Charging Your iPad or iPhone with a USB Hub

12/3/2012 Apple’s new devices with the 8/9 pin lightning connector is now BC 1.1 compatible! We now have a 4 port USB hub that charges these new devices with or without a PC. Older 30-pin connector devices are not compatible. See below for them.

“The only reason I bought this was that my computer’s USB doesn’t provide enough power to charge my iPad 2. Unfortunately, this hub doesn’t charge the iPad either, so it’s completely useless to me.”

“Bought this as a powered USB hub so that an iPhone and iPad could be connected to a MacBook Pro and charge both. Does not work.”

“So much for a ‘powered’ usb hub, it doesn’t power my iPad …, which defeats the purpose of me even getting it.”

It seems like it should be so easy. You have a hub that is plugged into an electrical socket. Your iPad is plugged into the hub. It should recharge. But it says, “Not Charging.” Why?

Quick iPad Charging Steps: Connect it to the self-powered hub, hold the Sleep/Wake button to begin shutdown, swipe the 'slide to power off'' on screen, and the iPad will charge once shut downIt all has to do with how electrical current is supposed to flow through USB ports and with confusion caused by proprietary behaviors that Apple has implemented in its product ecosystem that lead to different recharging results in seemingly identical scenarios.

If you want to avoid the answer to the “why” question and just know how to charge your Apple iPad, iPhone, or iPod Touch when it’s connected to a self-powered hub, here are your two options.

Option 1: The iPad/iPhone/iPod is connected to a hub that is plugged into an electrical outlet and a computer simultaneously. The Apple device will recharge by pulling current at a rate of 500 milliamps when attached to this hub (the hub’s power supply must have enough amperage to provide this current).

  • The iPhone and iPod both will indicate they are charging in this state. Total recharge time will be about half as fast as when they are plugged directly into a Mac’s USB port or an electrical outlet.
  • The iPad will display “Not Charging” in this state if its screen is enabled. Put the screen to sleep with the Sleep/Wake button on the iPad’s exterior, and the device will start to charge. In our tests, an iPad charging at a 500-milliamp rate will add about 10% to its battery meter every 1.5 hours.

Option 2: The iPad/iPhone/iPod is connected to a hub that is plugged into an electrical outlet but not a computer. The Apple device’s power must be completely turned off for the device to recharge when attached to this hub. Here are step-by-step instructions.

  1. Plug the iPad, iPhone, or iPod into the hub. If the device was previously shut down, it will turn on upon sensing power from the hub.
  2. Perform Apple’s shutdown routine for the device. You can’t  just let the screen go blank. You need to hold down the physical Sleep/Wake button on the exterior of the iPad, iPhone, or iPod until you see the red arrow on screen that you can swipe to turn off the device.Screen capture of Apple's "power off" slider
  3. Swipe the red arrow to complete the shutdown process.
  4. Once turned off, the Apple devices will draw power through the hub at the 500-milliamp rate.

Please be aware that if you attach multiple Apple devices at one time to your hub in either scenario that you might start to exceed the amperage available in your hub’s power supply. We cannot verify charging will occur once this has occurred.

In our tests, when we overloaded the available power supply, we saw varying results in how the attached devices consumed power. However, we did observe that iPhones and iPods (not iPads) still would charge–albeit very slowly–when drawing power at the 100 milliamp rate.

If you want to know more about how USB power works and where Apple deviates from the USB 2.0 standards, read on.

USB Power Primer
The USB 2.0 spec permits devices to pull current at a default rate of 100 milliamps from a USB 2.0 port (we’ll call this the host)–enough to power a mouse but hardly enough to charge an iPad battery.

If a USB 2.0 device needs current at faster rate than 100 milliamps to function, it is allowed to negotiate with the host to increase its consumption rate to a maximum of 500 milliamps from the host’s port.

Screenshot of the warning in WIndows 7 when USB devices are trying to draw more power than is available through the portWhen a device tries to draw more current than is available to the host–often described as overcurrent–you can end up with a warning that there isn’t sufficient power to meet the device’s needs. This warning might appear on the host (e.g., a popup in the Windows taskbar, like the one shown to the right). But others, like the Mac, disable the port without any warning, often creating the erroneous impression that the devices are broken. They aren’t–they’re just not able to draw any power from the port anymore. A reboot re-enables the port, but the port will shut down again if you don’t take any action to reduce the power consumption by the mix of devices attached to the port.

When multiple devices are connected to a single USB 2.0 port via an unpowered hub, it can lead to an overcurrent situation, especially because all the devices attached to the hub have to share the 500 milliamp current available through the host’s port. The hub can only split the available current, not multiply it.

