25 Replies Latest reply on Jan 12, 2014 6:22 AM by lui_gough

    element14 (AU) power supply for Raspberry Pi - poor voltage

    nevoz

      Hello, I purchased a couple of these power adaptors in the same order..

       

      http://au.element14.com/jsp/search/productdetail.jsp?SKU=2254795

       

      As you can see, they are specifically marketed towards RPi. The PDF data sheet says "A 5vdc 1A Australian Micro USB power supply is manufactured specifically for use with the Raspberry Pi device.."

       

      I tested the voltage across TP1/TP2 . One adaptor came to 4.77 volts, and the other one 4.69 volts. Ethernet & HDMI connected. Nothing else connected (no USB etc). Running Raspbmc sitting at the main menu.

      I have to admit, being marketed as designed for the RPi, I was disappointed with the result.

       

      Anyone else purchase these?

        • Re: element14 (AU) power supply for Raspberry Pi - poor voltage
          Colin Barnard

          What voltage do you measure when it is not connected to the Pi?

           

          Colin

          • Re: element14 (AU) power supply for Raspberry Pi - poor voltage
            John Beetem

            Actually, 4.77V is within the specified RasPi range for TP1-TP2 which is the standard USB Vbus range of 4.75V to 5.25V.  A proper USB power supply is usually 5.1V which helps compensate for the voltage drops across the micro USB cable and polyfuse F3.

             

            You might try checking the voltage drop across polyfuse F3.  It may be that the power supply is fine, but your RasPis have iffy polyfuse F3 which have higher voltage drops than normal.  However, since you've checked two RasPis I would suspect the power supply and its cable.

             

            You can also check TP1-TP2 with no cables attached and the SD card removed.  This should have minimum voltage drop so you can get close to what the power supply would be with no load.

             

            Some micro USB cables have very thin conductors which result in a substantial voltage drop, and replacing them fixes the problem.  However, according to the photo your power supply has the cable built in so there's no way to run this test.  I suspect that the Chinese manufacturer has skimped on the conductors in the cable and that's where the voltage drop is.  I just checked the spec sheet on the supply and it lists the cable length as 1.8m.  That's a lot of resistance with thin conductors -- IMO you're much better off with 1m or less.  If the problem is the cable, element14 needs to know that its RasPi-targetted power supplies "have been measured and found wanting".

             

            Lots of power supply troubleshooting info at the RasPi Troubleshooting wiki: http://elinux.org/R-Pi_Troubleshooting#Troubleshooting_power_problems

              • Re: element14 (AU) power supply for Raspberry Pi - poor voltage
                nevoz

                John Beetem wrote:

                 

                You might try checking the voltage drop across polyfuse F3.  It may be that the power supply is fine, but your RasPis have iffy polyfuse F3 which have higher voltage drops than normal.  However, since you've checked two RasPis I would suspect the power supply and its cable.

                 

                hi John, I think you may have misread .. I checked only one RPi at the time, but I had purchased 2 of these exact same adaptors (one adaptor showing 4.77 volts and the other showing 4.69 volts when fully booted with XBMC, HDMI & LAN connected, voltage was checked over TP1/TP2).

                 

                I have just performed some more tests as per your suggestions

                 

                My original RPi adaptor is an old Canon Printer AC adaptor, made in Japan (about 15 yrs ago), output is 13V 1.8A, and I've attached a down-step converter bringing it down to 5.2 volts (it has a variable resistor to set the voltage, so I should bring it down a bit more I know). Power is sent through the GPIO pins.

                 

                Canon Adaptor, RPi with everything removed, only power connected:

                Input: 5.20V (tested before connecting to RPi)

                TP1/TP2: 5.18V

                TP2/F3 (outside side): 5.18V

                TP2/F3 (inside side): 5.18V

                TP1/TP2 Raspbmc booted (SDCard, & HDMI only): 5.11V

                 

                Element14 AC adaptor, RPi with everything removed, only power connected (I tested with the worst performing out of the two Element14 adaptors I purchased):

                TP1/TP2: 4.84V

                TP2/F3 (outside side): 4.86V

                TP2/F3 (inside side): 4.84V

                TP1/TP2 Raspbmc booted (SDCard, & HDMI only): 4.72V

                 

                The above voltage tests were done on a 512Mb RPi. I also tried the TP1/TP2 test on the above Element14 AC adaptor using an old 256Mb RPi. Result was 4.83V.

                 

                Nev

                • Re: element14 (AU) power supply for Raspberry Pi - poor voltage
                  nevoz

                  John Beetem wrote:

                   

                  Some micro USB cables have very thin conductors which result in a substantial voltage drop, and replacing them fixes the problem.  However, according to the photo your power supply has the cable built in so there's no way to run this test.  I suspect that the Chinese manufacturer has skimped on the conductors in the cable and that's where the voltage drop is.  I just checked the spec sheet on the supply and it lists the cable length as 1.8m.  That's a lot of resistance with thin conductors

                   

                  That's correct, it's a long, fixed cable. I am tempted to crack open the adaptor to measure the voltage at the start of the output wire.

