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LED

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Tweefo
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LED
« on: 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.
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BoogieMonster
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« Reply #1 on: 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.
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brianvds
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« Reply #2 on: October 20, 2017, 21:54:33 PM »

Only four hours? LED lights typically last around 70 to 90 hours on common dry cells.
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Tweefo
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« Reply #3 on: 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.  ; Huh?
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Mefiante
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« Reply #4 on: 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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SKEPRat
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« Reply #5 on: October 21, 2017, 14:51:22 PM »

Hi Tweefo. What needs to be remembered is that all plugs or lights in a house have two power wires connected to them. The live and neutral. When the live is connected via the switch the light or plug is "On". When it is disconnected via the switch the power is "Off". What many fail to remember is that the return conductor, the neutral, always has a voltage of 220V. An electrician will easily measure which is the neutral in a plug by measuring the earth contact to the power contacts. When off the voltage will register if the neutral and earth are measured. This is how the light "knows" that there is still power in the system and there is not a power failure. During a failure the voltage between the neutral and earth will be zero.
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Mefiante
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« Reply #6 on: October 21, 2017, 17:03:20 PM »

What many fail to remember is that the return conductor, the neutral, always has a voltage of 220V. An electrician will easily measure which is the neutral in a plug by measuring the earth contact to the power contacts. When off the voltage will register if the neutral and earth are measured.
I’m afraid the above is incorrect.  If you were to measure the voltage between earth/ground and neutral, you will measure only a small potential difference of less than 3V, which is due to stray self-induction from AC current flow in other parts of the house.  With shielded cables throughout, you’d measure 0V.  Measuring between the mains live and neutral terminals, or live and ground/earth, you’ll measure around 220V.  You can confirm this yourself with a suitable multimeter that can handle AC.

In fact, except for earth leakage detection, the neutral plug connection is actually redundant in single-phase mains electrical supply because you could run any AC appliance by connecting it to live and earth, rather than live and neutral (try this only if your house doesn’t have earth leakage protection because it’ll trip immediately). At the power station’s generators themselves, neutral and earth are identical: A giant electrode sunk into the ground.  Again, with a suitable multimeter, you’ll measure around 220V between the mains live terminal and something grounded, such as a water tap fed by steel or copper piping.  (The resistance of the multimeter when measuring potential differences is so high that only the tiniest current will flow, and hence the earth leakage won’t trip.)

Also, if the passage cited above were correct, the single-bulb restriction wouldn’t be necessary.

While this stray self-induction may indeed present a possible mechanism for differentiating between being switched off and a power failure, it’s far too unreliable.  With no other appliances drawing any power in the house, it’s likely to misidentify such a situation as a power failure.

'Luthon64
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Faerie
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« Reply #7 on: October 22, 2017, 05:33:36 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.  ; Huh?
The occupational hazard of associating with clever peiple!! Did you understand Mefi's post?
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brianvds
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« Reply #8 on: October 22, 2017, 06:37:05 AM »

The occupational hazard of associating with clever peiple!! Did you understand Mefi's post?

It's every bit as simple and straightforward as the specifications for the turboencabulator...

https://en.wikipedia.org/wiki/Turboencabulator

:-)
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Tweefo
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« Reply #9 on: October 22, 2017, 11:42:12 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.  ; Huh?
The occupational hazard of associating with clever peiple!! Did you understand Mefi's post?
It's a tough word out there. Way back when, if a guy walks on water or changes water into wine, you just assume he was a god. Now we want explanations for everything but first, you have to go to school and all that, to understand said explanations. Better to just call her (Mefi) god, cut off a chicken's head in her name, and pray to her if the light does not go on. However, if she can walk on wine I will have to spell god with a capital G.
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brianvds
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« Reply #10 on: October 22, 2017, 12:25:18 PM »


The occupational hazard of associating with clever peiple!! Did you understand Mefi's post?
It's a tough word out there. Way back when, if a guy walks on water or changes water into wine, you just assume he was a god. Now we want explanations for everything but first, you have to go to school and all that, to understand said explanations. Better to just call her (Mefi) god, cut off a chicken's head in her name, and pray to her if the light does not go on. However, if she can walk on wine I will have to spell god with a capital G.
[/quote]

Yeah, but verily, remember that she can smite thee too. In fact, you sound like you're a bit smitten. :-)
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Mefiante
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« Reply #11 on: October 22, 2017, 20:00:45 PM »

However, if she can walk on wine…
Beyond a certain point on wine, I tend to stagger a bit. Tongue

'Luthon64
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SKEPRat
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« Reply #12 on: October 22, 2017, 20:41:50 PM »

Mefi, with all due respect, I have been doing this for 30 years and more. Open any plug in your house. Now, with a multimeter set on AC Volts scale above 220V:

1. Ensure the switch on the plug is off.
2. Measure the contact in the plug from neutral to earth. 220V right?
3. Measure the contact in the plug from live to earth. 0V right?
4. Measure the contacts in the plug from neutral to live. 0V right?
5. Switch the switch to on.
6. Measure the contact in the plug from neutral to earth. 220V right?
7. Measure the contact in the plug from live to earth. 220V right?
8. Measure the contacts in the plug from neutral to live. 220V right?

Anyone checking if a system is live always measures all conductors to earth, never from live to neutral or just between phases ignoring the earth. I have worked on systems with 1000's of volts. If I was wrong I would have been fried.
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BoogieMonster
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« Reply #13 on: October 22, 2017, 21:06:33 PM »

Well foo, here I was thinking you were asking the question because you were electrically minded, but was willing to explain my theory further. However my theory was incorrect so blegh.

Here is a (higher grade) explanation of exactly how it works. In short (pun intended) it is indeed trying to send electricity through the circuit (house wiring) and if anything else in the cicuit (other lights, appliances, anything else plugged in lets even a teeeny little power flow it means the light cannot be switched off, since it's still connected to the circuit (the switch is still on). I expect this also goes for any transformers on the supplier (Eskom) side.

Even easier explanation: It's checking if anything else is connected to the power line it's connected to. If so, the switch is not off, and since it's not getting power.... it means there's a power failure.
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Mefiante
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« Reply #14 on: October 22, 2017, 21:45:46 PM »

SKEPRat, with all due respect for your decades-long experience, my SO just performed your stepwise protocol with me observing (because we have nothing better to do of a Sunday night are obsessive fact-checkers).  I encourage others on the forum to do likewise so that they can ascertain for themselves what’s true.  Here are the results:

1. Ensure the switch on the plug is off.
Done.

2. Measure the contact in the plug from neutral to earth. 220V right?
Incorrect: 0.168V measured.  (In fact, this simply can’t be right because it would mean you can be shocked by sticking, say, an iron nail into the neutral terminal of a plug that’s been switched off.)

3. Measure the contact in the plug from live to earth. 0V right?
Near enough: 0.172V measured.

4. Measure the contacts in the plug from neutral to live. 0V right?
Near enough: 0.023V measured.

5. Switch the switch to on.
Done.

6. Measure the contact in the plug from neutral to earth. 220V right?
Incorrect: 0.273V measured.

7. Measure the contact in the plug from live to earth. 220V right?
Almost exactly, as expected: 220.6V measured.

8. Measure the contacts in the plug from neutral to live. 220V right?
Again almost exactly, as expected: 220.1V measured.

The erroneousness of points 2. and 6. individually and collectively refute your claims, and are in line with what I wrote before.  Ergo, I stand by my earlier assertions.

'Luthon64
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