A Battery Management System monitors and protects a lithium cell pack by controlling charge and discharge current, balancing cell voltages, and reporting battery status in real time. Daly BMS manufactures a range of protection boards — the HKMS series — that span five current tiers from 40A up to 800A. Each tier is built around a specific application class. This guide explains how to match the right model to your pack.
What 'Smart BMS' Means in Practice
A smart BMS differs from a basic protection board in one key way: its protection thresholds, SOC parameters, and communication settings can be adjusted in the field using a PC tool or mobile app. This means one board model can serve multiple pack configurations without hardware changes. All five Daly HKMS series models are software-configurable. All support three battery chemistries — NMC, LFP, and LTO — with chemistry-specific thresholds set before the board goes into service.
H Series vs K Series: The Key Difference
The H series supports up to 16S at 60A, has no pre-charge function, and has one UART channel. The K series supports up to 24S at 100A, includes a pre-charge circuit and integrated parallel current-limiting module, and has two UART channels. If your motor controller has a large input capacitor bank above 22,000µF, the pre-charge function in the K series is essential to prevent inrush current from tripping protection on connection.
Communication Interfaces
All HKMS models include UART as standard. The full-feature variant adds RS485 and CAN simultaneously. Key operating figures:
- Cell voltage sampling: every 200ms
- Temperature sampling: every 500ms
- RS485 protocol: Modbus RTU — slave address increments from 0x81 for multi-board parallel systems
- Scheduled wake-up in sleep: every 6 hours; 30-second active window, returns to sleep if no activity
Thermal Runaway Detection
All HKMS models run thermal runaway detection continuously. Protection triggers if any of the following conditions occur:
- Cell voltage drops ≥0.1V/s for 3 consecutive seconds AND temperature rises ≥5°C per 2 seconds
- Cell voltage drops ≥0.2V/s for 3 consecutive seconds AND temperature rises ≥10°C per 2 seconds
- Cell temperature exceeds 70°C AND temperature is rising ≥10°C per 2 seconds
On trigger: both charge and discharge MOSFETs open immediately; buzzer activates if connected. BMS must be manually restarted before the pack can resume operation.
5-Step Selection Checklist
1. Confirm cell chemistry (NMC / LFP / LTO) — determines all voltage thresholds
2. Count cells in series — BMS series count must match exactly
3. Identify maximum continuous current — select BMS rated at least 20% above this
4. Decide on communication interface (UART only, or UART + RS485 + CAN)
5. Verify B–P cable gauge against the table above
Frequently Asked Questions
Q: Can one HKMS board serve both NMC and LFP cell types?
A: Not simultaneously. Each chemistry needs its own threshold configuration. Switching chemistry requires reconfiguration via PC software.
Q: What is the standby current consumption?
A: In sleep mode, HKMS boards draw less than 900µA. No deep-sleep mode with complete MCU power-down is available. Minimum sleep interval is 10 seconds.
Q: How many packs can run in parallel?
A: K, M, S, and D series have a built-in parallel current-limiting module. Default firmware supports 8 packs in parallel; up to 16 with a firmware customization request.
Q: Bluetooth connects but shows no data — what is happening?
A: This typically occurs when the BMS is in undervoltage sleep mode. The UART port 3.3V supply stays active so Bluetooth can still broadcast, but the MCU is off. Charge the pack to bring the BMS out of sleep, then reconnect.
Q: Does the H series support an external pre-charge resistor?
A: No. The H series has no pre-charge circuit — internal or external. Applications with large capacitive loads should use the K series.
Post time: Apr-06-2026
