www.goanna.com

We are going to be using aquaponics to grow a large part of our veggies so I want to get cracking with building the system.  The only problem is that there is no point building the system until we have moved!  In order to satisfy my desire to get started I decided to build some of the small components & take them with us.  First off the rank is the relay setup to switch on our battery backup system if the power fails.  Basically the fish in an aquaponics system need oxygen created by constant water movement and aeration.  As this is acheived by electric pumps, no electricity = dead fish.  To overcome this you run a simple 12v pump off a car battery to cover those times when the mains are kaput!  As I only want the 12v system to work when there is no power I need a reliable way to switch it on when the power goes off.  Luckily it's pretty cheap and simple to build one.  My main considerations were; safety, minimum of moving parts, easy to test, no 240v being mixed with the 12v, ease of installation and some sort of visual indication that the power is off.  The devices I have seen tend to use a 240 relay to switch the 12v side of things.  Being a sparkie I'm always wary of mixing 240v with water so I decided to go down a different path.  I, and no doubt many of you, have a heap of now redundant plug pack power supplies from old phones, appliances etc.  As many of these are 12 volt I decided to use one of these to power my unit. Whilst it does add another point of failure to the system, it does recycle the supply which means there is no 240v within cooee of your relay unit.  An additional advantage of this approach means that pretty much anyone in the world can build one of these and recycle a plugpack with their local plug configuration.

So a quick trip to Jaycar got me most of the bits I needed, I'm sure a bit of shopping around would find far cheaper components.  For my unit I purchased:

LA5302 Strobe Light (29.95)

HP0742 Cable Glands (5.45)

HB6126 Enclosure (12.95)

SP0717 Pushbutton Switch (1.95)

SY4074 12v Horn Relay (12.95)

PT4562 Battery Lugs (2.95)

I also had in my shed the necessary plugpack in-line female socket, 12v cable, solder, soldering iron, drill & drill bits required to do the job.

The first job was to mark the enclosure so I could drill the holes required for the strobe lamp, switch and the two cable glands.

The next step was to drill out the marked holes, I won't bore you with pictures of me drilling, here's the finished case after drilling.

Then I installed the test switch & strobe on the case along with the cable glands.

Stay tuned for part two!  Until then here's a quick version of the circuit I'm going to use.