rich...@laptop.org said: > Speaking from experience measuring the power draw of a single XO with these > low cost power meters is tricky. They can be very inaccurate at lower > power measurements. The kill-a-watt for example has a typical accuracy of > 1% with a max of 4%. Full scale is 1800W which would be 18W minimum > measurement. You can play some games with the gain into the ADC's and > reduce that but its not clear if the kill-a-watt does that. I can't > remember the exact output numbers when I tried a kill-a-watt.
Good point. Thanks. It's even worse than that. In the power mode, the Kill-a-Watt only shows whole watts, no fraction. So at roughly 20 watts, it can easily be off by 5%. (Maybe somebody should add that to a UI lessons for kids.) I haven't carefully checked the accuracy of my Kill-a-Watt, but it's passed all my sanity checks. At $20, it's a useful tool. (The technology for this sort of thing must be reasonably solid. My new electric meter has an LCD rather than a spinning wheel and dials.) >> If it takes 2 hours to charge the battery, that's 40 watt hours. > In my talks about power to deployments and groups I have a standard saying > that if the answer to "How much power does it take?" is a simple answer > with no qualifiers then its wrong. ;) Thanks again. The question I was commenting on was roughly: Can a person put out enough power to usefully charge the battery on an XO? In that context, I think anything within a factor of 2 is close enough. > Is the XO running or powered off? Is it for a XO-1 or XO-1.5? Is it DC > measured at the input jack or is it AC? If its AC what power adapter is it > using? The 17W, the 24W or the 25W adapter? What AC voltage and frequency > is the adapter running at? Here is a data point. XO-1, system running, not doing much (no human), backlight off. 17W Adapter. (12V, 1.42A) running on 120V, 60 Hz. The battery says LiFe, 6.5Vdc, 3.1Ah. Kill-a-Watt reads 19-20 watts. It took 2 hours to charge the battery from 10% to 80%. The charge% was quite linear up to 80%. At 80%, it started to round off. After another half hour it got to 90%, then jumped to 100%. I'll make a pretty graph if anybody wants. -- These are my opinions, not necessarily my employer's. I hate spam. _______________________________________________ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel