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# Can I run 10w 12v leds directly form a switching power supply? Answered

Hi, I have a regulated switching power supply with 12vdc 400w output (similar item pictured below) and I need to power around 20 10W LEDs which are rated at 900mA. Can I wire these in parallel directly from my power supply since I know the voltage can't change meaning that the current (and heat) shouldn't really change?

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These are actually "smart" driven LEDs. They have their own electronics to control each LED. Just run them in parallel on your supply.

Yes !.......

20 x 10w = 200w that is good because the 400w PS power supply could supply almost 40 LEDs.

LED voltage = 10w / 0.9amps = 11.1v that means a 12 volt supply should work,

But I would put an 1N400x diode in series with each LED to drop the voltage going down going to each 10w LED.

Or the PS may have a voltage adjustment that will let you reduce the output down to 11 volts.

A

I will check to see if I can advust the volage on my power supply now, thank you for replying.

Its not often I actually disagree with Iceng, but this is it. NEVER run LEDs in parallel, and never run them from a constant voltage supply. The only safe way to run them is with a constant current supply, and put them in a series string.

Though the VOLTAGE is constant with the supply you have, the current is NOT. As the LEDs warm up, the warmer ones take more current, stealing current from the others, and you get a nasty reaction where one LED steals all the current and promptly blows up. Then another LED takes over, and the whole lot can blow in a matter of seconds.

I agree with you. Don't put plain LEDs in parallel. See the uneven LED intensity of 125 LEDs in parallel.

The 12 Volt 10 Watt LEDs that I have been using, come with internal resistance built in for automotive use.

Of course if they are some kind of direct series LED only groupings then you have to add a series current limiting device to each one and a 12v supply may be too low a voltage to do that.

Thanks for your reply. I have got 20 12v 900mA drivers (which look something like this http://i.imgur.com/i5H9qs8.jpg), my reason for not using these was only to simplify the circuit. Would you object to running these in parallel since they each will receive a 12v input and each will deliver 900mA to every LED? I'm not sure if my terminology is correct so I have included a crude diagram to try and explain what I mean http://i.imgur.com/TuAoB89.jpg

Sorry for asking so many questions but this is my first attempt at working with high power LEDs. I know that they need a lot of cooling have already got heat sinks which are much bigger than the recommended size.