cheapest, safest and most simple way to power a led from 240V AC

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alec_t said:
I challenge 'must'. That's one way, but the diode would need to be mains-rated. The other way is to use an anti-parallel diode which needs only a low voltage rating. This diode can advantageously be another LED to reduce the blink effect.
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I thought about shorting the LED with a anti-parallel diode but then the resistor power will be doubled.
I agree that another LED can be used as the anti-parallel diode like my Christmas tree light strings.
 
Briefly,

If not isolated from the AC line, make it impossible for users to come in contact with metal parts connected to either line or neutral.

Using an anti-parallel LED is a good idea -you waste as much power as with a diode as Audioguru indicated. An additional benefit of using an LED as an antiparallel diode is that you get light on both phase of the AC cycle, thus less preceptable flicker.

If you want to use a capacitor instead of a resistor to limit the current be sure to add a bleeder resistor and surge protection (plugging it in at the peak of the AC line voltage can cause many amps to flow while the capacitor charges quickly). Fusing is also a good idea.

**broken link removed**
 
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Questions:
Why two 120 ohm resistors? The one in the bottom right corner is in series with R1. Why not 240 ohm fusible R1 and remove the other.
Why two fuses? Oh yes 220 and you need a fuse in each power leg. Then why not two 120 ohm fusible resistors and remove F1?

Any way, there is often that 120 ohm resistor, that I don't think is needed. C0.47uf/400V is limiting 50/60hz current. R1 limits high frequency current.

**broken link removed**[/quote]
 
Nigel Goodwin said:
What is the unit?, and does it have low voltage supplies inside?, for that matter is it completely sealed and inaccessible if you were to use a permanently live light?.
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Maybe I should have explained what I am planning to do.

Basically I have a few of these https://www.tlc-direct.co.uk/Products/MKK3041.html but they are very dim and use a neon. I am hoping to replace the neons with a couple of LEDS. Space is very limited in the 35mm knock out box.

Thanks
 
I designed and did production on a product like that. Passed UL,CSA, VDE etc.

If I wanted some for my house and did not care about government approval:
Use the above schematic, remove R120 (short out), For the fuse and 120 ohm fuse-able resistor use 120 ohm film resistors. They will blow open in the case of a short. Remove the MOV.

For my house I would bring the LEDs out to the front panel. For UL we had to add a plexiglass window. (double insulated)
 

Hi Ron. Interesting stuff about the product passing UL, CSA, VDE etc.

I have always had a gut feeling on my little design an LED poking out through the face would fail it in Safety testing. I thought about that a while ago and now you have confirmed it.

Relatively easy for me to fix though. Without any PCB changes or such. With a little bit of luck, this design of mine is going to fly through testing by the relevant Authorities.

If things go the way they should I would be happy to submit to VDE, CSA, UL or any others out there.

Electrically, within reason, I know they will not break it. I tried and failed.

For me now is to learn as much from the people that have actually gone there as far as casings go.

Thanks Ron,

tvtech
 
You might read up on the 'bowling ball' test. I can't remember the real name. They will take a weight like a hard ball and connect a string to the roof. Then drop the ball into your switch plate.
Your project needs to survive or to break in such a way no wires are hanging out to shock a person.

How are you getting power? Most switch boxes don't have both legs of the power line. Can you show how to attach your light to the switch?
I have been down this road before.
 

I rarely look for advise here Ron. You have been through it. I am all ears to hear all about what you went through. So I can learn from you.

It's to keep the casing safe. And the frigging tests they are put through....BOWLING BALL test.. Well, no wires will be exposed if the casing breaks open, because there are none. Double Sided PCB breaks and that is it.

I need to know what I am in for when real testing comes

I might be a little surprised, I might be ready. At least I know what I have to deal with.

Not just stand there and say stuff all

All the best,

tvtech
 
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Hi all. its been a while, still haven't started this project yet - to be honest forgotten about it to some extent, but the other day I accidentally left my loft lights on and thought that I should add a led indicator.

Don't have low voltage supplies in any of the backboxes, only 240v ac - I'll just be running a neutral line as the boxes will have permanent live feeds already. Got a couple of these - https://www.electricalsupplies.co.u...ogic-plus-neon-locator-plate-switch-230v.jpeg the wiring is strange, it seems that the neon glows by relying on a current passing through the bulb filaments, since im using CFL bulbs the neons slowly flicker, looks like a capacitance thing.

