by Filip Kemp.

Basically this unit will switch on/off anything that is 240vAC that is plugged into it. For example, I am using it to switch off my sump return pump if my main tank if it is about to overflow. This is done by having the float switch on the lip of the main tank and when the water rises the float goes up and switches off the power to relay, which inturn switches off the pump. This is done safely with no 240vac in contact with water due to using the relay, which can be power by any simple 4-32vDC power supply (I used a mobile phone recharger). The relay will also never fail as it uses no mechanical parts to switch the 240v line (which also means its completely silent!).

Diagram of the water level switch.

A couple of notes:

• The relay needs to have 240vAC load running through it otherwise it wont work. I have tested for conductivity while just powering it using 4vDC and it didn't work. Once I put 240vAC load onto it, it worked fine.
• The float switch can be reversed so that it switches on when it rises by flipping the float around. There is just a small circlip on the bottom that you pull off, then flip the float, then put back on. Takes 5 seconds!
• I enclosed the relay and all connections in a plastic box from Jaycar. Worthwhile keeping it all neat and away from water.
• You can use a horizontal type float switch instead of the vertical one.

The relay can be found at Jaycar. Search for "solid state relay" or "SY4080".

The float switch can be found at RS Components. Search for 331-017 or "float switch".

Everything else can be found at Jaycar's or Dick Smith etc.

PS Mine has stopped my tank from flooding about 3-4 times now.

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