Run a string of LEDs from the mains

[The Master]

Hi, I would like to run 80 LEDs directly from the mains. Here in the UK the mains is 240V. That gives 3V per LED and they are rated at 3-4V. Would there be any problems with this? Ive been told that i should use a current limiting resistor when running LEDs from 12V. As far as im aware thats only needed if the input voltage is greater than whats required (i still dont completely understand this stuff).

As its AC then there would be a slight flickering on the LEDs. Could i use 4 diodes to make a rectifier? The diodes are only meant for about 50V 1A. Technically they would be in series with the LEDs so it shouldnt matter. Could it cause any problems though?

I thought about adding a capacitor aswell to reduce the flicker as much as possible. I found one thats 470N 250V. Would 470N be enough?

[mackrackit]

Hey Sparky

Why not buy a string of lights and save the possibility of letting your magic smoke out for another day?

[The Master]

Because that would be too simple

These LEDs are going to be on a PCB and used to make a really bright light. Ive been thinking about a few other projects that would need the same kind of thing so now would be a good time to get it right.

[mackrackit]

If you are serious about this we need to look at the data sheet for the LEDs.
You say 3-4 volt... That is quite a range.
Amps per LED? 0.025???
And does the mains fluctuate any? Here I get anything from 110 to 120.

[khoog]

Current limiting resistors limit current draw, not voltage. You will need the resistors.

[The Master]

The datasheet can be found here. They use 50mA so the whole string should only use 50mA.

I keep hearing all the time that things only take as much current as they need. So a 50mA string of LEDs will be fine on a 13A mains circuit. I read that they will only take too much current if i put too many volts into them.

The power in our house can be a bit strange. We are supposed to be getting only 230V but ive never seen it drop below 240 and quite often its as high as 250. Dips wont be a problem and spikes should be fine as i could put over 300V into the string and still be within the max voltage

[Melanie]

Don't do it.

As an experiment, put a string of LED's across your Car Battery without any form of Current Limiting - that's a reasonably constant voltage - then go rev your car engine up...

> Could i use 4 diodes to make a rectifier?

Yes

> The diodes are only meant for about 50V 1A.

Well that's kinda stupid to use them on 240v then!

> I found one thats 470N 250V. Would 470N be enough?

Depends on how much current you're pulling... but the 250v bit is totally inadequate, because by the time you full-wave rectify mains you'll have close to 340vDC.

Back to my first line... DON'T DO IT. You are running the risk of harming yourself, your property and putting at serious risk those around you.