USB port power over load

[jellied]

I've bought a whizzy Nokia phone charger that allows me charge from a USB port.

when i plug it in i get an error saying it has over loaded the port and then stops charging and disables the port until i next reboot my laptop.

if i turn off the mobile phone first it works fine, but not ideal.

any idea what the solution could be? is there a setting in windows to disable a port and just use it for power if that makes sense?

[vorsprung]

Apparently the maximum load for a single device is 500ma

I would guess that what is happening is that you are plugging the phone into the USB socket on the computer.   The computer already has stuff like a keyboard and mouse on it and perhaps (like mine) it has other stuff like a multifunction card reader.

The phone charger must be pulling a fairly large current which is enough to overwealm the current limits

I doubt that you can fix it in software

[Lucky]

The USB specification normally limits the current that a device may draw to 100mA. However, a device may request more power from the host, and if the request is granted, may draw up to 500mA.

Many PCs don't enforce the current limit too strictly, but a laptop on battery power may well be doing so, so my guess is that the charger is drawing between 100 and 500mA either without requesting the extra current, or after the request is denied. It may even be that the charger is simply drawing power from the port without even initialising as a USB device.

Either way, the device is not USB compliant, and the manufacturer shouldn't be using the USB trademark.

[jellied]

bother - that is annoying. it works fine at home where i plug it into an 8 way multi-hub.

at work i have 2 ports, one chains off to the monitor to provide 2 further ports, one is spare and one is for the keyboard.

i wonder if the mouse draws less power.

the charger was purchased from ebay for 99p, not quite the £8 i was charged some years back for a similar official Siemens device.

thanks for the help

[Greenbank]

I got one from eBay for about 2 quid (well I got 2 for about £4 including postage).

No problems with it on my laptop (IBM T60) but then my phone (Nokia 6230i) may not try and draw enough current to trip the USB port current limit gubbins.

I bought mine for emergencies¹ and so I'd be quite happy to have to turn off the phone if it was a choice between doing that or having no phone due to a flat battery.

I have one proper charger at home, and another on my desk at work to keep the phone topped up all the time.

1. One lives in the laptop bag, the other lives with the 4 AA battery USB power pack that I also got off eBay which is carried as an on-the-road emergency phone charger (which also helped charge my Garmin Forerunner 405 on a recent Audax).

A (mains) powered USB hubs may not have the same problem although my Mac loses connection with everything plugged into it if I've got my iPod Shuffle, Garmin Forerunner 405 and mobile all charging from it at once.

[hulver]

You can get special usb cables with two ends. One of the two ends that goes into the computer is power only. Plug them both in, then into the device and all your power problems are solved.

I use one to run an external hard disk off the usb ports.

A powered USB hub will often supply more power as well.

[Lucky]

Yes, a self-powered hub should power the charger fine, as it will normally allow 500mA to each port by default (as this is simpler, and therefore cheaper to design and manufacture, than enforcing the two different current limits).

Doesn't help if the objective is to charge a phone from the laptop because mains isn't available, though.

[Adam]

Jellied - how old is your laptop?  On my PC, if I plug my camera into the USB ports at the front which are USB v1.1, then I get an overload comment whilst it's fine plugged into the ones at the back which are the more modern Hi Speed 2.0 versions.

[jellied]

It's a newish one at work - less than 2 years. I'm not even sure if the ports of 1.0 or 2.0.

It's annoying but something i'll live with, I've got USB power plug which is good compromise and basically saves me lugging around half a dozen chargers.