the Update! The BMS on my system is now version 1022.14
Then I performed the discharge / charge steps. So far, everything looks okay again.
I will monitor the system for some time and then let you know the result.
Hi @southside, Thank you for your update, we are glad to hear that!
We hope everything goes smoothly from here!
Please feel free to contact us if you need our help.
By the way, please note that if you need my assistance, please @BLUETTI_CARE, otherwise, I might not see your message and be able to help you promptly.
Hi @BLUETTI_CARE, I did the SOC calibration and want to share some results. I am using HomeAssistant to control the AC500 and added two screenshots with measurement results, as following:
In the beginning, the system is charged via solar input. Now watch “Total Battery percent”:
At postion (1) the SOC reaches 99% and stays at 99% for more than 1 hour, although solar continues to charge (not okay).
At position (2) the SOC reaches 100% and the AC500 shuts down solar charging
Then 2 hours later, I started to discharge with 2300W (10A * 230V)
At position (3) the SOC reaches 1% stays there for 20 min, while continuously discharged (not okay)
At position (4) the SOC reaches 0% and the AC500 switches AC-Output off then shuts the system down
20 minutes later I started to charge the systen via AC-Input with 1150W (5A * 230V). Solar charge is disconncted.
At position (5) the SOC reaches 99% again and stays there for over an hour. However the AC500 reduces charge power to 850W.
At position (6) the SOC reaches 100% and the AC500 stops charging via AC-Imput.
I found these results quite interesting and wanted to share this. Hopefully the SOC is calibrated now correctly. I will send a followup in some time.
Hi @southside, Thank you for sharing this. I believe it’s normal for the battery to remain at 99% for about an hour. When the power station is nearly full, the BMS (Battery Management System) enters a trickle charging mode and limits the charging speed to prevent overcharging, which can be harmful to battery lifespan.
We look forward to your further updates.
Hi @BLUETTI_CARE, in the meantime I did many cycles of the system. I usually charge via solar and then load my electric car with 2300W.
All in all I’m not very satisfied with this software version. Reasons:
SOC is not linear
When charging, very often SOC stays at 99% for up to more than an hour. We already discussed this above.
When discharging, SOC stays at 1% for up to more than 30 minutes while continously discharging. In my new example, it is 23 mins. This is very annoying, because the system delivers much of its energy only in this last percent. I can only get it when discharging to zero percent, which should be avoided for a longer battery life.
AC500+B300S does not deliver full capacity.
In many cycles from 100% to 0%, I get only 2.5 kWh into the car, sometimes even less down to 2.2 kWh. Capacity of the systen is 3.072 kWh, so I should get at least 2.7 kWh (calculated -10% losses). With the old software version, this was much better. I think, that the new software version has a problem to use the full range of the battery correctly.
What to do now?
The first chart is SOC
Hi @southside, Thank you for sharing. The information is very detailed.
Please note that the discharge depth of the B300S is 90%, and the inversion efficiency of the AC500 is 90%. So the normally available power is approximately 2.4 kWh. If it has been used for a long time, the battery capacity will also decrease accordingly. For example, for a mobile phone battery, when it is newly bought, the battery health is 100%, and after one or two years of use, it may only be 90% or 85%, which is normal.
When charging, the SOC remains at 99% for up to 1 hour, and the last 1% of the battery can also last for a long time during discharging, which is also a normal situation. This is mainly related to the characteristics of lithium iron phosphate batteries and the charging management mechanism.
When the lithium iron phosphate battery is close to being fully charged, the chemical reaction inside the battery will change. As the power increases, the resistance of the lithium ions moving from the positive electrode to the negative electrode increases, and the speed of embedding into the negative electrode slows down. When charging from 99% to 100%, this resistance is more obvious, making the charging process slower and taking more time. When discharging, the remaining 1% of the battery can last for a period of time because the discharge platform of the lithium iron phosphate battery is relatively stable. When the battery level is low, the voltage drops relatively slowly, and as long as the voltage can be maintained within the normal operating range of the device, it can continue to supply power to the device.
To protect the battery and extend its service life, the BMS will adopt a current reduction charging strategy at the end of the charging process. When it detects that the battery level is close to full (such as 99%), the BMS will reduce the charging current to prevent damage to the battery caused by overcharging. This leads to a significant decrease in the charging speed, and it takes more time to charge from 99% to 100%. The BMS will monitor and manage the discharging process of the battery to ensure that the battery can discharge stably even at a low battery level, so the remaining 1% of the battery can also discharge for dozens of minutes.
Hi @BLUETTI_CARE, thanks a lot for your detailed und very interesting answer. I now understand much better how the BMS works and that my system operates normally (in that sense).
One last question:
If the discharge depth of the B300S is 90%, does that mean that there always remain 10% in the battery? And is it okay to discharge to a displayed SOC of 0% often? That would make my life easier 
Hi @southside, You are welcome, it’s our pleasure to answer the question. We’re delighted to hear your system is functioning properly!
Regarding your question about the B300S, please note that the B300S has a 90% Depth of Discharge (DOD), which provides 2,764.8Wh of usable capacity (from the total 3,072Wh).
When the system displays 0% SOC, this indicates 0% of the usable capacity (2,764.8Wh); the protected 10% reserve capacity (307.2Wh) remains unaffected
Yes, you may safely discharge to 0% (displayed) as the built-in reserve protects the battery.
But please note that for optimal battery health, avoid leaving at 0% for extended periods. Recharge periodically when possible.
