Could i replace chrismas light bulbs with LEDs?

[Angie_MY]

just passed wonderful chrismas 2007, but found out quite some chrismas light bulbs(small light with wire go around chrismas tree) burnt.

i go electronic shop, but they told me they not selling this kind of light bulbs...

therefore, i am thinking to change all the light to LED...

but could LED stand 240Vac?

thanks

 

[IanP]

In general, LEDs can not be used as a drop-in replacement for bulbs ..
However, if you are prepared to modify this light string and make it almost “indestructible" here is what you can do:

- replace all bulbs with LEDs ..
- use bridge rectifier (1A-400V) to convert AC voltage to DC ..
- count the number of LEDs and multiply it by 2.5 (≈voltage drop across an LED) ..
This will give you voltage across the whole chain ..
Example:
If your chain had 30 LEDs ..
30*2.5V = 75Vdc
240Vac rectified, but without smoothing capacitor, can be treated as equivalent 240Vdc ..
240-75 = 165V
This is what you have to drop from 240V to operate 30-LED string ..

Next assumption:
LED current ≈16mA
165V/16mA ≈ 10kΩ

One option is to use 10kΩ/5W resistor, another option is to use 330nF/250Vac capacitor ..
Both will drop ≈165V but if you use 330nF capacitor it will not generate any heat, whereas the 10kΩ/5V resistor will ..

Make sure that this capacitor is rated for 250V AC and is not-polarised ..

So, you modified Christmas-tree LED chain will look like this:
240Vac-Line ---> 330nF capacitor --> rectifier --> LED-string --> back to bridge rectifier --> 240Vac Neutral ..

More info on circuit that use capacitors to drop the AC voltage you can find here:
https://ww1.microchip.com/downloads/en/AppNotes/00954A.pdf

Regards,
IanP

 

[Angie_MY]

thanks a lot.
gained a great lesson!