[Power] Haiti power questions

[Richard A. Smith]

On 12/07/2010 12:58 PM, Timothy Falconer wrote:
> Okay, so for my bottom line, is it safe to say that:
>
> Starting with an empty battery and plugged into the grid for 2.5
> hours, while using Etoys with ticking clock, it should take 85 kwh
> per laptop?

For AC yes thats what The Math says.  If you use that number then you 
should not be short.

There are reasons that The Math may be higher than reality:

1) I'm conservative when I do these calcs.  Better to be off on the high 
side rather than low.  Excess capacity is seldom unused.

2) The numbers are 2 different calcs based on various chunks of measured 
and manufacturer provided data added together.

However, in the real world they happen at the same time.  So the AC 
adapter is going to stay up at full load for longer. Its most efficient 
at full load so I think the real number will be less < 85Wh.  How much 
less I don't know.

I encourage you (or someone) to do some measurements with 10 or so XOs.

> And yes, I have a kill-a-watt ... don't know why I didn't think of
> that before :)

Meters like the kill-a-watt were not designed to measure low power draw 
devices like the XO.  They can be very inaccurate at low wattages.  Make 
sure you test a whole bank of them at once.

My suggested test would be to connect at least 10 XO with dead batteries 
(20 - 30 would be better) up on a big power strip or a power strip chain 
and then connect that chain to a zeroed kill-a-watt.  Then quickly power 
all of them on and start etoys ticking.  Come back 2.5 or 3h later and 
see what the Peak W and Wh readings are.  The Wh reading is only good 
down 10W but will at least let us verify how close to reality the 85Wh 
estimate really is.  If you are able to use 20 or 30 XO's then you 
should get a pretty good average.

-- 
Richard A. Smith  <richard at laptop.org>
One Laptop per Child