This wiring example shows how to connect a GRNbms MK3 system in a low-voltage setup, using three relays and a precharge resistor.
It is intended for 12 V or 24 V systems and uses the „Jump Start“ 12 V input for powering the BMS.

LV Relay Wiring Diagram

HV Battery: Supplies the low-voltage system (e.g. 12 V / 24 V)

Fuse: Protects the entire system from overcurrent

HV Relay Precharge: Routes current through the precharge resistor to limit inrush

HV Relay Positive: Connects main power after precharge

HV Relay Negative: Closes the negative path to the load

Precharge Resistor: Limits inrush current to the inverter during startup

Current Shunt: Measures current flowing to the inverter

Inverter: The main load (can be any DC consumer)

Jump Start Input: Powers the BMS directly with 12 V via GND / 12 V input pins

Connect 12 V to the Jump Start input on the BMS

The BMS uses this input to power itself – no high voltage required

The BMS controls all three relays directly via its outputs:

Precharge relay closes briefly to limit inrush

Positive and Negative relays close after precharge completes

The BMS monitors all timing and status automatically

Termination resistor and CAN wiring must still be set correctly

Precharge path must include the shunt to allow current monitoring during startup

This wiring is intended for LV systems only – use HV wiring for 150–1200 V setups

🔥 Always follow safety guidelines and consult a professional installer.
Incorrect wiring can cause damage, malfunction, or fire. Use at your own risk.