[Power] Richard Smith Previews XO-3 Power Consumption

[Adam Holt]

Subject: 	Re: XO-3 Announcement?
Date: 	Tue, 10 Jan 2012 18:28:20 -0500
From: 	Richard A. Smith <richard at laptop.org>
Organization: 	One Laptop per Child
To: 	Alan Eliasen <eliasen at mindspring.com>
CC: 	devel at lists.laptop.org


On 01/07/2012 06:40 PM, Alan Eliasen wrote:

>      I'm also curious about the power claims.  What is its power
>  consumption and charging requirements?

Its still much too early to lay out exact claims for this.  These are A1
prototypes.  This is the stage where we start finding all the things
that are using more power than we would like and try to reduce them. The
exact size of the battery is also changing as we maximize the space in
the battery cavities.

We don't/won't start making any exact claims on power until it moves
well into the B and C series builds.

That said, a lot of the internals are almost identical to the 1.75 so
the things I've previously said about 1.75 are going to be a good
approximation of the XO-3.  As John indicated the traditional display
does consume more power than the Pixel-Qi.

In case you missed my previous comment on 1.75 on devel@ the maximum
runtime power draw of the 1.75 is 5W. (Not including the extra 5W you
can draw from the USB port.)

The power input front end of the XO-3 is currently identical to the
XO-1.75 which matches the specifications of XO-1.5.  11V-25V input range
and a maximum input rating of 25W.  Unlike the XO-1.5 the XO-1.75 almost
never gets to the 25W maximum because its runtime power is much lower.
So the peak power draw only happens if its charging a very low battery.

One difference between the XO-1.75 and XO-3 is that the XO-3 can _also_
be powered by USB On-The-Go (OTG).  OTG has a strict 5V/7.5W power
specification so charging via OTG will take longer.  No. I've not yet
measured how much longer. :) Sadly its not a nice linear thing that you
can just do the math and figure out.  There are many variables some of
which will change with the next prototypes.

Having a robust, wide voltage range, high power input is an important
feature when using alternative power sources.  Alternative power can be
very unclean and very sporadic.  You must be very forgiving on what you
allow and when its available you want to maximize your input.

I don't think any other tablet made so far would survive long term if
you connected it directly up to an automotive 12V power system.

>  Has it actually been
>  demonstrated to be chargeable by "solar panels, hand cranks and other
>  alternative power sources?"  Especially ones not requiring systems which
>  cost many times more than the price of the laptop, nor require someone
>  with the green skin color of the XO to crank.

This claim isn't really new.  Evey XO generation we have made to date
matches this claim.  In each generation we made an improvement over the
previous.

Its always been possible to charge an XO from alternative power sources.
There are sites in Rwanda, Peru, Haiti and the Solomon Islands (just to
name a few) that are powered entirely by solar.  These are using XO-1
and XO-1.5.  Some of these use a more commercial type solar system and
some just are just raw solar panels that connect directly to the XO.

The XO-1 and XO-1.5 both had maximum runtime peak power draws in the 10W
range.  Running things like the camera activity which keeps the system
busy would draw that power continuously. If you didn't have 10W of input
you go backwards.  Most people don't really realize how much work 10W of
continuous power is.  The physical size of a 10W solar panel isn't huge
but its still pretty large and you need perfect solar conditions for
that 10W.  So what you really need is a 20W solar panel that so that a
wide range of solar conditions still work.  A 20W panel is pretty large
and not something easy to lug around.

The 1.75 (and tablet) have a runtime peak power draw in the 5W range and
they idle even lower.  So now devices that produce power in the 10W
range can fully power the new XO devices in a variety of conditions.  So
you can envision taking an XO outside into the field connected to
smaller solar panel (say 5-7W) and have a net power draw very close to
zero.  A 10W panel would almost certainly have a net draw of zero unless
the solar conditions were really terrible.

In my testing here in Boston I have powered a 1.75 directly (no battery)
from the OLPC 10W panel in January sun.  Here's a video Chris Ball and I
shot Jan 9, 2012 showing a 1.75 completely powered by our 10W thin-film
PV panel.

http://www.youtube.com/watch?v=ITHNbOrPQyM

Hope this info helps,

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