# Getting full power output from 120VAC to 5V40A DC supply?

Oct 27, 2017
2
Hey all,

I'm currently planning on building an 8x8x8 RGB LED cube for class using a series of discrete WS2811 LEDs. Using the usual 60mA/LED figure while at full brightness on all 3 LEDs, I've calculated that the end design will draw about 31 amps in the worst case.

I'm planning on driving the LEDs with this power supply, but I've read in reviews online that power supplies like this with multiple output rails actually only output a fraction of the rated current on each rail. Is this true, or will I be fine pulling up to 31 amps on just one of the three rails? If the rails do only output a certain current (below the total supply rated current), would it be safe to join all the positive outputs and negative outputs in order to create a single rail capable of outputting the rated current?

Additionally, will I need any extra precautions when using this supply in my build? Looking at a tutorial which used a similar (but significantly lower-power) supply, it looks like I should be fine driving the LEDs with just a switch between 120VAC and the supply, wiring the 5V outputs straight to the power and ground pins of the LEDs.

And a final side question, how hot can these supplies get under load? I'm currently planning on throwing the supply in the case with my RPi, will I need to expose the ventilation holes of the supply through the (likely acrylic) case or can I get away with enclosing the whole thing?

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
You missed any useful description of the power supply.

BTW, your calculation assumes 120mA per WS2811. <-- or very poor maths by me! :-(

Last edited:

#### AnalogKid

Jun 10, 2015
2,671
Please post the datasheet for the supply. We don't know if it is linear or switching, a huge difference in your application. In general, no, you cannot just combine multiple outputs together for more output current unless the supply is designed specifically for that.

8 x 8 x 8 = 512
512 x 0.06 = 30.72 A

ak

Last edited:

Oct 27, 2017
2
I could not find the datasheet for the power supply I posted anywhere, but I am now planning on purchasing the power supply with datasheet available here. The datasheet states it is a switching power supply.

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