DarkPatate
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[Solved] Is there any current limitation while powering the Pi by GPIO?

Mon Sep 27, 2021 7:05 am

Hello,
I'm powering two Raspberry Pis with the same source that can deliver 6 A. One RPi is powered through the USB-C port and the other one with GPIO pins (+5 V and GND).

On the one powered by GPIO, I have a low power warning, especially when requiring resource-consuming algorithms. Is there any current limitation on the GPIO pins, contrary to the USB?

I tried to increase the over_voltage to 6 in config.txt, but it didn't change anything.

Thanks in advance.

PS: I know the powering pins are not technically GPIO, but I don't know the specific name.
Last edited by DarkPatate on Mon Oct 04, 2021 9:18 am, edited 1 time in total.

pcmanbob
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Re: Is there any current limitation while powering the Pi by GPIO?

Mon Sep 27, 2021 7:12 am

So your problem is one of the following.

Cable between gpio header pins and power supply is too small , leading to volt drop.
Poor connection between gpio header pin and cable, common problem when using dupont cables.

Its recommended that if you are going to power the pi via the gpio header pins you have 2 connection for both 5V and ground between the pi and the power supply.

All current limits remain the same no matter how you supply the 5V to the pi.
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HawaiianPi
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Re: Is there any current limitation while powering the Pi by GPIO?

Mon Sep 27, 2021 7:17 am

Your problem is likely the diameter of the wires you are using to supply power to the GPIO header pins.

You need fat power wires to carry higher currents, and the typical GPIO connecting wires are much too thin. Another problem could be the pin connectors adding resistance and causing additional voltage drop. The fix would be fatter power and ground wires, and using both 5V pins and a pair of ground pins (or solder the power and ground wire connections).

EDIT: Ninja'd by pcmanbob.
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DarkPatate
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Re: Is there any current limitation while powering the Pi by GPIO?

Mon Sep 27, 2021 8:07 am

Thanks, @pcmanbob and @HawaiianPi

Ok, so maybe the cables are the problem. Actually, the first part is a PCB I made, so for me, that part is not the problem (the tracks are thick enough). But after I'm using a 40-pins ribbon cable to plug it from the PCB into the RPi.

I'll try to connect with thicker wire to see if it improves it. I thought using the two +5 V pins at the same time (and all the GNDs) would be enough. So maybe not, the ribbon wires are probably too small.

I'll let you know the results when I found a way to manage the connection.

pcmanbob
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Re: Is there any current limitation while powering the Pi by GPIO?

Mon Sep 27, 2021 8:16 am

Well when you consider ribbon cable is about 26AWG and a pi power supply uses 18AWG ( smaller number bigger cable ) you can see that the ribbon cable is much smaller that what's required to supply the pi reliably.

26AWG is only 0.14mm² while 18AWG is 0.75mm² some sites even list 18AWG as 1mm²

You need to use bigger cable for the power supply part of your project.
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DarkPatate
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Re: Is there any current limitation while powering the Pi by GPIO?

Mon Sep 27, 2021 8:26 am

Is it dangerous to power the RPi by the GPIO and by USB? Because a simple solution for my project would be to use another USB cable, while the ribbon cable is still plugged.

LTolledo
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Re: Is there any current limitation while powering the Pi by GPIO?

Mon Sep 27, 2021 8:29 am

I do power my RPi via GPIO header pins 2,4 (5v) and 6 (Gnd) using a buck converter board on a RPi specific protoboard.
the wire I use for the interconnection is ⌀.45mm solid core polyurethane coated wire
seen below:
RPi buck converter board bottom view.jpg
RPi buck converter board bottom view.jpg (194.53 KiB) Viewed 530 times
no low voltage warnings...ever

for your case... get any electrical wire rated 7A...
the pin connector must be rated at least 3A

added:
another of my power board with extended pins... to accommodate ribbon cables
some pins were covered by the black plastic.
RPi with stacked boards view3.jpg
RPi with stacked boards view3.jpg (190.86 KiB) Viewed 525 times
Last edited by LTolledo on Mon Sep 27, 2021 8:34 am, edited 1 time in total.
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pcmanbob
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Re: Is there any current limitation while powering the Pi by GPIO?

Mon Sep 27, 2021 8:32 am

DarkPatate wrote:
Mon Sep 27, 2021 8:26 am
Is it dangerous to power the RPi by the GPIO and by USB? Because a simple solution for my project would be to use another USB cable, while the ribbon cable is still plugged.
As long as both the the 5V and ground for the ribbon cable and the USB cable are from the same power supply you should be ok.

If you want to use 2 different power supplies then you need to disconnect just the 5V connection between the pi gpio header pins and the ribbon cable.
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rpdom
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Re: Is there any current limitation while powering the Pi by GPIO?

Mon Sep 27, 2021 8:34 am

DarkPatate wrote:
Mon Sep 27, 2021 7:05 am
I tried to increase the over_voltage to 6 in config.txt, but it didn't change anything.
The "over_voltage" setting is internal to the main chip. It won't have any effect on the 5V supply low voltage trigger.
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drgeoff
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Re: Is there any current limitation while powering the Pi by GPIO?

Mon Sep 27, 2021 9:11 am

DarkPatate wrote:
Mon Sep 27, 2021 7:05 am
On the one powered by GPIO, I have a low power warning, especially when requiring resource-consuming algorithms. Is there any current limitation on the GPIO pins, contrary to the USB?
FYI: On a 4B the power pins on the USB-C socket and the power pins in the GPIO header are directly connected. Other than the PCB traces (which are adequate for non-fault currents) there is no electrical difference.
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DarkPatate
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Re: Is there any current limitation while powering the Pi by GPIO?

Mon Sep 27, 2021 9:46 am

@pcmanbob It would be the same power supply, so should be fine. I think it's the easiest solution. Otherwise, I would have to remove the pins on my PCB.

pcmanbob
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Re: Is there any current limitation while powering the Pi by GPIO?

Mon Sep 27, 2021 3:02 pm

DarkPatate wrote:
Mon Sep 27, 2021 9:46 am
@pcmanbob It would be the same power supply, so should be fine. I think it's the easiest solution. Otherwise, I would have to remove the pins on my PCB.
Just make sure which ever USB cable you are going to use is short and fat, i.e uses large cable size.
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boyoh
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Re: Is there any current limitation while powering the Pi by GPIO?

Mon Sep 27, 2021 4:00 pm

What you are doing is Parraleling separate loads off one power supply, There is no problem with this,

What rules you must stick to is the total load placed on the main power supply, must not exceed

its maximum current output ( Impedance )

As a precaution, I would have some OVER CURRENT protection feeding each load connected to

the single power supply ( Each load will only take as much current it needs to satisfy it,s full load

working current .

Regards Boyoh
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DarkPatate
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Re: Is there any current limitation while powering the Pi by GPIO?

Mon Oct 04, 2021 9:18 am

Hello,
I added a USB cable, in addition to the GPIO powering, and now it works perfectly, no more warning. So the ribbon cable was the problem.

Thanks a lot for your help!

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