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Power

Not All USB Power Is Created Equal 240

Posted by Soulskill
from the it-should-consider-a-constitution dept.
jfruh writes "We've reached a point in our electronic lives where most of our gadgets draw power from a USB cable, and we have lots of USB ports to choose from — some of which live on other gadgets, some of which live on adapters that plug into your wall or car. But those ports supply wildly varying amounts of power, which can result in hours of difference in how long it takes your phone to charge. The Practical Meter, the product of a successful Kickstarter campaign, can help you figure out which power sources are going to juice up your gadgets the fastest."
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Not All USB Power Is Created Equal

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  • by cosmin_c (3381765) on Wednesday November 20, 2013 @05:24AM (#45471179)
    Like this little thing and also learn what the numbers and values mean. Got two, they work great and they're consistent with more pricier measurement options.
  • kickstarter link (Score:2, Informative)

    by Anonymous Coward

    http://www.kickstarter.com/projects/david-toledo/the-practical-meter-know-your-power

  • When it comes to USB DVD drives, some laptops cannot give enough energy to keep the disk spinning. There's a category of machines which seem to ditch the USB power regulation spec and just connects the USB Vcc rail to the 5V rail of the laptop. That's good and practical in my opinion. Then there's the another category which try to limit the power and have a polyfuse or something more smarter in place.
    • I've seen that before - USB to 5V direct. Someone vandalized a mouse, tearing the cable apart. It was smoldering and melting a hole in the keyboard when I found it.

    • by Joining Yet Again (2992179) on Wednesday November 20, 2013 @07:15AM (#45471475)

      In what way is it "good and practical" to ignore a standard, possibly damaging electronics which assume the standard by providing a variable non-guaranteed maximum current? At worst this is a fire hazard, as you'd end up delivering an unreasonably high current. If the device isn't intelligent enough to ask for the right current, it should be delivered a safe trickle - as the USB standard asks.

      • In what way is it "good and practical" to ignore a standard

        For starters, it allows me to burn and read optical discs. Most external DVD drives want to suck all the power through USB and, while they might have a separate DC power connector too, finding just the right power supply is a pain in the ass. If everything was done properly, every external DVD drive would ship a discrete AC/DC power supply, because the USB spec does not actually allow delivering these crazy, over 1A currents which is needed. But what can you do...

        possibly damaging electronics which assume the standard by providing a variable non-guaranteed maximum current?

        You are of course correct. As a comment abov [slashdot.org]

    • by Joce640k (829181)

      Then there's the another category which try to limit the power and have a polyfuse or something more smarter in place.

      ALL USB sockets are required to have a polyfuse, it's part of the specification.

      Whether they're 500mA or 2A or whatever is another matter, but they have to have them.

  • by mlk (18543) <michael.lloyd.le ... @ g m a i l .com> on Wednesday November 20, 2013 @05:31AM (#45471201) Homepage Journal

    At work I could plug my phone into the computer or... Buy a second plug, that seams a bit pointless even it if it does knock and hour of the phones charging time.

    At home I do have choice, but why would I really worry as each night it gets charged and has all night. So again an hour does not really matter.

    What am I missing from this?

    • by mean pun (717227) on Wednesday November 20, 2013 @05:58AM (#45471279)

      What am I missing from this?

      One example: my Nexus 7 draws so much power, even when sleeping, that it is possible to connect it to a weakly charging USB port, come back a few hours later, and it has a lower charge level. I'm sure the same is true for other tablets, and possibly even some phones.

      • by heypete (60671)

        One example: my Nexus 7 draws so much power, even when sleeping, that it is possible to connect it to a weakly charging USB port, come back a few hours later, and it has a lower charge level. I'm sure the same is true for other tablets, and possibly even some phones.

        Interesting. My wife has a Nexus 7 (2012 edition). It charges just fine (albeit relatively slowly) from 500mA USB chargers. It charges faster with the 2A charger that comes with it, but I've never had issues with it losing charge while plugged in to a standard charger.

