Posts: 35
Joined: Fri Jan 11, 2013 9:54 pm

Strange electric question.

Mon Oct 12, 2015 4:13 am

I have a question for someone that knows the technical side of power supplies that is more curiosity on my part then a problem. I bought a great power supply from a electrical component supply store that works amazing for the Pi, they actually sell Pi's + accessories in store and recommend this one.

It is 5 volt 3 amp with a 5 foot fixed cable for less loss, brand name is "Circuit Test".

Under my testing with a multimeter the lowest voltage I could get it down to was 4.95v and that was with a 2.5" hard drive and a high drain Wi-Fi adaptor plugged into the Pi itself and only powered by the Pi.

During the test I was watching a full 40GB Blu-Ray video streaming over the Wi-Fi connection (can only keep up when max_usb_current is on since I get 8x the speed then without) from a NFS server and simultaneously ssh'd in and running a dd command to copy part of the 2.5" drive (drive can only turn on with max_usb_current)

So you can see I was trying hard to get it using the power and only made it down to 4.95v

So why if this supply is so amazing for the Pi which is supposed to be one of the most picky devices you can get does the same power supply suck at charging phones?
When I had a family member need a emergency phone charge I just was going to quickly let them use it but
the Blackberry phone wouldn't charge
another Android phone I tested charges but with this error in the notification drop down "Slow charging Battery is charging slowly due to low electric current of TA/USB connection."
another separate Android phone charges but slowly without saying anything.

Posts: 3172
Joined: Sat Aug 18, 2012 1:21 am
Location: Korea

Re: Strange electric question.

Mon Oct 12, 2015 4:20 am

Maybe your power supply cable does not have any connections to the USB data lines?

Here's some background. Please don't blow up your expensive phone. ... -charging/

Posts: 35
Joined: Fri Jan 11, 2013 9:54 pm

Re: Strange electric question.

Mon Oct 12, 2015 4:29 am

Thank you for the info, at least I know it is something like that and not a strange problem.

It is just sad because the power supply was only $14.80 CAD and that price for a 3A with 5' cable is a amazing price in my area and I was thinking of suggesting it to anyone looking for a new phone charger. (Before ever testing it on a phone) Looks like that can't happen. But I will still recommend it for Pi use since it is great for the Pi.

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