I’m trying to understand the BMS behavior when the battery is fully discharged to prevent battery damage. My application will use solar to charge the batteries daily and drain the batteries daily / overnight. Here are a few questions I would like to have clarified:
What is the recommended, and safe, level of discharge for the B300K? Specifically, can I safely discharge to 0%?
How long can the battery safely remain in the fully discharged state?
How does the BMS handle a full discharge? Will the BMS disconnect the AC / DC outputs or do you expect this to handled manually by the customer?
What is the recommended discharge level (SOC) to maintain battery health long ter m? ie. if I discharge to 5% regularly will this reduce battery lifetime on a long term basis?
How many charge cycles is the battery rated for? Or how else is the battery spec’ed for lifetime usage?
Please let me know of any additional recommendations and guidance with respect to overall battery health. Thanks!
Setup:
AC500 with 2 B300K batteries.
Discharging: Various AC / DC loads connected
Charging: charging will happen using JMK315P (2s2p into each MPPT)
You can discharge to 0% since there is a internal buffer that doesnt allow a real full discharge to protect the battery from overdischarge and extend lifespan. But, when you drain it to 0% charge it promptly after use to prevent damage. Keep the battery in the environment
of at least 10°C (50°F) for at least 12 hours beforehand. Personally, i would keep atleast 10% left. Not recommended to do it on a daily base.
There isnt a specific value published. Would not leave it more than a few hours.
The BMS shutdown its energy output when a certain SoC is reached. You dont need to turn off in manually. Depending on the Host Unit, you can even set a custom SoC, when the unit turn off AC/DC
• When the SoC drops to 1% without any power input, power off the unit promptly to
prevent overdischarge.
• Before storing, charge it to 60%-80% SoC and fully cycle every 6 months to maintain
battery health.
• For long-term storage over 6 months, charge it to 40%-60% SoC and fully cycle every 3
months.
• Safe storage temperature: -20°C to 40°C (-4°F to 104°F). For storage over a month, aim
for a range of -20°C to 25°C (-4°F to 77°F). Perform a cycle charge before reuse.
• Avoid extended storage periods as it can impact the battery’s performance and lifespan.
4000+ cycles until its reach 80% of the original capacity
Thanks, Erik! Appreciate the quick response and info :)
The AC500 does not have a programmable cutoff based on what I’ve learned after digging through the forums. Do you know of anything off the shelf which can be used for this function?
I’m surprised there’s not more safety margin built into the system design here. My application, which I imagine is common, will source power from the batteries overnight when input power is unavailable. Fully draining the battery seems like a realistic use case here, but can pose a risk to battery health (ie. battery drains overnight and can’t be charged until EV available hours later). Am I missing something here or does the Bluetti AC500 + B300K design not really handle this scenario?