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USB Power Supply

so you only need the one.
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I'm a bit of a gadget fan and almost every piece of electronic goods I buy comes with its own (differently specified) power supply or charger.

Why aren't those devices that have power requirements below that provided by USB take power from a standard USB cable (and transform it internall if needed)?

For times when you're away from your computer :o) you could have a mains transformer that supplies current down a USB cable. ----- For those not familiar with the acronym it stands for Universal Serial Bus and is a data cable that is capable of powering low powered devices.

[additional thoughts 17 Jan 2002]
egnor was right all along. USB supplies too little power to make it useful for devices across the board. USB provides 2.5W, IEEE1394* provides 12W (according to howstuffworks.com). My digital camera needs 9W to charge it.

The trouble with IEEE1394 is that it is not that common yet. Apple support it and Sony will put the port onto anything they touch but every other computer user seems to have to buy a board to get the port.

What we want to be able to do is transfer data (say from a digital camera) using USB but power the camera using IEEE1394. Putting two ports on the camera (or other portable device) increases production costs. What we need is a USB powered USB to IEEE1394 connector. [goes away and posts idea] (see link)

*aka Firewire, iLink

[additional thoughts 6 December 2002]
Palm have now brought out the Zire m150 which, although it trickle-charges itself from the USB cable still ships with a wall-wart. This is a device which has been pared down to low power consumption and Palm still felt it necessary to bundle it with something that can charge it faster than USB.

st3f, Apr 18 2001

12 volt house http://www.halfbake...a/12_20volt_20house
more on the elimination of wall warts. [st3f, Apr 18 2001, last modified Oct 05 2004]

USB mobile phone chargers http://www.dansdata.com/usbcharge.htm
And other daft things to do with USB sockets. [StarChaser, Apr 18 2001, last modified Oct 21 2004]

iPod http://www.apple.com/ipod/
Text about charging via Firewire at the bottom of the page [wiml, Jan 16 2002, last modified Oct 21 2004]

USB powered USB to IEEE1394 connector http://www.halfbake...EEE1394_20connector
As mentioned above. [st3f, Jan 17 2002, last modified Oct 05 2004]

USB-rechargable AA battery http://www.usbcell.com/
Heh. [jutta, Sep 25 2006]

Standards http://xkcd.com/927/
"Fortunately, the charging one has been solved now that we've all standardized on mini-USB. Or is it micro-USB? Shit." [spidermother, Apr 20 2013]

[link]






       Potential problems:   

       1. I believe USB supplies 5V. For efficiency, many wall warts supply 15V or so (because it's more efficient to step down than it is to step up).   

       2. The spec may limit the current capacity of a USB connector to something relatively low, like 500mA. There are relatively few devices that you'd use a wall-wart for that have such a limited power need.
egnor, Apr 18 2001, last modified Apr 19 2001
  

       More and more devices are going below the 5v limit. However, given the energy loss stepping power up coupled with the low power rating for USB, this idea may be limited to those power supplies (wall warts - I like it) that are used to charge devices.   

       These devices are either off or in a low power consuming mode when they are plugged in so they don't need high voltage or high power. [is this true? - st3f]. [finally gets round to checking out his digital camera charger and finds that it is rated well above the power that USB can supply]   

       So this might work for mobile phone chargers, digital camera chargers, MP3 player chargers etc - all those devices that are portable with an internal recharable battery. In fact these are the very devices that I would want to target; the portables which are only portable if you don't have to lug a charger about with you.   

       This would solve internationalisation too. The power supply for my digital camera cannot switch input voltages so if I go abroad I'm limited to one charge of the internal battery.
st3f, Apr 19 2001
  

       The link I added is to a review of cables that convert the 5 volt power from a USB out to charging power for a couple of different cellphones, but it also gives vague directions on how to hack a cable to deliver 5v wherever you want it.
StarChaser, May 01 2001
  

       A single USB port on a computer is limited to a maximum of 500mA. A single port on a hub which doesn't use an external power supply may not be able to get more than 100mA.   

       A set of four AA rechargeables can supply 500mA (the max for a USB port) for almost 3.5 hours. Most digital cameras go through batteries faster than that--ergo, they use more than 500mA.   

       To be sure, it might be nice if the cameras could just power up the memory circuitry to allow computer access without having to power up all the current-guzzling stuff. But USB is fast enough that it's generally possible to power-up, connect, get stuff, and power down without taking too much time or battery juice.   

       I recall seeing an ad by some silicon company (Linear Technology, maybe?) showing a design which used their chip for a simple USB-powered battery charger, so the concept isn't out of the question. But charging four AA NiMH's would take over four hours, so it's hardly a panacea.
supercat, Jan 16 2002
  

       This is pretty close to what the Apple iPod (pocket-size mp3 player) does, actually, except the iPod is a firewire (IEEE1394) device. So it will leech off your computer's supply to recharge its battery while you are transferring music to/from it. It doesn't have a separate charger port - -- only the firewire port --- so the battery charger wall- wart that comes with the iPod just has a firewire port. (Presumably the battery charger isn't actually a firewire device and just supplies power on the bus.)   