Back on the led subject, just seen this video on youtube what do you guys think about this method?
 
I forgot about this thread. Thank you Dan for bringing it back to life.

I will post my design for my little light that is going to be entering it's second year of testing now soon. On 24/7/365 on Mains @220VAC (except for battery testing from time to time).

Little Duris E3's have lost no brightness. The (original)PP3 has worn out after hundreds of cycles. No failures of any components or any other noticeable wear and tear though. It even runs on a Simulated Sine Wave output from a cheap UPS. My friend who bought the first one I sold swears by it and relies on it with all the crap our power utility ESKOM is putting us all through.

For those that don't know what I am on about check here: https://www.electro-tech-online.com...he-public-domain-at-last.136196/#post-1146578

Stay well and safe Guys.

tv
 
Please keep one hand in your back pocket at all times if you work with line voltage.

Just a note: The rectifier prevents excessive reverse bias current through the LED to the reverse leakage of the rectifier, which is what would damage it by causing shorts between the anode and cathode. It would be safer for the LED if the rectifier were in parallel with it so as to shunt reverse reverse voltage, that way there would be virtually no reverse current through the LED.
 
You are asking 5 years later what we were thinking about???? I can't remember what I had for breakfast today!


This is the same as post #3 but you don't need an 1N4003 or higher. You can use an 1N914 or even a good old 1N34 because the voltage across either diode is a few volts or less. The worry that you dissipate twice the power with this method is not really an issue in my book when you are still talking about milliwatts.

I have a night light in the hallway of the bedroom part of the house and in one bathroom. The nightlight takes only a few tens or milliwatts whenever we have the inlaws over, they turn it off all the time. Hey, its a few dollar or two a year!

Below is that circuit. It has the LEDs conducting all the time, so it wastes little power.


I have two of these in my house and they have run nearly 14 years straight (not counting the occasional power failure) and the are still working fine. It has survived many fierce thunderstorms in the village including those that inducted failures in my house and those of my neighbors.
 
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In the interest of safe and sane I would just do a Google of 230 VAC pilot light or 230 VAC Panel Indicator Light and then see what works for you as to form, fit and function. These come as nice sealed enclosed units and no assembly is required other than installing it. Be it Neon or LED easy install, safe install and thousands of hours of operation. This keeps it safe and as simple as it gets.

Ron
 
Dick Cappels said:
The worry that you dissipate twice the power with this method is not really an issue in my book when you are still talking about milliwatts.
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Disagree. For the small schematic in #36, it is W, not mW.

For a single LED (Vf = 2 V) at 240 Vac and a peak current of, say, 25 mA, the resistor is 13.5K and the peak power in the resistor is 8.5 W. 99% of the input voltage sinewave is across the resistor, so the real power is over 4.2 W.

ak
 
SobhanJahanipsrast said:
Use a 100nF/400 V capacitor in series with your LED.
Use a 1n4148 resistor in parallel with your LED.
Click to expand...

If you use a capacitor to drop the voltage, be sure to include a bleeder resistor that can bleed the voltage across the capacitor down to less than (for example) 20 volts in 100 milliseconds to preclude the possibility of electric shock in the case of the appliance being disconnected from the mains near the peak of the input voltage and a person touching the now exposed mains connection (the plug). I think of the precaution as being similar to smoothing the edges after cutting something out of metal. It is not likely to be a problem but a little care and greately reduce the risk of problems.

Also include some series resistance so that in the case of connecting the circuit to the mains while the voltage is at its peak, which could be some amps, you don't blow up your LEDs. This is also useful for protecting against transients such as nearby lightning spikes and surges that sometimes appear on the mains because of load shedding. A fuse is a good idea too, especially if you don't want a fire in you home.



You've got a point there. I care about wanton waste of power so I used the larger circuit shown in post #28. The reason for posting that smaller circuit was to show a simple use of the anti-parallel diode. I figure that the larger circuit in post #28 costs about US$1.60 a year to operate. The circuit is probably too expensive for a commercial design but it works well and after a lot of testing I feel that it is safe enough to run in my home 24 hours a day (13 years now, so far no problems with either of them). If I only used half cycles to power the LEDs the cost would remain the same but I would only get 1/2 of the light, and also there would be and annoying 25 Hz flicker component.

If the moderator permits (and its truly up to them!) I leave a link to a description of the project, which covers some of the fine points of the design and testing of this luminaire.
 
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