        How weak is your "weakly charging" USB port? Is it one on a keyboard or some other low-power accessory, or is it a port on the computer itself?

        • by RabidReindeer (2625839) on Wednesday November 20, 2013 @07:40AM (#45471593)

          One example: my Nexus 7 draws so much power, even when sleeping, that it is possible to connect it to a weakly charging USB port, come back a few hours later, and it has a lower charge level. I'm sure the same is true for other tablets, and possibly even some phones.

          Interesting. My wife has a Nexus 7 (2012 edition). It charges just fine (albeit relatively slowly) from 500mA USB chargers. It charges faster with the 2A charger that comes with it, but I've never had issues with it losing charge while plugged in to a standard charger.

          How weak is your "weakly charging" USB port? Is it one on a keyboard or some other low-power accessory, or is it a port on the computer itself?

          The Color and Tablet Nook devices have two different charge rates. If you use the official "USB" cable with the LED indicator in it, it charges at a 1A (2A?) rate. If you use a stock micro USB cable, it charges at the official 500ma rate. The decision is made by the Nook itself, based on info from extra pins that are in the custom cable.

          Which (blankety-blank-censored-blank) is no longer available. And since the cables are no longer made or sold and since they were notoriously prone to fail means that I've been trickle-charging my unit for about a year now.

          Moral of story: always check new toys for screwball cables before buying.

          • by sjbe (173966) on Wednesday November 20, 2013 @09:06AM (#45472089)

            Which (blankety-blank-censored-blank) is no longer available. And since the cables are no longer made or sold and since they were notoriously prone to fail means that I've been trickle-charging my unit for about a year now.

            Exactly why I avoid devices with weird custom cables whenever possible in consumer electronics. It's been my experience that unless a custom cable is so popular as to become a standard itself (like Apple's Lightning) that eventually you are going to run into a problem. Furthermore it adds to the cost of the device (custom cables = $) and it usually means that the company making the device had lazy and/or incompetent engineers. Now admittedly the USB spec is pretty flawed, particularly when it comes to power, but even so I've still seen lots of devices that could have used standard USB (or Firewire etc) had they taken the time to do so.

            Now sometimes the standard needs to be updated. I think USB should be beefed up to handle up to 100 watts [computerworld.com] with all due haste.

            Bear in mind that my day job is to run a company that makes custom cables. Think about that. I make a living off of custom cables, have the ability and equipment to make a copy of pretty much any cable, and I still think they are a bad idea for most consumer electronics.

        • by necro81 (917438) on Wednesday November 20, 2013 @08:02AM (#45471679) Journal

          How weak is your "weakly charging" USB port

          The USB spec - ya know, that thing that every device carrying the USB logo is supposed to follow - permits a connected device to draw a maximum of 100 mA until it is properly recognized (enumerated) by the host. This is probably what the GP is referring to: 0.5 W of available power (less after conversion efficiency) isn't a whole lot for a device like a Nexus 7.

          After being enumerated, the connected device can request higher current levels, up to 500 mA max. It isn't supposed to draw more unless the host permits it. For many modern portable electronics (e.g., smartphones) that have a 3-10 Whr battery, a 2.5-W maximum charge rate isn't much.

          There are amendments to the spec that allow for greater power: in 2009, the spec created a Charging Downstream Port, which allows for up to 1.5 A from the host after enumeration; and the Dedicated Charging Port (DCP), which shorts the two data lines together and allows for 1.5 A charge power without enumeration.

          Individual companies, such as Apple and Samsung, supply their own USB chargers that allow for even greater charge current, but do so in a way that technically violates the USB spec.

      • This doesn't add up. The Nexus 7 has a 16Wh battery. The worst USB port possible (100mA) provides half a watt. Either a) your N7, rated for 10h active / 300h standby, is guzzling so fast that it would deplete a full battery in 32h of all-standby, or b) the USB port is defective.