A self-powered USB 2.0 hub–that is, one with its own AC adapter–can alleviate this situation, because it can tell the host, “Don’t worry, I can take over as the provider of the current that these devices want.”

For example, if the hub’s the power supply can deliver current at a rate of 2.5 amps (100 milliamps = .1 amps), and there are five ports on the hub, the host now can let each USB 2.0 device attached to a port on the hub negotiate for up to the USB 2.0 maximum of 500 milliamps (2.5 amps / 5 ports = 500 milliamps / port) without exceeding the hub’s power capacity.

When There’s No Host
When a self-powered hub is plugged into an electrical outlet but not connected to a host–think of it as a USB-based power strip in this configuration–it becomes wildly unpredictable how devices attached to the hub will behave when trying to draw power. The original USB 2.0 spec just didn’t envision how important USB-based power consumpution would become.

Without guidance from the spec on what to do in this scenario, device manufacturers can implement whatever behaviors they desire. Some devices will pull power at the same rate as they do when attached to a host-connected hub. Other devices will downgrade to the 100 milliamp default. Certain devices may try to exceed the 500 milliamp limit in the USB 2.0 spec–not necessarily a bad thing for improving device charging times.

In the case of the Apple iPad, iPhone, and iPod Touch, we saw different power consumption behaviors depending on whether the devices were powered on or off. When powered on, they could draw only 100 milliamps of power. When turned off, as explained earlier, they would draw 500 milliamps of power.

Side-by-side images show the change in power draw by the iPad when plugged into a self-powered hub that isn't attached to a computer

This image shows an iPad's power consumption when plugged into a self-powered hub that has no data connection: On the left, the iPad in a powered-on state is drawing 100 milliamps from the hub. On the right, the iPad in a powered-off state is drawing nearly 500 milliamps from the hub. Click the image for a larger view.

If you have questions about whether your specific phone, tablet, or handheld device will charge if it’s plugged into a hub that’s being used like a power strip, the only way to know is to plug the device into the hub and see what happens.

Apple Bites Back
Apple makes great devices, but it also makes the USB-charging situation even more confusing. As explained, the iPad, iPod, and iPhone will recharge when pulling 500 milliamps of current. But Apple has engineered these devices to prefer to pull more than USB 2.0-specified  maximum of 500 milliamps. However, to do so, the devices must be connected directly to USB ports that have been customized with Apple’s proprietary charging extensions.

Graphical link to Apple's explanatory document about its proprietary extensions

Click the image to go to Apple's support document that explains the proprietary USB charging behaviors in Apple's product ecosystem.

In a support document on Apple.com about USB charging, Apple explains that “some Apple computers and displays can provide up to 1100 milliamps [1.1 amps] … through the port to which the Apple peripheral or device is connected.” In other words, when an iPad or iPhone is connected to a newer Mac as its USB host, an iPad can draw current at more than twice the standard USB 2.0 rate.

The current isn’t delivered at as fast a rate as the 2.1 amps provided by Apple’s special AC wall adapter for recharging an iPad. Gizmodo has done a speed test of the fastest (and slowest) ways to charge an iPad. Charging via a Mac’s USB port at the 1.1 amp rate was the slowest way in the Gizmodo test, but it still got the job done. As we’ve identified, even 500 milliamps will get the job done as long as the iPad’s screen or power is off.

And 500 milliamps is the only rate that you’ll ever get from a Windows PC or any other USB 2.0 host that lacks Apple’s proprietary charging extensions.

You might be thinking that the ideal solution is just to get a Mac plus a USB hub. Then you can have all the benefits of multiple USB ports and can use one to charge your iPad, iPhone, or iPod Touch at the faster rate available when connected directly to a Mac.

Unfortunately Apple only allows these devices to draw the 1.1-amp current from a Mac’s USB port via a direct connection. Apple explains: “An Apple peripheral device must be plugged directly into an Apple computer or display. Apple peripheral devices connected to hubs will not have access to extra power above the standard USB specification of 500 milliamps.”

In other words, if you connect a hub–powered or not– to your Mac, you lose access to the proprietary charging extensions in the Mac’s USB port that allow the Mac to charge your iPad, iPhone, or iPod at the 1.1-amp rate.

If you want to know how Apple establishes these proprietary USB charging behaviors, Ladyada.net has a great video and blog post on the technical underpinnings of the mysteries of Apple device charging. As she explains, it has to do with how Apple has engineered its devices to deviate from the USB 2.0 spec when they sense a special amount of voltage from the power source on two of the four lines that make up a USB connection.

Where Do We Go from Here
There is hope that in the future USB-connectable devices will consume power in a way that meets the “universal” promise in the USB name.

