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Pi accessories from Farnell ... USB chargers?

morgaine

Selecting "View all accessories" from Farnell's Pi "Register your interest" page doesn't show a single USB charger.  Using the search function isn't too successful either, as most of the hits are for car chargers.  I found only one micro-USB charger in (minimal) stock, and that didn't even have a datasheet link provided.  Perhaps there are others, but I didn't find them.

 

This situation isn't too great.  The quality of micro-USB supply is absolutely critical for proper Pi operation.  Ideally I'd like to see Farnell evaluating a number of chargers for us and offering high-current and well-regulated chargers as Pi accessories.

 

 

Morgaine.

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  • in reply to morgaine

    STOP PRESS.  The last suggestion may not be possible.

     

    The Pi is not USB compliant on its power input, since its micro-USB data lines are not connected.  It won't self identify as a USB device nor will it announce to an upstream hub that it wants more than 100mA, so the whole idea may collapse on its face.  It depends entirely on how the hub will treat this rogue anonymous device that is trying to obtain current illegally.

     

    Morgaine.

  • in reply to morgaine

    Some USB hubs (like my Inland US$5 special from Fry's) don't to anything clever with +5V.  They just connect +5V directly to the USB A connectors for the downstream devices and couldn't care less what the data lines are doing.  So your trick should work fine with my cheap hub provided that my micro USB cable is conductive enough.  My hub's +5V either comes from an external +5V power supply or from the connection to the upstream host through a 1A Schottky diode so hub +5V won't power the upstream host.

     

    A smart hub might protect itself from rogue downstream devices by controlling how much current goes to them and implement nice things like slow start to prevent voltage glitches when you plug in new devices.  I don't have experience with such a hub, or even know if such actually exist.

     

    I like the idea of powering RasPi from a dumb powered hub so I don't have to run current for USB external devices through PTC fuse F3.

  • in reply to johnbeetem

    I was doing this originally with my Pi.

     

    I found that even with a pretty dumb/cheap powered USB hub, there was still a good amount of voltage drop when measuring the TP1 and TP2 points.  I found that the tracks inside the hub were generally not heavy enough to carry more than 500mA and I was often seeing around 4.7v even though I had a decent 5v 3A PSU supplying the hub.  I eventually opted for creating my own Y cables (to power the hub and Pi from the same PSU) and that seems to give me the best voltage across TP1 and TP2 as I now get around 4.89v using a Y lead with the same PSU. 

     

    YMMV.

  • in reply to Former Member

    The USB current thing is interesting.

    Apple devices won't charge from an 'non apple' usb charger, even though other devices will.

     

    Since the chargers don't contain anything the device can talk to, they apply a voltage to the D+ and D- pins, and the apple device then decides how much it can suck.

    I suspect that all the usb chargers are the same, unless they incorporate an intelligent usb device, the device will need to know it can suck more.

     

    In the case of the Pi, the micro USB doesn't have any data pins connected, so it will suck as much as it needs from the charger.

     

    I went through 5 different chargers that had a USB socket, all capable of 1A or more, and they all failed to provide enough volts.

    The cord drop was measured and sure different cords varied slightly.

     

    Even a genuine charger for a smartphone with a micro usb plug didn't provide enough.

    I suspect that most phone batteies now are 3.6v, so it doesn't really matter if its 5v or not.

     

    In the end I used a 1A charger made by Brightlink and distributed by Brightpoint.com thru The Warehouse (here in NZ and AUS)

     

    Mark

  • in reply to morgaine

    image

    The interesting thing is that this setup allows for the next picture.....

    image

    Please ignore the mess, and the spider.... and the snakes.... and the complete lack of anything even vaguly like cable routing......

     

    That is a RPi running off a USB hub without throwing a paddy (also had it running off the power supply that I was less than generous about a couple of days ago)