Previous 1 2 Next 28 Replies Latest reply: Jul 13, 2013 6:06 PM by Zac Wilkes
Kunio Mitsuma Level 2 Level 2 (160 points)
Does anyone know if there is a USB hub that can supply 2A current to EACH port on the hub so that it can be used for simultaneously syncing and charging an iPad?

As we all know, simply connecting an iPad to a Mac with a sync cable will not charge the iPad adequately.

Mac Pro (MacPro1,1), Mac OS X (10.6.6), MacBook Pro (2007)
  • Julian Knight Level 1 Level 1 (15 points)
    Most computer (well PC anyway) USB ports WILL charge the iPad fine - _as long as_ you leave the iPad off, if the screen is on, there is not enough power.

    I don't know of ANY hubs that will deliver the required power over all ports. Though I do now have a battery power pack that has two USB ports, one of which will charge the iPad.

    The doesn't mean that there aren't any though. You need 1 amp or above to charge the iPad whilst it is active so you would need it to be a powered hub, short of trying a load, you will have to ask some vendors.
  • Kunio Mitsuma Level 2 Level 2 (160 points)
    Thanks for the "iPad-off" idea!!
  • Rudegar Level 7 Level 7 (21,925 points)
    usb is speced as 5volt 0.5amps

    if a hub was made which could provide more then 0.5amps it would not be compliant to the standard and would be illegal many places as malfunctioning usb devices which by accident would draw more then they were made to could catch fire
  • Kunio Mitsuma Level 2 Level 2 (160 points)
    Oh, I see. I didn't know the 0.5amp spec.

    That means that Apple's 2A AC-USB adapter for an iPad (and similar products) would be the only way I can charge the iPad while it is in use, then.
  • Rudegar Level 7 Level 7 (21,925 points)
    well yes and know
    one could make a cable

    many small external harddisks use more power then only 1 usb port can provide
    so they come with a usb cable which split into 2 usb in the other end
    that would give 1amp power and those are not
    suspect in the eyes of the standard as far as I know

    guess if you have 2 of those and connect then to 4 usb ports
    and then took a third one of them and connected to the 2 using some sort of female usb in both ends cables
    you would get 2 amps

    if it's bothersome or if that funkey wiremess would be suspect I can't say
    but you can at least get 1amp using the 2 way splitter
  • Kunio Mitsuma Level 2 Level 2 (160 points)
    Interesting. I have another question. How about the following approach:

    - Use a USB Y-adapter with A plugs on top of the Y and B plug on the leg.
    - Connect one of A's to a Mac and another A to Apple's 2A AC-USB adapter.
    - Connect B to a standard iPad/iPhone sync cable, then onto the iPad.

    This would certainly sustain 2A supply (and more though not needed).
  • Rudegar Level 7 Level 7 (21,925 points)
    yes I suppose it should be I would make sure both the computers was well grounded
    it don't matter as much with DC like usb
    but with AC 2 devices giving (110/230volts) may not have the same level in relation to 100% ground which could cause power interferences

    had a friend who (crazy as he was) back in the day connected 2 computers using a normal serial cable but the cable was 130meters running though a sewer and the ground (zero) level differences between the 2 computers blew the serial port curcit of one of the computers
    because the rs232 signal which was suppose to be 12+- end up being different maybe +15 -9 or something along those lines
  • Kunio Mitsuma Level 2 Level 2 (160 points)
    I see. A volt meter would give continuity, but ground potentials would be vastly different.

    OK. I am going to give my approach a try. The idea is, as you know, to use the iPad while it is charged and to sync it with iTunes without swapping cables.

    I will post my result later here. Thanks again for your initial idea. It was brilliant.
  • Michael Morgan1 Level 7 Level 7 (23,825 points)
    Profinite wrote:
    .......

    This would certainly sustain 2A supply (and more though not needed).

    Yes, and it would also supply 2A at the power out pin of the computer's USB port. The only way this is not a problem is if a) there are blocking diodes installed, which there are likely to be, and b) if those are big enough to handle this over-spec load for extended periods, which is not likely at all.

