High Voltage Relay Wiring – with Precharge
⚠️ Disclaimer – Safety First!
The wiring diagrams and connection examples provided here are suggestions only and may not cover all edge cases or safety requirements.
All high-voltage components must be installed and verified by a qualified electrician or professional installer.
Incorrect wiring or misuse can lead to severe damage, fire, or personal injury.
The manufacturer assumes no liability for damages resulting from improper installation or handling.
Below is the recommended HV wiring setup for systems using 3 relays and precharge functionality:
🧩 Components:
- HV Battery: Provides the main power
- HV Fuse: Protects the system from overcurrent
- HV Relays (3 total):
- Precharge Relay: Connects via precharge resistor to slowly charge input capacitors
- Positive Relay: Main high-side connection to the load
- Negative Relay: Switches the low side (Battery -)
- Precharge Resistor: Limits inrush current when first connecting to the inverter
- Current Shunt: Measures total current flow
- Inverter / Load: Final consumer of the HV power
- Chassis connection (
Epin): Must be connected to battery chassis – ideally with 2 separate wires
🔌 BMS HV Connector Pins:
- B+ / B-: Connect directly to the battery
- O+ / O-: Connected after the relays, represents the output side
- E: Earth/Chassis connection
⚠️ Important: The precharge path must always lead through the shunt to ensure current measurement during precharge. The positive and negative relays must remain open during precharge phase and close only after precharge completes.
👉 This wiring ensures proper current monitoring and safe soft-start of the system.
Relay Control
The GRNbms MK3 directly controls all three HV relays using integrated 12 V outputs.
Each relay is connected via its dedicated connector:
- HV Relay Positive
- HV Relay Negative
- HV Relay Precharge
Requirements:
- Relays must have a 12 V coil
- No external power supply is needed – the BMS provides the 12 V directly
- Each output is internally protected and current-limited
👉 We recommend using relays with economizer to avoid unnecessary load on the BMS power supply
✅ Just plug in your relays – the BMS handles power and timing automatically