JK BMS Balance Settings: Start Voltage, Trigger, Current

The JK BMS balance settings are four values: the Balancer switch, Start balance voltage, Balance trigger voltage and Max balance current. The active balancer works only when the switch is on, at least one cell is above the start voltage, and the gap between the highest and lowest cell is larger than the trigger. For LFP, a start voltage around 3.40 V and a trigger of 0.005 to 0.01 V is a good starting point.

How the JK active balancer decides to act

The JK balancer is active, not passive. It moves energy from the highest cell to the lowest instead of burning it as heat. Two conditions must both be true before it moves anything:

• A cell is above Start balance voltage.
• The difference between the highest and lowest cell is larger than Balance trigger voltage.

It keeps working until the difference drops below the trigger. Max balance current is the ceiling for how much current it moves between cells. The Balancer switch turns the whole function on or off.

The four parameters

Balancer (switch)

This enables the active balancer. Keep it on. The editor help says to combine it with a sensible start voltage so it does not work on the flat part of the curve.

Start balance voltage

Balancing runs only above this cell voltage. Keep it below Cell RCV, otherwise the cells never reach it. The editor also warns when Start balance voltage is not below Cell RCV.

Balance trigger voltage

This is the cell difference that starts balancing, and it also stops balancing when the difference falls below it. 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.

Max balance current

The highest current the balancer moves between cells. Match it to the hardware: 2 A on PB2A boards, 1 A on PB1A boards.

Why LFP should balance only near the top

An LFP cell has a long, flat voltage curve. Between roughly 10% and 90% state of charge the voltage barely changes, so a 20 mV gap there says almost nothing about the real charge difference. Real differences show up at the top knee, where voltage rises fast.

If Start balance voltage is too low, say below about 3.35 V, the balancer works on the plateau. It wastes energy moving charge based on noise. Worse, it can move charge the wrong way and push the pack further out of balance. Starting at 3.40 V keeps balancing in the part of the curve where voltage tells the truth.

This is also why RCV time matters. If charging ends before the cells spend time above the start voltage, the balancer has no window to work. See JK BMS settings for LiFePO4 for the full voltage set. Unbalanced cells also make the SOC reset early, which is covered in JK BMS SOC calibration.

JK BMS balance settings by chemistry

Ranges come from the recommendations in the editor. The NMC and LTO start voltages are less well sourced than the LFP ones, so treat them as a starting point and check your cell datasheet.

The gentle LFP preset tightens the trigger to 0.005 V. The presets never change Max balance current, so set it to match your board. You can see all levels on the presets page.

JK BMS balance not turning on

Check these in order:

1. Balancer switch is off. Open the settings and confirm it is enabled.
2. All cells are below Start balance voltage. A pack resting at 3.30 V will not balance with a 3.40 V start. Charge higher or lower the start voltage within the range above.
3. The difference is below Balance trigger voltage. If the cells differ by 4 mV and the trigger is 5 mV, there is nothing to do. That is normal.
4. Start voltage is above what the pack reaches. If Cell RCV or the charger stops below the start voltage, the balancer never starts.

There is no separate "balance only while charging" flag among the fields this editor reads, so the four parameters above are the full balance set.

To tell imbalance from a charger setpoint problem, load the Detail Log on the log analysis page. Read finding a weak cell in the log to see how a lagging cell looks in the data, and why cell overcharge protection keeps tripping for trips caused by a charger set above cells × Cell OVP.

Common mistakes

• Setting the start voltage on the LFP plateau to "balance all the time".
• Setting the trigger very low and chasing noise.
• Trusting cell differences when wire resistance is off. A bad balance lead gives wrong readings, and the BMS then balances a gap that is not real. Healthy leads read about 0.045 to 0.055 Ω. See JK BMS wire resistance.

What is a good balance trigger voltage for JK BMS?

For LFP, 0.005 to 0.01 V. Use 0.005 V for cells over 50 Ah and 0.01 V for smaller ones.

Does a higher balance current balance faster?

Yes, up to the hardware limit. Do not set more than the board supports: 2 A on PB2A, 1 A on PB1A.

Should the balancer always be on?

For most packs, yes. Keep the switch on and control when it works with the start voltage. For every other field, see JK BMS parameters explained.

Connect your BMS or open your .jkcfg in the editor to check the balance values, or start from a ready preset.