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First of all I am no electrical engineer (would love to be one!) so apologies upfront if this question is only fit for the sci-fi section. If it is, I'd still like to see a solution to this:

Appliance is connected to switch X which is plugged into mains AC socket. Switch is set to ON, but appliance stays off. Upon a power failure, switch X detects the power loss and upon power resumption, becomes "active" and allows power to flow through, powering up the connected appliance. Possible reset of switch X through second power off and on at the AC socket or a button push.

Is this available/ possible?

I want to hook up a vacuum pump to an aquarium sump set-up but don't need that appliance running 24x7. Upon a power failure, the sump will fail. When power resumes, the sump will still not work, requiring the vacuum pump to draw water into the pipes, hence the need for this relay.

Thanks in advance!

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  • \$\begingroup\$ I'm not sure if there are devices that do exactly that, but you can wire a relay to do that for you. You would essentially have it so when power is on, you press a button to switch a relay to turn the vacuum pump OFF. When power is lost, the relay returns to its normal state and after power returns the pump comes back on. \$\endgroup\$
    – AngeloQ
    Feb 27, 2017 at 14:26
  • \$\begingroup\$ There are examples that turn a device off when power is lost so it doesn't come on again, but with the correct choice of NO and NC contacts you can make it do what you want. Take a look at this for some more detail: electronics.stackexchange.com/questions/268259/… \$\endgroup\$
    – AngeloQ
    Feb 27, 2017 at 14:26
  • \$\begingroup\$ Do you want the pump to be on only for certain duration after you power on using mains switch? \$\endgroup\$
    – User323693
    Feb 27, 2017 at 14:27

1 Answer 1

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The circuit below would do that for you. When power is on, the pump would start immediately. Press the button to shut it off by holding the relay energized. The next time power goes out the relay will return to the de-energized state and when power returns, the pump would automatically come on again.

Note that the relay would be drawing power constantly when there is power, when the pump is off, so it may not be the most efficient way to do it. Make sure the relay coil and button are rated for the supply voltage and the relay contacts are rated for the pump current.

schematic

simulate this circuit – Schematic created using CircuitLab

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