JK Preset Studio

JK-BMS settings explained with recommended values

Every JK inverter BMS setting explained: OVP, UVP, RCV, RFV, SOC, current, short circuit, temperature and balancer, with LiFePO4, NMC and LTO values.

Cell voltages

Cell OVP

V

What it does

Over-voltage protection. Charging stops immediately when any cell reaches this voltage.

Recommended values

LiFePO4 (LFP)
3.550 – 3.650 V
Suggested: 3.650
Li-ion NMC/NCA
4.100 – 4.200 V
Suggested: 4.200
LTO
2.600 – 2.800 V
Suggested: 2.700

Best practices & common mistakes

  • OVP is the last line of defence, not the charge target. The inverter charge target is RCV.
  • Keep OVP > RCV > SOC-100% voltage, otherwise the BMS trips before the charger finishes.
  • Quick chemistry check: 4.20 V means Li-ion, 3.60–3.65 V means LFP, 2.70 V means LTO.

Related parameters

Sources

Cell OVP recovery

V

What it does

Charging is allowed again once the highest cell drops to this voltage after an over-voltage cut-off.

Recommended values

LiFePO4 (LFP)
3.350 – 3.550 V
Suggested: 3.400
Li-ion NMC/NCA
3.900 – 4.100 V
Suggested: 4.000
LTO
2.350 – 2.650 V
Suggested: 2.400

Best practices & common mistakes

  • If OVPR is above RCV, charging restarts right after a trip and the cell can hit OVP again and again.
  • On LFP 3.40–3.45 V is a common choice: it lets the pack settle before charging resumes.

Related parameters

Sources

Cell UVP

V

What it does

Under-voltage protection. Discharging stops as soon as any cell falls to this voltage.

Recommended values

LiFePO4 (LFP)
2.500 – 2.950 V
Suggested: 2.600
Li-ion NMC/NCA
2.800 – 3.200 V
Suggested: 3.000
LTO
1.700 – 1.900 V
Suggested: 1.800

Best practices & common mistakes

  • Keep the order Power off < UVP < SOC-0% < UVPR. If the values are out of order the JK app reports a sending failure.
  • Leave 0.05–0.1 V between UVP and UVPR, otherwise the cell voltage bounces back after the cut-off and the output keeps switching on and off.
  • For longer cycle life on LFP, 2.8–3.0 V leaves a small reserve with almost no loss of usable capacity.

Related parameters

Sources

Cell UVP recovery

V

What it does

Discharging is allowed again once the lowest cell recovers to this voltage after an under-voltage cut-off.

Recommended values

LiFePO4 (LFP)
2.650 – 3.100 V
Suggested: 2.700
Li-ion NMC/NCA
3.100 – 3.400 V
Suggested: 3.200
LTO
1.950 – 2.050 V
Suggested: 2.000

Best practices & common mistakes

  • Must be higher than UVP. A gap of 0.05–0.3 V prevents rapid on/off cycling.
  • A higher value forces some charging before the load is reconnected.

Related parameters

Sources

Power off voltage

V

What it does

The lowest working voltage of the BMS. When cells fall below it the BMS shuts down completely to stop its own consumption.

Recommended values

LiFePO4 (LFP)
2.400 – 2.850 V
Suggested: 2.500
Li-ion NMC/NCA
2.700 – 3.100 V
Suggested: 2.800
LTO
1.600 – 1.800 V
Suggested: 1.700

Best practices & common mistakes

  • Must be below UVP.
  • After a power-off a deeply discharged pack needs a charger or the emergency switch to start again.

Related parameters

Sources

Smart sleep voltage

V

What it does

When every cell is below this voltage and the current stays under about 1 A for the smart sleep time, the BMS switches itself off to save the battery.

