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Official Power Supply Question

Posted: Mon Jul 01, 2019 5:59 pm
by gtechn
Hello. I know this is a really, really odd question. I have a new official Raspberry Pi power supply coming, and I am wondering what would happen if I wasn't using my Pi and used it to charge a phone (or if someone got it mixed up as a phone charger). Phones charge at about 2.1A, but the charger outputs 3A. Will it step down the voltage to 2.1A or 1A automatically, or will it always output 3A at slight risk of damaging a phone?

Re: Official Power Supply Question

Posted: Mon Jul 01, 2019 6:05 pm
by jbudd
I don't know about the new PSU because my phone has micro USB not USB-C.
However my phone will not charge from the original official Raspberry Pi power supply. It doesn't blow up either, just doesn't charge

Re: Official Power Supply Question

Posted: Mon Jul 01, 2019 9:13 pm
by W. H. Heydt
gtechn wrote:
Mon Jul 01, 2019 5:59 pm
Hello. I know this is a really, really odd question. I have a new official Raspberry Pi power supply coming, and I am wondering what would happen if I wasn't using my Pi and used it to charge a phone (or if someone got it mixed up as a phone charger). Phones charge at about 2.1A, but the charger outputs 3A. Will it step down the voltage to 2.1A or 1A automatically, or will it always output 3A at slight risk of damaging a phone?
Any device will only draw as much current as it--wildly anthropomorphizing here--wants. You could hook up a 100A supply to your phone or a Pi and the phone or Pi would still only draw 2A to 3A. (In practice, don't do this. If there is any sort of electrical fault in the device, it could short the 100A PSU and the results would be...spectacular. And not in a good way.)

Many's the time I've used Pi PSUs to change phones or tablets with no issues at all. Indeed, given the price and quality, I wouldn't be surprised if a great many Pi 3A PSUs aren't bought specifically to be used as chargers.

Re: Official Power Supply Question

Posted: Mon Jul 01, 2019 10:54 pm
by solar3000
the pi supply won't fast charge your phone though. if you plug it in, your phone might complain.

Re: Official Power Supply Question

Posted: Wed Jul 03, 2019 5:51 pm
by hardwaremack-orginal
my Samsung note 8 will only charge at max 300ma with this new usb c 3a charger... annoying... but expected.
my Dollar Tree $1 dollar 1000ma 110v plug in charger pulls 1047ma!! lol with my phone... go figure.
if dollar tree ever sells these again i will buy a whole case.

Re: Official Power Supply Question

Posted: Wed Jul 03, 2019 6:39 pm
by Andyroo
hardwaremack-orginal wrote:
Wed Jul 03, 2019 5:51 pm
my Samsung note 8 will only charge at max 300ma with this new usb c 3a charger... annoying... but expected.
my Dollar Tree $1 dollar 1000ma 110v plug in charger pulls 1047ma!! lol with my phone... go figure.
if dollar tree ever sells these again i will buy a whole case.
Watch Big Clive on YouTube and as of 3rd July, he describes his channel in part as
The trashiest electronic channel on YouTube. We test and use affordable electronic soldering equipment and tools to build, teardown, modify (and sometimes destroy) random electronic stuff.
Though based this side of the Atlantic he tests a lot of cheap power banks and saved me a fortune over the years :lol:

Re: Official Power Supply Question

Posted: Wed Jul 03, 2019 7:03 pm
by rpdom
Andyroo wrote:
Wed Jul 03, 2019 6:39 pm
Though based this side of the Atlantic he tests a lot of cheap power banks and saved me a fortune over the years :lol:
Clive has cost me a fortune with some of the stuff he reviews. I just had to go out and buy it (but not "Fanny Flambeaux" :lol:).

Re: Official Power Supply Question

Posted: Wed Jul 03, 2019 7:04 pm
by Andyroo
rpdom wrote:
Wed Jul 03, 2019 7:03 pm
...
Clive has cost me a fortune with some of the stuff he reviews. I just had to go out and buy it (but not "Fanny Flambeaux" :lol:).
Oh - I had forgotten that one :oops: :o

As for buying things - I need some new lights in the loft and he just reviewed some today - perfect timing :D

Re: Official Power Supply Question

Posted: Wed Jul 03, 2019 7:06 pm
by B.Goode
Phones charge at about 2.1A, but the charger outputs 3A. Will it step down the voltage to 2.1A or 1A automatically, or will it always output 3A at slight risk of damaging a phone?


The 'A' in expressions like 2.1A is an abbreviation for Amperes, often contracted to 'amps'. An Ampere is a unit of current, not voltage.

Re: Official Power Supply Question

Posted: Wed Jul 03, 2019 7:48 pm
by rpdom
Andyroo wrote:
Wed Jul 03, 2019 7:04 pm
As for buying things - I need some new lights in the loft and he just reviewed some today - perfect timing :D
Those LED strip lights looked pretty good and not too expensive. IIRC the 20W version he reviewed was around 8 quid.