Configuring the JK BMS Settings for DIY Lithium Batteries

Steps

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   Step 1: Understanding the BMS homescreen

   When opening the app, the homescreen shows the current state of charge percentage, total pack voltage, and charging or discharging amperage. It also displays any error messages, the highest and lowest cell voltages, and the voltage difference between packs, which shows if the pack is in balance. Additional info like balancing amperage, remaining amp-hours, internal temperature, and battery type can be seen at a glance.

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   Step 2: Reading the status page details

   The status page provides deeper information including bed power, which is the wattage going in and out of the battery. It shows total and remaining capacity, the BMS CMOS temperature, and thermistor temperatures T1, T2, and T5 distributed across the battery housing. You can also see if a heater is connected, which is useful for preventing frost in cold locations like sheds or caravans.

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   Step 3: Checking additional status metrics

   On the right side of the status page, you can check the minimum and maximum cell voltage differences and the number of cycles the battery has run compared to its expected lifetime. It also shows total pack voltage, battery current through the shunt, individual cell voltages, and balance wire resistance measured across the balancing cables.

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   Step 4: Logging in and verifying passwords

   To log into the BMS and view settings, the standard password is 1234. If you want to modify and change settings, you need to click verify password at the top of the screen and enter the password 123456, unless you have changed it yourself.

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   Step 5: Configuring basic chemistry and import export

   At the top of the settings, you choose the battery chemistry, with LFP for lithium-iron-phosphate being the most common choice today. You can also use import and export settings to copy the configuration from one battery pack to multiple identical packs. Control options allow you to enable charging and discharging, use emergency mode for low voltage situations during power outages, and keep the LCD screen always on.

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   Step 6: Setting core parameters and capacity

   Under core parameters, you set the number of series cells, which is 16 for my standard 51V nominal packs, or 15 if you use cells like Pylontech with a wooden block filler. You must also enter the correct battery capacity, such as 314Ah for my cells, because lithium-iron-phosphate cells have a flat voltage curve and the BMS calculates the state of charge based on energy throughput.

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   Step 7: Configuring the cell balancer

   The balancer should generally be turned on so it can equalize cell charges when the battery is full. You set the balance delta voltage to 0.01V so it triggers when cells drift apart. The balance start voltage is set to 3.42V because balancing at lower voltages wastes energy.

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   Step 8: Setting voltage protections

   Lithium-iron-phosphate cells must not exceed 3.65V, but I set my cell overvoltage protection to a safer 3.5V, which keeps my total pack voltage under 56V when multiplied by 16 cells. The state of charge 100 percent voltage is set to 3.445V per cell, equaling 55.12V total, to synchronize with my Victron MultiPlus charger set to 55.2V. The cell overvoltage recovery is set to 3.4V.

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   Step 9: Configuring under-voltage protections

   I set the 0 percent state of charge under-voltage protection to 2.7V so the BMS blocks discharging if cells drop too low. The under-voltage protection recovery is set to 2.9V, and the absolute power off voltage is set to 2.49V to shut down the entire system for battery protection.

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    Step 10: Setting current protections

    My cells support a maximum of 0.5C, which is 157A for my 314Ah cells, but pushing this maximum constantly hurts lifespan. I set my continuous charge and discharge current to 100A instead, with a 60-second overcurrent protection delay for charging and a 300-second delay for discharging, matching my 35mm2 cables.

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    Step 11: Configuring temperature and heating control

    Temperature limits come pre-configured, and short circuit protection detects faults in 5 microseconds. Heating control can be set to turn on a heating element when temperatures approach -10 or 0 degrees Celsius to prevent frost damage in sheds or campers, turning off at 5 degrees Celsius.

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    Step 12: Setting up alarms and communication protocols

    You can configure alarms and dry contacts for high temperatures or external fans. For communication, set the CAN protocol number to 4 for Victron CAN-bus BMS communication. UART1 protocol handles RS485 inter-battery communication with identical settings across packs, while UART3 should not be changed because it controls display communication.

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    Step 13: Using factory calibration settings

    Factory only settings allow advanced users with calibrated meters to adjust voltage and amperage calibration if measurements deviate from the BMS. Since units are factory calibrated, you should only change this if you know what you are doing.

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    Step 14: Takeaways

    • Always set the correct cell count and battery capacity in the BMS core parameters.

    • Use conservative voltage limits like 3.5V per cell to protect battery health and prevent swelling.

    • Match your BMS 100 percent state of charge voltage with your inverter charger settings for synchronization.

    • Limit continuous current below the absolute maximum cell rating to preserve long-term battery lifespan.