On 14.01.2009, at 17:39, Mike Dawson wrote: > Hi All, > > Unfortuantely I am just stuck in Jalalabad at the moment as bad > weather cancelled our flight back to Kabul but I met the folks who are > doing the Fab Lab here (if anyone has heard of that). > > So we did a quick back of the envelope calculation along these lines > that refreshed my high school physics as soon as they reminded me that > W = FD > > 1. Assuming someone is normally doing about 60 rpm on a bike > (apparently the figure is 60-90) > > 2. Take the distance that a foot pedal gets pushed as being 15 cm > > 3. Work done = Force x Distance > > 4. Dynamo as being 50% efficient (apparently an alternator can be up > to 60% efficient http://en.wikipedia.org/wiki/Electrical_generator) > > 5. > > P = 0.15F / 2 > > P = Power in Watts out > F = Force in Newtons > > (as at 60rpm the output in Joules will be for 1 second, which is > therefor the power rating in Watts) > > So the force required to generate 9W (e.g. for charging a little and > running the laptop): > > 9 = 0.15F / 2 > F = 120N = 12.23kg (given gravity = 9.81N per kg) > > Which does not seem to be an unreasonable amount... Our idea is to > see if it is possible to generate continuous power during usage in a > manner that is both quiet enough and reliable enough. We can get > Dynamos from the local market for about $0.80 each. > > I know that calculation does not include the required loss to a bridge > rectifier... but it all just seems a little too simple - can anyone > spot the mistake here? > > If that's correct then when the chopper takes us back to Kabul we can > try to connect up the rectifier to the machine and see how we might be > able to charge the XO... > > Would also be interested to calculate if one assumes that most of or > all of the calories burned by the human body come from a certain > source, then how much will this add to the food bill? Given that I am > told a human normally produces 60W of just heat... hopefully not too > much. > > Regards, > > -Mike
Producing just 10 watts should be very easy given proper equipment. See the table at the bottom of this page: http://www.los-gatos.ca.us/davidbu/pedgen/stats.html - Bert - _______________________________________________ Olpc-open mailing list [email protected] http://lists.laptop.org/listinfo/olpc-open
