Category Archives: Device Charging

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USB Stock Chargers, Dedicated Multi-Port Chargers, or Charge & Sync Hubs. What’s Best for Me?

In today’s world of mass portable devices with USB connectivity, charging should be as simple as plug and play. Unfortunately, it’s not that easy. Take me for example. On my desk I’ve got a Google Nexus 5, Dell Venue 8 Pro, Apple iPhone 4, and several generations of iPad. Each one came with a completely different power adapter for charging! My Nexus will charge off of almost anything, my Dell Venue 8 Pro is quite picky, but Apple might be the most confusing of them all.

The reason is USB charging has not been well standardized until recently. Apple has been charging devices via USB with special signaling since the first USB connected iPod. Devices determine whether and how fast to charge, and make that decision based on different non-standard methods to recognize “their charger.”

Take for example the following charging signals commonly seen today:

  • Apple 2.4A (12W)
    (iPad Air / iPad Mini, likely any subsequent iPad releases)
  • Apple 2.1A (10.5W)
    (original iPad through iPad Retina)
  • Apple 1A (5W)
    (first seen with the iPod all the way back in 2002, commonly found with all iPhones including the newly released iPhone 6/6 Plus)
  • Dedicated Charging Port, DCP (wattage varies per device)
    (often referred to as the Android charging signal, common for almost all non-Apple devices)
  • Samsung 2.4A (12W)
    (usually seen with Samsung tablets, potentially some phones)
  • USB-IF BC1.2 CDP 1.5A (7.5W)
    (the official USB charging standard, it’s not well adopted yet, but more devices are becoming compliant)

What exactly does all of this mean?

In short, taking my Dell Venue 8 Pro as an example, I can’t plug it into just any USB charger and expect it to charge, it works on Android and Apple 1A signals but won’t charge on any of the others. Or if we take my iPad Retina and plug it into my iPhone 4 charger, it’s going to charge at an overly slow rate.

Because of scenarios like these, most users have a preconceived notion that they must use the stock charger that came with their device. Sometimes with the fear that if they do not, their device won’t charge, or worse, could actually be harmed.

Fortunately this isn’t the case. In fact, most devices on the market can actually charge from the Apple 1A signal as it has unofficially been adopted as the universal USB charging standard; mainly because it’s been around for so long. Also a device will only pull as much power as it needs, so using a more powerful charger may actually help your device charge faster. The newly released iPhone 6 and 6 Plus ship with the standard Apple 1A charger, but will charge much faster on the Apple 2.1/2.4A chargers or another charger that the iPhone 6 recognizes.

Many consumers don’t realize they can downsize their growing pile of stock chargers for a more convenient multi-port charger that can charge almost every USB charging device in their home simultaneously from just one AC wall outlet. Take our flagship multi-port charger, the Plugable USB-C5T (temporarily out of stock 10/3/2014). It has 5 USB charging ports with enough power (7.2A, 36W) to charge two iPads and three iPhones concurrently (or three iPads and one iPhone, etc) at their maximum charging rates.

Click to enlarge.

The Plugable USB-C5T, bringing order to chaos.

Three of the C5T’s USB ports simulate the standard Apple 1A signal which will charge most devices, including my picky Dell Venue 8 Pro, but where the C5T really shines is with the two outer ports which are equipped with a smart charging chipset made by the folks at Genesys Logic. The GL888F chipset can simulate almost all of the aforementioned charging signals (sans Apple 2.4A) and will intelligently select the best one for your device. This is great because if your device happens to not be compatible with the standard Apple 1A signal, chances are it will charge off of the smart ports.

Great. Sign me up!

Not quite yet, but we’re almost done. Have you ever tried to charge your device from your computer only to be let down by slow charging or no charging at all? If so, you’re not alone, it happens to the best of us. When you connect a phone or tablet to a computer, the device wants to put itself into a mode where data can be synced. Often syncing while charging either isn’t possible or is extremely slow, only drawing around 0.5A from the host computer’s USB port. This behavior is also expected on all USB hubs unless they are BC1.2 compliant. The BC1.2 charging signal, CDP (charging downstream port), is compatible with all current Apple Lightning Cable devices like the iPad Retina / iPhone 5 (and newer) and many new Android and Windows Mobile devices are moving this direction as well.

Our flagship 7-port USB 2.0 hub, the Plugable USB2-HUB7BC, is BC1.2 compliant and devices can charge at up to 1.5A while syncing data. The HUB7BC can also act as stand alone dedicated charger when the computer is turned off or not connected. To many this is the proverbial “holy grail” of USB charging despite slightly slower charging rates (1.5A) compared to a dedicated smart charger like our GL888F (up to 2.4A) equipped USB-C5T due to the added convenience of charge and sync.

