LED in parlallel and power consumption

[yassin.kraouch]

Hi,
If i have 10 LED connected in paralllel, which consume 60mA and Vf=3V,
and i have a power supply that gives 12V and output power max is 6W,
normally the load power consumption is 3*0,06=1,8W,
can i say that the power supply is able to supply the LEDs ?
i am confused because if we calculate the current consumption of the LED it is equal to 600mA,
which is more than 500mA,

 

[barry]

Your power supply can supply 6W, but only 500mA. You can't connect your leds directly to your 12 volt supply. (Well, you can if you want damaged leds.) You need to drop the voltage to the leds, and that means wasting a lot power in a dropping resistor. THAT'S where your losing a lot of your power.

 

[kam1787]

use http://ledcalc.com/

use 3 LEDs in series with a resistor - called that a string, connect 3 strings in parallel

 

[D.A.(Tony)Stewart]

1st specify the tolerances on everything. Is it 12V +/-2% 10% 20%? and are the LED specs 3.2V+/- 0.2? or more?

Then to optimize the load, choose 3 LEDs in series (conservative) with 1 R to limit the current using Ohm's Law on the difference voltage and thus 3x60mA is the load.
A 6W supply is often unregulated and drops to rated voltage at max load, in this case 500mA and with no load can go as high as 40% over nominal (1.4= root 2 = peak/avg of sine wave bridge rectified)

Following this assumption....
You will be using 180/500mA or 36% of rated power of source, your source may be closer to 13.7V .

It is possible to run strings of 4 with a smaller R depending on the LED if it is 3.0 or 3.2 or ??

Most people use strings of 3 so it can be operated on cars from 12 to 14.5V such as in SMT Reels for WHite