[OLPC India] charging XOs using bicycles

[JV Avadhanulu]

Dear Richrad,
John, CTO of Freeplay was here in Auroville recently and he showed me
portable mechanical charger meant for OLPC that generates up to 8 W easily 
and costs only about $ 10. Please
contact him (giving the reference of JV from Auroville) at
jhutchinson at freeplayenergy.com
Regards,
JV Avadhanulu
+91-9443797563
----- Original Message ----- 
From: "Richard A. Smith" <richard at laptop.org>
To: "Arjun Sarwal" <arjun at laptop.org>
Cc: "Holden Bonwit" <hbonwit at alumni.nd.edu>; "OLPC India Mailing List"
<india at lists.laptop.org>
Sent: Sunday, April 27, 2008 6:38 PM
Subject: Re: [OLPC India] charging XOs using bicycles


> 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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