In a time where USB charge and sync functionality can be unnecessarily complicated, we work hard to deliver simplicity to the equation. With charge and sync being available on nearly any BC 1.2 compatible device, which is most mobile devices produced in the last few years, why would you want to haul around an individual charger for each device?

 

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Plugable Launching Kickstarter for the Pro8 Docking Station with Charging for the Dell Venue 8 Pro on Wednesday, June 25th, 2014

Update: November 17th, 2014 – Now available on Amazon US and CA! See our product page for information and links to purchase.

Update: October 30th, 2014 – Take a look at our latest updates on Kickstarter.

Update: August 8th, 2014 – Where Can I Get One?

There has been a flood of inquiries to where individuals who missed the Kickstarter can get the Pro8. Once production is finished and units ship out to our Kickstarter backers in November, we plan to begin selling units on Amazon. We do not yet have an exact date, but we hope to have the Pro8 available to the public in time for the holiday season. Visit http://plugable.com/kickstarter for more information and sign up for our email mailing list to get the latest updates on the Pro8 and availability.

Update: July 27th, 2014 – Our project was successfully funded!
Thanks to all 367 of backers who helped us raise $29,831 of our $24,000 goal.

Update: June 25th, 2014 – The Kickstarter is Live!


Our Dock Connected to a Dell Venue 8 Pro with a Monitor, Keyboard, Mouse, Ethernet Connection, & Headset Attached! All that with 2 USB ports to spare!

We released a demo video on YouTube last November showcasing the Dell Venue 8 Pro with our flagship UD-3900 USB 3.0 Dual Display Universal Docking station, essentially turning the tablet into a full desktop workstation. We received an extremely warm welcome from the Dell Venue 8 Pro user community and even caught the attention of Michael Dell (CEO, Dell) himself who retweeted our video. To this date we have over 150,000 views and almost 400 user comments.

Although this video showed the full capability of the tablet, it also highlighted a major flaw that could limit its uses: there is only one USB Micro B port that can only be used to either charge the tablet or to connect it with external USB devices. This seriously limits the Dell Venue 8 Pro’s capabilities as it cannot remain connected to a monitor, keyboard, and mouse during a full 8+ hour work day without running out of battery well before then. Consumers quickly realized this problem and the solution to this constraint quickly became an active topic of conversation on the comments on the YouTube video and in many tech forums. This Kickstarter is the culmination of our work to make that happen!

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Some of our early prototypes

After months of development and multiple prototypes, we have created a product that allows full desktop replacement functionality and to charge at the same time. Furthermore, this docking station also works with the Lenovo Miix 2 which faces the same critical limitation as the Venue. Currently we are in the final phase of prototyping and are working with our manufacturing partner to perfect the docking station so that it can be brought to the market in mass.

Do  you know someone with a Dell Venue 8 Pro or Lenovo Miix 2 8″ Windows Tablet? Let them know about our Kickstarter! Even if you don’t and just want to support Plugable, please pledge just $1 and we pledge to keep you up to date on our progress with exclusive updates along the way. This will give you special access once the device goes on the market and a huge thank you from us! Every single dollar will help us reach our goal!

We are launching our Kickstarter on Wednesday, June 25th 10AM PDT for this exciting new product and we need your help! If you are interested in supporting this project then you can sign up for email notifications here at http://plugable.com/kickstarter

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Custom PCB Prototype
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Also Compatible with Laptops

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Single 20W Power Adapter for Dock and Tablet

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Included Items (power adapter varies per geography)

Plugable USB-C5T

New Plugable 5-Port Smart USB Charging Station

A USB Charger with better compatibility, more power, and lower cost.

With so many USB devices such as phones and tablets needing wall wart style adapters to charge, it is easy to run out of power outlets. Buying spare or replacement device-specific chargers for each one is an expensive mess. The Plugable USB-C5T can help solve the dwindling wall outlets conundrum by offering 5 USB charging ports off of one wall outlet. Its small size and longer power cable make it easy to create a great charging setup.

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USB charging is standardizing around the Battery Charging 1.2 standard. But for now, there are still a lot of legacy devices on the market which require proprietary signals to charge. The USB-C5T supports BC 1.2, and also has a smart IC to detect all of the major proprietary charging methods on the market. USB-C5T vs. Apple 12W Charger

Supported devices include all existing Apple products (iPad, iPhone, iPod), Kindle devices, Nexus phones/tablets, Samsung products, the Dell Venue 8 Pro, and even our power banks

Note this is a dedicated charger – it’s not a USB hub (there’s no USB “B” port for connecting back to a PC). The included cable connects back to a US wall plug. Connecting into the charger, you use the USB charging cables that already come with each of your devices.