                   

                  These actually make a decent, cheap, phone charger. Nice long cable, and has the Australian certifications.

                • Re: element14 (AU) power supply for Raspberry Pi - poor voltage
                  morgaine

                  Nev, there's a long history of official "Pi accessories" not necessarily being Pi-compatible --- take a quick peep at my old thread about Incompatible self-powered hubs .

                   

                  I suspect that  the Pi's  low cost and the tiny profit margins mean that only a very cursory attempt to verify Pi compatibility is being made, because to invest any significant amount of engineering time would wipe out the business margins entirely.

                   

                  It's not an ideal situation, but it's hard to see a sustainable solution for a commercial enterprise like Farnell.  Maybe they should avoid claiming Pi compatibility entirely and leave that matter for the community to judge.  Alternatively, perhaps RPF could give certain items its stamp of approval, since it is best positioned to have good knowledge of its board design and hence of accessory types or brands that could cause Pi a problem..

                    • Re: element14 (AU) power supply for Raspberry Pi - poor voltage
                      nevoz

                      Just read that thread of yours Morgaine, interesting stuff.

                       

                      As for tiny profit margins, I understand, but at the same time how much would it add to the cost of each adaptor to get it right .. better parts/design, and thicker cable ... $3 ? (just very much a guess, I would have no idea!) Even at $AU9.00 it would be decently priced.

                       

                      In fact, here in Australia any element14 order for at least $45 gets free shipping. The RPi is $36. If they were able to make a decent AC adaptor at a $9 selling price, then I'm sure they would sell loads of them as they would tip the order into the free shipping zone.

                       

                       

                       

                      Morgaine Dinova wrote:

                       

                      Nev, there's a long history of official "Pi accessories" not necessarily being Pi-compatible --- take a quick peep at my old thread about Incompatible self-powered hubs .

                       

                      I suspect that  the Pi's  low cost and the tiny profit margins mean that only a very cursory attempt to verify Pi compatibility is being made, because to invest any significant amount of engineering time would wipe out the business margins entirely.

                       

                      It's not an ideal situation, but it's hard to see a sustainable solution for a commercial enterprise like Farnell.  Maybe they should avoid claiming Pi compatibility entirely and leave that matter for the community to judge.  Alternatively, perhaps RPF could give certain items its stamp of approval, since it is best positioned to have good knowledge of its board design and hence of accessory types or brands that could cause Pi a problem..

                        • Re: element14 (AU) power supply for Raspberry Pi - poor voltage
                          mcb1

                          Nev

                          I will do when I get it....

                           

                          In the meantime I thought I would check the one I have been using a Brightlink 1A travel charger from The Warehouse

                          Its out of spec.

                          No card/cables = 5.37

                          Login prompt   =  5.26

                          Graphic screen = 5.25

                           

                          I also have  Galaxy Y charger supplied with the phone that is 0.7A ...

                          No card/cables = 5.07

                          Login prompt   =  5.02

                          Graphic screen = 5.04

                           

                           

                          So hurray for Mr Samsung.

                          Its also got a 1.5m tiny cable, but obviously better internals.

                           

                          Mark

                          • Re: element14 (AU) power supply for Raspberry Pi - poor voltage
                            morgaine

                            Nev V wrote:

                             

                            As for tiny profit margins, I understand, but at the same time how much would it add to the cost of each adaptor to get it right .. better parts/design, and thicker cable ... $3 ? (just very much a guess, I would have no idea!) Even at $AU9.00 it would be decently priced.

                             

                            You're right.  USB chargers delivering a paltry 1A aren't exactly high tech, and adding a hefty low resistance lead would add negligible cost to the BOM.  If Farnell got one manufactured to their own spec, they'd probably be making more profit on it as an official Pi accessory than they make on the Pi itself.

                              • Re: element14 (AU) power supply for Raspberry Pi - poor voltage
                                mcb1

                                Nev V

                                 

                                Finally my E14 Power supply arrived.

                                I have a Logitech wireless that has a marking of 55mA on the USB dongle, Pi camera attached and Ethernet plugged in.

                                A real world scenario ...

                                 

                                E14 Code 2254795 Supply.

                                In shutdown = 4.85

                                Login prompt   =  4.73

                                Graphic screen = 4.73

                                Camera on = 4.70

                                 

                                I also have  Galaxy Y charger supplied with the phone that is 0.7A ...

                                In shutdown = 5.07

                                Login prompt   =  5.02

                                Graphic screen = 5.04

                                Camera on = 5.02

                                 

                                Hardly what I expect from a special supply and in my opinion only just making the grade, with no significant USB draw.

                                 

                                Mark

                          • Re: element14 (AU) power supply for Raspberry Pi - poor voltage
                            nevoz

                            Thanks for reporting back Mark.

                             

                            Your results are much as I expected ..., yes, disappointing.

                             

                            My 4.77 voltage adaptor is working so far alright on my Mum's RPi for some standard definition video streaming. But I wouldn't want to tax it too much more than that.

