Charging devices via USB plugs

[StinkyPete]

I raise this matter as my electrical knowledge is at about the level as sub-atomic nuclear physics knowledge, and the question may be relevant to all of us.  I anticipate there's expertise on the forum to provide good answers and information.

Many devices today are designed to be charged by plugging into a USB socket, and this is common to phones, tablets, cameras, GPS devices and so on.   This is all the kind of stuff that we take with us while touring, and each manufacturer of such devices usually stresses that only their particular wall socket charging adapter should be used.  That can therefore require taking a handful of wall socket USB chargers, one for each device you might travel with.   Typically we may fit USB power outlets to our motorcycles, and I carry a third party wall socket USB charger with four outlets, with two rated to 2.1A and two rated to 2.4A, and all at 5 volts.

Is the manufacturers warning valid, or can any USB wall socket device or bike mounted power outlets be used to charge any of our essential devices?
Is there an industry standard, and will the device being charged only suck in what it needs?

[cravenhaven]

I think Yes and No is the appropriate answer, perhaps even a maybe :).
USB is standardised but the standards bodies didnt move quickly enough when USB became a big hit as a common means of providing power. Consequently many manufacturers (particularly Apple) made up there own standards to provide the level of power required for their devices. These manufacturer 'standards' only relate to controlling the current provided between the USB adapter and the device as the voltage is fixed at nominal 5v.

The upshot is that it is quite safe to plug any USB powered device into any USB adapter, however it may not be optimal for the device such that the charge rate may be very slow. eg an Apple iPad probably wont charge on your $5 kmart USB adapter, but it wont damage it either.

This is quite apart from the problems that occur with cheaply made USB adapters that struggle to charge anything.

[Williamson]

I think Yes and No is the appropriate answer, perhaps even a maybe :).
USB is standardised but the standards bodies didnt move quickly enough when USB became a big hit as a common means of providing power. Consequently many manufacturers (particularly Apple) made up there own standards to provide the level of power required for their devices. These manufacturer 'standards' only relate to controlling the current provided between the USB adapter and the device as the voltage is fixed at nominal 5v.

The upshot is that it is quite safe to plug any USB powered device into any USB adapter, however it may not be optimal for the device such that the charge rate may be very slow. eg an Apple iPad probably wont charge on your $5 kmart USB adapter, but it wont damage it either.

This is quite apart from the problems that occur with cheaply made USB adapters that struggle to charge anything.

Are you sure about that?   The USB outlet socket on the charger for my Dell tablet is labelled Output 19.5V.  I won't be plugging anything but the Dell into that.

[Gadget]

As Cravenhaven pointed out it is to do with current capacity. Early USB device drew less than 0.5 A and their chargers were only designed to deliver that.

Some even relied on the current regulator in the charger rather than put another current regulator in the device.

So an older device on a 2.4 A charger is likely to 'cook' the battery which will either twice is life or cause catastrophic failure. Our it can cause the device itself to overheat and become unreliable as I experienced recently. I thought my Tablet had died after taking it off the high speed charger. After it cooled of it started working again, but is now occasionally flakey with lockups and go slows.

From memory the current limits are 0.5 A, 1A, and 2.4A.

Some 12V chargers allow two or more devices with one at 1A and the other at 2.4A. They're are new ones that support 2 x 2.4 A.

So it comes down to the designed charge rate of the devices you are connecting.

Cheers,
Gary

[Gadget]

A few links to USB info

https://en.m.wikipedia.org/wiki/USB

https://en.m.wikipedia.org/wiki/USB_3.0

Cheers,
Gary

[alans1100]

Our Samsung phones tend to bit more flexible with the 240 volt USB charger pushing out 5V and 2amps and on the bike I use one of these

http://www.ebay.com.au/itm/Retractable-Micro-USB-Car-Charger-for-Samsung-Galaxy-S4-S3-S2-Mini-Note-2-/400703112673?hash=item5d4bc445e1:g:4yMAAOxyc2pTYDP1

It does power the Tom Tom GPS ok but the mini USB isn't as secure as the one on the Tom Tom supplied charge cable so I use that one even though it now means miles of cable laying on the dash shelf.

We also have a Samsung 12 volt charger but rarely use it now as the cheap one I bought above works ok.

[Brock]

A USB charger, will have a current limit. That doesnt mean that the charger will push 2 amps into your device, it means that it will supply up to 2 amps. As the device nears full charge the current will decrease.

As for the dell power supply, I seriously doubt that the USB outlet will will be running ap 19 volts (the Dell does use 19ish volts though) You will need to post a pic or part number for investigation.

[Williamson]

A USB charger, will have a current limit. That doesnt mean that the charger will push 2 amps into your device, it means that it will supply up to 2 amps. As the device nears full charge the current will decrease.

As for the dell power supply, I seriously doubt that the USB outlet will will be running ap 19 volts (the Dell does use 19ish volts though) You will need to post a pic or part number for investigation.

On closer examination it reads 19.5V or 5V, now I'm really confused.



 

[alans1100]

A USB charger, will have a current limit. That doesnt mean that the charger will push 2 amps into your device, it means that it will supply up to 2 amps. As the device nears full charge the current will decrease.

The charger that came with Heather's Samsung S7 is an adaptive fast charger with a rated output of either 9volts/1.67amps or 5 Volts/2 amps so if you're looking for an aftermarket USB charger then you should be getting one with the same output.

I do charge the tablet with the new fast charger as well though the tabs own charger is rated at 5volts/1amp

 

[cravenhaven]

On closer examination it reads 19.5V or 5V, now I'm really confused.

I guess it means that it has 2 output ports. 1 for the Dell and the other for USB.

[Williamson]

On closer examination it reads 19.5V or 5V, now I'm really confused.

I guess it means that it has 2 output ports. 1 for the Dell and the other for USB.

Nope!  Only one output port.

Still 

[cravenhaven]

Just did a bit of searching on this Dell adapter and I must admit it sounds dangerous to me. As I mentioned earlier, Apple and others came up with schemes to allow higher output from an otherwise standard USB port and eventually the standards bodies caught up, so that now there are multiple software and hardware methods for getting higher current through the USB port. Seems like Dell have come up with an absolute beauty that uses a special hardware configuration to tell the USB port on the charger to output 19V instead of the normal 5V. Without that special bit of hardware the charger outputs the normal 5V so is compatible with normal USB devices.

Still, I think I would be wary of using that charger with anything other than the Dell device it came with.

[Brock]

OK,

What the power supply has, is a regulator that can detect what is plugged in. This means, you can charge your phone or laptop.

[cravenhaven]

Actually I believe they use one of the data lines to indicate whether the dell device is plugged in. This is very similar to the way the various 'normal' devices communicate with chargers as per international standards, which is why I thought it was rather dangerous to potentially wack out 19V if your cable has incorrect wiring. I'm sure the Dell engineers are well aware of this and have taken steps to avoid destroying innocent USB devices, but it begs the question of why they did it this way?.

[Williamson]

OK,

What the power supply has, is a regulator that can detect what is plugged in. This means, you can charge your phone or laptop.

The only device or accessory I charge with the Dell charger is the Dell tablet, everything else, iPhone, iPad, Sena units - that's about it, get charged via the chargers supplied with them, or sometimes via the USB port on the Laptop or PC.

If someone wants to charge their device from the Dell charger they are welcome.

[Brock]

I have a 6 port charger from Amazon (I think) 3 are 2,4 A and 3 are 1 A. its a great bit of kit