    Hey, it might work and, even if it doesn't, there'd be little mystery to those little wisps of smoke drifting out of your suddenly dark computer. ...
  • Kunio Mitsuma Level 2 Level 2 (160 points)
    Isn't it that the current is drawn by the device that is attached to a port? So, why would the computer's USB port be drawing the current then? It's the iPad that will draw the current from the ports, isn't it?
  • Chris CA Level 9 Level 9 (77,475 points)
    if a hub was made which could provide more then 0.5amps it would not be compliant to the standard and would be illegal many places

    It would not be illegal. It would just not meet the USB standard.
    as malfunctioning usb devices which by accident would draw more then they were made to could catch fire

    What if the hub or the computer are defective and draw more power than they are designed to and catch fire? Are they illegal?
    Devices that draw more current than they were made to draw are defective. Defective devices are not illegal. They are just defective.

    And note that many Apple computers can supply more than 500mA to USB devices.
    -> Powering Apple and third party peripherals through USB
    "Some Apple peripheral devices may request more than 500 mA (Milliamps) at 5 V (Volts) from a port to function or to allow for faster charging. Such Apple peripheral devices include:

    Apple MacBook Air SuperDrive (when connected to supported computers)
    Aluminum Wired Keyboard
    iPod
    iPhone
    iPad
    To meet requests for additional power from these Apple peripherals and devices, some Apple computers and displays can provide up to 1100 mA at 5 V through the port to which the Apple peripheral or device is connected. This power is available under certain conditions:"

    Profinite,
    As we all know, simply connecting an iPad to a Mac with a sync cable will not charge the iPad adequately

    It will. I can charge and use my iPad on my Mac mini jusst fine.
    Note that the *Mac Pro (Early 2008) and later* (see link above) will supply 1100mA to a single USB device.
    Plug your iPad directly into the back of your Mac Pro and it should charge while you are using it.
  • Julian Knight Level 1 Level 1 (15 points)
    There is definitely some confusion here!

    The first thing to note is that the USB specification calls for devices to REQUIRE no more than a certain amount - NOT that hubs cannot be CAPABLE of supplying it. Even so, there are many USB connected bits of hardware that break this specification (such as external hard drive enclosures).

    Secondly, the fact that a plug CAN provide high amperage doesn't mean that it DOES.
    The device requests an amount, if that request exceeds what the plug can provide then it doesn't get it but the plug will not force extra power down the wire - otherwise everything around your house connected to the mains would blow up!


    So hubs and power connectors are certainly allowed to provide the power (as I said, 1 amp seems to be plenty though the Apple power supply is 2 amps). As I also said, I already have a battery power supply that gives 1 amp but just on one of its 2 ports, that 1 amp is plenty to charge the iPad even when left on.

    I fully expect that 1 or 2 amp capable USB power supplies will appear over time.

    Finally, let me re-iterate that you can plug a low-power device (such as my smart phone) into a higher-power USB supply (such as my Apple iPad one) *without any ill effects*. Similarly, you can plug laptops into power supplies with higher ratings and even into lower ratings as long as the input voltages are OK.
  • Kunio Mitsuma Level 2 Level 2 (160 points)
    Yes, that's exactly what I thought. Thanks for the clarification.
  • Michael Morgan1 Level 7 Level 7 (23,825 points)
    Profinite wrote:
    Isn't it that the current is drawn by the device that is attached to a port? So, why would the computer's USB port be drawing the current then? It's the iPad that will draw the current from the ports, isn't it?

    No, my point was that the computer's port isn't supposed to be drawing current at all. There's no question that the iPad's charging circuitry would sense the voltage and set itself to take whatever current was appropriate, but what happens at the other end of that common 10W DC potential?

    Wait, just thought of a way to find out. Take the iPad Power Adapter, replace the cable with an A-A one, plug it into the wall and plug the other end into the computer's USB port.

    Message was edited by: Michael Morgan1
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