      • by bemymonkey (1244086) on Wednesday November 20, 2013 @07:20AM (#45471503)

        Your Nexus 7 has runaway background processes. Otherwise there's no way it draws more than 500mA in standby - it would be empty after just a few hours. Check your battery stats to find the culprit...

        My girlfriend's Nexus 7 charges just fine off of good old 500mA USB2.0 ports when it's in standby...

      • by Ash Vince (602485) *

        What am I missing from this?

        One example: my Nexus 7 draws so much power, even when sleeping, that it is possible to connect it to a weakly charging USB port, come back a few hours later, and it has a lower charge level. I'm sure the same is true for other tablets, and possibly even some phones.

        I used to have the same problem with an old PC too. If I plugged most devices into my main computer they charged just fine, I had a really shit old small form factor packard bell thing I used to leave always switched on as a router though and if I plugged anything into that to charge via USB it ended up actually drawing power out of the device instead. This was not due to the device though, anything I plugged in to charge did the same thing.

        Weirdly though I could plug anything that needed power to run like

        • Mod parent interesting. Can anyone explain what happened in that scenario? Is it a load impedance issue? And, wouldn't there have been a diode to prevent current flow into wrong direction?
      • by wbr1 (2538558)
        I have had two LG phones that either keep a static charge or lose charge when plugged into a cheap car charger with the GPS on. Without GPS it is okay, but I guess GPS and the nav app are such a drain that the poor charger can't deliver enough current. It would be nice to be able to test a charger to see what it's actual output is.
      • by Speare (84249)

        A lot of the replies here are incredulous about Nexus 7 power.

        My Nexus 7 2012 edition would charge up, even if the screen and wifi was on, if left on a 500mA laptop USB port (usb debugging / storage enabled).

        My Nexus 7 2013 edition would not charge up, even if the screen and wifi was off, if left on a 500mA laptop USB port (even with usb debugging / storage disabled). It would drain slowly. It required a 1A from a wall-wart to tread water with the screen on. It took a 2A wall-wart to actually charge up

      • by Skater (41976)
        I had something similar happen with my Samsung S3. It turned out the cable I was using (an Amazon Basics 6' cable) is bad - if you page through the reviews for it, you'll find a few reviews mentioning the same issue. The charger was delivering a full 1 amp or whatever, but the cable had too much resistance. If I was in an area with a weak cell signal and no wifi, my phone would take practically all night to charge, even with Wifi and Bluetooth turned off. Sometimes I'd even wake up in the morning and fi
        • by mean pun (717227)

          Exactly! For me the cable was the problem as well. The Nexus 7 2012 I mentioned comes with a wallsocket-to-usb charger, and a special USB cable. I managed to mislay that cable, and with most ordinary cables I had very long or even negative charging rates, even with the original charger. As far as I can tell the trick is to find a cable with low wire resistance, either because it is short, or because it has thick wires.

          In any case, I think the whole discussion illustrates that some kind of measurement instru

      • You probably arent using it then anyway.

      • One example: my Nexus 7 draws so much power, even when sleeping, that it is possible to connect it to a weakly charging USB port, come back a few hours later, and it has a lower charge level.

        If you need a portable fusion reactor to power your tablet and/or phone *while it is sleeping* then there's something really wrong with your device.

        (Bad hardware design, bad OS power management, or you installed too much background shit).

      • by xeoron (639412)
        I had the same problem with my Nexus 7 (2012), until I did these four things. 1) Go into the system settings and in the section for Apps and kill any process running that you don't want to run. 2) Uninstall the power hungry apps that are always running that you really don't use much or at all. 3) In the Play store go into your settings and tell it to not auto update 4) Install Deep Sleep Battery Saver Pro [google.com] to tweak how the device will act with regards to power usage while asleep or with the screen merely off
    • by Teun (17872)
      Like when I've used the phone as hotspot and have Bluetooth on as well, power goes down rapidly and the day isn't over yet.

      Having a quick top-up before getting on the train home is rather useful...

    • by evilviper (135110)

      What am I missing from this?

