Angie_MY
Joined: 10 Oct 2007
Posts: 22
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 03 Jan 2008 10:08 Could i replace chrismas light bulbs with LEDs? |
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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
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IanP
Joined: 05 Oct 2004
Posts: 6490
Helped: 1542
Location: West Coast
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03 Jan 2008 11:28 Re: Could i replace chrismas light bulbs with LEDs? |
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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:
http://ww1.microchip.com/downloads/en/AppNotes/00954A.pdf
Regards,
IanP
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