Battery A battery management system (BMS) sits between the cells and everything else. It cuts the pack off before any cell is overcharged, over-discharged, overheated or shorted, and it keeps the cells at the same voltage so the whole pack can be used. Choosing one comes down to three numbers: how many cells are in series, how many amps you will draw, and whether the battery has to talk to an inverter.
1. Match the string count
“S” is the number of cells in series. The BMS must support the exact count in your pack, because it has one sense wire per cell.
| Battery | LiFePO4 cells in series | Nominal / full charge | Lithium-ion cells in series | Nominal / full charge |
|---|---|---|---|---|
| 12V | 4S | 12.8V / 14.6V | 3S | 11.1V / 12.6V |
| 24V | 8S | 25.6V / 29.2V | 7S | 25.9V / 29.4V |
| 36V | 12S | 38.4V / 43.8V | 10S | 37V / 42V |
| 48V | 16S | 51.2V / 58.4V | 13S | 48.1V / 54.6V |
| 60V | 20S | 64V / 73V | 16S | 59.2V / 67.2V |
| 72V | 24S | 76.8V / 87.6V | 20S | 74V / 84V |
A JK BMS listed as 4S–8S covers both 12V and 24V LiFePO4 packs. A 16S model covers 48V. For 60V and 72V bikes, look at the 24S models.
2. Work out the amps
Divide the biggest load in watts by the pack’s nominal voltage, then leave about a quarter of headroom.
| Load | Battery | Current drawn | BMS to choose |
|---|---|---|---|
| 1000W inverter | 12V (12.8V) | about 78A | 100A |
| 2000W inverter | 24V (25.6V) | about 78A | 100A |
| 3000W inverter | 48V (51.2V) | about 59A | 100A |
| 5000W inverter | 48V (51.2V) | about 98A | 150A |
| 1500W e-bike motor | 72V (76.8V) | about 20A | 40A–60A |
The charge current counts too. If your inverter or charger can push 100A into the battery, the BMS has to accept 100A.
3. Smart BMS or Inverter BMS
- JK Smart BMS has Bluetooth, so you read every cell voltage in the phone app. It suits e-bikes, 12V and 24V packs, and any battery that works on its own. See the JK BMS 4S–8S 60A–100A and the 24S 60A–100A.
- JK Inverter BMS (PB series) adds RS485 and CAN, the links a hybrid solar inverter uses to read the battery’s state of charge. Choose it for 24V and 48V home batteries. See the JK-PB1A16S10P 100A and the JK-PB1A16S15P 150A.
4. Check the balancing current
JK boards use active balancing, which moves charge from the highest cell to the lowest. The balancing current runs from 0.4A on small models to 2A on the large Inverter BMS. Big cells need more: a 0.4A balancer is fine for a 15Ah bike pack and slow on a 280Ah or 314Ah home battery.
5. Set the chemistry before first use
JK BMS supports lithium-ion, LiFePO4 and LTO. Set the cell type and cell count in the app before you connect a load or charger, because each chemistry has different voltage limits.
Not sure which model fits? Send us your cell type, number of cells and inverter or motor size on WhatsApp at 0332 9891510 and we will suggest one. Browse all JK BMS and balancers.