How to Choose the Right BMS
How to Choose the Right BMS?
1. Continuous current
Continuous current is the current the BMS can support continuously during charging and discharging. The rated or nominal current refers to this continuous current value. For example, a 200A BMS supports continuous charge and discharge current up to 200A under its specified operating conditions.
Choose a BMS with a continuous current rating that meets your maximum continuous battery current. Check the exact model's specifications, installation conditions and the limits of your cells, cables and other components. Allow for your project's operating conditions rather than applying a fixed margin to every system.
2. Instantaneous current
Instantaneous current refers to brief current demand, such as during equipment startup. It may also be described as startup surge or inrush current.
All JKBMS protection boards have an instantaneous current protection threshold, generally calculated at 1.5–2 times the rated or nominal continuous current. For a 200A BMS, the corresponding protection threshold is generally around 300–400A.
This threshold is not a continuous operating current rating. Confirm the exact model's instantaneous current protection threshold and protection delay against your equipment's startup current and duration. Do not assume that every board permits the same duration or three times its continuous current.
Supported Cell Count & Available Current Ratings by Series
B & BD Series
| Cell Count | Available Protection Current |
|---|---|
| 8S (3S–8S for B series; BD4A also starts from 3S) | 40A / 60A / 80A / 100A / 150A / 200A / 300A |
| 17S | 40A / 60A / 80A |
| 20S | 40A / 60A / 80A / 100A / 120A / 150A / 200A |
| 24S | 40A / 60A / 80A / 100A / 120A / 150A / 200A / 300A |
PB Series (Inverter BMS)
| Cell Count | Available Protection Current |
|---|---|
| 8S – 16S (24V – 48V) | 100A / 150A / 200A / 300A |
📖 For a full product selection guide, please refer to our JKBMS Product Selection Manual.
Battery Connection Methods
- Series Connection: Total pack current = single cell current. Current is identical throughout a series circuit.
- Parallel Connection: Total pack current = single cell current × number of parallel cells.
- Series-Parallel Combination: Total pack current = single cell current × number of parallel cells per block.
Example — A 20S Battery Pack with 3 Parallel Cells per Block
For a battery pack built with 20 cells in series and 3 cells in parallel per block:
- 3 parallel cells per block means the pack current = single cell current × 3, assuming equal current sharing.
- If each cell delivers 20A, total pack current = 20A × 3 = 60A under that assumption.
- Select a BMS whose continuous current rating meets the actual continuous load, with installation conditions and component limits checked.
- Check startup demand separately against the model's instantaneous current protection threshold and delay; do not use instantaneous current as a continuous rating.
BMS Selection by Protection Current
| Protection Current | Typical Use Case | Common Applications |
|---|---|---|
| 40A | Light load | Small e-bikes, electric scooters, portable power stations |
| 60A | Light to medium load | E-bikes, electric skateboards, backup power systems |
| 80A | Medium load | High-performance e-bikes, energy storage systems |
| 100A | Medium to high load | Electric vehicles, industrial battery packs |
| 120A | High load | High-voltage e-bikes, EVs, large energy storage |
| 150A | High load | Large EVs, commercial energy storage |
| 200A | Very high load | Heavy-duty EVs, large-scale energy storage |
| 300A | Ultra high load | Industrial-grade systems, large battery arrays |
How to Choose the Right Balancing Current
Balancing current is separate from the BMS's continuous charge/discharge current. Check the active-balancing specification and operating conditions of the exact model.
Larger Batteries: Consider Higher Balancing Current
As battery capacity increases, we recommend considering a higher balancing current. Otherwise, balancing will take longer. For a comparable relative imbalance, a larger-capacity battery requires more charge to be redistributed. A lower balancing current takes more time to move that charge.
A higher balancing current can shorten the time needed to correct an imbalance when balancing is active. Choose among the available balancing options based on battery capacity, cell condition, the amount of imbalance and the time available for balancing, alongside the exact model's specifications.
Practical Selection Checks
- Compare the balancing-current ratings of the exact BMS models you are considering.
- For larger-capacity batteries, favour a higher balancing-current option when a shorter balancing time is needed.
- Do not treat 1A as universally optimal for a 280Ah battery, or use a fixed capacity range as a guarantee that a particular balancing current is sufficient.
