White LED 240 Volts 16 mA lamp -- project 3

[hangu143]

thanks

but Resistors is heat up in 220V

what i do

[bestamerica]

'

nice show video about LEDs,,,

but LEDs can be short time and easily burn out anytime if too long leave the light on all the time

[cktino]

how if 240 volt light the 3 - 5 white LED....how many Resistors and diodes need it ?can hv a drawing ?

[RODALCO2007]

@cktino For a 3 to 5 LED lamp it becomes less efficient with a resistor, so a capacitor would waste less energy, but it affects reliability too (spikes etc).

But for 15 mA led current and 5 LED lamp ( white about 3 Volts drop per led )

240 - ( 5 x 3 ) / 0.015 = R

therefore R = 15000 ohms

I x I x R makes 3.375 Watt resistor needed.

Use two 7k5 or 8k2 Five Watt resistors in series.

[cktino]

@RODALCO2007 thx brother..with the project 4 schematic i can understand the conection led n resistors..... the therefore R = 15000 ohms, so the (I x I x R makes 3.375 Watt resistor ) part i dono the calculatioan I x I is what.... can explain the( I )...

sorry i not a electronic engineer...

[RODALCO2007]

@cktino Power = (current)squared x resistance.

You need to have a look in an electronics book.

It is a standard formula.

Led current max 20 mA = 0.02 Amps

I used 15 mA in previous example.

Then whatever the result is double the R value to have the resistor run under less stress.

[cktino]

@RODALCO2007 thx...now i know the formula to all find the right resitor , mA & watt..

thx for ur explain.

[cktino]

@RODALCO2007 how to calculation the resitor watt need for the resitor ?

[Iseekoutthetruth]

how do you make one for 110 electricity?

[RODALCO2007]

@Iseekoutthetruth For 110V and 19 leds (white) use 4 x 1000 ohm 1 Watt resistors in series before the bridge rectifier. (Instead of the 5 x 2k2 resistros used for 240V)

[kakureru]

you don't need schematics for this.

[dimebag3000]

Can you send me the schematic of this project? is very interesting your Idea.....

[RODALCO2007]

Watch Led project 4 which gives you a detailed schematic, with parts.

[jonathancocaud]

Hi, nice project...But you should use a 400V capacitor instead of your power resistor to avoid heat dissipation and to save power...470nF / 400V should be ok...(look for capacitor reactance...) ask me if you want some explanation about reactance. (in AC, a capacitor can be used to make a resistor that doesn't dissipate power...)

[RODALCO2007]

Thanks for your offer, I know the formula for reactance of a capacitor.

My issue is reliability. In New Zealand we have a lot of overhead lines and occasional surges during storms. Hence the resistive option is choosen.

A cap. can pass a spike through with no problem regardless if a 1 k.ohm series resistor is fitted and destroy the leds.

[DrCassette]

That's really a great idea! It sure saves a lot of money using these lights instead of the normal ones or the compact flourescent ones!

[RODALCO2007]

Just use the old base when the CFL fails.

When the leds run below 20 mA they have an almost unlimited life.