I needed a low voltage disconnect to disconnect my loads from the battery when the battery voltage drops below a predetermined level. This is a hybrid relay, as I put a MOSFET in parallel with the relay contacts. The Arduino turns on the MOSFET, then the relay. On shutdown, it deactivates the relay, then the MOSFET. This does two things:
1. Prevents arcing (welding) of the relay contacts
2. Prevents over heating of the MOSFET
This could also be used as a solar / wind dump load controller, turning on a water or air heating element when the battery voltage exceeds maximum, and turning it off when the battery voltage returns to normal.