Simple AC Powered LED

[delphijustin]

Hey everyone, when i was taking apart a power strip the LED that shows it on was just connected to a ceramic capacitor so all u need is a
1 Capacitor thats not a electrolytic
1 LED
1 AC power cord
**broken link removed**
here's the youtube video

I don't know what good value of capacitance so expreiment it and i would like it if you would tell me which capacitor you used.

I took apart the power strip for connectors for my xmas light flasher which is coming soon.

 

[DerStrom8]

I don't think this is a very good idea, DJ. You're putting a 12 volt LED backwards in a 120 volt AC circuit with only a ceramic disc capacitor in series? IMHO you're lucky this is working at all. I would have expected the capacitor, LED, or both to explode as soon as you plugged in the cord. I would stop using this setup if I were you, for the sake of safety. Running LEDs safely off mains voltage requires a lot of additional circuitry that you do not have. I am guessing you missed a major part of the circuit.

Der Strom

 

[delphijustin]

well this powerstrip was made in 1986. So things might have change like now a days. They might have found this circuit bad to use

 

[DerStrom8]

well this powerstrip was made in 1986. So things might have change like now a days. They might have found this circuit bad to use

I am also guessing they didn't have the circuit THIS simple, either....

Do you have a picture of the power strip before you took it apart? Or perhaps even the circuitry inside?

 

[Reloadron]

If you scroll down this page you will see a few examples of lime powered LED lights. Personally I agree with DerStorm8 in that doing this is not a very good practice. It is more of a novelty thing than having much as to practical use other than as you saw in a power strip. Additionally when you used your meter you would do better to set it to measure AC as in your circuit, as drawn, there is no rectification. In reality the LED is turning on and off at a 60 Hz rate (US Power Mains). Anyway, while nothing new, it really isn't a good practice to wire a LED to run off mains power.

Just My Take
Ron

 

[4pyros]

it really isn't a good practice to wire a LED to run off mains power

I don't think this is a very good idea

But its done all the time.

 

[Reloadron]

Yes, it's done all the time. I simply said in my opinion I don't think it's a good idea to screw with. I also said "Just My Take". I based that in part on watching the video. Given a choice, if I were designing a power strip, I likely would have shoved a little NE2 lamp in the thing with a series resistor. Then too, when I was younger I got bit my share of times screwing with mains so maybe I should not be too quick to say it's a bad idea.

Ron

 

[Diver300]

You might want to read another thread:-

https://www.electro-tech-online.com/threads/led-pilot-light-powered-from-230v.117495/

before this one goes through the same arguments..........

 

[carbonzit]

My power-line powered LEDs, same as what you drew above (except there are 2 back-to-back, a red and a green) are still shining brightly after about 3 months ... (120-volt land here).

 

[alec_t]

IMHO it's ok to run LEDs at low current from a capacitor acting as voltage dropper cum current limiter, provided a good quality X2-rated cap is used and all components (any of which could carry a lethal voltage) are safely enclosed to prevent electric shock.

 

[audioguru]

LEDs work on DC, not AC.
The original circuit is wrong because the LED gets a very high reverse voltage that is much more than its 5V absolute max allowed reverse voltage.
Therefore DC is used or two LEDs are connected back-to-back so that each LED lights when the voltage reverses and limits the reverse voltage on the unlit LED.

Connecting two identical LEDs back-to-back charge and discharge the capacitor symmetrically. They also prevents a single LED from acting like a rectifier and charging the capacitor with a DC voltage until the LED will not conduct anymore.

 

[colin55]

Placing a LED and capacitor in series on AC creates a problem as you must have a component to discharge the capacitor. You can use a diode connected across the LED to discharge the capacior or another LED connected across the first. If only a single LED is used, you are relying on the reverse breakdown characteristic to conduct in the reverse direction and this reverse voltage is about 5v to 7v. That's why the voltage reading in the video above is about 5.3v
You are supplying the LED with a reverse voltge and this is causing a reverse current to flow.
This may have an effect on damaging the LED.

 

[carbonzit]

Placing a LED and capacitor in series on AC creates a problem as you must have a component to discharge the capacitor.

NO YOU DON'T! That's BS.

Otherwise, why is my LINE-POWERED LED LIGHT STILL BURNING BRIGHTLY AFTER 3 MONTHS? Voodoo?

Sorry to SHOUT, but I keep hearing this same wrong argument made over and over again here.

You do not need to discharge the capacitor. The circuit works fine as shown.

Disclaimer: This is not to say that this is a safe or practical circuit for production. It is not. It will, however, work, and work well.

I have proven this in Real Life.

 

[colin55]

carbonzit
Learn a little bit about electronics.

You are using the reverse zener of the LED to discharge the capacitor.

That is the component that discharges the capacitor.

 

[picbits]

I've had some 240v mains operated fluid valves which have an LED in the connector which lights up when energised. These all used a capacitor in series with the LED.

 

[carbonzit]

I'm going to build one later today and plug it in to disprove what's been stated here. (I've done this before, a single LED and a single capacitor, successfully.)

 

[colin55]

I am not saying a capacitor and LED will not work. I am saying you are using the reverse voltage breakdown of the LED to discharge the capacitor. Put a LED, 400v diode and capacitor in series and see if the LED illuminates.

 

[audioguru]

I have never exceeded the absolute maximum allowed reverse voltage of an LED (only 5V) so I don't know the damage that is caused.
Do you think the manufacturers are joking about the limit?

 

[ronv]

No, I think it breaks down at that voltage, just not enough current to fry it. It only dissipates about twice as much in break down as when it's forward biased.
That's my guess and I'm sticking to it.

 

[ronv]

Carbonzit,
If you are going to build one why not set the current close to max peak. Then maybe we could get a little better idea about how long it will last.