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I need a switch that stops power supply(220VAC) to led tv when power comes back after outage. So i need a circuit breaker that breaks the circuit when power supply is off and needs manual switch on from this circuit breaker device when power supply is on. I have two ideas:

  1. I feel its possible using microcontroller and relay but i think it would be costly and time consuming to make such device.
  2. I am also having idea about using magnetic coil as in magnetic circuit breakers but not confident about its effectiveness. As i am unable to find such device on commercial websites, so i need help in finding such device if commercially available and/or making such switch/circuit breaker in a simplest and cheapest possible way.
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5 Answers 5

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A standard latching relay circuit seems appropriate for this: - enter image description here

When AC is first applied you need to press the trigger switch to activate the relay and that also activates the load. The normally open (NO) contact of the relay re-inforces power to the coil via the contact closing and so if you stop pressing the trigger button, the relay has latched. This can be optionally "tested" by the reset switch.

If power is removed the relay unlatches until power is returned and the trigger button is pressed.

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Consider using a COTS item called a Magnetic Switch commonly used in conjunction with wood working power tools.

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  • \$\begingroup\$ Apologies for using a link to a commercial Magnetic Switch product. I could not find a more neutral web site example. If anyone knows of a generic source of Magnetic Switch information I would be happy to change this answer. \$\endgroup\$
    – st2000
    Commented Jul 13, 2018 at 12:21
  • \$\begingroup\$ no, I think this is quite fine! It's not like you're posting advertisements for your own company all over stackexchange, and honestly, a link to how things look when bought as a COTS device will be best if you link to a C website (C as in COTS). \$\endgroup\$
    – Marcus Müller
    Commented Jul 13, 2018 at 12:35
  • \$\begingroup\$ good answer , tad expensive \$\endgroup\$
    – D.A.S.
    Commented Jul 13, 2018 at 13:05
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Well, a latching relay configuration is what you're looking for:

schematic

simulate this circuit – Schematic created using CircuitLab

Idea is simple: when you press the pressbutton SW1,you connect the relay's coil to your power outlet. It then energizes, and closes the integrated switch in the relay, connecting the output to the input voltage. At the same time, it also connects the relay's coil to the input voltage, so that the relay's coil stays connected even after you release the button.

The relay has then latched.

When the voltage on Live in drops out, the coil loses energy, the relay opens, and you have to press SW1 again to energize the coil.

Things needed:

  • Power cord to connect to your wall outlet
  • momentary switch SW1
  • an outlet that you can connect your screen's power plug to
  • a Relay rated with (in parenthesis the values that I assume, based on the assumption that "power often failing" statistically means you might be in India)
    • coil voltage = grid voltage (220V)
    • switched voltage = grid voltage (220V)
    • switched current = maximum current draw of a device pluggable into outlet (12 A)
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  • \$\begingroup\$ You assumed "power often failing" and you are assuming too much. Also you are finding probability of me belonging to India based on your assumption. There are too many countries that use 220V power supply and out of these many have frequent power outages. There is a chance that you are right but also there is a chance that you are wrong. So why toss the coin. You might like to show the source of your statistics. My statistics say that you are an arrogant German as you are talking too much out of context of my question. \$\endgroup\$
    – Anshuman
    Commented Jul 13, 2018 at 22:10
  • \$\begingroup\$ Sorry, didn't mean to upset you in any way! It's just that the most of questions asking for making consumer devices save against brown-outs that I read (and I'm fully aware that is not a representative statistic) were asked and declared as such from Indian users. I must admit I honestly don't understand why you think this is arrogant at all, or why it upsets you – nothing about that is negative toward any person; if anything, it's my expectation that there's a lot of internet users in India that have to deal with a not perfectly stable power grid; how's that arrogant? \$\endgroup\$
    – Marcus Müller
    Commented Jul 13, 2018 at 22:46
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enter image description here

The AC Relay must be rated for line transient voltages (>3kV) and Amps derated motor surge currents or Hp .

Alternative $15 Magnetic Relay Woodstock D4157 110/220 Volt Single Phase On/Off Switch

enter image description here

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The plug-through Earth Leakage / Residual Current (ELCB/RCD) devices just happen to do this.

You have to press RESET/ON to latch them on after a power cut. They do this, because they happen to use a self-latching relay arrangement (as described by Marcus) It also happens to be an RCD, but you don't care about that.

enter image description here

Note this behaviour is generic to RCD's that have the RESET and TEST buttons. So the wall socket versions also do exactly what you want

enter image description here

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  • \$\begingroup\$ Why would this device trip in a power cut? ELCB/RCD require an L-N current imbalance to unlatch the sprung switch. A power cut will not create this condition. \$\endgroup\$
    – Transistor
    Commented Jul 13, 2018 at 14:13
  • \$\begingroup\$ I'm in Ireland so I won't find that brand. Seems odd though. \$\endgroup\$
    – Transistor
    Commented Jul 13, 2018 at 14:18
  • \$\begingroup\$ Not especially odd. You wouldn't want it to automatically come back on , when there was faulty equipment. Since it lacks the special mechanical mechanism an mcb has, this is an easy way to be latched out. (they are not an electromechanical EL circuit breaker). It's generic behaviour \$\endgroup\$
    – Henry Crun
    Commented Jul 13, 2018 at 14:22
  • \$\begingroup\$ Henry, thanks for answering to my question but this device is not what i need. This device is more like a mcb, it breaks circuit when it detects higher voltage across it. But what i need is a circuit breaker that breaks circuit when there is power outage and keeps breaking circuit when power comes back until i switch on the circuit breaker. \$\endgroup\$
    – Anshuman
    Commented Jul 13, 2018 at 20:13
  • \$\begingroup\$ @APS Would you like a nice tummy rub with that too? In today's online world it is not necessary to see a device, one can get all information just by its name. Apparently you can't. Might want to check out meatspace for some authentic experience. Its great, if a bit slow moving, I recommend it \$\endgroup\$
    – Henry Crun
    Commented Jul 13, 2018 at 22:58

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