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This circuit probes a power outlet to activate an emergency light when there is a power outage. I power my emergency light (LED strip) with a lead acid battery. I published two variations of this circuit, but prefer variation 2, because I hate optocouplers and I dont want to use so many capacitors.
This variation uses a transformer to probe mains voltage and to isolate it from the main circuitry. It does not have to be a big transformer, but make sure the primary side can handle around 0.1A without getting hot. MAKE SURE THE TRANSFORMER AND THE CAPACITOR ON THE LEFT ARE IN A CASE SO YOU DONT TOUCH THEM ACCIDENTLY. You should also make sure, all voltages in this circuit are low enough, because most of them depend on your transformer. If you do not have the necessary tools to do that, use version 1 of this circuit.
I got the idea to design such a circuit when I had my first mains voltage shock yesterday. The breaker opened immediately, so I sit in the dark, being dizzy as hell. It took me around 2 minutes to find a flashlight so I can turn off everyting to activate the breaker again. If you want to know why I was shocked: I was working with my autotransformer. To change the setup, I turned it's output down to 0V, but I did not unplug it. When I touched the neutral output of it, WAAAMMM. Seems like I have connected the phase of mains voltage to the neutral input which is shortened to neutral output. It was not a dumb mistake, but it was still pretty shocking.
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