So the other USB thread got me to thinking about the limitations I've seen with electronics that charge via USB ports.

I have a variety of things that can charge via USB.

smart phone
flip phone
GPS
iPod
lights
etc.

What I have observed however, is that most of them do NOT charge from a typical USB adapter. I also have poor results attempting to charge them from a radio or flashlight with a USB charging port (while cranking of course - have to do it at the right speed). I get the best results when I load the specific driver on a laptop and charge them directly from there.

I've tried cigarette outlets to USB adaptors where you use your own USB cable and they don't charge the phones or GPS. However, I can use a simple AC/DC inverter to plug my laptop or netbook into the car, then connect a USB hub and charge all of them at once.

Examples of limitations:
** I can't get my GPS to charge via USB on anything but a computer or it's specific cigarette to USB adapter. The generic cigarette to USB adapter in which you connect your own USB cable will power it up in a mode in which it tries to "connect" to a computer. But does not charge.
** My smartphone won't charge on anything but its AC adapter, designated DC adapter or a computer with a USB port and drivers installed.
** A standard basic Motorola flip phone with USB charging port will charge off my computer, designated wall adapter, and one of my crank flashlights. But another crank radio will not charge it. Nor will the generic cigarette to USB adapter in which you connect your own USB cable.

In summary - If you think you have found a "system", you had better TRY IT out on everything you intend to use it on to make sure it works.

The USB standard limits the total power to the USB bus, and certain devices exceed this standard.

From Wikipedia:

The USB 1.x and 2.0 specifications provide a 5 V supply on a single wire from which connected USB devices may draw power. The specification provides for no more than 5.25 V and no less than 4.75 V (5 V±5%) between the positive and negative bus power lines. For USB 3.0, the voltage supplied by low-powered hub ports is 4.45–5.25 V.

A unit load is defined as 100 mA in USB 2.0, and 150 mA in USB 3.0. A device may draw a maximum of 5 unit loads (500 mA) from a port in USB 2.0; 6 (900 mA) in USB 3.0. There are two types of devices: low-power and high-power. A low-power device draws at most 1 unit load, with minimum operating voltage of 4.4 V in USB 2.0, and 4 V in USB 3.0. A high-power device draws the maximum number of unit loads permitted by the standard. Every device functions initially as low-power but the device may request high-power and will get it if the power is available on the providing bus.

Some devices, such as high-speed external disk drives, require more than 500 mA of current[37] and therefore cannot be powered from one USB 2.0 port. Such devices usually come with Y-shaped cable that has two USB connectors to be plugged into a computer. With such a cable a device can draw power from two USB ports simultaneously.

A bus-powered hub initializes itself at 1 unit load and transitions to maximum unit loads after it completes hub configuration. Any device connected to the hub will draw 1 unit load regardless of the current draw of devices connected to other ports of the hub (i.e. one device connected on a four-port hub will draw only 1 unit load despite the fact that more unit loads are being supplied to the hub).

A self-powered hub will supply maximum supported unit loads to any device connected to it. In addition, the VBUS will present 1 unit load upstream for communication if parts of the Hub are powered down.

In Battery Charging Specification, new powering modes are added to the USB specification. A host or hub Charging Downstream Port can supply a maximum of 1.5 A when communicating at low-bandwidth or full-bandwidth, a maximum of 900 mA when communicating at high-bandwidth, and as much current as the connector will safely handle when no communication is taking place; USB 2.0 standard-A connectors are rated at 1.5 A by default. A Dedicated Charging Port can supply a maximum of 1.8 A of current at 5.25 V. A portable device can draw up to 1.8 A from a Dedicated Charging Port. The Dedicated Charging Port shorts the D+ and D- pins with a resistance of at most 200 Ω. The short disables data transfer, but allows devices to detect the Dedicated Charging Port and allows very simple, high current chargers to be manufactured. The increased current (faster, 9 W charging) happens if both the host/hub and devices implement the new charging specification.

