Author Topic: Under Power RPi 3 Symbol  (Read 1379 times)

mlapage

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Under Power RPi 3 Symbol
« on: August 05, 2017, 10:12:36 PM »
I know this has been discussed before, but my problem is low voltage across ATXRaspi R2.8. I have checked the input voltage from my power supply (5v, 2.5a). When I check the output volts it is 3.2v, 2.2a. I do have a 1tb usb drive powered as well using a PiDrive cable. The ATX output goes to the usb drive and then to the RPi 3. As you can see the ATX output is too low. Is this a normal drain across the ATX.
My setup is with a momentary button and the RPi3 boot/shutdown works fine.
Any suggestions or places to look for answers?
Thanks for any help you can give. 

sparky

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Re: Under Power RPi 3 Symbol
« Reply #1 on: August 06, 2017, 09:59:00 AM »
You have any photo's of your setup/solder joints?

Good quality power supply and jumpers could make a big difference.  Felix talks about the importance of this here;

https://lowpowerlab.com/guide/atxraspi/?view=all

Do you have another supply to try?
Look over all your solder joints?
What's the current draw on the usb drive?  Did you try without it connected?

Felix

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Re: Under Power RPi 3 Symbol
« Reply #2 on: August 07, 2017, 09:10:36 AM »
It's crucial the power from the ATXRaspi to your Pi is supplied from 1) a good power supply, and 2) using good wiring that is either soldered directly (best) or has very good/high quality crimped connectors.
There is very little voltage drop across ATXRaspi itself, but weak connections introduce a lot of resistance between the ATXRaspi output and your Pi, and that's what is causing the tiny voltage drops which the Raspberry Pi (it actually has a voltage monitoring chip) will interpret as low voltage and the Pi will display the rainbow/thunderbolt low voltage warning.
I think in most if not all cases, even this is OK and the Pi will run just fine without any issues, except the annoying icon that will show intermittently, especially when the Pi is busy or working hard.
If you use a USB cable, from the ATXRaspi, you can either add another jumper wire from any of the "+" to any of your Pi 5V on the GPIO header, or only use the GPIO (ideally not both because there is a fuse on the Pi USB but not on the GPIO 5V). Sometimes depending on the total load of your Pi, a USB cable that is not very beefy can also cause the warning (imagine all the extra metal to metal connections that are introduced, versus a straight solid wire - all those are basically resistances that add to the drop and the less connections you have the better).