Recommended values

LiFePO4 (LFP)
3.350 – 3.500 V
Suggested: 3.350
Li-ion NMC/NCA
3.650 – 3.750 V
estimate
Suggested: 3.700
LTO
2.250 – 2.350 V
estimate
Suggested: 2.300

Best practices & common mistakes

  • On LFP, 3.35 V sits above most of the 3.2–3.3 V plateau, so an idle pack at mid charge will go to sleep. That is fine only if you have a power button to wake it.
  • Without a wake button, disable smart sleep or set the sleep time to 0 h.
  • Charging or pressing the BMS button wakes it again.

Related parameters

Sources

Charging & SOC

Cell RCV (request charge voltage)

V

What it does

Charge voltage per cell that the BMS asks the inverter for over CAN or RS485. Multiplied by the cell count it becomes the charge voltage limit (CVL). Ignored without inverter communication.

Recommended values

LiFePO4 (LFP)
3.450 – 3.550 V
Suggested: 3.500
Li-ion NMC/NCA
4.000 – 4.150 V
Suggested: 4.100
LTO
2.500 – 2.700 V
estimate
Suggested: 2.600

Best practices & common mistakes

  • On LFP 3.45 V is gentle on the cells but leaves little time for balancing; 3.50–3.55 V gives a better top balance and a reliable SOC reset.
  • On NMC every 0.1 V below 4.2 V roughly doubles the cycle life.
  • Keep RCV below OVP and above the SOC-100% voltage.

Related parameters

Sources

Cell RFV (request float voltage)

V

What it does

Float voltage per cell that the BMS requests after the absorption (RCV) phase has ended.

Recommended values

LiFePO4 (LFP)
3.350 – 3.400 V
Suggested: 3.375
Li-ion NMC/NCA
3.900 – 4.050 V
Suggested: 4.000
LTO
2.400 – 2.600 V
estimate
Suggested: 2.500

Best practices & common mistakes

  • Avoid keeping LFP at 3.45 V or more for long periods; 3.35–3.40 V is enough to hold a full pack.
  • Requires charging float mode to be enabled.

Related parameters

Sources

SOC-100% voltage

V

What it does

Cell voltage at which the state-of-charge counter is reset to 100 %.

Recommended values

LiFePO4 (LFP)
3.410 – 3.550 V
Suggested: 3.450
Li-ion NMC/NCA
3.950 – 4.100 V
estimate
Suggested: 4.050
LTO
2.450 – 2.650 V
estimate
Suggested: 2.550

Best practices & common mistakes

  • If your charger never reaches this voltage, SOC is never recalibrated and drifts over time.
  • JK suggests setting it about 0.04 V below RCV.
  • Calibrate the pack voltage with a multimeter first: a wrong reading can prevent the reset.

Related parameters

Sources

SOC-0% voltage

V

What it does

Cell voltage at which the state-of-charge counter is reset to 0 %.

Recommended values

LiFePO4 (LFP)
2.600 – 3.050 V
Suggested: 2.640
Li-ion NMC/NCA
2.900 – 3.300 V
estimate
Suggested: 3.050
LTO
1.800 – 2.000 V
estimate
Suggested: 1.900

Best practices & common mistakes

  • Set it slightly above UVP so the inverter sees 0 % before the BMS cuts off.

Related parameters

Sources

RCV time

h

What it does

How long the BMS keeps requesting the RCV voltage (absorption) before switching to the float voltage RFV.

Recommended values

Any chemistry
0.5 – 5.0 h
Suggested: 1.0

Best practices & common mistakes

  • 0.5–2 h is usually enough when the balancer can finish within that time.
  • Too short a time ends charging before balancing has happened, so cells drift apart.

Related parameters

Sources

Charging float mode

What it does

Enables the absorb-then-float logic: after the RCV time the requested voltage drops from RCV to RFV.

Recommended values

There is no universal value for this parameter. Follow the tips below and your hardware ratings.

Best practices & common mistakes

  • Enable it for inverters that would otherwise hold the absorption voltage for hours.
  • Some Victron users prefer to disable float and let RCV and re-bulk handle charging.

Related parameters

Sources

Current & protection

Max charge current

A

What it does

Charge over-current protection. If the charge current stays above this value for the OCP delay, charging is cut.

