No neutral, no earth, just live, power? - Page 1
Forum section: electronics / general

author: paulca
author_rank: Super Contributor
timestamp: August 01, 2019, 05:49:57 pm
content: So how do these work then?No neutral or earth required, just the live to power it?https://www.amazon.co.uk/Lightwave-Gang-Smart-Dimmer-Switch/dp/B075XTWJRR/The only thing I can think of, is assuming the switch out wire will go to a load and to "ground", they could allow a tiny amount of current to flow through a high ohm resistor and put it through a coil to generate an AC voltage and rectify it. Might only be a few mA at 3V. Of course it would depend on the load, aka the bulb characteristics?

author: soldar
author_rank: Super Contributor
timestamp: August 01, 2019, 05:55:28 pm
content: Quote from: paulca on August 01, 2019, 05:49:57 pmWhy cannot it be powered by the passing current? How much power does it need? What happens if you put a current transformer?

author: paulca
author_rank: Super Contributor
timestamp: August 01, 2019, 06:05:48 pm
content: If the switch is on, sure it can use a current transformer. But if the switch is off, does it run on a rechargeable battery?EDIT: Sorry, why not, a lithium cell and a current transformer. I suppose as long as they ship it with power and you use the lights once in a while it would work.

author: soldar
author_rank: Super Contributor
timestamp: August 01, 2019, 06:08:42 pm
content: Quote from: paulca on August 01, 2019, 06:05:48 pmIf the switch is off then you have all the voltage at your disposal. I guess you might need two ways of powering it OR, more probably, it never does 100% duty cycle so there is always some voltage available at the beginning.

author: james_s
author_rank: Super Contributor
timestamp: August 01, 2019, 08:01:03 pm
content: Lots of things work this way, or used to. When the light is off they draw current through the lamp which is well below the threshold at which it would glow or even get warm.Of course since CFL and later LED came along this doesn't work so well, the bulk filter cap in the lamp slowly charges and you get a relaxation oscillator.

author: SteveyG
author_rank: Unknown
timestamp: August 02, 2019, 09:20:41 am
content: I covered this in some of my videos. The light is never powered at 100%, when the light is on, some of the waveform is stolen to power the electronics. When the light is off, there is some parasitic current being drawn through the lamp.

author: GlennSprigg
author_rank: Super Contributor
timestamp: August 04, 2019, 01:22:15 pm
content: 'EARTH' is relative...Here in Australia, we have/had what they called 'SWER' systems out in the country.(This means Single Wire Earth Return). Just a high voltage Single Wire supply only.They referenced Earth for a 'return'. Our 'modern' Switchboards utilize that they call..."M.E.N." (Mains Earth Neutral). Within the main switchboard, there is a Main Earth, whichis connected to the main Earth-Bar. But it incorporates a LINK from this main Earth, to the"Main Neutral" bar!!

author: SiliconWizard
author_rank: Super Contributor
timestamp: August 04, 2019, 04:03:32 pm
content: Quote from: james_s on August 01, 2019, 08:01:03 pmYep, so the thing actually never really switches the lamp OFF. It just makes it look like it does.Of course in practice that's what real-life switches do anyway. There's always some amount of leakage current, however small it is.I'm curious how much current do these switches draw in the OFF state?