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Not All USB Power Is Created Equal
jfruh writes "We've reached a point in our electronic lives where most of our gadgets draw power from a USB cable, and we have lots of USB ports to choose from — some of which live on other gadgets, some of which live on adapters that plug into your wall or car. But those ports supply wildly varying amounts of power, which can result in hours of difference in how long it takes your phone to charge. The Practical Meter, the product of a successful Kickstarter campaign, can help you figure out which power sources are going to juice up your gadgets the fastest."
Like this little thing and also learn what the numbers and values mean. Got two, they work great and they're consistent with more pricier measurement options.
Being the fastest might not be the best for your battery life.
I believe most types of battery when charged faster actually degrade faster.
Life fast die fast ;-)
New things are always on the horizon
Instead of that ugly one, you may get something that gives an exact value, like this one. A new iPhone/iPad expects 2A, the MacBook (10W) expects also 10/5 = 2A.
Slashdot, fix the reply notifications... You won't get away with it...
What am I missing from this?
One example: my Nexus 7 draws so much power, even when sleeping, that it is possible to connect it to a weakly charging USB port, come back a few hours later, and it has a lower charge level. I'm sure the same is true for other tablets, and possibly even some phones.
In what way is it "good and practical" to ignore a standard, possibly damaging electronics which assume the standard by providing a variable non-guaranteed maximum current? At worst this is a fire hazard, as you'd end up delivering an unreasonably high current. If the device isn't intelligent enough to ask for the right current, it should be delivered a safe trickle - as the USB standard asks.
Your Nexus 7 has runaway background processes. Otherwise there's no way it draws more than 500mA in standby - it would be empty after just a few hours. Check your battery stats to find the culprit...
My girlfriend's Nexus 7 charges just fine off of good old 500mA USB2.0 ports when it's in standby...
Indeed they do. If the charger says "I can supply 1.5A" but due to thin wires in the long, cheap cable that results in a significant voltage drop the device backs down to a lower level.
const int one = 65536; (Silvermoon, Texture.cs)
SJW, n: "Someone I don't like, and by the way I'm a fuckwit" - AC
A USB port should react gracefully to a defective USB device - either limiting current or cutting power if draw is too high. It should not give the malfunctioning device the opportunity to catch fire by delivering it as much current as possible.
Liberal in what you accept; conservative in what you send.
One example: my Nexus 7 draws so much power, even when sleeping, that it is possible to connect it to a weakly charging USB port, come back a few hours later, and it has a lower charge level. I'm sure the same is true for other tablets, and possibly even some phones.
Interesting. My wife has a Nexus 7 (2012 edition). It charges just fine (albeit relatively slowly) from 500mA USB chargers. It charges faster with the 2A charger that comes with it, but I've never had issues with it losing charge while plugged in to a standard charger.
How weak is your "weakly charging" USB port? Is it one on a keyboard or some other low-power accessory, or is it a port on the computer itself?
The Color and Tablet Nook devices have two different charge rates. If you use the official "USB" cable with the LED indicator in it, it charges at a 1A (2A?) rate. If you use a stock micro USB cable, it charges at the official 500ma rate. The decision is made by the Nook itself, based on info from extra pins that are in the custom cable.
Which (blankety-blank-censored-blank) is no longer available. And since the cables are no longer made or sold and since they were notoriously prone to fail means that I've been trickle-charging my unit for about a year now.
Moral of story: always check new toys for screwball cables before buying.
This is why I build my own USB leads using #00 welding cable.
The USB spec - ya know, that thing that every device carrying the USB logo is supposed to follow - permits a connected device to draw a maximum of 100 mA until it is properly recognized (enumerated) by the host. This is probably what the GP is referring to: 0.5 W of available power (less after conversion efficiency) isn't a whole lot for a device like a Nexus 7.
After being enumerated, the connected device can request higher current levels, up to 500 mA max. It isn't supposed to draw more unless the host permits it. For many modern portable electronics (e.g., smartphones) that have a 3-10 Whr battery, a 2.5-W maximum charge rate isn't much.
There are amendments to the spec that allow for greater power: in 2009, the spec created a Charging Downstream Port, which allows for up to 1.5 A from the host after enumeration; and the Dedicated Charging Port (DCP), which shorts the two data lines together and allows for 1.5 A charge power without enumeration.
Individual companies, such as Apple and Samsung, supply their own USB chargers that allow for even greater charge current, but do so in a way that technically violates the USB spec.
I'm an Apple Abhorrent... I don't use any of their products, not even an Ipod. I'm an Android/Windows guy. But my daughter decided she had to have an iPhone and bought it with her own money. I have one of those little plugs you put in a cigarette lighter in the car. My car has two up front, one that is ignition keyed, the other is always on. The dongle is in the one that is always on. And I have a standard USB cable to charge phones and other devices from it. It charges all of my Android phones fine. It charges the GPS fine. It charges pads like the Galaxy Tab and the Nexus fine. It won't charge my daughter's iPhone, even with her white Apple USB cord. To this situation, my daughter tells me that the little dongle I have is a POS. I smiled and was reminded, yet again, why I won't buy Apple products.
Brawndo: It's what plants crave!