[OLPC India] charging XOs using bicycles

[Moz]

Hello All,

This is Moz writing. I and my wife have lived and worked in a forest 
village in an area populated by indigenous people in the western part 
of India (Gujarat) for the past 17 years. I run my house on solar 
photovoltaic energy for the past 8 years, running a couple of laptops 
and a dot matrix printer as well.

In 2004 we made a 1 kw windturbine and have been providing lighting 
to 10 homes since then. We also make solar cookers and LED based 
lighting. I have also made a pedal power generator along with my 
friends (read about that at 
http://www.thinkcycle.org/tc-filesystem/download/development_by_design_2001/pedal_powered_electricity_generator/ppg2-2.PDF).

I currently make 1 kw (at 600 rpm) axial flux generators myself, I 
hand wind the copper coils, use Neodymium Iron-Boron (NdFeB) magnets 
and polyester resin to cast the stators. These start generating about 
50 watts at 200 rpm and increase the energy as rpm goes up. I make 48 
volt generators which can be easily customised for a 12 volt systems.

You need to decide whether you need to compromise on efficiency (then 
use old car alternators) or make a long lasting low rpm alternator 
(this will reduce power lost in speed step up, easily made by 
yourself and so on).

Since you intend to put these generator in schools, have you thought 
of coupling these charging stations to see-saws, swings, 
merry-go-rounds and slides? This has been done before, I believe in Gaviotas.

Regards

Moz

At 27/04/08 06:38 PM, Richard A. Smith wrote:
>Arjun Sarwal wrote:
>
> > A while ago, I along with Richard did some approximate calculations
> > and as a rule of thumb , you'd need to give the XO about 1A @12V for
> > a little more than an hour to charge it completely.
>
>Arjun since then I've done a bit more in depth measurements:
>
>The later measurements I've taken are 26 Wh to charge the battery from
>empty to full.  Thats measured @ the battery so rounding that up I
>usually say 30 Wh.
>
>Depending output voltage of the setup you use to provide the input power
>the XO is going to draw between 15 and 18 Watts when its charging the
>battery at the maximum rate.  Most of the time it will be closer to 15W
>but I normally just use the 18W number so that any estimates have some
>room for error.  When its drawing 15W power delivered into the battery
>stays the same which is around 15W.
>
>So 15 to 18W @ 12V = 1.25 to 1.5A
>30Wh / 15W = 2 hours to charge.  The actually measurement when attached
>to the AC adapter is 1:47.  2 hours is a nice easy number to use.
>
>This is with the laptop "off".  If you charge with the laptop on and
>running then its a much more complex calculation.  But its only going to
>increase the time you need for a full charge.
>
> > This means your generator (bike dynamo in this case) would need to
> > supply approx 12W for an hour. I've found bicycle dynamos to usually
> > generate much less power, more in the range of 1-4W.
>
>Columbia is looking at using some bike setups with beefer alternators.
>I'll pass on the details when they actually do something.
>
> > (Richard: please correct me if I have been wrong on any of the
> > charging details, I will make sure to put the details down somewhere
> > on the wiki this time)
>
>Most of this is on the wiki somewhere but we can certainly redo the
>organization so its easier to find and all in one place.
>
>--
>Richard Smith  <richard at laptop.org>
>One Laptop Per Child
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