Recommended values

There is no universal value for this parameter. Follow the tips below and your hardware ratings.

Best practices & common mistakes

  • Limit it to the cell rating, for example 0.5C for EVE LFP cells, and never above the BMS rating.
  • When charge OCP trips, the PCL module can limit the current to about 10 A instead of cutting it.

Related parameters

Sources

Max discharge current

A

What it does

Discharge over-current protection. If the discharge current stays above this value for the OCP delay, discharging is cut.

Recommended values

There is no universal value for this parameter. Follow the tips below and your hardware ratings.

Best practices & common mistakes

  • Set it to what your cells, busbars, fuse and cables can carry continuously.
  • Keep it below the BMS rating.

Related parameters

Sources

Discharge OCP delay

s

What it does

How long the discharge current may exceed the maximum before discharging is cut.

Recommended values

Any chemistry
10 – 300 s
Suggested: 300

Best practices & common mistakes

  • Use a longer delay for inverter or motor start-up surges.
  • The JK default is 300 s; 10 s gives quicker protection for small systems.

Related parameters

Sources

Short circuit protection delay

µs

What it does

How long a short-circuit current may flow before the BMS disconnects, in microseconds.

Recommended values

There is no universal value for this parameter. Follow the tips below and your hardware ratings.

Best practices & common mistakes

  • The stored value and its accepted range depend on the firmware: a JK-PB2A16S20P on SW 19.26 stores 5 here and rejects a file with 1500. Change this setting in the JK app rather than in the file.
  • Inrush current into inverter capacitors can trip SCP. Users raise the delay to 3000–5000 µs, but precharging the inverter is the better fix.
  • Do not set it extremely high: a real short circuit must be interrupted fast.

Related parameters

Sources

Short circuit recovery time

s

What it does

Waiting time before the BMS reconnects after a short-circuit cut-off.

Recommended values

There is no universal value for this parameter. Follow the tips below and your hardware ratings.

Best practices & common mistakes

  • The stored value and its accepted range depend on the firmware: a JK-PB2A16S20P on SW 19.26 stores 5 here and rejects a file with 1500. Change this setting in the JK app rather than in the file.
  • Never make it short enough to retry quickly into a real short circuit.

Related parameters

Sources

Precharge time

s

What it does

How long the precharge circuit charges the inverter input capacitors through a resistor before the main MOSFETs close. Works only when the BMS turns on from the off state.

Recommended values

There is no universal value for this parameter. Follow the tips below and your hardware ratings.

Best practices & common mistakes

  • Increase it for large capacitor banks instead of raising the SCP delay.
  • The exact unit is not officially documented; compare with the value shown in the JK app.

Related parameters

Sources

Disable PCL module

What it does

PCL is the parallel current limiter: it limits current to about 10 A when charge over-current or short circuit is detected, which lets packs at different voltages equalize safely.

Recommended values

There is no universal value for this parameter. Follow the tips below and your hardware ratings.

Best practices & common mistakes

  • Keep PCL enabled when connecting packs in parallel.
  • With PCL disabled the BMS cuts charging instead and retries after about 60 s.

Related parameters

Sources

Temperature

Charge OTP

°C

What it does

Charging stops when the battery temperature rises above this value.

Recommended values

LiFePO4 (LFP)
45.0 – 60.0 °C
Suggested: 55.0
Li-ion NMC/NCA
40.0 – 45.0 °C
Suggested: 45.0
LTO
45.0 – 55.0 °C
estimate
Suggested: 55.0

Best practices & common mistakes

  • The JK factory default of 70 °C is above the LFP cell rating (55–60 °C): lower it.
  • NMC cells should not be charged above 45 °C.

Related parameters

Sources

Discharge OTP

°C

What it does

Discharging stops when the battery temperature rises above this value.

Recommended values

LiFePO4 (LFP)
50.0 – 60.0 °C
Suggested: 60.0
Li-ion NMC/NCA
50.0 – 60.0 °C
Suggested: 60.0
LTO
50.0 – 60.0 °C
estimate
Suggested: 60.0

Best practices & common mistakes

  • 55–60 °C protects most LFP and NMC cells.

