Rockbox mail archive
Subject: Error in Battery FAQ - Pause vs. shutdown & restart
From: Brent Geery (fasttimes_at_mochamail.com)
Q12: I often need to stop my player for about 15 minutes or so,
and when I do it runs off it's batteries. I was wondering, which
is best: shutting the player down completely and rebooting it when
I want to listen again, or leaving the unit on? Which way does it
draw more power?
A12: In our testing we found the following results:
HDD off, backlight off, idle 94 mA
HDD off, backlight off, play 97 mA
HDD off, backlight on, idle 129 mA
HDD off, backlight on, play 131 mA
HDD on, backlight on, play 230 mA
HD on, reading, backlight off ~ 600 mA
HD spin up before read max 800 mA
So leaving the unit on and paused consumes ~100mA, and thus
much less than needing to reboot the unit. Your mileage may vary.
This in incorrect! mA (a measure of power) does not equal mAh (a
measure of energy.) Power can tell you what the player is drawing,
but not what it has consumed. Another way to look at it, is to equate
mA to the speedometer in you car, and mAh to the odometer.
Using the example power draw examples shown above, lets look at the
example given-- power-down and restart vs. paused for 15 minutes.:
Pause will draw 94mA / 60 minutes X 15 minutes = 23.5mAh used.
Power-down and restart will draw about (800mA / 3600 seconds X 3
seconds = 0.6666 mAh) + (600 mA /3600 seconds X 6 seconds = 1.0 mAh) +
(195 mA / 3600 seconds X 3 seconds = 0.1625 mAh) = 1.83 mAh total
94 mAh / 3600 seconds = 0.0261-e
1.83 mAh / 0.0261-e = 70.085 seconds
Thus, if planning on pausing more than about 1 minute 10 seconds, a
shutdown and restart saves more power! I'm a little shocked, but the
numbers don't lie.
BRENT - The Usenet typo king. :)
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