EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: JacoRoselt on May 24, 2018, 06:41:30 am
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Hi,
I found the attached schematic on another forum. It describes a way to install a WiFi controlled light switch, which requires a live and neutral AC connection, in a wall box that does not have a neutral connection. It looks a bit weird to me.
Will it work and what are the possible problems with a setup like this?
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That will work for incandescent bulbs, but fluoros and LEDs will flicker or light dimly. EDIT: the cap bypassing the bulb might fix this.
The circuitry in the wall-plate does actually have a neutral going to it. Wires normally have a resistance much smaller than our circuits/loads, so we simplify things and assume this resistance does not exist. Similarly in this situation: the unlit lightbulb and capacitors will have an resistance much lower than the circuit in the switch. Enough current leaks through the light and capacitors to power the circuit, but not enough to light the bulb.
EDIT: from a safety point of view it is possible to use caps small enough to minimise any electric shocks given to humans (when they change bulbs and slip a finger), but you'll need to be clever in how you design in the in-switch circuit.
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If you can access the boxes, say from the attic then a better idea would be to run another cable that has a neutral. The solution outlined there may work if no other is available though.