Backyard Aquaponics
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Yeah, they're great. I've been buying stuff online from them for years. The other good one in Aust (Sydney I believe) is www.oatleyelectronics.com

Would I be correct steve in saying that a Square-wave to power the magnetic (back-and-forth valve) air pumps would be better that sine wave....

Think about it. It is still going on/off 50 times per second, just without the rise and fall time of sinewave. You would imagine it would improve efficiency...

Tim, could you explain your question in a little more detail for the rest of us? Instinctivly I would say no, but I don't know enough about what you're doing.

Tim is saying that an air pump is just a solenoid running at 50hz. Sine wave would give you slowly rising voltage to the peak (analogue) wheras square wave is 0 to total voltage (digital). I think

Not sure which is more efficient for this application and don't know how those battery powered air pumps work. mains ones are easy to see.

id have to say that the pumps are DESIGNED for sine wave hence the spacing and travel of the levers and also the design of the coil (inductance, hysteresis etc).

i have definatly found a drop in pump output on MODIFIED squarewave (this is where they make it closer to sinewave by stepping it up in steps (to picture this picture the sinewave in a 16 step resolution)

Yeah modified sux at the best of times. Square wave would put full voltage switching on the solenoid. This means (in the case of 240) that 300 odd volts goes from -300 to + 300. That's a big differential, perhaps enough to give your solenoid extra power, but certainly enough to give it a shorter life. I would not advise this modification. AC sinewave is nice and gentle with how it dows things.

I have a small system at home (200lt), I also have a small battery powered air pump, can anyone help me out?? I am looking for a switch that I can use like Muzzas 240v - 12v but to accomodate a small 1.5v pump, this pump I have runs for quite a few hours before the batteries die.

love my artwork.....

I'm confused Grombo... doesn't the battery air pump come on automatically when the power fails anyway??

no, its just a small battery operated air pump thats can only be turned on/off by pressing the on/off button at this point in time, I want to modify it, remove the on/off button and hook it up to a "power fail back up switch" so when the power fails the pump comes on.

Ok... gotcha...

I found some 12 volt relay switches, I can easily hook them up

Well I think you really need a 240VAC relay coil with 1x SPDT contacts. Disconnect the wires at the on/off switch and extend each side of the wires previously connected to the switch to the relay contacts. Connect one onto the COM and the other to the NC of the contacts, so really now the relay contacts are the switch.

How you want this to work is that when the 240VAC comes on, it pulls the relay in and open the switch. When power has failed, the relay will return to its rest position, hence closing the switch. So in the electrical world, your design will not work as drawn and described. You want to connect the wires to the normally closed contacts instead.

Hope you get what I am describing...

It actually would work as he has drawn it. ( except for the n.c / n.o bit ) 240v turns off, closes the circuit for the air pump 1.5v supply, and away it goes.

I however do not use 240v relays at all. Use a standard 12v relay, powered by a 12v wall plug transformer. While the mains power is on, relay is held open, power goes out and relay closes. No messing about with 240v at all.

my somewhat limited understanding of the electrical codes say that this even makes it legal for a non licensed electictician to do it

Cheers
pete

Yes, I would suggest doing what OBO has said as legally you need a sparky to wire circuits above 50volts (from memory).

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