Lightning bolt with 5.5 4A power supply

[rihiii]

Hi, i have pi 3 b+ and it is always displaying the lightning bolt icon. now i know that disabling it is stupid and am not trying to do that. and i thought that my power supplies suck so i connected it to my lab bench supply,
- set 5.1V 2.5A and turned it on. - jup still lightning bolt with under-voltage warning...
-- measured input voltage = ~4.6V
- set 5.3V 3A and turned it on. - jup still lightning bolt with under-voltage warning...
-- measured input voltage on raspi = ~4.8V
- set 5.5V 4A and turned it on. - no lightning bolt... aaand its back again (sometimes)
-- measured input voltage on raspi = ~5.1V

so after these tests i know that there is a problem - the lightning bolt should only appear if voltage is below 4.65V
i cant even tur on the raspi with 5V power adapter from the wall (rated 5V 2.5A) - it keeps rebooting..

so i have used it for some time now and am trying to make magic mirror and the lightning bolt all the time through the mirror is not immersive
so that is why i am here, maybe some suggestions? i really dont think that a higher rated power adapter would help...

[RaTTuS]

get a decent micro USB lead
stop using the wet string one you have

[fruitoftheloom]

Hi, i have pi 3 b+ and it is always displaying the lightning bolt icon. now i know that disabling it is stupid and am not trying to do that. and i thought that my power supplies suck so i connected it to my lab bench supply,
- set 5.1V 2.5A and turned it on. - jup still lightning bolt with under-voltage warning...
-- measured input voltage = ~4.6V
- set 5.3V 3A and turned it on. - jup still lightning bolt with under-voltage warning...
-- measured input voltage on raspi = ~4.8V
- set 5.5V 4A and turned it on. - no lightning bolt... aaand its back again (sometimes)
-- measured input voltage on raspi = ~5.1V

so after these tests i know that there is a problem - the lightning bolt should only appear if voltage is below 4.65V
i cant even tur on the raspi with 5V power adapter from the wall (rated 5V 2.5A) - it keeps rebooting..

so i have used it for some time now and am trying to make magic mirror and the lightning bolt all the time through the mirror is not immersive
so that is why i am here, maybe some suggestions? i really dont think that a higher rated power adapter would help...

https://www.raspberrypi.org/products/ra ... er-supply/

[Imperf3kt]

get a decent micro USB lead
stop using the wet string one you have

To put it a bit nicer, the cable you are using is probably very thin or made of cheap electrical steel which doesn't conduct electricity very well (contrary to its name)

[HawaiianPi]

Assuming that your bench power supply is actually outputting what it says, then the problem is with the cable between the power supply and the Pi computer. As others have said, you need a better power cable.

Many standard micro USB 2.0 cables are not designed to deliver much more than 500mA (0.5A) without voltage loss. You need to use a short cable with fat power wires. At least 24 AWG, and preferably thicker than that (lower AWG = fatter wires, so 22 is better than 24, and 28 is worse).

The official Raspberry Pi Universal power supply recommended above is a proven performer, and usually pretty affordable (depends on where you live and who you buy it from). https://www.raspberrypi.org/products/ra ... er-supply/

[rpiMike]

For reference the official PSU has 18 AWG cable

[rihiii]

ok, just ordered original power supply, will test with that.

[jamesh]

The RPF supply is not only high ampage, but also has a very high quality cable, which is the usual source of power issues. So recomending it covers both bases.

It's also constant. You know if you get one that you have a reliable power source, and if you still have problems then you know the problem is elsewhere. That cannot be said with power supplies from Random Power Suppliers R Us.

[W. H. Heydt]

It's not just the PSU, but also the cable. Remember that this is advice being given to people who are having problems. Absent better data, one may not know if a poster is using a "charger" with an integrated cable. So if someone hasn't read (or understood) enough of the available data to figure out the problem, the simple, easy to explain, inexpensive and reliable solution is: Get the official PSU.

But, yes, I've been getting cables from Monoprice for years (starting before the Pi appeared on the scene...they have really good prices on Ethernet data cables, too) and if someone idicates that they are using a separate cable--and they're in the US--then I'll recommend Monoprice, too. What would be really fantastic would be if Monoprice were to start carrying Power-only USB leads with really heavy gauge (say 20 ga. or even 18 ga.) wires. But--alas--the best I've ever seen there is 24 ga., though those have worked well for me.

[rihiii]

Thanks for all the answers, for now the official one works fine.
Still weird how, when i supplied enough voltage to PI it still showed undervoltage (i tested the incoming voltage on PI 5V rail with multimeter, it showed 5.2V i think)
Anyway, for now i guess the wires from the PSU were too small, so on a microsecond the voltage dropped and showed errror, while i couldnt see it on multimeter.
Thanks again!

[PeterO]

Anyway, for now i guess the wires from the PSU were too small, so on a microsecond the voltage dropped and showed errror, while i couldnt see it on multimeter.
Thanks again!

A multimeter will not react fast enough, The voltage only needs to drop too low for (at a guess) a few nano seconds to upset the SoC and cause a crash, and you need a good oscilloscope to see that sort of short drop. The low voltage warning is set to come on before you reach the point where the SoC malfunctions in order to give you a warning that a better PSU and/or cable is needed.

PeterO