The middle three ports on the USB-C5T provide an Apple 1A signal (the most common proprietary method, recognized by most devices), while the outer two are equipped for smart charging and will be recognized by devices looking for Apple 1A, 2.1A, or Samsung 2.4A signaling and most importantly, any of the current and future generations of BC 1.2 compatible devices.

The two GL888 smart charging ports are capable of automatically selecting the best charging method for the device attached. This feature can potentially charge some devices that do not charge on the regular Apple 1A port and can charge some devices a lot faster!

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Questions? Problems? Feel free to comment below, or email us at support@plugable.com. We’ll be happy to help!

Plugable Power 2014 5-Port 36W USB Smart Charger for Multiple Android, Apple iOS, and Windows Device... Product Details
$18.95

Device Charging Rates

Plugable does extensive testing to determine which devices charge at what rates on our chargers and charging capable hubs. This turns out to be important, because USB charging is not (yet) well standardized, and results vary by device.

If you’re looking for a charger, our data on charging rates will tell you exactly how much current, in milli-amps, specific devices will pull from our chargers. The higher the number, the faster the device will charge. We’ve tested many popular Apple and Android devices, and add new results frequently.

The complete list of results is available here at:
plugable.com/platforms/device-charging-rates

Plugable USB3-HUB4AC1

Plugable Launches New Aluminum SuperSpeed Hub

USB gets used for everything. Today’s tablets and ultrabooks just don’t have enough ports. You don’t want to be stressing the few ports you have with constant plugs & unplugs every time you want to use a different device.

And these same USB ports are needed for charging all your mobile devices — but charging on USB is not well standardized, and there are many devices out there (like Apple’s) that won’t charge on a “normal” USB port .. at least not while the computer is sleeping.

We designed our new USB 3.0 hub to solve both of these issues. Built in solid brushed aluminum, the Plugable USB3-HUB4AC1 provides 4 standard USB 3.0 ports with the latest chipset and firmware (VL812 firmware 9081). Plus it provides a single dedicated charging port, that will charge most devices at fast rates, even when your computer is off.

Using Aluminum for the body looks great, dissipates heat better, and is arguably more recyclable: the plastic ends can be removed, and the PCB slid out, leaving only aluminum to recycle. This new 4 port model rounds out our Aluminum USB hub line, which also includes an existing 7 port model.

Power Details

Unlike its larger 7 port predecessor, the USB3-HUB4AC1 has a 5th port dedicated to charging. This port stands out from the rest with a bold red connector. No data communication will happen here but for charging, it’s got you covered. This port replicates the Apple 2.1A charging signal. What that means is that it is fully compatible with iPhones, iPads, iPods, etc. Most Android devices will also recognize this signal.  The best feature of having a dedicated charge only port is when compared to other hubs that support charging and data, most charge functions only occur when the host computer is either off, in sleep mode, or not present. This port charges independent of a host PC regardless. Charging rates are device dependent, see the USB3-HUB4AC1 product page for details.

Compatibility

USB3-HUB4AC1 units have been tested to work well with both Windows 8.1, and OS X 10.9.x, as well as older systems running Windows 8, Windows 7, Windows Vista, Windows XP, and OS X systems with both USB 3.0 and USB 2.0. Older USB 1.1 devices connected to USB 2.0 systems via the hub are also supported.

Convenience

For desktop PCs where USB 3.0 ports may be hard to reach, the HUB4AC1′s design with top-facing angled ports can make connecting devices easier. The extra ports on a USB hub can also help avoid damaging built-in ports when frequently swapping devices. The built-in power button on the hub also makes for a convenient way to quickly disable all attached devices with the press of a single button, to make sure attached USB devices are off and saving power.

Power

With the included robust 12 volt 2.5 amp power supply, more than enough power to operate several power-hungry devices is available, 30 watts to be exact. Even when charging a 2 amp tablet, there is a full 20 watts left over to power all four data ports at the full USB 3.0 900mA per port specification.

One exception of note is the Apple “SuperDrive” which requires a direct connection to a supported Mac. From http://support.apple.com/kb/HT2801

The SuperDrive is designed exclusively for use with MacBook Air, MacBook Pro, and Mac mini’s that do not have a built-in optical drive. The SuperDrive must be directly plugged into the computer’s USB port, and cannot be used if connected to a USB hub.”

