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?

 

I suspect that the three terminals are simply connected together inside the supply - multiple terminals being provided for the convenience of the user. The spec says (if I understand it correctly) that at 60% maximum load it will be 60°C above ambient and that has a cooling fan inside. I expect you will need to ventilate the box it is in and it will possibly need a fan on the box to circulate air through the box.

 

Even at 90% efficiency, the supply will dissipate about 16W @ 31A output.
I would add a small fan to an opening in the box to vent the box, with another vent on the opposite side to provide a path for the air.

 

You may also need to put a fan on your LED cube as well given it will be dissipating some ~ 150+ watts on its own which might put the cubes working temp at the limits of what an LED may handle depending on its design and color.

In my early days of playing with large numbers of generic white LED's for lighting purposes I quickly found out just how hot large groups of LEDS can get when packed in tight. Way hotter than you would think!

 

Yeah, considering how hot the datasheet states the supply can get under load (I've switched to this supply by the way, but the thermals are the same), I'm definitely considering cutting a vent for the supply's built-in fan as well as adding some 40mm or 60mm fans to the lower (supply/logic) portion of the case

@tcmtech : Hopefully I won't run into heat issues due to the LED dissipation alone, the nature of the animations/programs I'll be running on mine will hopefully keep the number of active LEDs at any given time pretty low (and give the LEDs a break frequently). Even so, given your experience, would you advise adding another fan or to blow air into the LED chamber as well?

 

If your overall power consumption is not high then the whole cooling issue may be largely unwarranted.

Physical components take time to heat up so short peaks of high load still average out to low overall average power consumption and thus heat generation.

The issues I dealt with were with LED arrays that ran at maximum output 100% duty cycle for weeks to months at a time.