Hi Steve, Thanks for the quick reply - sure enough it comes back with 3V or so now... Dynamo claims to be 12V. Now it is though related to the rpms that we are doing - if I changed the gearing / speed then that should sort it out...
I don't know why I thought the dynamo was DC... Too long since doing physics properly I guess... Would you be able to let me know about what the suitable criteria might be for a bridge rectifier? If you have any web link to any online catalogue that would be great so I can see if we can find that locally... Or is it anyway possible to modify the rectifier from a normal AC brick adaptor to do the job? Thanks Again, -Mike 2009/1/7 Steve Holton <[email protected]>: > On Wed, Jan 7, 2009 at 7:36 AM, Mike Dawson <[email protected]> > wrote: >> >> Dear All, >> >> We tried to create a sewing machine based trial to power an XO - we >> geared it at about 90:1 so that the two dynamos should spin at about >> the same speeed as they would on a bike. >> >> When connecting the bike light it does light - a little dimmer than >> normal - but the digital voltmeter for some reason when just starting >> slowly to spin the wheel by hand registers 0.1V or so when it's going >> smoothly at full speed it registers absolutely nothing. I tested >> measuring a few batteries and it seemed fine. > > Most "bicycle dynamos' will produce alternating current. The XO requires > direct current for charging. A light bulb can operate off either. > > I suggest you re-test the bike dynamo with the AC setting of your volt > meter. > > If this is the case, you can use a bridge rectifier to change the > alternating current into direct current, at the cost of about 1.4 volts. > > > -- > Steve Holton > [email protected] > _______________________________________________ Olpc-open mailing list [email protected] http://lists.laptop.org/listinfo/olpc-open