Any questions? Feel free to comment below or just email support@plugable.com. We’re happy to help. Thanks for going out of your way for Plugable products!

USB3-HUB4AC1 Product Details
Currently Unavailable
PB-6K2

Plugable Launches Two Portable USB Battery Charger Banks

A portable Plugable power product for charging on-the-go is here!

PB-6K2 and PB-12K2

In fact, we’ve got two new products, the PB-12K2 and PB-6K2 Portable Battery Banks are here to help breath life into your power hungry devices on long flights or days spent out and about. With two different sizes, you can find the right battery pack for you.

Find your tablet needing to recharge mid trip? Then the PB-12K2′s slim, large capacity 12,000mAh power supply will keep your tablet going. Current generation iPads have a 11,560 mAh battery. The PB-12K2 has a 2A port which charges as quickly as Apple’s bundled charger, with enough capacity to fully recharge your iPad. It’s the perfect companion, and it works with phones and other devices too, with either 2A or 1A ports.

For a power bank designed for phones that’s a little more compact, choose the PB-6K2 battery with its 1A port. Smaller in size, but it still packs a large 6,000 mAh power supply. For comparison, the current generation iPhone 5S has a 1,560 mAh battery. You can charge it several times over and eliminate the worry of getting caught with a dead battery.

Easy to recharge from any USB port and long storage life between charge cycles means they are always ready when you need it most. It’s easy to check how much power you have remaining. With a simple push of a button, power level LEDs will let you know where you stand. These portable batteries are the perfect partner for any adventure.

And these batteries, especially the PB-12K2, is useful for powering any USB or 5V powered embedded device. You can gain mobile flexibility for powering for Raspberry Pi, Arduino, or other boards on the go.

Designed with compatibility in mind, the Plugable Portable Batteries can charge a multitude of devices like Apple products (iPad, iPhone, iPod), Blackberry devices, HTC smart phones, Nokia phones, Samsung phones, Motorola phones, Nintendo handheld devices (3DS, DS), Sony handheld devices (Vita, PSP), and other portable USB-based devices.

Never get caught with a dead phone or tablet again when you’re out for a long day or a short trip.

Have any questions? Just comment below or email support@plugable.com. We’re happy to help!

Plugable Launches the USB-C3T USB 3-Port Charging Station

With so many USB devices such as phones and tablets needing wall wart style adapters to charge, it is very easy to run out of power outlets. The USB-C3T can help solve the dwindling wall outlets conundrum by offering an additional 3 USB charging ports. In addition, it’s small size and lengthy cable make it very easy to create the perfect charging setup.

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The USB-C3T is compatible with a multitude of devices that charge over USB. We’ve had the chance to do a bit of testing ourselves. We’ve seen a lot of different devices charge with the USB-C3T; Apple products (iPad, iPhone, iPod), Kindle devices, Nexus phones/tablets, Samsung products, Chromebooks, the Dell Venue 8 Pro, and even our own new Plugable Wristband Watches! For those with a more technical curiosity, each port on the USB-C3T provides the Apple 1A signal. Click here for detailed charging information.

The USB-C3T also includes a single smart charging port which is capable of automatically selecting the best charging method for the device attached. This feature can potentially charge some devices a lot faster. We’ve seen that devices like the Google Nexus 7 tablet and the HTC HD2 phone can charge at nearly double their normal charging rate.

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Lastly, the USB-C3T is perfect for travel. Not only does it solve the problem of needing to carry around the various AC adapters for your power hungry devices. The 3-port charging station sports a long 4.5′ detachable power cable, allowing for the USB-C3T to compress into a nice small package for when you’re on the go.

Plugable Power 2014 3-Port USB 20W Smart Charger for Multiple Android, Apple iOS, and Windows Device... Product Details
$15.75

Plugable Launches Adapter to Enable Charging on Any Powered USB Port

It’s frustrating, but many devices won’t charge on a powered USB port the way you’d expect. This includes most Apple, Samsung, and Google phones and tablets.

This is because the phone must choose how much power to pull, and by the original USB spec devices are supposed to only draw 100mA at first. They can then negotiate up to 500mA. This negotiation requires a PC that’s attached and on.

The iPhone and most other non-tablets will charge at 500mA on a standard USB port this way. But they can also charge faster (up to 1000mA) if a port sends a special, non-standard signal to say “I’m an Apple 1A charger”. It does this by shorting the data lines (disabling data transfer at that point) and putting a specific signal voltage on each of USB’s two data lines. Even though it’s not a standard, nearly all phones and tablets on the market today recognize this signal.

