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I designed an automatic switch that turns on an inverter and switches over power to the air and water pumps in the case of a power outage. An alarm is played as well to notify any in the area that there is an issue with the power that needs to be solved.
All this was done with a 3 pole double throw relay, an 400W inverter from the auto store, a float charger to make sure our batteries are always charged, a pickup truck backup beeper, and some miscellaneous wires and connectors. All told, the unit was about $250 including a 120Ah deep cycle marine battery which should give us about 10 hours of backup time. More batteries can be added in parallel for longer run time.
Click on the schematic picture for a detailed PDF of the schematics. If you're going to do this yourself, make sure you know what you're doing with high voltage electricity. Needless to say, you could hurt or kill yourself working with 120V power. Make sure all connectors are insulated, that wires are strain releived, put dielectric grease on the connectors if you're in a corrosive environment like we are here near the ocean.
Where do you get all this stuff?
The relay was from Mc Master Carr Company part # 70315K33 for $14.12
2A Float Charger I got on Amazon for like $15
The Inverter and backup beeper, I got from JC Whitney for $14 and $49 respectively.
The enclosure and Terminal blocks I got from Home Depot
We used an Interstate Deep Cycle Marine Battery group size 29 with 115Ah