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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?

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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. – ppumkin Feb 15 at 8:34
    
@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 at 8:35
    
Yea I agree. Where did you read about that 50mA limit. It is very strange. – ppumkin Feb 15 at 8:37
    
@ppumkin Another question here, a long time ago. I'll see if I can't link it. – Patrick Cook Feb 15 at 8:37
    
@ppumkin Ah! Here: raspberrypi.stackexchange.com/questions/9298/… 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 at 8:39
up vote 4 down vote accepted

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

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Thanks! And welcome to the RPi Stack Exchange! – Patrick Cook Feb 15 at 8:47
    
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 at 8:53
    
@Ghanima I've heard others before say this about the 2B but I've never seen any sources/proof. – Patrick Cook Feb 15 at 8:59
    
Yes, absolutely certain, I do have the schematics and have checked! – GSH Feb 15 at 9:19
3  
@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 at 9:26

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.

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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 at 9:23

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