Powering the Pi

It turns out I’m having a little trouble powering my Octopi unit. I finally got fed up and started digging in with multimeters and adjustable power-supplies and stuff. Here are a few of my observations.

  • Most of my USB cables are apparently crap. Speed Test Even with a bench supply, I’m still seeing a lot of voltage drop even with a very short cable. (the short one actually keeps the Pi out of throttling but I see a 0.15V drop).
  • Watch out for those little USB power monitors. Solitaire I have had one inline but it has enough internal resistance to drop 0.1V which was enough to turn the above into a throttling mode issue.
  • My “Raspberry Pi” power supply works pretty well, apparently clocked in around 5.2V which is great until for some reason it boot-loops when the GUI starts. It was a Chinese knock-off so trashcan for that.
  • The 24V to 5V power converter I got to allow me to run my Pi from my 3D printer PSU is trash. It doesn’t keep 5V at any voltage unless there is 0 draw. It was supposed to be 3A. That’s $3 I’ll never see again (I guess you get what you pay for I take this back. With the shorter cable and no inline monitor, it appears to hold 4.82V on the Pi, 4.92 on the cable.)** .
  • Several of my phone chargers are fully capable of powering the Pi. It’s those shitty cables that are the culprit.

Now, I say I have shitty cables but I have a lot of cables. These may have just been bad luck. Does anybody know what the acceptable resistance for a USB cable for use with a Pi without causing throttling assuming an adequate power supply? I plan to run through all my cables and classify them (and I know for sure I have one or two that should go straight in the trash). Ideally I’d like to build a small tester.