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USB to charge a laptop??

  • 19-11-2007 2:28pm
    #1
    flogen
    Moderators, Society & Culture Moderators Posts: 10,247 Mod ✭✭✭✭


    I was having a geeky moment the other day and got thinking about laptop chargers and how they're all propriety and stupid and annoying.

    That thought then got crossed with one about a Wii accessory I just bought, that has a battery pack and dock so you can charge your wiimotes via USB... the idea being that you leave it plugged into your Wii.

    So that got me thinking. We all know that you can charge or power a device that's connected to USB (a PMP, HDD, whatever) but can it be made to work the other way? Could a USB port be designed so that power goes into it as well as out of it?

    I just thought of how handy it would be to have your power port double as a USB... for a start it could eventually become a standard port that does away with the 70 different types of charger heads out there but perhaps best of all it would allow for dual usage of a connection on your laptop (so you could use it as a normal USB port when on the go, and a way to charge it when at home).

    I know that if manufacturers wanted their laptops to all have the same type of power connection it would have happened by now but I'm just wondering if it's theoretically possible first even if it isn't going to actually get done!


Comments

  • #2
    watty
    Registered Users, Registered Users 2 Posts: 32,417 ✭✭✭✭watty


    It's not an impossible idea. However a Top of the range laptop is 150W and very basic 50W.

    At 5V that's 10A to 30A. Or more as converting from 5V is less efficent. Look at how big a 13A rated mains plug pin is. Hence the 17V to 20V that Laptop PSUs use. (3A to 7A).

    A USB connection is design for less than 1A. The spec says a max of 0.5A.

    Anderson Power poles are the solution. They are good existing standard. Design to use 10.6V to 16V* and a car can power / charge directly. The standard Anderson connector is 45A max current, that's up to 450W @ 10V!!


    * The car voltage was originally 13.8V. Hence CB PSUs. A Battery is FLAT at 10.6V (or 11V for longer life) and typical charged voltage on modern top up free car batteries (Calcium technology) is 14.2V. Max rating of most equipment designed for cars is 16V. Most external PSU routers, switches accessories that allege to use 12V PSU, in fact work well 10V to 16V.


  • #3
    flogen
    Moderators, Society & Culture Moderators Posts: 10,247 Mod ✭✭✭✭flogen


    watty wrote: »
    It's not an impossible idea. However a Top of the range laptop is 150W and very basic 50W.

    At 5V that's 10A to 30A. Or more as converting from 5V is less efficent. Look at how big a 13A rated mains plug pin is. Hence the 17V to 20V that Laptop PSUs use. (3A to 7A).

    A USB connection is design for less than 1A. The spec says a max of 0.5A.

    Anderson Power poles are the solution. They are good existing standard. Design to use 10.6V to 16V* and a car can power / charge directly. The standard Anderson connector is 45A max current, that's up to 450W @ 10V!!


    * The car voltage was originally 13.8V. Hence CB PSUs. A Battery is FLAT at 10.6V (or 11V for longer life) and typical charged voltage on modern top up free car batteries (Calcium technology) is 14.2V. Max rating of most equipment designed for cars is 16V. Most external PSU routers, switches accessories that allege to use 12V PSU, in fact work well 10V to 16V.

    Interesting - thought it might be the case that the power going through would be too low to make it practical.

    I suppose it would be great if manufacturers just agreed to have any kind of unified power module but it's unlikely to happen.


  • #4
    Capt'n Midnight
    Moderators, Recreation & Hobbies Moderators, Science, Health & Environment Moderators, Technology & Internet Moderators Posts: 93,599 Mod ✭✭✭✭Capt'n Midnight


    higher power usb ports give 500mA which at 5 volts is 2.5 watts
    low poer usb ports onlygive 100mA which is half a watt

    some old network cards had DC-DC voltage convertors on them 5v to 9V maybe . if the output was isolated you could wire up two to two usbports and have 18 volts output. because of inefficinecies you would only get 2W out of each not 2.5 w. and thats only if each usb port is on a different controller as at a guess the 500mA limit is on the controller not the port. you have 4watts you might be able to charge the battery once overnight :(


    there was a link for older tosh laptops - the gist was that you need about 14.5 volts to get it to recognise the external PSU (15V) but as long as the voltage on the external port was more than the internal battery (10.8v) it would draw power externally. So you could run it off a battery if you used two pp3's to start it , or on a car with a running engine - more research needed ;)

    some of the 3com stuff runs from 9V to 30V - check the ratings on the back of the device first, as a general rule you are safe it the polarity is right and you are a little under voltage (if the device needs two voltages I'd guess the higher one first - but you are really on your own there)

    but beware some very old 5V stuff had TTL chips so you only had a 5% tolearance on the voltage , 6V was guaranteed to kill it.


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