I have a hypothetical project in mind I would like to pursue but wanted to ask this before sinking too much time into it. That being having multiple SPI slaves connected to a Pi Zero. From what I've read here(Raspberry Pi Power Limitations) the Pi Zero is the simplest and safest board because "the use of a power safety diode is probably superfluous, as the Zero does not have one, or indeed any protection circuitry." Not really to sure what that is, but besides, it is also the lowest power consuming board of the Pi family which suites me regardless.

So let's say I have a 5V 8A PSU powering the Zero through the 5V pin, and then attached 6 Arduino Nano's over SPI. These Nano's would also be powered via their own 5V pins from the Pi's other 5V pin.

On a normal 2.5A micro-USB charger for the Pi Zero, 0.5A could be allocated to the Pi Zero, and then 1A each to 2 Nano's. This configuration should be within the Pi's normal design considerations. But with a 7-8A PSU supplying the Pi and 6 x 1A Nano's(30W), I was wondering if this would cross a point where the traces would potentially melt down?

I couldn't find a specific answer for this anywhere. What is the maximum Watt limit of the copper traces, or the 5V pin, before they melt?

Another solution would just be to power Pi and each Nano in parallel from the PSU instead of powering the Nano's downstream of the Pi. But once I started wondering about the max wattage of the traces I was curious if anyone knew?

  • what you are describing makes no sense ... why would you not power everything from the 5V 8A PSU directly?
    – jsotola
    Jul 18, 2021 at 18:20
  • 3
    One good thing about powering all of these devices from a single PSU is that you can destroy all of them in far less time than they could be destroyed individually :P It may not be smart - but it's efficient.
    – Seamus
    Jul 18, 2021 at 18:58

2 Answers 2


As the power pins are connected to the same pad this is unlikely to be an issue.

It is still a bad idea.

I think you are overestimating the current your devices would require, but it is significantly higher than the Pi and would lead to voltage drop in the cables, unless you use infeasibly large cables.

This probably won't worry the Arduinos but the Pi is sensitive to voltage.

An engineer would wire each device in star configuration back to the power supply to minimise voltage drop and common mode interference.

It is not true that "the Pi Zero is the simplest and safest board"; it may be simple i.e. primitive. Omission of protection may make it cheaper (these are built to a price, using the cheapest components available) but this makes it vulnerable.


Regarding PCB trace capacity, there is a lot of general information out there on the web. A calculator like https://www.mclpcb.com/blog/pcb-trace-width-vs-current-table/ may help you make an estimate. However, as the comments indicate, this is probably not a productive line of thought for your project. Reading up on the power requirements of each of your loads and designing a power solution which doesn’t route all power via the PI Zero could be an alternative way to approach it.

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