Driving LED with 12v adaptor

[cwloo]

Hi All,

Just wonder is that safe to run 3 x 3 watts LED (3.5vf x 3) over a regulated 12v adapter (e.g meanwell adapter) and use a 1amps fuse (pic below) to limit the current draw ?


*image removed by Greta... please read the rules regarding hotlinking images*


Saw someone else doing that in other forum .. seem to be a cheaper and easier options to run a multiple array of LED from the meanwell adapter.

 

[Light Sabre]

A fuse won't limit current draw the way that you are thinking, you need a resistor for that. You need to find the right resistance and wattage for the series resistor.

12 volts - (3.5 volts VF x 3) = 12 volts - 10.5 volts = 1.5 volts to drop across the series resistor so you don't over drive your LEDs.

Amps of circuit = Watts/Volts = 3*3 watts/10.5 volts = 9 watts/10.5 volts = 0.86 Amps.

Watts of resistor = Volts * Amps = 1.5 volts (across the resistor) * 0.86 (amps in the circuit) = 1.3 Watts dissipated by series resistor. Round up to 2 watts, preferably 3 or maybe 5 watts.

Resistor = Volts/Amps = 1.5 volts/0.86 amps = 1.74 ohms. Round up to 2 ohms.

So after all is said and done, you need a 2 ohm, 2+ watt series resistor for your circuit.

<crosses fingers> I hope I got all of that right.

 

[Mr_Light]

LED series/parallel array wizard

http://led.linear1.org/led.wiz

 

[cwloo]

understood.
hmm, so as long as I stay within the max current and safe voltage I am fine ? e.g connect 2 x 3 watt LED (3.5 x 2 = 7 vol) using 6 vol 600mah adapter ?

 

[TorchBoy]

Is it fine if you under drive your LEDs so much you could just use a couple of 5 mm LEDs instead?