LED Project Design Guide - Power Supplies
Power Supplies:
A very important aspect that is often over looked. A proper power supply is usually selected after all the other components. As the required ratings are dependent on the required voltage for the LEDs, and the required current based on how many LEDs need to be powered. This can be fairly complex or simple, not all power supplies will function the same.
Power supplies are available in many types and qualities. A poor quality supply can frequently ruin a project or cause numerous headaches. As power supplies can be responsible for inconsistent LED light intensity, data drop outs, flickers/strobes/noise, controller resets, over-voltage spikes, and so much more. Typically the heavier the power supply the higher quality it is, but that is not a rule.
Voltage: Check your LED's or pixel's specifications for the required voltage. Typically 5 volts for addressable pixels, some pixels may require 12 volts(WS2811 sometimes). Standard LED strip is usually 12 or 24 volts. Loose LEDs or high power LEDs have various requirements that would be listed on the specification sheet from the manufacturer.
Amperage: The more LEDs that need to be powered the higher this requirement is. It is recommended to use a power supply with a rating at least 10% greater than the requirement. The rating of the power supply can be above the amperage requirement, it is fine to use a 3A PSU to power 1A of LEDs, as an example.
Calculated Amperage: The calculated amperage rating will be the absolute maximum in theory. In practice, the LEDs or pixels would never draw that much current. It varies significantly and there are other factors that limit current.
Calculated Amperage Rating for Pixels: Each pixel is typically 3 LEDs(RGB), a typical single LED draws 20mA maximum, so absolute maximum draw is 60mA per pixel for RGB, 80mA for RGBW.
100 RGB pixels x 60mA = 6000mA = 6 Amps
50 RGBW pixels x 80mA = 4000mA = 4 Amps
Calculated Amperage Rating for Standard LED Strip: For 12 volt RGB LED strip there will be 3 RGB LEDs in series per strip section. LEDs in series use the same current at a higher voltage, each color requires 20mA per for a total of 60mA(for RGB) per section. In wattage that is 12 volts x 60mA = 0.72 watts.
Actual Real-World LED Amperage Draw: The values calculated above reflect the absolute maximum draw that could occur. In actuality the LEDs will never draw that much current due to a few reasons. In order to reach those values every LED would have to be set to the maximum color values which is usually (255,255,255). Most color sequences will never display those values, but it could easily or mistakenly be done. Additionally, the resistance of the wires, connectors, strips, and interconnects will limit the maximum current that is delivered to the LEDs. If the LEDs did draw their maximum, or close to, current it can cause issues in the entire system. Power supplies could droop and loose their voltage regulation which can cause over-heating in the PSU, controller resets, pixel resets, noise/flickering/strobing, and numerous other issues. That can sometimes require manual reset of the whole system, but disconnecting the pixels and allow a normal startup. Commonly it can be expected to draw 25-50% of the maximum calculated current during normal usage.
Power Supply Amperage Draw: Using ohms law a power supply that outputs 12 volts at 10 amps outputs 120 watts, and would draw around 1 amp from a 120VAC outlet. Or 0.5 amp from 240VAC.