       For some reason, firewire has a higher current capacity than USB.
wiml, Jan 16 2002
  

       Canon make scanners now which are 'single-cable' - i.e. powered by the USB connection.
hippo, Jan 16 2002
  

       Indeed hippo. I have just bought one, and very good it is too.
goff, Jan 16 2002
  

       //Perhaps a better place to suck power from would be the joystick port (pin 1 and pin 9 give +5VDC) but I've not verified this.//   

       I don't remember the pinouts, but at least on one board I used once the game port supplied enough current to visibly damage the insulation on the ribbon cable (a part on the board I was developing went into CMOS latch-up, and got very toasty. Surprisingly, though, the computer didn't even reboot!)
supercat, Jan 17 2002
  

       supercat: You're right. IEEE1394/Firewire/iLink can supply more power but USB is more popular. It looks like Firewire is therefore going to be the standard for 'wall warts' and that this will hopfully be baked.   

       Rods: I don't know what the USB spec says but you asking for trouble by plugging a device that takes its power from USB into an unpowered USB hub.   

       wiml: Thanks for the link. Apple look like they've baked this (albeit using Firewire rather than USB). Hopefully it won't be too long a wait for someone else to bring the same kind of thing to market.   

       hippo, goff: The powering of a computer peripheral by USB was baked by the people who designed USB. This is about powering and charging portable devices using a standard power supply and/or a cable from the back of your PC. The scanner is very pretty, though (I have one too)   

       [Added to idea after wiml's news]
st3f, Jan 17 2002
  

       I can now say this without looking like a total idiot: I use a Mustek 1200; dead cheap, dead basic, works fine. (I'd really like an A3-size scanner, but they start at around £2,000.)
angel, Jan 17 2002
  

       USB Mobile phone chargers are available (go to www.maplin.co.uk) and my digital camera will power itself from the USB when downloading images, but will not charge the batteries as it takes stanard AA's and there is no built in charger.
CasaLoco, Jan 17 2002
  

       sorry if this was sugested its late and i dont have tome to read the whole thread   

       why not have a totaly universal powersupply that every thing runs on say there are three setings or so say like ~6v ~15 v ~and somethnig larger   

       and every product is made touse one of those settings then u wouldnt have to shop around for a simple tranzformer powersupply thing   

       there would jsut be one type u can get and it will run all your house hold apliances if need be   

       so u could jsut have a stockpile if something didnt come with its own adapter   

       it would be no big hassle   

       pardon spelling mistakes and things its late christmas day and some things i injested are affecting my head a bit   

       so im gona sleep till next week or so meery christmas
halitus, Dec 25 2002
  

       Halitus has hit it on the head, an obvious small improvement to everyone's lives. Wall Warts are a real pain in the ass because a) they all have different voltages b) they all have different connectors and c) some even have different polarities, though I sincerely hope we have now settled for centre positive.   

       There should be legislation to limit to one input voltage at standard polarity. I know it's not difficult for the electronics to cope with a higher voltage, say 15, with a simple existing chip from Maxim or similar.   

       The legislation could alternatively just add a $5 tax to anything non- compliant.   

       Manufacturers would WIN with this one, because after a while they would no longer have to supply the wall wart, with savings in packaging and transport as well as the wart itself.   

       You'd just use one of the ones you already have.   

       The biggest winner would be the environment. No more wall warts thrown away (with all that copper) just because the item it was bought for is broken or lost.
RusNash, Jun 18 2003
  

       What you are looking for is USB PlusPower (aka Powered USB or poweredUSB). This is common in industrial enviroments and retail point of sale. The cable supports 5, 12 and 24 volt supplies at relatively high power.   

       The USB PlusPower design provides the following voltage and current options:   

       +5 volts DC at up to 6 amps per connector (up to 30 Watts)   

       +12 volts DC at up to 6 amps per connector (up to 72 Watts)   

       +24 volts DC at up to 6 amps per connector (up to 144 Watts)   

       The USB PlusPower design also includes a new USB cable design with two additional wire pairs inside the cable and modified connectors to support the new current and voltage. The new connector is backward compatible with the standard USB connector, so powered USB products also support traditional USB connections with no setting changes required.   

       You an find useful information about the standard at http://www.usbpluspower.org
everest, May 26 2004
  

       Many different devices have inherently different power needs. If a device needs +9V to operate, and has a linear regulator on the front end, it will work with higher voltages but become proportionally less efficient.   

       A different approach might be to have wall-warts provide a four-terminal connector, and have user devices include a couple of resistors to set the voltage and current limits. Unfortunately, this would probably require using a three or four wire cable, in place of the two-wire cable that's used today.
supercat, May 26 2004
  

       The new Motorola Droid comes with a charger that has a wall-plug "head" that can be separated from the rest of the cable, which becomes a USB cable when not attached to the "head". Very handy!
paix120, Mar 07 2010
  

       I should probably draw a line under this one (like this)...
========= ========= ========= ========= ========= ========= ========= =========
...and draw people's attention to the date of the idea. It was posted back in 2001, six months before the release of the first iPod and before, as far as I am aware, USB chargers existed at all. It seems strange that there was a time when these things did not exist, considering how prolific they now are. I'm even writing this annotation on a laptop powered by USB. Wow.
st3f, Jul 05 2015
  
      
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