If you want a USB charging station, you need one of these:

So, where do you get one of those new-fangled colon thingies?

I just use one of these or one of these . It will take a charge from the normal USB power limited 2.5W input (so will charge from a 4.5W Solar Panel or computer PC USB port). The charge will accumulate in the Lithium Battery and the outputs will have enough power (upto 10 Watts from the TecKNet iE380-II 7000mA Dual USB battery port) to charge all USB powered devices even up to iPad 2 etc. Its not as efficient to charge the main battery on the device you want to use but most device will allow operation when powered externally. It would take about 14hrs sun exposure using a 4-5W PV panel to fully recharge the iE380-II to give yourself a few hours iPad 2 use.

I wouldn't even bother attempting to hand crank charge anything as power hungry as a smart phone, even getting enough charge into a standard cellular handset to make a 1-2 minute phone call is a royal pain...

Here in the States, it's just a regular, plebeian pain.

Martin pretty much hit on the technical details. I have been trying to standardize a subset of my gadgets on USB for years simply because having the connectors all the same gives some versatility in charging them.

But the fact remains that just because it has a USB plug does not mean it uses all the USB standards; and while most such devices will charge when plugged into a computer's USB port, it can take much longer to charge than if you had used a charger connected to a 110v or 12v power source.

After Irene I used a battery booster pack with a 12v outlet to charge our cell phones. The car charger used for this has a wire with a micro-USB connector, as well as a standard USB port. By using another USB cable with a micro-USB connector I could charge both phones at the same time. However, the wire coming directly from the charger did the deed twice as fast as the cable from the USB port; presumably because the port was throttled to the voltage/amperage of the USB standard.

the cellphone commitie has standardized the plugs, but the adapters sometimes have to be specific. like a Nook will only charge from a Nook powersupply. If I were to guess I would say that it is becouse it is a higer voltage.

The drivers for each device helps with the charging becosue the device that you are charging with the drives "knows" how to manage the power comming in.

While this is certainly true, a lot of devices won't charge simply because the vendor has taken steps to try to only charge from "officially sanctioned" chargers. (Read: they want to force you to buy from them)

If you look around, some chargers are better than others at being accepted by various devices. Also, you can sometimes find cables or dongles that will allow various devices to be charged.

Examples:

While my various iPod devices will charge using a number of "line-out" style cables with my extended battery pack, my Verizon iPhone 4 will only charge if I use a SendStation PocketDock Mini dongle as a line-out enabled cable (even tho it complains about it):

http://www.amazon.com/gp/product/B002ACNZFI

I was never able to get my Motorola Razr V3m to charge from my battery pack regardless of the cable, but I was able to find a thingy that allowed me to charge the battery:

http://www.amazon.com/gp/product/B002MVQFMW

Here is the battery pack I'm using these days:

http://www.amazon.com/gp/product/B004OC0122

In general, I've found it a mix of research and trial and error and luck. Also, note that now that USB has more widespread appeal, I think newer devices are more likely to allow third party chargers.

Of course the rub is, as Martin pointed out, a lot of newer devices draw more power and are more likely to run into the USB 2.0 standard issues. On the other hand, more and more chargers are being built to charge devices wanting extra power.

The moral of the story is -- don't just throw a charger in your bag for emergencies and assume it will work for your devices! :-)

Also, if planning for emergencies, keep in mind that sometimes you may need to charge more than one device concurrently. Think through the logistics, keep in mind how long it takes to charge a device, how fast they are depleted, how many devices are likely to be on at once.

-john

Bingo. Verify things work as you expect.

Just like the saying: "Fail to plan and plan to fail", everyone must "Practice your plan or plan to fail".

My iPhone, radio, speakers, lights,AAs, etc so far have charged from my Joos Orange solar charger.

Now considering a USB chargeable point and shoot camera like the Sony HX9