                            My 4.69 voltage adaptor is being used as a phone charger for my Nexus 4..!

                             

                            Even for their own sake they should stop marketing them as engineered for RPi .. they will likely be getting returned RPi's from people not realising that the lack of voltage is the issue. They even have the RPi logo printed on these adaptors.

                            • Re: element14 (AU) power supply for Raspberry Pi - poor voltage
                              rekrezreb

                              The only solution that I have found is rpips.com.

                              They make a supply that will handle external HDD,WiFi, HDMI output and WiFi all at once.

                                • Re: element14 (AU) power supply for Raspberry Pi - poor voltage
                                  lostintime

                                  http://rpips.com claim that the Raspberry Pi's Micro-USB connector "is not designed to handle the current that is required to run the Pi and power additional USB devices."  This isn't true.  According to the USB Power Delivery Specification Revision 1.0 the Micro-USB connector is rated at 3 amps, same as the 26-pin header attached power supply they sell.

                                    • Re: element14 (AU) power supply for Raspberry Pi - poor voltage
                                      mcb1

                                      I seem to recall the very early discussions when the polyfuse issue first broke, and the suggestion of using the header was raised.

                                      It seems that the pcb tracks were not enough to run the Pi from the header alone.

                                       

                                       

                                      When Nev started this post, it was to highlight that the very supply being suggested by e14, wasn't doing the job.

                                      I'm not sure if e14 have resourced their supplies or not. ...they have been a bit quiet on it.

                                       

                                       

                                      Mark

                                      • Re: element14 (AU) power supply for Raspberry Pi - poor voltage
                                        rekrezreb

                                        The issue isn’t about the current carrying capabilities of a SINGLE  pin on the USB port as opposed to the TWO power pins and multiple ground pins on the GPIO. The issue with powering the Pi from a wall wart is 5 Volt regulation and transient response.

                                         

                                        Every power supply (linear or switching) monitors the output of its regulation circuit to adjust its voltage level output.

                                         

                                        It is very import to keep that voltage monitor very close to the regulation circuit, so important that power supply designers have to be aware of things like circuit trace length and circuit trace size to minimize inductance as well as isolate large currents that can cause voltage drops in that monitor circuit. 

                                         

                                        Those drops can cause the final regulated output voltage to the Pi to be several tenths of a Volt lower than 5 Volts, especially during high current demands. If you want to design a wall wart that will provide an accurate regulated 5 Volt output voltage under varying load conditions you need to do a 4 wire system. That is to say that two wires provide power and two are used to monitor voltage at the load.

                                         

                                        That being said, powering the Pi remotely from a wall wart without using a 4 wire monitoring scheme is the worst power supply configuration imaginable.

                                        Forgive the long winded response

                                    • Re: element14 (AU) power supply for Raspberry Pi - poor voltage
                                      gorski
                                      RPI-PSU-EU-MK1 POWER SUPPLY, RASPBERRY 5V, 1A, EURO 85044090RPI-PSU-EU-MK1

                                       

                                       

                                      Hi!

                                       

                                      Anyone with this one and a dead Rpi II or serious problems booting, please?

                                       

                                      I have a Logitech wireless keyboard attached to Rpi, HMDI and LAN cable.

                                       

                                      Thanx!

                                      • Re: element14 (AU) power supply for Raspberry Pi - poor voltage
                                        lui_gough

                                        Hi Guys,

                                         

                                        Just letting you know that I did get my hands on one of these Ideal Power Solutions HK-U-050A120-CP universal voltage input USB charger, with a 5v 1.2A rated output supplied by element14 for use with the Raspberry Pi XBMC Bundle. The rest of this comment is based upon my discussions in the RoadTest review.

                                         

                                        My particular unit has a measured voltage of 4.72v when fully booted with the RPi overclocked to 1000Mhz core/400Mhz Graphics/440Mhz SDRAM with Overvolt level 4, a tad on the low side for my sample, although not having experienced any instability whatsoever despite this. In light of that, I suppose the result is slightly disappointing given that it is very much a "recommended" supply for the Pi, although it shows that it may not have the headroom for all use cases (e.g. hefty Wi-Fi adapters, less tolerant CPUs on some Pi's). I have no lock-ups even over several days of usage, and no noise on the HDMI output although the adapter does make occasional coil buzz.

                                         

                                        I suppose I would still go for my favourite adapter if I had to be bothered to obtain one - a 2A genuine Google/Asus Nexus 7 tablet charger (or even the Blackberry charger). I've had no problems with those either, and I can confirm that with the same setup, my Asus Nexus 7 charger gives a TP1-TP2 voltage of 4.94v (a result that I find hard to beat)!

                                         

                                        Of course, voltage only tells part of the story. The SoC itself runs from a much lower voltage, so chances are some others with stability problems are seeing poor regulation to transient loads, insufficient capacitance/filtering of spiky noise (say, from a poor ringing-choke style power supply e.g. counterfeit eBay Apple Chargers) causing problems and not only voltage.