Simple power supply that can be embedded in a wall socket

staylor97_

Oct 18, 2018
3
Hi, i wish to develop a simple power supply that can convert ac signal to a dual polarity dc output. I want this to be a cheap but effective power supply which could be used to show where a switch is on a wall, via a light, or to indicate whether or not a power switch is on or off. Any ideas?

BobK

Jan 5, 2010
7,682
At least in the U.S., there is no neutral line in the switch box. One is live and one is the other goes through the load to neutral. You cannot draw power from this arrangement. Don't know if it is the same where you are, but if there are only 2 wires, you are out of luck.

That said. You can put a neon light across the switch, which will light when the switch is off. This draws so little current through the load that it will not be affected. A 240V LED might draw enough current to turn LED lighting fixtures on a little if connected that way.

Bob

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Bluejets

Oct 5, 2014
6,593
Clipsal make a "saturn" range with an LED encased.
Choice can be one of 4 different configurations including the 2 wire A/sw wire arrangement Bob mentions.

Expensive little mothers though. Neon/resistor for 10c would work just as well on most lighting also as Bob quoted.

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Externet

Aug 24, 2009
886
Or, DIY

Better use a 0.1μF / 400VAC capacitor with a 100K resistor in parallel to it for the above circuit.

duke37

Jan 9, 2011
5,364
Or, DIY

Better use a 0.1μF / 400VAC capacitor with a 100K resistor in parallel to it for the above circuit.
The resistor and capacitor are in series, not in parallel

Is the resistor 1k or 100k?
What is its purpose?

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,509
The primary purpose of the resistor is to act as a fuse for when the capacitor eventually fails.

Externet

Aug 24, 2009
886
The 1K resistor in the circuit stays.
An additional 100K-200K resistor in parallel to C is convenient to implement.

The ~ symbol can be across the wall switch terminals. Turns leds on when 'ceiling' lamp is off.

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duke37

Jan 9, 2011
5,364
The 100k resistor should be 1W and 250V minimum.

Externet

Aug 24, 2009
886
Made several, been working 6 years. Simple thin hand carved copper clad board, for pin insertion type switch, self locks in-place, notches on the board allow removal. Low enough profile to fit in existing boxes.
Two 0.25W resistors (1K, 220K), 1 capacitor 0.1μF, 250VAC, two 11000mcd white leds, perforated plastic plate. LED leads protected with a dual tube kind of coffee stirrer as insulator.
Attached.

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