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> Usb Power Budget, Is powering usb peripherals unsafe?
post Nov 18 2006, 08:09 AM
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From: Cardston, AB, Canada
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I'm running OZ on my C1000, but I think this is a fairly general question.

In kernel 2.16 and newer, if a USB device requires too much power, it is not enabled. 'dmesg' output might look like:

usb 1-2: no configuration chosen from 1 choice

To find out how much power a USB device wants, one can invoke:

lsusb -v | grep MaxPower

My card reader wants up to 250 mA, and my USB to serial converter says it might use up to 500 mA!

Post #3 on this ubuntu forum thread describes a work-around.

So my question is, is it safe to do this? [Also, I assume that people who are using kernels before 2.16 could well ask the same question, even if the device isn't automatically disabled.] Are the manufacturers of these USB products giving a high margin of error? Can a high-current device damage a Zaurus, or will it simply shorten battery life or just plain not work?

Thank you,

[Edit]. PS. Does it make any difference if the Z is plugged in or not?
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post Nov 18 2006, 07:36 PM
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there was a recent bug fix that turns off devices that will draw more power than is avalible. this affected many people as they had been running devices off unpowered ports without relising that the device wanted a powered one

there is somthing in the /sys tree to turn off this feature but i cant remeber where, it should be fine to turn off but its not recommended, if i remeber correctly the Z can do about 200mah and there is the chance that the power requirements were overstated or reflecta milisceond power spike to power up the device (in which case the capaitors will take care of the spike without loading the Z's power supply
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post Nov 20 2006, 03:56 PM
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the guy who put usb wifi and bluetooth inside a C1000 found he could increase the power available to the usb port using a resistor... the risk is as much from heating and/or burning a track on the PCB as anything else.

personally, I'd use a battery-powered hub (hmmm, really, you just need one with rechargeable battery or ultracapacitor than recharges from usb bus, so it will handle peaks of current?). I see figlabs have a nice usb external hard drive which is rechargeable, and probably ideal for many people.

on the subject of external hard drives, I note that Asus (used to) do a usb/wifi hard drive which runs samba... ideal to put in the car, sync your MP3's to it when you get home, and stream audio from it using your Z!
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