I want to connect 20 Raspberry Pi Zeros (5V, .200-.300A) to a 5V 10A power supply shown below. The setup Im planning will look like the photo below but with many more Raspberry Pis.enter image description here

I posted my setup on the Raspberry Pi Stack Exchange here where I was told this was unsafe, but I did not really understand why or how to fix it. The guy was telling me something about a polyfuse on the Pi Zero that might blow, but when I googled that, apparently a polyfuse is not a component on the Pi Zero, so I figured I would come here for a second opinion.

My thoughts are this, please correct me if Im wrong (in simple terms since I'm a noob). The power source is 5V 10A rated so if I were to just connect that 1 Pi shown in the photo it should be totally fine since it runs on 5V and it will only draw the amperage that it needs from the power source. Alternatively, I could also hook up 20 Pi Zeros to that terminal block in the photo, since cumulatively they would only draw 4-6Amps of the 10amps available (and they all run on 5V). This seems safe to me but maybe I'm missing something.

  • \$\begingroup\$ You should be just fine. \$\endgroup\$ – Ale..chenski Aug 31 '18 at 22:43
  • \$\begingroup\$ @Ale..chenski thank you. Can I take that to mean that my logic in the last paragraph is correct - I just want to make sure I'm not about to break all my Raspberry Pis :P? \$\endgroup\$ – Matt Aug 31 '18 at 22:45
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    \$\begingroup\$ If you are sure that each Pi Zero doesn't consume more than 500 mA, then you should be fine. Keep in mind that any additional USB peripherals that you or someone might connect to RPiZ will draw extra current from the same power cord. Webcams, for example, can consume a lot. \$\endgroup\$ – Ale..chenski Aug 31 '18 at 22:51
  • \$\begingroup\$ @Ale..chenski very good point. I'll measure the amperage with peripherals on 1 Pi to be sure. Would you also be able to share your opinion on what the person in the post I linked here was trying to tell me in the comments of his answer. He seemed very concerned about something that I wasn't advanced enough to grasp. I'm worried I am missing something \$\endgroup\$ – Matt Aug 31 '18 at 22:53
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    \$\begingroup\$ In the hope of preventing reverse polarity connections, I would use different coloured wires for the positive and negative connections. Traditionally, Red is used for positive, and Black for negative. \$\endgroup\$ – Peter Bennett Aug 31 '18 at 23:06

Just be aware of what happens during a failure.

If you short circuit something inside the rpi, or powered through the rpi, then >10amps will flow through the rpi, cables (e.g. usb cables) etc

Do you want this to happen? Can it turn the fault from "crashes program" to "destroys rpi" or "burns down house"?

I would power each individual rpi through a polyfuse.

Also be aware that a 10A power supply likely means "not more than 5A running 24/7"

5V/10 amps used to be a fairly safe level when shorted, as the voltage drop across the wires would be very small, and the psu would shut down. However now cables like usb cables have such thin copper that there can be significant resistance, a large voltage drop so the psu does not shut down, and enough heat generated in the cable to melt the plastic.

When I tested some cheap USB cables a while ago, they caught fire at ~5amps. This was not surprising when I cut them as the conductor was fuse wire thickness. The plastic was not self extinguishing

  • \$\begingroup\$ Ok so if I understand correctly, then it should work fine UNLESS it short circuits, then that is a major issue with my current setup. To mitigate that issue I can get 40 polyfuses (do these have different amperage/voltage ratings?) and stick each polyfuse between its respective white usb cable and black 18gauge wire (as shown in the photo). By doing this, the polyfuse will block the 10amps from flowing to the Pi and USB cable in the event of a short, thereby preventing overheating/fire. Am I understanding correctly? \$\endgroup\$ – Matt Aug 31 '18 at 23:05
  • \$\begingroup\$ @Matt Yes. And yes (like all fuses) PF have many different ratings. They are thermal, they heat up to shutdown, so they must have resistance. You have to balance your desire to have a low shutdown current, with the need to have low voltage drop during normal operation. However 2A (say) is far less damaging than perhaps 15A fault current the supply can deliver. \$\endgroup\$ – Henry Crun Aug 31 '18 at 23:10

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