There is now a USB battery-charging spec that was developed to standardize USB-based charging behaviors. Unfortunately, the spec has not yet been widely adopted. And the lack of any strong industry efforts to market or brand spec compliance makes it difficult for customers to identify and buy products that already follow the spec.

In a world where following this spec was the norm, you could plug your hub into a wall, attach a bunch of devices, and get them all to recharge in a reasonable and predictable amount of time without having to take any special action.

Regardless of what happens in the future, our aim always is to make sure that you know what to expect from Plugable products today and that you are satisfied with the ones you purchase. If you have questions or comments about this article or device charging in general, feel free to leave a reply here, and we’ll respond.

If you have other questions about any Plugable hubs, docking stations, adapters, or cables, get in touch with us through our support website at support.plugable.com or e-mail us at support@plugable.com. We’re here to help.

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19 thoughts on “Charging Your iPad or iPhone with a USB Hub”

  1. Plugable USB 2.0 10 Port Hub (with Power Adapter) by Plugable Technologies

    befor I buy I have a question see if I understood this artical.

    I have 10 Ipods that need to be charge ( the charging will be over night) this product wont do the job right?

    Thank you
    Eddie

    1. Thanks for the great question. In general, we do not recommend the 10-port hub as a charging station. Whether it works is based solely on how individual devices behave–not any industry standards that customers can rely on.

      However, in our testing, we have determined that you can get Apple iPods to charge by the methods described in the article. The 10-port hub only has a 2.5 amp power supply, so with 10 iPods connected simultaneously, no iPod will be able to draw more than an average of 250 milliamps, resulting in slower-than-normal recharge times.

      Best Regards,

      Aaron
      Plugable Technologies

  2. Thank you for the post. Would any of your products be used to simultaneously charge and alternatively sync one iPhone 4 and one iPad2?

    Thanks in advance for your response

    1. Thanks for great question.

      First, you need to have a self-powered hub (that is, one with its own external power supply) connected to your computer with at least a free amp of current to provide to devices that draw power via the USB bus. For example, if you were using a self-powered hub with a 2.5 amp power supply, you couldn’t attach so many power-consuming devices (e.g., flash drives, network adapters, etc.) to that hub that there was less than an amp of the current remaining in the hub’s power supply.

      Second, if you use the process defined in the article of turning off your iPad once it is plugged into a powered hub, the iPad will pull 500 milliamps of current and recharge, albeit at a slower rate than when it is either plugged into the wall with its AC adapter or connected to a high-power USB port on a recent vintage Mac.

      Third, you can plug into the iPhone and synch at the same time that the iPad is charging if you started with the requirements listed in step No. 1.

      I hope this answers your question. If you need additional answers or support for this scenario, you can write us at support@plugable.com. We’re here to help.

      Best Regards,

      Aaron
      Plugable Technologies

  3. If I used Apple’s special AC wall adapter with a non-powered USB 4 port hub plugged into it, would this mean that the 2.1 amps could be distributed as 500 milliamps to each of the 4 ports?

    1. I assume you want to hook the hub up to Apple’s wall charger via the hub’s data port. That’s an interesting question for sure. The answer is that I don’t know what would happen, and I wouldn’t recommend trying it unless you’re willing to see your hub get fried.

      Since the hub is designed to draw power through the power lines in that port when connected to a computer, it might be willing to accept the 2.1 amp AC current that flows from the wall charger. Or the current might fry the hub, seeing as the hub is designed to take only 500 milliamps from the host computer rather than the 2.1 amps in the wall charger. Or the hub might not have the facility to accept the current from the wall charger at all given that it would not find a corresponding data connection.

      Even if it did accept and handle the power, there’s no way to ensure that you’ll get 500 milliamps per port. You’re at the mercy of how your devices work with a powered hub that has no data connection. The USB 2.0 spec says devices connecting to a USB 2.0 port can only draw 100 milliamps unless the computer host negotiates for them to draw up to 500 milliamps. There wouldn’t be a host here, so some devices would just get a trickle of power, others might draw up to 500 milliamps, and some might go against the spec and just pull as much power from the power supply as they could.

      But I go back to what I said at the beginning: I wouldn’t do this. You’re basically trying to create a powered hub from an unpowered hub–a risky proposition. I’d just recommend buying a powered hub. I’m not trying to make a shameless pitch here, but Plugable does offer a couple four port hubs that can provide an average of 500 milliamps per port based on their power supplies (again, that doesn’t mean the attached devices will pull the 500 milliamps without a data connection). One of hubs even supports the USB battery charging spec that allows devices compliant devices like the Galaxy S III to pull above 500 milliamps with no corresponding data connection. See http://plugable.com/2012/07/03/charging-the-samsung-galaxy-s-iii.

