This optional battery contactor arrangement can be fitted as part of the 4QD-200/300 installation to provide reverse polarity protection and also an emergency power disconnection.
The relay should be chosen so that it is capable of carrying the expected motor current.
The relay coil is fed from the ignition switch connector. A 470ohm, 2 watt resistor should be fitted across the relay contact to pre-charge the main capacitors in the controller.
When the battery is connected, current flows through the resistor to charge up the main capacitors. When the ignition is switched on, the capacitors are connected across the relay coil which pulls in, shorting out the resistor. If the battery is reversed the MOSFETs in the controller short out the capacitors so they do not charge up and the relay cannot operate. The fault current is limited by the resistor to a safe value.