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I want to power my Pi Zero from the header pins, pin 2 and pin 6 specifically. I know that my Pi Zero can consume up to 120mA, and my power supply can provide up to 500mA. I've heard that the 3.3v rail on the header can output up to 50mA, but I doubt this is related to how much the 5v rail can be supplied.

So my question:

Is the header capable of being supplied 120mA?

and

What is the max current that I can supply to the header?

Patrick Cook
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  • If it can output max 50mA then that is the max it can handle for in and out? But that seems a bit low though, I suppose you are wondering why the limit is 50mA too. – Piotr Kula Feb 15 '16 at 08:34
  • @ppumkin I'm almost 100 percent sure that the limit for input isn't 50mA. I've powered a 2B from the header, and the 2B cannot run from 50mA. – Patrick Cook Feb 15 '16 at 08:35
  • Yea I agree. Where did you read about that 50mA limit. It is very strange. – Piotr Kula Feb 15 '16 at 08:37
  • @ppumkin Another question here, a long time ago. I'll see if I can't link it. – Patrick Cook Feb 15 '16 at 08:37
  • @ppumkin Ah! Here: http://raspberrypi.stackexchange.com/questions/9298/what-is-the-maximum-current-the-gpio-pins-can-output It turns out that there is no limit to the output current (it's whatever the usb input has) it's the 3.3v rail that has the total max of 50mA! – Patrick Cook Feb 15 '16 at 08:39
  • Heehehe. Yea 5V should be fine to 1A even 2A but I wouldnt push it that far. – Piotr Kula Feb 15 '16 at 08:41
  • Sorry, Iwill vote to close this question as its really a dupe. Did you get your answer though? – Piotr Kula Feb 15 '16 at 08:41
  • @ppumkin where is the duplicate? I'm asking about input, not output. – Patrick Cook Feb 15 '16 at 08:42
  • I suppose, the same difference. Ehh.. I will leave it to the moderators. – Piotr Kula Feb 15 '16 at 08:58

2 Answers2

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The header power is connected directly to the uUSB connector power and therefore you can power up to 2A through that power supply.

But there is still a current limited between 5V and VBUS on the USB so you're limited to pushing 1.2A out of the VBUS

So your total supply would be around 1.32A to the Pi Zero

GSH
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  • Hello and welcome. Are you absolutely positive about this connection between header and µ-USB port? That would be a significant design change compared to the power circuitry of the other Pi models. – Ghanima Feb 15 '16 at 08:53
  • @Ghanima I've heard others before say this about the 2B but I've never seen any sources/proof. – Patrick Cook Feb 15 '16 at 08:59
  • Yes, absolutely certain, I do have the schematics and have checked! – GSH Feb 15 '16 at 09:19
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    @GSH the Pi Zero's schematics haven't been released yet I thought. Would you mind sharing what you're looking at? – Patrick Cook Feb 15 '16 at 09:26
  • Can you clarify what you mean by limitations on current 'out the the VBUS' pin? Do you mean a limit in the USB spec, a limit on current that can be supplied to other devices on the bus, or a limit on current that can be supplied via the 5V pin to the Pi Zero itself? – dcorking Feb 15 '16 at 14:00
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    Sorry, looking at the schematic again I missed the point that U13 is not fit. So actually R74 is a zero ohm link between 5V and USB VBUS. So there is no limitation between the GPIO 5V and the USB output supply. No I can't share the schematics, that's what you get for being Director of Engineering at Raspberry Pi... – GSH Mar 16 '16 at 21:23
  • Ok so if I am using 6 leds (20mA each) on GPIO pins directly, will it burn my RPI2 or not? What's about thos 50mA? – Flash Thunder May 08 '16 at 07:54
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There will be many ifs and buts here... For one thing, there are no schematics available from raspberrypi.org so we have to assume that the power circuitry is somewhat similar to other models - lets look at the B+. Using the pin header and not the micro-USB port to power the Pi will circumvent the protection circuit including the poly-fuse - you have been warned.

Is the header capable of being supplied 120mA?

It's highly likely that this is possible.

What is the max current that I can supply to the header?

The max amperage of header pins is listed with 1 through 3 A (depending on which product you look). However the Pi Zero does not provide a populated header pin, just via holes in the PCB. So the current is only limited by the width of the traces on the board. I'll go with the educated guess here that the board is designed that way to support the current necessary to operate the Pi.

Glorfindel
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Ghanima
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  • I don't think the Pi Zero has a polyfuse or any input voltage protection circuitry. Powering through the microUSB rather than the header only protects against polarity reversal (assuming you use a correctly wired microUSB plug). – joan Feb 15 '16 at 09:23