<br><br><div class="gmail_quote">On Wed, Jan 7, 2009 at 8:57 AM, Mike Dawson <span dir="ltr"><<a href="mailto:mikeofmanchester@gmail.com">mikeofmanchester@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Hi Steve,<br>
<br>
Thanks for the quick reply - sure enough it comes back with 3V or so<br>
now... Dynamo claims to be 12V. Now it is though related to the rpms<br>
that we are doing - if I changed the gearing / speed then that should<br>
sort it out...</blockquote><div><br>If it's similar to ones I've seen, the voltage out will be related to spin speed. You'll need 12-14 volts to power an XO, and should avoid going above 18v. For a prototype that shouldn't be an issue.<br>
<br>You'll also need about 15-20 watts to recharge an XO in about the same timeframe you're expecting from an AC wall source. <br>That means you'll need power recitfiers rated for at least 20 watts, or about 2 amps at these voltages.<br>
<br>Good info, as always, at Wikipedia:<br>- <a href="http://en.wikipedia.org/wiki/Bridge_rectifier">http://en.wikipedia.org/wiki/Bridge_rectifier</a><br><br> </div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<br>
I don't know why I thought the dynamo was DC... Too long since doing<br>
physics properly I guess...<br>
<br>
Would you be able to let me know about what the suitable criteria<br>
might be for a bridge rectifier? If you have any web link to any<br>
online catalogue that would be great so I can see if we can find that<br>
locally... Or is it anyway possible to modify the rectifier from a<br>
normal AC brick adaptor to do the job?</blockquote><div><br>If you can find a disfunctional AC brick which supplies 12 or so volts at 1-2 amps it will likely include either a monolithic bridge rectifier package (a 4 pin block with a heat sink) or a bridge built from four discrete power diodes. Generally speaking, any device which runs on AC and has both electronics and moving parts will need a bridge rectifier similar to what you're looking for. If I were scavenging, I'd look at broken printers, FAX machines, VCR's or audio equipment with high power output.<br>
<br>I'm sure some place like DigiKey would have a 'technically correct' part. <br>As a general rule look for something rated for roughly 12 or more volts, 1 to 2 amps, or around 20 watts.<br><br><br></div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<br>
2009/1/7 Steve Holton <<a href="mailto:sph0lt0n@gmail.com">sph0lt0n@gmail.com</a>>:<br>
<div><div></div><div class="Wj3C7c">> On Wed, Jan 7, 2009 at 7:36 AM, Mike Dawson <<a href="mailto:mikeofmanchester@gmail.com">mikeofmanchester@gmail.com</a>><br>
> wrote:<br>
>><br>
>> Dear All,<br>
>><br>
>> We tried to create a sewing machine based trial to power an XO - we<br>
>> geared it at about 90:1 so that the two dynamos should spin at about<br>
>> the same speeed as they would on a bike.<br>
>><br>
>> When connecting the bike light it does light - a little dimmer than<br>
>> normal - but the digital voltmeter for some reason when just starting<br>
>> slowly to spin the wheel by hand registers 0.1V or so when it's going<br>
>> smoothly at full speed it registers absolutely nothing. I tested<br>
>> measuring a few batteries and it seemed fine.<br>
><br>
> Most "bicycle dynamos' will produce alternating current. The XO requires<br>
> direct current for charging. A light bulb can operate off either.<br>
><br>
> I suggest you re-test the bike dynamo with the AC setting of your volt<br>
> meter.<br>
><br>
> If this is the case, you can use a bridge rectifier to change the<br>
> alternating current into direct current, at the cost of about 1.4 volts.<br>
><br>
><br>
> --<br>
> Steve Holton<br>
> <a href="mailto:sph0lt0n@gmail.com">sph0lt0n@gmail.com</a><br>
><br>
</div></div></blockquote></div><br><br clear="all"><br>-- <br>Steve Holton<br><a href="mailto:sph0lt0n@gmail.com">sph0lt0n@gmail.com</a><br>