Battery Backup in Aquaponics

One thing most people don’t take into account when running an aquaponics system is – power failure. It often strikes when people least expect it. Many experienced aquaponics people will tell you the following tale. Their system was running perfectly for over a year. The fish were ready to harvest. Around Christmas, relatives came to visit and over the course of the day, the kids were looking at the fish and one of the children pulled the power cord out of the mains that was supplying the main pump in the aquaponics system. No one noticed that the fish had all died until the next morning.

A battery backup system in Aquaponics

A battery backup system in Aquaponics

Sometimes people do it foolishly themselves. They need the power to run a drill or circular saw on the weekend. Finish their project and forget to plug the aquaponics system back into the mains. The aerator is switched off and no oxygen to a tank full of fish means the end to a dream – very quickly. It can happen to us all.

Thats why battery backup systems are a wise investment. You will never appreciate having a battery back up system installed – until the night of a storm and the power gets suddenly turned off. You can see it in action in Fig.1 squirting a stream of water into the fish tank.

A small 12 volt bilge pump keep the water in the fish tank circulating and splashing the surface. Dissolved oxygen gets returned back into the water and the fish are able to survive – for as long as the little bilge pump is able to function.

So how does the 12v pump spring into action in the event of a mains power failure?

You will notice in Figure 3 we have a 12v car battery and behind it a small box or backup power fail switch with a relay 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  or bilge pump device. The instant the mains power goes off the 12 volt system will start, and the instant 240 volt mains power is restored the 12 volt system switches off. Very simple.

Battery’s do lose their charge over time. We’ve made a modification to the backup system by fitting a very inexpensive 5 Watt solar panel to trickle charge the 12v battery every day and keep it fully charged. You can buy a small solar panel for charging battery’s with clamps on ebay for around $60. We’ve noticed from hard experience that unless you  recharge the battery regularly, come the day there is a power failure – the battery may not have a sufficient charge to do the job properly. Our old battery ran out of grunt after 2 hours. Not long enough for our liking.

With a little solar charger constantly trickle charging the battery for only an hour a day – we’ve found its enough to keep the system full charged and able to keep the system running all night if the need arises.

There is no need to mount the solar panel in full sun all day. You don’t want to to over charge the battery and risk boiling it dry. We have positioned our panel on the western wall of the house so it only captures an hours sun at sunset. That seems to be more than enough to keep the batter charged at 13.9 volts which is fully charged and more than enough to do the job. A inexpensive multimeter Fig 4 is also a good investment to reassure yourself that any backup system you have installed is functioning properly and at full capacity.

But the best investment for ease of mind is a portable petrol generator. Fig 6 Keeping a aquaponics system running is only as good as your backup plan.  You might be lucky and never experience a power outage. But if you ever do notice that the lights are suddenly out or something has tripped the mains – only then will you suddenly wish you had installed a backup plan.