Here is how I implemented a Low voltage cutoff for my solar battery bank. This feature is used to turn on an emergency charger to replenish the batteries should they deplete before sunrise.
This charger is already installed and controlled by my Home Assistant but due to certain issues with the USB ports, a Windows restart makes the charger come on without reason. A hardware based control will remove this nuisance behavior for me.
Step 1: The Outback Fm80 Auxiliary Output.
My fm80 charge controller has a spare output that provides 12v to control any low powered relay.
Basically the aux menu is selected and the auto feature for low batt disconnect is used.
Step 2: The Settings.
I want the emergency charger on when the battery drops below 22.5v and off when it rises to 25v.
Step 3: Interface Relay.
I used a standard automotive relay to interface the outback fm80 auxiliary output. This relay will be powered continuously until the low voltage condition is reached.
Step 4: Accessing the Auxiliary Output.
The access panel needs to come off and the terminals for the auxiliary output are shown in the last pic. They are snap type terminals with the levers up to access the terminals themselves.
Step 5: Wiring in the Interface Relay.
The relay coil leads I plugged into the auxiliary output. The common of the relay contacts I wired to the negative of the battery terminals and the NO I tied to a wire leading into my automation cabinet.
Step 6: The Emergency Charger.
This 5amp charger I have as part of my home automation system. Now the outback fm80 auxiliary output will control turning on this charger.
Step 7: The Wiring of the Interface Relay to the Charger Controls.
This relay card is part of the remote IO interface of my home automation system. Two relays turn on power to the emergency charger. I tied the wire from the interface relay inside the fm80 to the inputs of these 2 relays on the automation relay card.
Step 8: A Little Insulation.
I put Liquid tape onto the exposed wires.
Step 9: Completion!
Now my solar power system has a hardware based emergency charger. My home automation system will now only visually on the gui and verbally annunciate that the emergency charger is on.