Raspberry PI:- USB power cables, crashing and other problems

RE: Raspberry PI:- USB power cables, crashing and other problems

k12h — Sun, 10 May 2015 13:50:44 GMT

Thanks for the in-depth investigation. I have done measurements with a bunch of cables and power supplies that further confirm your conclusions (http://www.element14.com/community/roadTestReviews/2031).

RE: Raspberry PI:- USB power cables, crashing and other problems

Former Member — Thu, 10 Jul 2014 21:43:33 GMT

About a year ago, I purchased the Adafruit supply, USB cable, Raspberry PI, from Element 4U / Newarks Electronics. I've been having stability problems with the SD card. After taking a look at everything the supplied cable is a piece of junk. It is thick, but drops way too much voltage. I compared it with my cable from my Nexus 7. I get almost .1 volt more from the Nexus 7 cable then the cable from Element 4/Newark. I feel that my trust was violated, paying for a recommended cable that isn't sufficient. -Dan

RE: Raspberry PI:- USB power cables, crashing and other problems

Former Member — Thu, 17 Apr 2014 12:22:37 GMT

A little off topic, should I be concerned, I bought some Android TV boxes and some came with a power supply that has spikes on the 5v output.

This is what they usually look like.

http://i181.photobucket.com/albums/x41/maxx3/Goodpsu.jpg

spikes from poor power unit

http://i181.photobucket.com/albums/x41/maxx3/SpikesJC-0050.jpg

The setup, powered up Tv box, monitoring USB out while connected to the oscilloscope.

Video clips of the different psu.

Zippyshare.com - Good.mp4

Zippyshare.com - JC-0050.mp4

Just wondering if the spikes would reduce the life of the unit.

thanks

RE: Raspberry PI:- USB power cables, crashing and other problems

Robert Peter Oakes — Sun, 06 Apr 2014 06:00:40 GMT

I will try to do that soon. To confirm though, in all my tests I did monitor the output of the adapter and it was always very close to the nominal 5V supply it is designed to provide. I also used the same adapter for ALL the tests to keep the focus on the cable, not the adapter. As you can see in the blog, I used a very good and confirmed 20 AWG cable for my break out and then plugged int he test leads to it. I was specifically measuring the drop across the cable length

I do agree there may well be many bad adapters out there too. it just was not part of my test.

Sounds like combining both your evaluations and mine we can come up with quite a comprehensive set of recommendations

Peter... Now my turn to go bed [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-a1f60339-45b0-4a0d-a255-364f51977e1c/contentimage_5F00_1.png:16:16]

RE: Raspberry PI:- USB power cables, crashing and other problems

johnbeetem — Fri, 07 Mar 2014 23:22:12 GMT

Great article! I especially liked your analysis of Micro USB cables, which are often problematic. As far as I can tell, there's no way to tell when you order a Micro USB cable whether it's going to work or not. RasPi really needs to ship a known good Micro USB cable with the product -- it would save lots of problems.

I have an original Model B with 1.0 PCB, which I use with an Atrix Lapdock. The Lapdock back-powers USB by design. Since the 1.0 Model B has USB fuses F1 and F2, I can back-power by replacing polyfuses F1 and F2 with single-blow SMT fuses. This gives me fuse protection with a tiny voltage drop. The 2.0 PCB eliminates F1 and F2, so there's no way to protect when back-powering unless you add a fuse to your hub or cable.