For tablets like the iPad, this mechanism is even more important. Because these batteries are larger, charging at 500mA would be slow. The 1A “I’m an Apple charger” signal becomes the minimum for the tablet to report charging at all.

This new Plugable USB-MC1 Charging Adapter simulates that 1A signal, turning any powered USB port with at least 1A power available into a charging port.

Charging both a iPad 4 and iPod 3

Charging both a iPad 4 and iPod 3

This also has the effect of disabling data transfer, so you can safely plug your phone or tablet into a public computer and the phone or tablet will charge, but not be visible to the computer otherwise — you’re safe to charge without worrying about exposing your data.

Leave this attached to your phone or tablet’s USB charging cable to greatly expand the set of USB ports you can charge on.

iPad Not Charging        Ipad Charging

Above on the left is an Apple iPad connected to a standard USB hub that has plenty of power available, but you can see on the iPad’s screen in the upper right, that it’s not charging.

On the right is the same setup with our adapter in-between the iPad and the hub. You can see the iPad now sees the hub as a charger, and is charging the battery.

How many of these adapters can be safely used on a powered hub at once?

The AC adapter of your powered hub needs to be rated for at least 1A per USB charging adapter connected. If it is not, over-current may be triggered (causing all power to the hub to shut off), or the hub circuit or power supply may heat up from too much current being pulled through by the device. If this happens, remove devices until you’re back within the rated amperage.

So before you go running off and buy 10 of these little dongles to turn your 10 port hub into a charging super station, keep in mind that you are still limited by how much power the USB hub has access to. For instance, our 10 Port USB 2.0 Hub comes with a power supply of 2.5A, that is only enough to actively charge 2 devices at the Apple 1A Charger rate with .5A left for spare devices on the hub.

More questions?

The Plugable USB-MC1 product page has more detail, including a table of charging rates with some common phones and tablets. Have any other questions? We’re happy to help. Feel free to comment below or email support@plugable.com anytime. Thanks for your support of Plugable products!

Where to buy

Plugable Power USB Universal Fast Charge-Only Adapter for for Android, Apple iOS, and Windows Device... Product Details
$7.95

Raspberry Pi and Plugable Devices

We recently received a Raspberry Pi at the Plugable offices and we have been using it to test how our various devices interact with it. The Raspberry Pi has 2 USB 2.0 Ports, and no USB 3.0 ports, so our testing was focused on USB 2.0 devices and a couple USB 3.0 storage devices.

All of these tests were carried out on a Raspberry Pi Model B using the latest version of Raspbian wheezy. Here’s a video of the full setup, followed by a bunch of detail about our tests:

Hubs

  • Plugable USB 2.0 7 Port Hub with 3A Power Adapter – No Issues
  • Plugable USB 2.0 4 Port Hub with 2.5A Power Adapter – No issues
  • Plugable USB 2.0 10 Port Hub with 2.5A Power Adapter – Causes the Raspberry Pi to reboot upon connection, because it supplements the 2.5A wall power with 500mA from the upstream port. This is too much for the Pi., but just at the moment it is plugged in. If you plug the 10 port hub in when the Pi is powered down, you can boot into the Pi and all will be well. But since there are better options (like the 7 port hub above), we don’t recommend our 10 port hub with the Pi.
  • USB2-2PORT – Causes the Raspberry Pi to reboot upon connection. This is simply because this is an unpowered hub. Only hubs with their own power adapter should be used with the Pi.
  • USB3-HUB7-81x – USB HID devices(Mice, Keyboards) are known not to work with this hub on the Raspberry Pi.
  • USB3-HUB81x4  - USB HID devices(Mice, Keyboards) are known not to work with this hub on the Raspberry Pi.
  • USB2-SWITCH2 – No issues

Other Devices

The common pattern with all devices is you must have one of the powered usb hubs above and connect the device through that. If you don’t, the Pi won’t be able to handle the power draw, and it will drop voltage and reset.

Ethernet:

Storage:

Plugable USB2-Micro-200X USB Microscope:

  • On a Raspberry Pi running Raspbian we have test our Microscope connected through a powered USB hub to work with GTK+ UVC Viewer by using the following terminal commands:

    “sudo apt-get install guvcview”
    “guvcview”

Let us know if there are any other Plugable products you’d like us to test, or if you have any questions at all – we’d be happy to help. Thanks for your support of Plugable products!

Where to Buy
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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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