I want a box that reads the battery voltage and has a simple mechanism to program it. It accepts and puts out 120v. Just like an appliance timer, but can also be programmed to turn on/off depending on battery power.
Such a device could be used to consume excess solar power (like powering grow lights when your batteries are full, and shuts them off again if clouds move in and voltage drops), and also knows what time it is, so won't deplete your batteries at night when there is no solar power. In this scenario it would be plugged into an inverter.
Alternatively, such a device could be programmed to turn something on when power is low, and turn it off when it gets to a certain level (like a battery charger). In this scenario it would be plugged into the grid, generator, or other non-solar power source.
I can buy an appliance timer for $5. But I can't buy an appliance timer with voltage detection at any price.
Cheap, easy to program, and battery backup. Along with the items I mentioned before, I use it to control when my loads power up, based on expected average solar capture performance. I also use these devices to control switching back and forth between my Lycan PowerBox and my other inverter. The switching is so fast, my computers don't notice (I have them connected via CyberPower UPS).
So, to summarize, I use the voltage sensing switches to prevent my batteries from being drawn down below 40 - 50%, and to signal the inverter when to make power available to the load. Then the timers are set to connect the load during certain times of the day, or to decide which inverter is being used. This has allowed me to build my system in stages, and make it work as though it were a single bigger system.