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I've got a raspberry pi 3b+ mounted in my wall with the official 7″ touchscreen, and after some time i noticed the symbol in the top right corner notifying that it does not get the voltage it's supposed to have.

I'm powering it with a switched powersupply that is rated for 50W(5VDC) which should be plenty enough. I took a measurement with my multimeter and it was reading ~0.800A the pi is connected via the pin header. When i instead connect this with a mobile adapter 4A, i don't seem to get the low voltage notification.

I can recall that i a while ago accidentally connected the pi with reverse polarity, this was less than 1s it still boots up fine can this be the reason or do you think this can be caused by the power supply being faulty or doesn't recieve enough load?

Is there a practical way of putting load on the PSU to see if it's capable of drawing more than 0.8A?

Edit: One thing that is relevant that i forgot to add is that i tested the voltage given by the power supply and got a reading of 5.1V

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  • You could use a cpu burner program to get the CPU running hot and using lots of power. core-electronics.com.au/tutorials/…
    – Dougie
    Sep 16, 2019 at 14:24
  • Why did you meassure the current (Ampere) when the Raspberry Pi report a under voltage (Volt) ?
    – MatsK
    Sep 16, 2019 at 17:46
  • Because i was suspecting that either the pi is not receiving enough current or that the PSU is not giving enough current, which would result in under voltage as they both drop together right?
    – Ogelami
    Sep 18, 2019 at 7:21

2 Answers 2

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Your switching power supply is industrial standard and has good auto recovery over current, short circuit, thermal protection. The factory output voltage adjustment is sometimes not exactly 5V. It might be 4.9V, or 5.1V. Sometime it drifts a bit, due to aging, temperature fluctuation, or total loading changes.

The fine tuning screw is at the low right corner of the chassis. You need a multimeter and a small screw driver to adjust the voltage to say 5.1V or 5.25V max.

meanwell psu

AWG Chart

awg chart

References

(1) Meanwell LRS50 110/220VAC to 5DVC Power Supply

(2) Rpi3 PSU Cable and Power Supply Tests - tlfong01 2019feb04

(3) Rpi3 PSU Yellow Lighting Notes - nachoparker 2019feb04

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  • Sorry, i should have mentioned this in my initial post, i measured 5.1V coming off the powersupply when it was not in use, should i adjust this under load or do you think the value will be more or less the same?
    – Ogelami
    Sep 16, 2019 at 14:55
  • @Ogelami, Actually you don't need to be that precise. I usually think 5.25V is OK. It also depends on the connecting wires to your Rpi. If you use long and thin wires, there might be a voltage drop of 0.5V or more. And I don't really bother the yellow lighting warning sign. As long as Rpi works OK, then there is now worries.
    – tlfong01
    Sep 16, 2019 at 15:00
  • @Ogelami, the datasheet gives the "load regulation". If it is 1%, say, then if no load is 5V, then full load might drop 1%, or 0.01 x 5 = 0.05V . Again, not exact figures.
    – tlfong01
    Sep 16, 2019 at 15:08
  • when adjusting the power supply, measure the voltage at the RPi .... measure the voltage at the power supply after adjustment just to determine how much voltage is being dropped by the power cable
    – jsotola
    Sep 16, 2019 at 15:50
  • Okay! I'm using short jumper wires and i just screwed the pin on to the power supply pretty firmly tho maybe it doesn't have enough contact since the jumper wire pin is completely stiff. I will replace those and see if it makes a difference!
    – Ogelami
    Sep 17, 2019 at 6:56
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You need to measure the voltage at the Pi as the cable can reduce the voltage if it is too small.

Replace the cable with a larger one. Measure the voltage at the Pi under load to see if it is too low. The under voltage is triggered at 4.65 v on the board, I've seen it trigger at 4.85 v at the port.

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