I want to connect my Pi Zero directly to a 5V 10amp power adapter (shown below) which in turn connects to a wall outlet. I know that with LEDs you can't just connect it directly to the power source without sticking a resistor in between. Is that also the case when wiring up Raspberry Pis to an adapter or am I fine to just connect it directly to V+ and V- on the adapter?

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    How much adjustability does that supply have? I'd be more concerned about that than overcurrent. (absent-minded fiddling...poof!) – AaronD Sep 1 '18 at 4:25
  • @AaronD I'm actually not even sure what you mean by adjustability, do you mean like the ability to adjust the output voltage?.. I don't think it has any adjustability – Matt Sep 1 '18 at 4:30
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    There's an ADJ screw next to the PSU's terminal block that sets the exact output voltage. "5V" is more of a nominal figure, given that. – AaronD Sep 1 '18 at 4:37
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    Yep! That's the idea! I have to remember that myself when I use an adjustable DC-DC converter to power a Pi. The ones that I like are set way high by default, so I put a meter on it and turn it down to 5V before I hook up the Pi or anything else I might want to hang off of that rail. (maybe 5.1V to allow for some tiny-wire loss - datasheets for 5V parts typically have 5.25V as an absolute max, and my meter isn't actually calibrated) – AaronD Sep 1 '18 at 4:49
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    Nope. There's only ONE thing that could be useful between PSU and Raspberry.... A fuse. And that is only for boards without a polyfuse. – svin83 Feb 9 '19 at 7:09

Do NOT use a resistor; on the contrary the resistance of the leads on many power supplies is too high (even though a fraction of an ohm) which causes low voltage problems for many Pi users. Use generously sized leads to connect to the Pi.

The PSU you show is suitable - they have good regulation. I use a similar model to power up to 4 Pi.

NOTE the comments about current rating are an urban myth; it is a problem if the rating is too low, but there is no problem with higher rated supplies.

Similarly the comments about poly-fuses is misleading - the Pi Zero doesn't even have one!

  • Thanks @Milliways you basically reiterated the conclusion I'd come to as well after further research :). One question for you on the polyfuse part. I will be connecting up a lot of raspberry pi Zeros to that power supply. Should I still in polyfuses of my own for safety if something shorts and 10amps accidentally gets sent into one Pi? – Matt Sep 1 '18 at 3:45
  • still connect polyfuses in case something shorts** – Matt Sep 1 '18 at 4:19
  • @Matt "10amps accidentally gets sent into one Pi" is meaningless. You supply a voltage. If you short 5V you will actually get a much higher current - the 10A is just the current the PSU can SAFELY supply. You will find it difficult to get polyfuses in small quantities and are invariably surface mount devices. If it worries you use a normal (fast blow) fuse - but the additional wiring increases the possibility of mishap. – Milliways Sep 1 '18 at 5:10
  • thank you for the great explanations. With that in mind, if I somehow accidentally short the 5V with my given setup, do you see there being risk of fire or will it just fry the Pis and stop working? If risk of fire I'd be inclined to buy a fast blow fuse just in case. – Matt Sep 1 '18 at 5:14

Don't put any resistor in series with the Pi when connecting it to a voltage source. — Uh, and 10A is overkill. You can't run 10A through the 5V tracks on the Pi's board. These are for about 2A only. You can of course run another set of +5V/GND wires to the devices you want to control with the Pi.

The reason you use a series resistor for LEDs is that they have almost no internal resistance. So you have to limit the current, or the LED, and probably other components, will burn out or blow up.

  • Gotcha, makes sense. I know 10amps is too much for 1 Pi but it's what I have lying around. Shouldn't it be fine since the Pi Zero will only draw whatever amps it needs to use? – Matt Aug 31 '18 at 21:54
  • Yes. It will only draw as much it uses. The only problem you will run into is when you overload/short the +5V line on the GPIO connector or the USB. You will burn the polyfuse then because the power source just can. If you used a 1A power source, it will simply go into overcurrent and the fuse stays intact while the Pi is crashing. – Janka Aug 31 '18 at 21:55
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    Huh? The problem is only about the possible overload through the tracks of an individual Pi board. That's why they have the polyfuse. Minimizing defective parts. But you can minimize that even more by not allowing the power source deliver more current than the polyfuse can handle. – Janka Aug 31 '18 at 22:04
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    If your +5V power source can deliver 10A and you have a short on the USB or GPIO +5V pins, there will be 10A running through the +5V tracks of the Pi's board. That's too much, it would fry the tracks and your Pi would be gone then. That's why the polyfuse exists. It's still a hassle to replace it but at least the Pi not damaged beyond repair. If you used a power source that has a limit of e.g. 1A, it would not deliver +5V any more if you have a short on the GPIO +5V pins or USB. It either limits the current to 1A (at a lower voltage then) or goes into a complete, but recoverable failure. – Janka Aug 31 '18 at 22:14
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    Either way, both the Pi and its polyfuse stay intact. No chance to shoot them. (The polyfuse is a tiny SMD fuse soldered on the backside of the Pi, near the Micro-USB connector.) – Janka Aug 31 '18 at 22:15

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