- Check the model's balancing activation conditions and chemistry-specific settings. Actual balancing time depends on both the charge imbalance and the effective balancing current.
- If imbalance persists, investigate the cells and wiring rather than assuming a higher balancing current will resolve every issue.
For help choosing, provide your cell model, chemistry, capacity, pack configuration and observed cell readings to technical support.
Connecting to an Inverter? Read This First
If you plan to connect your BMS to an inverter for off-grid solar systems or home energy storage (ESS), please note the following:
- B/BD HC and HCRPB versions can use the optional P-LINK module for soft parallel expansion. P-LINK is not restricted to HCRPB and does not require the HCRPB hard-parallel interface as its defining prerequisite. Confirm the cable and setup for your exact BMS and P-LINK model.
- P-LINK and the Parallel Module are different accessories. The Parallel Module requires a board with the corresponding Parallel Module Interface. Do not use hard-parallel module requirements to decide P-LINK compatibility.
- The PB-series Inverter BMS includes CAN and RS485 for inverter integration. P-LINK is not applicable to PB boards; use the PB-specific interface documentation.
- Inverter compatibility must be checked for the exact BMS version, inverter model, protocol, firmware and cable pinout. A CAN or RS485 port alone does not guarantee a working pairing.
Supported Inverter Brands & Protocols
The following is the existing protocol-reference list, not a verified compatibility matrix for every inverter model. Confirm every protocol, communication setting and menu instruction against the exact inverter and BMS manuals before use. If your inverter is not listed, please contact technical support.
| Brand | Protocol | Communication | Notes |
|---|---|---|---|
| Deye | Low-voltage hybrid inverter CAN protocol | CANBUS-500K | Battery Setup Menu → Lithium; Advanced Function → BMS_Err_Stop |
| PYLON | PYLON CANBUS Protocol V1.2 / Low voltage RS485 | CANBUS-500K / RS485-9600 | — |
| Growatt | CAN Bus REV_05 / RS485 ESS Protocol V2.01 | CANBUS-500K / RS485-9600 | Set 05 to LI; Set 36 to 1 for CAN or 51 for RS485 |
| Victron | CAB-BUS BMS Protocol 201707 | CANBUS-500K | Via Cerbo GX |
| INVT | CAN Bus Protocol V1.02 | CANBUS-500K | BD5KTL-RL1 |
| GoodWe | LV BMS Protocol V1.7 | CANBUS-500K | GW5000-ES-20; Select GoodWe → SECU-A5.4L×1 |
| SMA | FSS-ConnectingBat-TI-en-10 V1.0 | CANBUS-500K | — |
| Voltronic | Voltronic Power Inverter & BMS 485 Protocol V0 | RS485-9600 | Long press SET → Set 05 to LIB |
| SRNE | PACE BMS Modbus Protocol for RS485 | RS485-9600 | Set 39 to BMS; Set 32 to BMS; Set 33 to WOW |
| MUST | — | — | — |
| SOFAR | — | — | — |
For a compatibility enquiry, provide the exact BMS and inverter models, hardware and firmware versions, and intended CAN or RS485 connection to technical support.
Parallel & Series Expansion Limits
Parallel Expansion
- Confirm the supported pack count and wiring for your exact board, firmware and system. Do not apply one universal parallel-unit limit to every JKBMS series.
- B/BD HC and HCRPB can use P-LINK for soft parallel expansion. The separate Parallel Module requires the corresponding Parallel Module Interface. PB parallel systems use PB-specific connections and do not use P-LINK.
Series Expansion (Custom Order Only)
Series connection of multiple BMS units is available as a custom order, limited to 8S protection boards only:
| System Voltage | Max Units in Series | Notes |
|---|---|---|
| 12V system | Up to 6 units | Custom order only; 8S boards only |
| 24V system | Up to 3 units | Custom order only; 8S boards only |
⚠️ Series expansion is not available as a standard product. Please contact us to discuss custom requirements.
BMS Wiring Diagrams
BD & B Series BMS Wiring Diagram
PB Series Inverter BMS Wiring Diagram
LCD Display Selection Guide
JKBMS offers optional LCD displays for real-time monitoring of cell voltages, SOC, current, temperature, and protection status. Display compatibility differs between BMS series — please confirm your BMS model before ordering.
