JK BMS Parameters Explained: Every Setting by Group

JK BMS parameters explained in short: the settings fall into a few groups. Cell voltage limits protect the cells, balance settings even them out, SOC voltages calibrate the fuel gauge, RCV and RFV tell the inverter how to charge, current and temperature limits cut the MOSFETs, and the switches turn whole functions on or off. The names below match the JK app and the JK Preset Studio editor.

Cell voltages

These are the main protections. Each one has a trip value and a recovery value.

• Cell OVP (over-voltage protection): charging stops when any cell reaches this voltage.
• Cell OVP recovery (OVPR): charging is allowed again once the highest cell falls below this voltage.
• Cell UVP (under-voltage protection): discharging stops when any cell drops to this voltage.
• Cell UVP recovery (UVPR): discharging is allowed again once the lowest cell rises above this voltage.
• Power off voltage: the lowest working voltage of the BMS. Below it the BMS shuts down completely to stop its own drain.

The trip value always sits further from the normal range than the recovery value. For a LiFePO4 pack the order from the bottom is power off voltage, UVP, UVPR, then OVPR and OVP at the top.

Balance

• Balancer: the on/off switch for balancing.
• Start balance voltage: balancing runs only while a cell is above this voltage.
• Balance trigger voltage: balancing starts when the gap between the highest and lowest cell is larger than this value, and stops when it falls below.
• Max balance current: how hard the balancer pushes energy around. Typical values are 1 to 2 A, depending on the board. See JK BMS balance settings.

SOC calibration voltages

• SOC-100% voltage: when a cell reaches it, the state-of-charge counter is reset to 100 %.
• SOC-0% voltage: when a cell falls to it, the counter is reset to 0 %.

These do not protect anything. They correct the percentage that the BMS reports. See the SOC calibration guide for how to pick them.

Charge voltage control

• Cell RCV (request charge voltage): the per-cell voltage the BMS asks the inverter for over CAN or RS485. Multiplied by the cell count it becomes the charge voltage limit.
• Cell RFV (request float voltage): the lower voltage requested after the charge phase ends.
• RCV time and RFV time: how long each request is held. The maximum is 18.2 h.
• Charging float mode: switches the float stage on.

RCV and RFV only matter when the inverter talks to the BMS. Without communication they are ignored.

Current protections

• Max charge current and Max discharge current: the limits in A.
• Charge OCP delay and Discharge OCP delay: how long the current may stay above the limit before the BMS cuts the MOSFET.
• Charge OCP recovery time and Discharge OCP recovery time: how long the BMS waits before it switches back on.
• Short circuit protection delay: how long a short-circuit current may flow, in µs.
• Short circuit recovery time: the wait before a retry after a short circuit.

Short-circuit values are firmware specific. On firmware V19 a delay above 50 is rejected on import. The OCP and SCP guide covers safe values.

Temperature protections

Each limit has a trip value and a recovery value, for charge, discharge and MOS temperature:

• Charge OTP and Charge UTP: over and under temperature for charging.
• Discharge OTP and Discharge UTP: the same for discharging.
• MOS OTP: protects the power MOSFETs from overheating.
• Heating, Heating start temperature, Heating stop temperature: on models with a heater output, the heater runs while charging is requested below the start temperature.

Charging LFP below 0 °C damages the cells, so keep Charge UTP at 0 °C or above.

Switches

• Charge MOSFET and Discharge MOSFET: enable or cut the charge and discharge paths.
• Balancer and Heating are covered above. Smart sleep and Disable temperature sensors are optional functions you rarely need.

JK BMS parameters explained: typical LFP ranges

These are ranges collected from JK manuals and cell datasheets, not single correct values. Check your cell datasheet.

Current limits have no fixed range because they depend on the pack. The editor presets scale them by C-rate and cap them by the BMS rating.

Write order rules

The firmware checks every written value against the values it holds at that moment. The chains it enforces are OVPR < SOC-100% voltage < RCV and UVP < SOC-0% voltage < UVPR. Equal values are rejected. Break a chain and the app answers with "This parameter does not apply to the connected device. (Sending failure)". The editor checks these rules for you, and when it writes over Bluetooth it picks an order that keeps every chain intact. See the sending failure guide for the fix.

To check your values against reality, load a Detail Log on the log analysis page. Read what each log message means as the companion for the text the BMS writes there.

Common questions

What is the difference between OVP and RCV?

OVP is a hard protection that cuts charging. RCV is the target the inverter should charge to. Keep RCV clearly below OVP.

Should SOC-100% voltage equal OVP?

No. It must sit above OVPR and below RCV, or the firmware rejects the value.

Connect your BMS or open your .jkcfg in the JK Preset Studio editor to see these values from your own battery. The parameter reference has tips for every setting, presets give ready values, and the LiFePO4 settings guide covers a full setup.