Related parameters

Sources

Charge UTP

°C

What it does

Charging stops when the battery temperature falls below this value.

Recommended values

LiFePO4 (LFP)
0.0 – 10.0 °C
Suggested: 2.0
Li-ion NMC/NCA
0.0 – 10.0 °C
Suggested: 3.0
LTO
-30.0 – -5.0 °C
estimate
Suggested: -20.0

Best practices & common mistakes

  • Critical: some JK factory defaults are -20 °C. Charging LFP or NMC below 0 °C plates lithium and permanently damages the cells.
  • Use 0–5 °C for LFP and NMC. LTO is the only common chemistry that can be charged deep below zero.
  • Use the heating function if the battery lives in a cold place.

Related parameters

Sources

Charge UTP recovery

°C

What it does

Charging resumes when the battery warms up to this temperature.

Recommended values

LiFePO4 (LFP)
5.0 – 13.0 °C
Suggested: 5.0
Li-ion NMC/NCA
5.0 – 15.0 °C
Suggested: 8.0
LTO
-20.0 – 0.0 °C
estimate
Suggested: -10.0

Best practices & common mistakes

  • Keep it at least 3–5 °C above Charge UTP to avoid cycling near the limit.

Related parameters

Sources

Discharge UTP

°C

What it does

Discharging stops when the battery temperature falls below this value (newer firmware).

Recommended values

LiFePO4 (LFP)
-20 – -10 °C
Suggested: -20
Li-ion NMC/NCA
-20 – -10 °C
Suggested: -20
LTO
-40 – -30 °C
Suggested: -30

Best practices & common mistakes

  • LFP and NMC cells are usually rated for discharge down to -20 °C, LTO down to -30…-40 °C.

Related parameters

Sources

Discharge UTP recovery

°C

What it does

Discharging resumes when the battery warms up to this temperature.

Recommended values

LiFePO4 (LFP)
-15 – -5 °C
Suggested: -10
Li-ion NMC/NCA
-15 – -5 °C
Suggested: -10
LTO
-30 – -20 °C
estimate
Suggested: -20

Best practices & common mistakes

  • Keep it a few degrees above Discharge UTP.

Related parameters

Sources

MOS OTP

°C

What it does

Over-temperature protection of the BMS power MOSFETs. Charging and discharging stop when the MOSFETs get this hot.

Recommended values

Any chemistry
80.0 – 100.0 °C
Suggested: 90.0

Best practices & common mistakes

  • Frequent MOS OTP trips point to excessive current or poor cooling of the BMS.
  • 80–100 °C is typical.

Related parameters

Sources

Heating

What it does

Enables the heater output of the BMS. The heater turns on while charging is requested below the heating start temperature.

Recommended values

There is no universal value for this parameter. Follow the tips below and your hardware ratings.

Best practices & common mistakes

  • Requires a heating pad connected to the BMS heater terminals.
  • Make sure the charger can supply the heater power.

Related parameters

Sources

Heating start temperature

°C

What it does

The heater switches on when the battery temperature drops below this value.

Recommended values

LiFePO4 (LFP)
0 – 5 °C
estimate
Suggested: 3
Li-ion NMC/NCA
0 – 5 °C
estimate
Suggested: 3

Best practices & common mistakes

  • The JK default of -20 °C is useless for LFP: start heating at 0–5 °C so charging can proceed safely.
  • On some firmware the heater follows Charge UTP / UTPR instead of these values.

Related parameters

Sources

Heating stop temperature

°C

What it does

The heater switches off when the battery temperature reaches this value.

Recommended values

LiFePO4 (LFP)
8 – 10 °C
estimate
Suggested: 10
Li-ion NMC/NCA
8 – 10 °C
estimate
Suggested: 10

Best practices & common mistakes

  • Keep it above Charge UTP recovery so charging can start once heating finishes.
  • Users report about 1 °C of hysteresis around the set points.

