XO power consumption under 8.2-759

[James Cameron]

Measurements with a mass production unit SKU1 serial number CSN75000153
and Joyride 2436, using a digital multimeter in current mode, with
another digital multimeter in voltage mode showing the voltage after the
current meter, presented to the XO.  In Control Panel, "Automatic power
management" is enabled.

I'm confirming your results, by not using the battery management chip or
olpc-pwr-log.

a.  fully on, at activity ring, no activities running, 6.49W (0.54A at
12.02V),

b.  turned off backlight, 5.40W (0.45A at 12.02V), a saving of one watt,

c.  turned off radio using Control Panel, 4.08W (0.34A at 12.02V), a
saving of just over one watt,

d.  one minute idle, power LED slow-blinking, screen image still
present, 1.09W (0.09A at 12.12V, or 91.2mA at 11.95V), a saving of three
watts,

e.  closed lid, power LED blinking, presumably screen image gone, 0.61W
(50.8mA at 12.04V), a saving of just under one watt,

f.  removed battery, current fell to 46.5mA, or 0.55W.  Battery LED
extinguished.  At this point the unit is consuming the least DC power
while still "operational".

Perhaps the kids would like a power budget ...

1.  base load, half a watt,

2.  keeping the battery fully charged, a tenth of a watt,

3.  showing a screen image, half a watt,

4.  running the keyboard, touchpad, processor, three watts,

5.  running the radio, one watt,

6.  running the backlight, one watt.

That's neat.

Now, onto something else.

The AC adaptor conversion loss is significant ... during these tests I
had a cumulative energy meter attached on the 240V AC feed to the
adaptor.

At the point where the laptop is demanding 0.55W as 46.6mA at 12.05V,
the energy meter shows the AC adaptor is drawing 0.97W, which is roughly
double.  Conversion efficiency of 56%.

Back to full power, where the laptop is demanding 6.13W as 0.51A at
12.02V, the energy meter shows 9.11W, which is roughly 50% more.
Conversion efficiency of 67%.

(This is the 110V or 240V global "universal" AC adaptor supplied with
the C2, the one with the XO on both sides).

It reminds us that power budgets at AC level will have to be quite
different.

-- 
James Cameron    mailto:quozl at us.netrek.org     http://quozl.netrek.org/