Hi all,
I'm new to AAC, so please forgive me any sins I am about to unwittingly commit...

I have seen a few posts in these forums, that have been cut dead with variations on the commandment "Thou shalt not connect LEDs directly to the mains"!

I can certainly understand both the safety perspective, and at least some of the technical reasons why this is a bad idea - so, I am intrigued as what "directly to the mains" actually means in this instance.

My backstory that has led me to this line of enquiry, is that I want to wire a new in-line socket onto a mains extension lead that had an argument with the lawn mower (the mower won!). The existing socket end is a single moulded translucent piece that has a neon indicator in it - so that you can see if it is switched on at the wall outlet from far away and round the corner.

The replacement socket pieces that are available here in Australia, are completely dismantle-able (if that is a word), and the one I have purchased has some spaces in the moulding that are isolated from the mains connections, and would be an ideal location for an indicator, as it doesn't have one built in.

I've found a few 'tutorials' that suggest whacking an LED with a resistor in series directly across Live and Neutral, some with the suggestion of a reverse voltage protection diode in opposition to the LED, and others with complex arrangements of capacitors as droppers and multiple resistors, half-wave rectifier diodes and all manner of other circuitry - which is all a bit too advanced for my needs (and probably way too bulky to fit in the space I have available), for what I originally perceived as a simple modification. I think most are probably intended for some sort of panel mounting and assume oodles of available space, or are based on questionable youtube videos from lands where health and safety has not yet become fashionable, showing a pair of hands holding and poking at bare cables and components soldered together free-form, with mains voltage coursing through them

So the option I am looking at most seriously, is using 4 diodes to create a full-wave bridge rectifier, and then connecting an LED with current limiting resistor in series, to the DC side of the rectifier. I am hoping that this at least allows me to honour the spirit of the commandment above, and continue this query with your blessing?

If so - I am wondering what the difference between the two following circuits would be; if one is preferable to the other, and if so, why?
(schematic diagram of disallowed technology removed by moderator)

Many thanks in advance,
Graham.

 

You can acquire small neon indicator devices. Other than that, I'd at most do a simple 2 LEDs in series with each other and the appropriate resistor for your highest encountered peak voltage (not RMS!), and a fusible link; a link which will clear if any failure occurs in those other 3 items.

 

Many thanks tranzz4md. So peak voltage on a 240VAC mains supply is going to be in the region of 340V - is that correct?
Could you explain the purpose of having two LEDs in series, and is your suggestion to apply these 4 components in series, across the AC live and neutral, or across the rectified DC... Sorry if I'm asking obvious questions, but I am not so familiar with AC circuits as DC (and I'd only class myself as an enthusiastic novice in DC). My only real experience of AC is with domestic light fittings, mains socket, and the odd oven element
I'm beginning to think that paying the exorbitant cost of $1.35 for a neon bulb is going to be far easier for me to get the repair done, but I like the challenge of learning something new along the way - so I'd still like to pursue an LED based solution, even if only for the theoretical knowledge it will bestow upon me.
Cheers
G

 

Those cheap wall socket timers often use a red AC LED (a DC LED would flicker at mains frequency) connected across mains via a simple power resistor, so it's definitely possible, but the resistor gets VERY warm in an enclosed space.

 

Those cheap wall socket timers often use a red AC LED

LEDs specifically for AC use? That's a new one on me... I'll have to go and look them up. Thanks for the heads-up on the resistor temperature.
Cheers
G

 

LEDs specifically for AC use? That's a new one on me... I'll have to go and look them up. Thanks for the heads-up on the resistor temperature.
Cheers
G

Yes it was a surprise to me too.... Somebody at work bought a load of them for building AC test rigs and I considered it a waste of money given that they still need resistors and the test rig was a complete abortion any way., so "why would it matter if they flickered a bit?".

 

...If so - I am wondering what the difference between the two following circuits would be; if one is preferable to the other, and if so, why?

In first circuit we have about 5V max reverse voltage on diodes, but in second one 340V.

 

Stick with a lamp designed for 220 VAC line voltage.

It's just not worth the effort - you will end up with some unsafe sketchy stuff for sure.
You want to burn the place down saving a few cents?

 

All the diodes in those schematics can be LEDs, and you will have 5 lit for those circuits, not only one.

AC LEDs ? Been around for a while. Tried to buy them for several applications but hardly any distributors, none in USA.
Ideal would be one 'cold' and one 'warm' emitter counterparalleled. No luck yet.

 

LEDs powered directly from the mains may not be discussed at allaboutcircuits.com, as that would be in violation of the User Agreement.

The circuits you proposes are unsafe, as others here have said before me, and unfortunately we cannot discuss the details or possible solutions. If you would like you can discuss your circuits at Electro-Tech Online where you will find some of the same people in a forum that permits the discussion of LEDs power directly from the mains.