      Your car charger would be a big one... Fire up Google Navigation for your weekend drive out-of-town, and connect it to your $2 cigarette lighter charger, and before you get to your destination, your phone shuts off because it has run out of juice. Other apps like the free MapQuest use less power and offer better routing, but even those commonly use more than the 500mAH basic old USB chargers can supply, so your battery will be drained rather than charge.

      The second would be a li

      • by evilviper (135110)

        In all those cases, though, I read the specs on the charger, and/or observe how fast my phone is charging, and don't NEED a stupid meter to tell me what I'll find out in a few minutes.

        In fact it doesn't MATTER how much power your charger can supply, if it isn't wired in a way your cell phone recognizes it, it won't TRY to draw that much power, anyhow. And Apple and Android were oh-so-nice to choose mutually-incompatible methods of signaling this, so one charger cannot work for both. Though expensive "char

    • I plug into my computer even though I have a wall adapter that charges roughly 5 times faster. My phone's battery lasts 4-6 years instead of 1 before losing over 50% of its capacity.
  • It's not sex... (Score:4, Insightful)

    by Anonymous Coward on Wednesday November 20, 2013 @05:33AM (#45471209)

    Being the fastest might not be the best for your battery life.

  • by Lennie (16154) on Wednesday November 20, 2013 @05:34AM (#45471211) Homepage

    I believe most types of battery when charged faster actually degrade faster.

    Life fast die fast ;-)

    • The Fukushima rods would indirectly charge anything very fast. But they won't die any time soon, unfortunately.
    • by Sockatume (732728)

      The device should only draw as much power as it wants, which is controlled by the charging circuit in the phone, regardless of how much is available. Which raises the obvious question of how they're getting iPhones which want a 120-minute charge cycle, to charge in 90 minutes by using a special cable.

      • Remember, power over USB is negotiated. It doesn't just supply 2A to each port. The USB 3 spec allows for up to 900mA, but will only provide 150mA if the device doesn't ask for more. There is a separate "charging" spec which supplies up to 5A, though it wasn't supported by motherboards until fairly recently.

        The phones want a 90 minute charge time; it's just that they communicate their want for more power in a way that not all USB hosts understand -- often they use some non-standard way that only their power

  • Basically an Ammeter (Score:5, Informative)

    by hcs_$reboot (1536101) on Wednesday November 20, 2013 @05:34AM (#45471213)
    Instead of that ugly one, you may get something that gives an exact value, like this one [amazon.com]. A new iPhone/iPad expects 2A, the MacBook (10W) expects also 10/5 = 2A.
  • by leehwtsohg (618675) on Wednesday November 20, 2013 @06:11AM (#45471313)

    Samsung seems to measure the "reliability" of the supply or the cable, and limits power based on those values. Then the same supply will charge at different rates depending on the cable used.

    • by AmiMoJo (196126) * <[ten.3dlrow] [ta] [ojom]> on Wednesday November 20, 2013 @07:22AM (#45471505) Homepage

      Indeed they do. If the charger says "I can supply 1.5A" but due to thin wires in the long, cheap cable that results in a significant voltage drop the device backs down to a lower level.

      • by ThatsNotPudding (1045640) on Wednesday November 20, 2013 @07:50AM (#45471637)

        Indeed they do. If the charger says "I can supply 1.5A" but due to thin wires in the long, cheap cable that results in a significant voltage drop the device backs down to a lower level.

        This is why I build my own USB leads using #00 welding cable.

      • I don't think it has to do with voltage drop. A cable usually will not show a voltage drop ~0 resistance for 2m of cable. And, same cable will charge other devices without any problem. A cable might burn out with too much current. Maybe that's the worry? I haven't really heard of that happening....
        Even the originally supplied cable is rejected sometimes. And, if you get a bad charging rate, just unplug and replug the cable for another roll of the dice.
        No, I think it is a simple bug in the charging control i

        • Re: (Score:2, Informative)

          by Anonymous Coward

          Voltage loss over such a cable is very real. At 0.14 mm^2 (AWG 26) you get 0.14 mOhm/m. For a 2m cable, 2 wires you end up with 0.56 Ohm. At 1.5 A that's a voltage drop of 0.84V.