      1. Thanks Aaron for the reply.
        Much like many people today I am starting to accumulate a number of devices that need constant charging.
        Example: 2 iPod touches, Galaxy S phone, iPad, 3DS, 2 DS Lites…
        So if I built some sort of charging station for all these, maybe having a power bar with Apples USB wall plug, Galaxy S wall plug then a powered USB hub for the rest might be the best approach in terms of charging speed.

  4. HI Aaron Knopf
    IF I USED EXTERNAL POWER SUPPLY THAT PROVIDE 5VOLT-7AMP
    TO USB HUB CAN THAY CHARGE UPTO 10 IPADS?

    1. We don’t recommend this. The hub is designed to work with the 2.5-amp power supply with which it ships. To use any other power supply would put the hub’s circuitry at risk and void your warranty.

      1. WHY NOT IF I GIVE EACH IPAD WHAT HE WANT FROM VOLT AND CURRENT
        I THINK THE POWER SOURCE SHARING WITH IT’S CONNECTORS AND SO THERE ARE NO PROBLEM TO EACH ITEM TAKE WHAT IS NEED FROM THE CURRENT

        1. Thanks for the follow-up question. It is not an issue of what each iPad wants but whether the hub can handle the amount of current flowing through it. It wasn’t designed to handle the 10 x 500 milliamps that the iPads would be pulling through it. You are certainly welcome to try, but we expect that you will burn out the hub’s internal components rather quickly, and we wouldn’t be able to offer a replacement, because the failure would not have come from normal usage. I am sorry I can’t recommend this hub for you use case.

  5. My iPhone is damaged and will no longer work unless it it plugged into an outlet – it will not turn on if it is connected to the computer. Additionally, neither the phone nor wifi are functioning. If I could charge it through an outlet AND connect it with a USB cord to the computer I could retrieve my data. Any ideas on how to do this? It appears from this post that it may not be possible…

    1. Hi Sarah,

      Unfortunately, you’re right — it’s not possible to sync and charge without Apple’s proprietary USB extensions. You have those when connected to an iPhone charger, but obviously that’s charging only. The only other sure way you’ll get that is when directly connected to a recent vintage Apple Mac computer.

      Another idea is to head into an Apple store — they’ll be able to recover the data for you. Sorry for the bad news, but hope it saves you some trouble.

      Best wishes! Bernie

  6. If the methods for Apple’s secret 2.1 amp charging methods have been reverse engineered, then build a powered hub using those methods. I don’t see what the problem is. Reverse engineering is a valid and legal method for developing compatible products where no official spec exists.

    I am looking for multi-iPad fast charging that is less insanely expensive than Datamation’s Sync and Charge at US$1000 for 16 ports: DS-IP-SC-16

    Five powered ports per hub would be a nice round number for retrofitting iPad carts. 52.5 watts power draw, pluggable into a low-current parent USB 3.0 hub to divide up the data amongst the high-current 5-port hubs.

  7. I am very confused now. I purchased the charger to charge two iPhones and an iPad but now it seems this will not work. I called Amazon and they suggested I purchase another one just like this one and return the one I have now. Shouldn’t they know and tell you this will not work is this is the case. I just did not want to have these spread out all over the house to charge. Is there anything made that will do what I want to do. If it would charge the phones together (I have 3 iPhones) then I would charge my iPad at a separate location. Why does it have 10 USB ports if they can’t be used. Now I guess I will have to return both after I get the new one. Someone should be able to advise customers of what they need. I am very disappointed as I believe it is advertised to do the job.

    1. Hi Betty — Thanks for commenting! As you can tell from the above article, charging compatibility is complicated. You need the right hub and right (newer) Apple devices.

      If you have older Apple devices (30 pin connector), they’re only designed to charge in Apple chargers.

      If you have a newer Apple device (Apple lightning connector 8/9 pin) — those devices are compatible with the USB Battery Charging specification, and particular hubs like this one: http://plugable.com/products/usb2-hub4bc/ will charge them.

      It sounds like you have our 10 port USB hub, which is just a standard hub (no charging extensions). Just visit http://amazon.com/returns for easy return of that.

      Unfortunately, Apple hasn’t made the situation simple, because their earlier devices just won’t choose to charge at all with most normal hubs. So you’ve got a lot to digest to make sure you can charge every device in the house. But the above notes and article have all the gory details.

      And if you any specific questions, we’d be glad to help — just email us at support@plugable.com with the exact models of devices you’re hoping to charge, and we can figure out the right product for you. In most cases, it’s the USB2-HUB4BC linked above. Best wishes! Bernie

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