Related parameters

Sources

Disable temperature sensors

What it does

Ignores missing or faulty battery temperature sensors (NTC).

Recommended values

There is no universal value for this parameter. Follow the tips below and your hardware ratings.

Best practices & common mistakes

  • Only for troubleshooting: without sensors there is no over- or under-temperature protection.

Related parameters

Sources

Balancer

Balancer

What it does

Enables the active balancer, which moves energy from the highest cell to the lowest.

Recommended values

There is no universal value for this parameter. Follow the tips below and your hardware ratings.

Best practices & common mistakes

  • Keep it enabled. Combine it with a sensible start voltage so it does not work on the flat part of the curve.

Related parameters

Sources

Start balance voltage

V

What it does

Balancing runs only when a cell is above this voltage and the cell difference exceeds the balance trigger.

Recommended values

LiFePO4 (LFP)
3.400 – 3.450 V
Suggested: 3.400
Li-ion NMC/NCA
3.900 – 4.000 V
estimate
Suggested: 3.950
LTO
2.400 – 2.500 V
estimate
Suggested: 2.450

Best practices & common mistakes

  • Common LFP mistake: balancing on the plateau below about 3.35 V. Voltage differences there do not reflect charge differences, so the balancer can push the pack out of balance.
  • Keep it below RCV, otherwise the cells never reach it.

Related parameters

Sources

Balance trigger voltage

V

What it does

The balancer starts when the difference between the highest and lowest cell is larger than this value and stops when it drops below it.

Recommended values

LiFePO4 (LFP)
0.005 – 0.010 V
Suggested: 0.005
Li-ion NMC/NCA
0.005 – 0.015 V
Suggested: 0.010
LTO
0.005 – 0.015 V
Suggested: 0.010

Best practices & common mistakes

  • JK recommends 0.005 V for cells over 50 Ah and 0.01 V for smaller cells.
  • Below about 5 mV the balancer mostly reacts to measurement noise and wire resistance.

Related parameters

Sources

Battery

Cell count

What it does

Number of cells connected in series.

Recommended values

LiFePO4 (LFP)
4 – 16
Suggested: 16
Li-ion NMC/NCA
7 – 14
Suggested: 14
LTO
10 – 24
Suggested: 22

Best practices & common mistakes

  • Must match the physical series count exactly: 16S for a 48 V LFP pack, 13–14S for NMC, 20–24S for LTO.
  • A wrong count disables protection for the missing cells or triggers false alarms.

Related parameters

Sources

Battery capacity

Ah

What it does

Rated capacity of the battery in ampere-hours. Used by the coulomb counter to calculate SOC.

Recommended values

There is no universal value for this parameter. Follow the tips below and your hardware ratings.

Best practices & common mistakes

  • Enter the real capacity of the cells, not the BMS rating.
  • For cells connected in parallel enter the total capacity.

Related parameters

Sources

Charge MOSFET

What it does

Allows charging. When off, the BMS blocks all charge current.

Recommended values

There is no universal value for this parameter. Follow the tips below and your hardware ratings.

Best practices & common mistakes

  • Keep it on for normal operation; turning it off is useful only for maintenance.

Related parameters

Sources

Discharge MOSFET

What it does

Allows discharging. When off, the BMS blocks all discharge current.

Recommended values

There is no universal value for this parameter. Follow the tips below and your hardware ratings.

Best practices & common mistakes

  • Keep it on for normal operation; turning it off is useful only for maintenance.

Related parameters

Sources

Functions

Smart sleep

What it does

Enables automatic shutdown when the battery is idle and below the smart sleep voltage.

Recommended values

There is no universal value for this parameter. Follow the tips below and your hardware ratings.

Best practices & common mistakes

  • Disable it for always-on inverter systems or packs without a wake button.

Related parameters

Sources

Smart sleep time

h

What it does

How long the battery must stay idle (current under about 1 A) below the smart sleep voltage before the BMS goes to sleep.

