LEDs in Parrallel

i have 15 LEDs connected in parallel so there are one GND and one supply 5 Volt ,

how to calculate the power consumed to put the right resistor .

i'm going to use 320ohm but how much watt .

P=I^2 V

i don't the consumption of the 3mm LEDs

It is not good to connect LEDs in parallel. They are not exactly the same (flashlight manufacturers test them then sort them into groups so they are nearly the same).

Their voltages will be a little different. So the one with the lowest voltage will hog all the current and burn out, then the one with the next lowest voltage will hog all the current and it will also burn out. Then the one ...

They will burn out qhickly until a few with the same voltage will be extremely bright and last for a couple of minutes.

If their voltages are matched fairly then they will each have a different brightness.

Each LED needs to have its own current-limiting resistor. Then they will last a long time and their brightnesses will be the same.

If the LEDs are 2V red ones then 3V would be across the 320 ohms resistor (not a standard value) and produce a current of only 9.4mA. Each of the 15 LEDs would have an average current of only 0.6mA which is extremely dim.

If the LEDs are 3V white or blue ones then their total current is 6.25mA and only 0.42mA each.

Most ordinary LEDs have a max allowed current of 30mA. Use 25mA to be safe.

If the 320 ohm resistor has 2V across it then it dissipates only 0.0125W. Exactly 1/20th of 1/4W. Almost nothing.

What is the forward voltage and color of the LEDs?

if you need to work out how much watts a led is going to use,

first lets say your LED runs at 2.1V, from a 5V supply, you would be using a 150ohms resistor at 0.020Amps so 20mA

so thats 5V - 2.1V = 2.9V then 2.9V divided by 0.020Amps = 150ohms

(the answer is 145ohms but they dont make one of them so go to 150ohms)

then if you want to find the power(watts) you simply go 2.1V x 0.020 = 0.045 so thats 45 milliwatts

hope this helps

i'm using the same type for the 15 led , and all is red colour

What about using strings of LEDs in series? Say, 3 strings of 4 LEDs each and one string of 3 LEDs? Each string needs its own current limiting resistor.

Would something like the attached work?


Torben

Torben said:

What about using strings of LEDs in series? Say, 3 strings of 4 LEDs each and one string of 3 LEDs? Each string needs its own current limiting resistor.

Would something like the attached work?


Torben

Click to expand...

Morning Torben,
I think the RED LED's the OP are using have a Vfwd of 2V, also it wants to use a +5Vsupply.

Best he could do is 2 LED's in series, times 8 sets.

ericgibbs said:

Morning Torben,
I think the RED LED's the OP are using have a Vfwd of 2V, also it wants to use a +5Vsupply.

Best he could do is 2 LED's in series, times 8 sets.

Click to expand...

Oh yes, you're right. My solution would have required 8V and therefore different resistors.


Sorry (and thanks),

Torben

My solar garden lights have a simple switcher circuit with a tiny inductor to boost the 1.2V from a Ni-Cad cell up to 3.5V to light a multi-colour LED.