          Also note that such a cable is only rated for 0.36 A

          • by CSMoran (1577071)

            Voltage loss over such a cable is very real. At 0.14 mm^2 (AWG 26) you get 0.14 mOhm/m. For a 2m cable, 2 wires you end up with 0.56 Ohm. At 1.5 A that's a voltage drop of 0.84V.

            A factor of 1000 snuck out on you here. You went from milliohms to ohms in a second.

  • ... USB ports have to supply (and USB devices may draw)? Drawing more power is outside the spec.

    Also, don't USB devices usually have to request the high power mode explicitly? Some USB power supplies are "dumb" and only supply power, but don't speak USB. Some devices are curteous enough not to draw 500mA if they haven't received permission from the USB host to do so. In this case, they'll slowly load with 100mA ...

    • ... USB ports have to supply (and USB devices may draw)? Drawing more power is outside the spec.

      Also, don't USB devices usually have to request the high power mode explicitly? Some USB power supplies are "dumb" and only supply power, but don't speak USB. Some devices are curteous enough not to draw 500mA if they haven't received permission from the USB host to do so. In this case, they'll slowly load with 100mA ...

      There are several generations of specs. The original was hard-wired for 500ma max. Later versions can negotiate.

    • Which manufacturers blissfully ignored. Apple with there secret handshakes. Nearly all of the USB power specs required to much intelligence at the charger end thus cost. The latest is rather fun supping up to 100w. The previous supplying 1.5a assumed simply by shorting the data lines together.

  • Different devices have subtly different ways of asking how much currently they can draw. Your iDevices and Androids and whatever are fairly interoperable with each other's chargers now, but there's still the occasional stupid outlier like the PS Vita that insists on having a specific shorting of the USB pins before it'll draw more than 500mA. I'd like to see a gizmo that could not only measure the current available, but act as a universal adaptor for those sorts of devices.

    • I'd like to see a gizmo that could not only measure the current available, but act as a universal adaptor for those sorts of devices.

      The answer is not a different gizmo to work around existing limitations in the spec but updating the USB spec to reflect real world conditions and handle more power and handle power more gracefully than it does now. There is some evidence [computerworld.com] that this might occur in the near future.

  • by coolmoose25 (1057210) on Wednesday November 20, 2013 @08:44AM (#45471959)
    I'm an Apple Abhorrent... I don't use any of their products, not even an Ipod. I'm an Android/Windows guy. But my daughter decided she had to have an iPhone and bought it with her own money. I have one of those little plugs you put in a cigarette lighter in the car. My car has two up front, one that is ignition keyed, the other is always on. The dongle is in the one that is always on. And I have a standard USB cable to charge phones and other devices from it. It charges all of my Android phones fine. It charges the GPS fine. It charges pads like the Galaxy Tab and the Nexus fine. It won't charge my daughter's iPhone, even with her white Apple USB cord. To this situation, my daughter tells me that the little dongle I have is a POS. I smiled and was reminded, yet again, why I won't buy Apple products.
    • by gl4ss (559668)

      the properiaty stuff is in the cable, it should charge. maybe it expects the datalines to be in other state though than they are on your charger.

    • by m.dillon (147925)

      I have a multitude of Apple and Android devices and a multitude of Apple and non-Apple usb chargers and power sources, and also have a little non-Apple dongle charger in the car in the front.

      It all works just fine. Apple might have weird charging cables but they still have usb on one end and they've worked with the dozen or so different usb charging sources I've got in the house and in the car.

      Most USB chargers only throw out 2-5W. It's gonna take a while to charge-up Apple's big batteries with one of tho

  • This is /. after all. http://www.accesscomms.com.au/reference/usb.htm [accesscomms.com.au]

    • by Khyber (864651)

      That isn't going to tell you how much power that port is capable of outputting or will output.

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