Backup Power Fail switch and leads
Backup Power Switch, .
While there is 240 volt power the relay is held open and no 12 volt power flows to the 12 volt water or air pump.
When 240 volt goes off the relay closes and 12 volt power flows through from 12 volt battery to the aeration device.
The instant the 240 volt goes off the 12 volt system will start, and the instant 240 volt mains power is restored the 12 volt system switches off.
My choice of aeration device is a 12 volt marine bilge pump sending water through a small upright with a defuser spray head at the top creating a waterfall effect thereby breaking the water surface and providing very effective aeration of the fish tank.
The device will also switch a second pump in the sump to clear water back to the fish tank.
This function makes it worthwhile to set up this system. If the mains power fails and there is still a large volume of water in the grow beds that will continue to drain into the sump. A 12 volt sump pump is very necessary to move this water back to the Fish tank, otherwise the sump will overflow and precious water will be lost.
The bigger the battery the longer the standby pump/device will run. The size of the battery is important.
The purpose of this system is to hold the fish tank aerated for an hour or two, as a safety device if power went out due to a storm or a car hitting a power pole etc, during the night or while you are at work.
I have learned the hard way the effects of no areation for very short periods of time, especially with high density fish stocking in aquaponic systems.
If there was a long term power outage due to a cyclone or similar, that would have the power out for several hours, or a day or more then you would only expect this device to aerate the fish tank until one could get a 240 volt generator set into place to run your normal pumps etc
To run a small 12 volt water pump, say 500 gph, a battery costing around 100.00 would run such a pump for 5 or 6 hours, more battery = more running time.
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