[Olpc-open] Fwd: Foot power revisited...

[Mike Dawson]

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 <sph0lt0n at gmail.com>:
> On Wed, Jan 7, 2009 at 7:36 AM, Mike Dawson <mikeofmanchester at gmail.com>
> 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
> sph0lt0n at gmail.com
>