Elecrical Question

[drdichotomy]

Hi All,

I was wondering if anyone could tell me how to plan on using a PSU rail which outputs 12VDC at 18amps. Do I need to try to use every amp or will my array of high power LEDs (plus resistors) just draw what they need?

The LEDs: Vf=2.9 & If=1000mA
(Max @ Vf=3.2 & If=1500mA)

I was thinking of doing multiple strings of 4 LEDs which are wired in series. Will I need to do 18 strings?!

 

[LEDependent]

A 12V power supply will maintain 12V across its load, varying the current with the resistance of the load. Your power supply is rated at 18 amps MAX, so you don't want to exceed that amount.

You didn't mention how many total LEDs you have, but stringing 4 LEDs in series will negate the need for resistors. Each 4-LED strand will draw between 1 and 1.5A. Connect multiple 4-LED strands in parallel.

-Jason

 

[steve6690]

short answer = no
a power supply rated at 12 volts, 18 Amps will supply 12 volts constantly, at a current of up to 18 Amps maximum. So it's perfectly happy giving 12 volts at 1 Amp too..

 

[Oznog]

You didn't mention how many total LEDs you have, but stringing 4 LEDs in series will negate the need for resistors. Each 4-LED strand will draw between 1 and 1.5A. Connect multiple 4-LED strands in parallel.

This is not a good idea. If the devices are on the low end of rated Vf, then currents can be very high... and Vf goes down with temp, increasing the current further. They can runaway and burn up. You need a current drive.

With a regulated 12v, 3x in series and then a ballast resistor to eat up the voltage difference will probably be ok, although 2x in series with a larger resistor still would be better regulation but less efficient and the resistor will need to be huge.