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A great feature of the Raspberry Pi Zero is that you can tether it to a PC, Mac or iPad Pro by connecting it directly to a USB port. It can act as a USB-Ethernet-adapter and you can ssh into the Pi.

The original Pi Zero draws little power so the USB port is able to provide enough current to power it.

The new Raspberry Pi Zero 2 W is comparable in performance and power usage to a Raspberry Pi 3. It can draw up to 2,5 A of power. I worry that this is a problem when powered by a computer's USB port only.

Is the 2 W able to throttle its power use in this situation? Will it overload the USB port? Can the power dip and cause random reboots or memory card corruption?

gray
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1 Answers1

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I found the official guideline so decided to post an answer.

  • Recommended PSU current capacity: 2A
  • Maximum total USB peripheral current draw: Limited by PSU, board, and connector ratings only.
  • Typical bare-board active current consumption: 350mA

The power requirements of the Raspberry Pi increase as you make use of the various interfaces on the Raspberry Pi. Combined, the GPIO pins can draw 50mA safely; each pin can individually draw up to 16mA. The HDMI port uses 50mA. The Camera Module requires 250mA. USB keyboards and mice can take as little as 100mA or as much as 1000mA. Check the power rating of the devices you plan to connect to the Raspberry Pi and purchase a power supply accordingly. If you’re not sure, use an externally-powered USB hub.

You can check the status of power output to the USB ports using vcgencmd.

There is also a table "power (in amps) drawn by different Raspberry Pi models during various workloads" but sadly Zero 2 W is not part of it. But I think the 3B model can be used a s a reference.

  • Boot: max 0.75, avg 0.35
  • Idle: 0.30
  • Video playback (H.264): max 0.55 avg 0.33
  • Stress: max 1.34 avg 0.85
  • Halt current: 0.10

My Zero 2 W though idles at around 0.1A according to a cheap USB charging meter (but I've seen it occasionally over 500mA). And during boot and installing packages I've didn't see it go close to 1A. It's wifi is single band instead of dual band. CPU is 1Ghz instead of 1.4, so I expect a lower consumption than the 3B.

Given that I connect no external devices to it, I decided to run it on an old smartphone power supply rated 1A. I don't have any stressing workloads on it, just a simple linux network service for the local network, so I believe it should be pretty much safe to run like that without special optimizations.

Worth mentioning is the article posted by @gray about Raspberry Pi Zero 2 W power consumption in the comments section of your question that explores different ways to load and optimize power for a Zero 2 W device with and without external devicces.

P.S. another interesting section of documentation is "Power supply warnings". It is possible to see in logs when "the supply voltage drops below 4.63V (±5%)". But it is not specified whether the Zero 2 W model has it. It is absent from the other Zeroes.

akostadinov
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