Below is the recommended HV wiring setup for systems using 3 relays and precharge functionality:

• 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 -) to GND
• 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 (E pin): Must be connected to battery chassis – ideally with 2 separate wires

• 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.

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

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

✅ Just plug in your relays – the BMS handles power and timing automatically