Run a string of LEDs from the mains

[mackrackit]

falingtrea: If i use a transformer inside a device then would it make a difference? 240V would still be going into it so i would need to look at all that safety stuff anyway

But the "safety stuff" would be isolated to one point.

[The Master]

But the "safety stuff" would be isolated to one point.

Thats a good point. Most of these projects would involve having the LEDs on the same board as the transformer but while testing its probably a good idea if most of the PCB has low voltage running through it

[mackrackit]

mackrackit: This confuses me a bit. you say theres no need to worry with 5 LEDs on 12V but they could be a bit dim. Are you saying theres no need for any resistor? I wouldnt normally use a resistor in this case anyway.

Now the wheels are turning...
You tried 4LEDs across 12 volts with out a resistor. Put in a 220 or whatevere and see what happens to the color.

I know this is all a bit confusing. Maybe another reason not to run from mains directly. At least not untill you get all of this sorted out.

[Ioannis]

I think you need some basic classes on electronics. Maybe the Art of Electronics is a book all have to read first.

That picture shows the relation between Current and Voltage. Do you notice how steep is the curve at the point where the diode starts to contact? A very little increase at Voltage and the current will be infinite!. Thats why a resistor is needed or even better a current source to stabilize the current at 30 or if you insist on decreasing ED life at 50mA.

A battery is very constant and 12 will never be 13 volts without any good reason. But Power line? No ones guarantees the 240Vac. So what will happen to you precious diode (read LED) when the voltage across the pins moves away from the knee of the curve? Bam!

Ioannis

[The Master]

Nothing happens to the color. What should i be seeing?

The LEDs im using work on a min of 3V. They can go upto 4V if needed. With 80 LEDs that gives me an extra 80V to play with. If the voltage goes up over 320V then you would expect things to blow up anyway. If i were running 4 LEDs through a 12V transformer then i would expect 320V input to give me 16V output so still 4V per LED

[mackrackit]

You should see a color change when running at the peak voltage.

Just curious.... What does RMS stand for and how is applied to electronics?

[The Master]

With 4 LEDs running on 12V they are all running at their lowest voltage. I have accidentally put too many volts into some of these LEDs before. They dont change color they just get slightly brighter and stop working after a few days.

Do you mean root mean square? I think someone has mentioned this in one of my previous threads but i didnt quite understand it