LED

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Tweefo (October 20, 2017, 16:43:55 PM):
One for the technical brain cells. I bought a LED light bulb from Pick & Pay. It claims to provide light for up to 4 hours in case of power failure. It's got a battery build in that charge while the power is on. So far so good. It uses the normal switch to switch it on / off, but if the power should fail, it stays on or you can switch in on during the blackout. My problem is how does it know that the power was switched off as opposed to a power failure? It works as advertised.
BoogieMonster (October 20, 2017, 17:55:59 PM):
My guess would be capacitive sensing of the circuit it's connected to. It can probably baseline on what the capacitance of the wires are when the switch is in the off position vs. what it is in the "on" position.
brianvds (October 20, 2017, 21:54:33 PM):
Only four hours? LED lights typically last around 70 to 90 hours on common dry cells.
Tweefo (October 21, 2017, 08:27:05 AM):
My guess would be capacitive sensing of the circuit it's connected to. It can probably baseline on what the capacitance of the wires are when the switch is in the off position vs. what it is in the "on" position.
Instead of a simple explanation, we get this. Never even heard the word, nevermind understanding what it means. Think it's maybe time to go back to my cave now. ; ???
Mefiante (October 21, 2017, 10:35:16 AM):
My guess would be capacitive sensing of the circuit it's connected to.
It’s actually simpler than that, but it will only work in a circuit that operates a single bulb. The LED bulb manufacturer specifically mentions this single-bulb proviso: “It works for 2 way and 3 way switches but a switch can control only one bulb in the circuit.

In such a single-bulb circuit, when the power to the LED bulb unit goes off, it tries to send a small current through the power supply line. If the current flows, it means the light switch is on and a power failure has occurred, in which case it switches over to drawing power from the battery. If the light switch is off, no current can flow, and the unit can thus tell the difference between a power failure and being switched off.

'Luthon64

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