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If there is not enough power rating (the power supply unit) to support the
number of USB devices attached to an older machine, could this lead to
corrupt file transfers from a CF camera card (and/or the machine
spontaneously rebooting) ?

thanks
Frank

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frankg wrote:

> If there is not enough power rating (the power supply unit) to support the
> number of USB devices attached to an older machine, could this lead to
> corrupt file transfers from a CF camera card (and/or the machine
> spontaneously rebooting) ?

It is possible to get erratic behaviour if you put too much load onto
the USB 5v rail. Running your cell phone recharger and Xmas lights off
it is not recommended. I have had one card reader that was very fussy
about what else was plugged in at the same time on XP.

Simple way to test is unplug all the other USB peripherals.

Regards,
Martin Brown

Martin Brown wrote:
> frankg wrote:
>
>> If there is not enough power rating (the power supply unit) to support
>> the number of USB devices attached to an older machine, could this
>> lead to corrupt file transfers from a CF camera card (and/or the
>> machine spontaneously rebooting) ?
>
>
> It is possible to get erratic behaviour if you put too much load onto
> the USB 5v rail. Running your cell phone recharger and Xmas lights off
> it is not recommended. I have had one card reader that was very fussy
> about what else was plugged in at the same time on XP.
>
> Simple way to test is unplug all the other USB peripherals.

Or use a USB hub with its own power supply.

Really though, if the PSU doesn't have the "oomph" to power the USB
ports, you're likely to start seeing other weird things, like serious
system crashes...


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Matt Ion wrote:

> Martin Brown wrote:
>
>> frankg wrote:
>>
>>> If there is not enough power rating (the power supply unit) to
>>> support the number of USB devices attached to an older machine, could
>>> this lead to corrupt file transfers from a CF camera card (and/or the
>>> machine spontaneously rebooting) ?
>>
>> It is possible to get erratic behaviour if you put too much load onto
>> the USB 5v rail. Running your cell phone recharger and Xmas lights off
>> it is not recommended. I have had one card reader that was very fussy
>> about what else was plugged in at the same time on XP.
>>
>> Simple way to test is unplug all the other USB peripherals.
>
> Or use a USB hub with its own power supply.

I don't know what the newest hubs are like now, but several things I own
are megalomanic and refuse to work properly through a hub. Their user
manuals warn of this problem too.
>
> Really though, if the PSU doesn't have the "oomph" to power the USB
> ports, you're likely to start seeing other weird things, like serious
> system crashes...

It is more that if all the devices attached to the PCs USB ports ask for
near maximum current they could affect each other adversely. A Seagate
white paper discusses the matter obliquely and says drives with spin up
start current < 1A and steady state < 700mA should be OK.

However, if you get several devices that are power hungry and one that
is over sensitive to voltage fluctuations the weakest link in the chain
fails first.

Regards,
Martin Brown