Recommended values

Any chemistry
0 – 24 h
Suggested: 24

Best practices & common mistakes

  • 24 h is the JK default. 0 h disables sleeping.
  • Wake methods: power button, LCD switch, or connecting a charger.

Related parameters

Sources

Display always on

What it does

Keeps the LCD from turning off after a timeout.

Recommended values

There is no universal value for this parameter. Follow the tips below and your hardware ratings.

Best practices & common mistakes

  • Slightly increases standby consumption.

Sources

Special charger

What it does

Dedicated charger identification mode.

Recommended values

There is no universal value for this parameter. Follow the tips below and your hardware ratings.

Best practices & common mistakes

  • Leave it off unless your charger documentation asks for it.

Sources

GPS heartbeat

What it does

Watches the heartbeat of an external 4G/GPS tracker module.

Recommended values

There is no universal value for this parameter. Follow the tips below and your hardware ratings.

Best practices & common mistakes

  • Leave it off unless a JK GPS module is installed: a missing heartbeat can block the battery.

Sources

Communication

Device address

What it does

Address of the pack on the RS485/CAN bus when several packs work in parallel. Usually set with the DIP switches.

Recommended values

Any chemistry
0 – 15
Suggested: 0

Best practices & common mistakes

  • The master pack connected to the inverter must be 0; every other pack needs a unique address from 1 to 15.
  • Some settings, such as re-bulk SOC, are only active on the master.

Related parameters

Sources

Shared port mode

What it does

Selects how the shared communication port works: CAN or RS485.

Recommended values

There is no universal value for this parameter. Follow the tips below and your hardware ratings.

Best practices & common mistakes

  • Choose what your inverter uses, then select the matching protocol number.
  • Examples from the JK protocol list: Victron uses a CAN protocol at 500 kbps, Deye uses protocol 001.

Related parameters

Sources

CAN protocol number

What it does

Inverter protocol used on the CAN port, as numbered in the JK app protocol list.

Recommended values

There is no universal value for this parameter. Follow the tips below and your hardware ratings.

Best practices & common mistakes

  • Check the JK protocol list for your firmware: the numbering can change between versions.

Related parameters

Sources

UART1 (RS485) protocol number

What it does

Inverter protocol used on the first RS485 port, as numbered in the JK app protocol list.

Recommended values

There is no universal value for this parameter. Follow the tips below and your hardware ratings.

Best practices & common mistakes

  • Check the JK protocol list for your firmware: the numbering can change between versions.

Related parameters

Sources

Device

Device name

What it does

Name shown in the JK app and broadcast over Bluetooth. Up to 16 ASCII characters.

Recommended values

There is no universal value for this parameter. Follow the tips below and your hardware ratings.

Best practices & common mistakes

  • Use a unique name per pack to tell them apart in the app.

Device passcode

What it does

Password for connecting to the BMS in the app. Up to 16 characters.

Recommended values

There is no universal value for this parameter. Follow the tips below and your hardware ratings.

Best practices & common mistakes

  • Change it from the default if the battery is in a shared place.

User data

What it does

Free text stored in the BMS.

Recommended values

There is no universal value for this parameter. Follow the tips below and your hardware ratings.

Best practices & common mistakes

  • Handy for an installation date or owner contact.

Setup passcode

What it does

Password required to change settings in the app. Up to 16 characters.

Recommended values

There is no universal value for this parameter. Follow the tips below and your hardware ratings.

Best practices & common mistakes

  • Keep it different from the device passcode.

Wire resistance

Wire resistance, cell N

Ω

What it does

Resistance of the balance lead for this cell. The BMS uses it to correct the voltage drop on the lead during balancing. It is measured automatically at power-on.

Recommended values

Any chemistry
0.000 – 0.080 Ω
Suggested: 0.050

Best practices & common mistakes

  • Healthy leads read about 0.045–0.055 Ω and should all be close to each other.
  • A value above about 0.08 Ω points to a bad crimp or loose connection and leads to wrong cell readings.
  • 0 means the value has not been measured or set.

Sources