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I'm planning on controlling a 5m 60 LED/m WS2812B chip 5V strip with a Raspberry Pi Zero W. According to the website it draws 18 watts per meter (90 watts total). What current would this strip draw, and what would you recommend on powering both the Pi and the strip from one PSU? Any link to some decent, budget ones would be appreciated.

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90W at 5V comes out to 18A. You can find several 5V 20A power supplies around.

P(power)=V(volts)*I(amps) therefore I=P/V 90W/5V=18A

I have built several similar projects using WS2812b with Arduino and LPD8806 with Raspberry Pi. I used this 5V 60A power supply and it has been running in my attic for years with no issues. Its a bit large for what you need but at $20, you're not going to find much cheaper.

Unrelated to the power supply, its a lot easier to use the LPD8806 or some similar 4 pin cable with RPi because you can control the clock. The three pin addressable strips need to have their data output at a very specific frequency and it can be troublesome to run long strips. It can be done, especially with the short run you have, and the 3 pin version are usually cheaper.

P.S. Hardware Recommendations is a good site for these kinds of questions.

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90 Watts at 5 volts is 18 Amps, so you need a 5 volt power supply that can supply at least 20 Amps - perhaps 25 Amps to allow a safety margin.

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I'm surprised that existing answers didn't explain how to calculate this. If you don't know the relationship between voltage, current, resistance, and power, you'll forever be asking the same sorts of questions.

Ohm's Law and electric power (sometimes called Watt's Law) are fundamentals that might well be considered Electronics 101.

Ohm's Law:

\$I = \frac{V}{R}\$

Electrical Power:

\$P = VI\$

Where:

  • \$I\$ is current measured in amperes (A),
  • \$V\$ is voltage measured in volts (V),
  • \$R\$ is resistance measured in ohms (Ω),
  • and \$P\$ is power measured in watts (W)

The two relate to each other, so you can rearrange the equations to find missing terms. There are countless helpful "cheat sheets" like this one:

Ohm's Law with Power

(Sometimes you will see E for 'electromotive force' instead of V for 'voltage'. They're the same thing.)

Now that you have this information, you can rearrange to use what you know (power = 90W, voltage = 5V) to find out what you want (current = ?A).

If \$P = VI\$, then \$I = \frac{P}{V}\$. 90/5 is 18. That's how the current was determined from the other information you gave.

I also suggest that you read this excellent Q&A by Olin about selecting power supplies, which will explain more about how current is drawn by the load and may shine some light on why you want a power supply that can meet your requirement of 18A as a minimum.

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  • \$\begingroup\$ "Electrical Power" is called "Watt's Law". \$\endgroup\$ – Harper - Reinstate Monica May 1 '20 at 23:53
  • \$\begingroup\$ Yes, I mentioned that in parenthesis. \$\endgroup\$ – JYelton May 1 '20 at 23:58
  • \$\begingroup\$ Funnily enough, I actually found 18 amps before I posted this question; however, I thought that was far too high for an LED strip (I've only worked with 12v ones in the past). Perhaps I should have included that in my original post. Thank you for your reply \$\endgroup\$ – Aden Rob May 6 '20 at 5:12

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