B & BD Series — Standard LCD Displays
The B series and BD series Smart BMS are compatible with the following standard LCD displays:
| Model | Screen Size | Compatible Series |
|---|---|---|
| JK-LCD20 | 2.0 inch | B series, BD series only |
| JK-LCD32 | 3.2 inch | B series, BD series only |
| JK-LCD43 | 4.3 inch | B series, BD series only |
PB Series (Inverter BMS) — Dedicated Displays Only
The PB series Inverter BMS requires a dedicated display and is not compatible with the standard B/BD series LCD displays above.
| Model | Screen Size | Compatible Series |
|---|---|---|
| JK-LCD43-TTL-P | 4.3 inch | PB series only |
| JK-LCD-7.0-TTL-P | 7.0 inch | PB series only |
⚠️ Important Compatibility Warning:
- ❌ PB series displays (JK-LCD43-TTL-P, JK-LCD-7.0-TTL-P) cannot be used on B or BD series BMS.
- ❌ B/BD series displays (JK-LCD20, JK-LCD32, JK-LCD43) cannot be used on PB series Inverter BMS.
- ✅ Always purchase the display model that matches your specific BMS series.
PC Software Monitoring (Upper Computer Connection)
B & BD Series — USB-TTL Module via GPS Port
- Use a USB-TTL module connected to the protection board's GPS port for B/BD PC-software communication.
- Follow the model-specific PC-software documentation for available monitoring and parameter functions.
- B/BD displays use matching RS485 display models. Do not confuse the GPS PC connection with the display connection.
- Solar Assistant support must be confirmed for the exact BMS, adapter, protocol and software version; PC connectivity alone does not establish monitoring-software compatibility.
PB Series — USB-RS485 Cable via RS485 Port
- Use a USB-RS485 cable connected to the RS485 port on the separate interface board for PB PC-software communication.
- PB UART and display connectors are on the protection board and serve the display function, not PC-software communication.
- The PB PC connection does not use the B/BD USB-TTL cable; the two cable types are not interchangeable.
Standard Features (All JKBMS Smart BMS)
- ✅ Bluetooth status indicator
- ✅ APP Bluetooth remote operation & monitoring
- ✅ Battery capacity calculation (SOC)
- ✅ High-precision voltage acquisition (±3mV)
- ✅ High-precision current acquisition
- ✅ LCD display interface support
- ✅ Accurate time logging
Protection Features
- ✅ Charge overcurrent protection
- ✅ Charge overvoltage protection
- ✅ Charge over-temperature protection
- ✅ Low-temperature protection during charging
- ✅ Discharge overcurrent protection
- ✅ Discharge undervoltage protection
- ✅ Discharge over-temperature protection
- ✅ Short-circuit protection
Optional Add-ons (Smart BMS only — not applicable to Inverter BMS)
- ✅ RS485 communication
- ✅ CAN communication
- ✅ Parallel expansion function
- ✅ Alarm function
- ✅ Heating function
- ✅ ACC detection function
- ✅ LCD display — JK-LCD20 / JK-LCD32 / JK-LCD43 (B & BD series only)
- ✅ USB-TTL module for PC monitoring via GPS port (B & BD series only)
JKBMS Inverter BMS — Fully Integrated Features
- ✅ Active cell balancing
- ✅ Bluetooth connectivity
- ✅ NTC temperature sensing
- ✅ RS485 communication
- ✅ CAN communication
- ✅ Display interface (JK-LCD43-TTL-P or JK-LCD-7.0-TTL-P)
- ✅ Heating function
- ✅ Dry contact (alarm output)
- ✅ Charge overvoltage protection
- ✅ Overcurrent protection
- ✅ Short-circuit protection
- ✅ Battery parallel current limiting
- ✅ Discharge pre-charge
- ✅ PC monitoring via USB-RS485 cable
Related Selection and Technical Guides
Use the JKBMS Technical Hub to find model-specific resources. For interface selection, compare the B/BD interface guide and PB interface guide. For parallel accessories, see the P-LINK soft parallel guide. Download exact-model documentation from the Download Center.
Need Help? Contact Us
If you have any questions about BMS selection, compatibility, or your specific application, our team is happy to help!
- 📧 Email: service@jkbms-ess.com
- 💬 WhatsApp: +1 818 938 3175
Need help choosing? Contact us with your battery specs and we will recommend the right model.