From: Michael O'Quinn <michael_at_oquinn.info>
Date: Sat, 12 Apr 2003 19:53:52 -0700 (PDT)

On Sat, 12 Apr 2003, Johan Vromans wrote:

> Björn Stenberg <bjorn_at_haxx.se> writes:
>
> > I also want the USB screen to show estimated battery time left,
>
> That reminds me... Q12 of the BATTERY-FAQ does not mention a
> difference in current whether USB connected or not. This could
> indicate that USB connect hardly matters. However, I have noticed that
> when I keep my R20 on a charger and USB the unit gets (slightly)
> hotter, while without USB it stays cool for longer periods of time.
> This would indicate that USB connect _does_ make a relevant difference
> in power consumption.
> Is this the right conclusion?

I don't think the USB interface itself is necessarily drawing that much
power, but (at least with my Player) when the USB i/f is active the HD is
constantly spinning, which increases power consumption. If a file
transfer is in progress, even more power is being consumed than if the
drive is just spinning at idle.

This brings up another issue. The conclusion at the end of Q12 is
completely bogus. Drawing ~ 94 ma for 15 minutes is far more power
consumed than ~ 800 ma while it boots. Take the worst case booting, (I
don't think it's ever actually this much)...

    800 ma * 20 seconds = 16 amp seconds

...but idling for 15 minutes...

   94 ma * 15 minutes * 60 seconds/minute = 84.6 amp seconds

...a difference of over 5 times.

Clearly idling for more than a minute or two consumes more power. And
note that I chose extreme values that understate my case. More realistic
numbers would give an even greater difference.

Michael
Received on 2003-04-13