Bicycle Dynamo iPhone Charger

task;

Actually, it's easier. Just use a small transformer to boost the voltage, then switching regulate it down.

Do I need to rectify to get all the current possible?

task;

Yes, of course. Transform AC then rectify to DC.

An ordinary bridge rectifier (4x 1N400x or a bridge in one package) should give you what you need for power - then for a charger, all you need is a regulator. IOW, you can copy their circuit, but interpose a regulator or dedicated battery charger chip, and you should be good to go!

Good Luck! Rich

First point is that unless you consistently ride faster than 10mph, preferrably 15mph, then battery lights are far easier.

AFAIK, all bicycle generators are AC and when supplied straight to older lights (aka not leds), then this isn't a problem.

If you want to store power from the generator, then you need to convert it to DC. this is easiest and simply done by using a diode.

If you want to collect maximum power, then a bridge rectifier (4 diodes) and something like a super cap would be simple and easy to do. When you start riding, the super cap just collects the excess power and stores it until you stop (say lights)when it takes over supplying the light until the dynamo kicks back in(you gain enough speed for the dynamo to be putting out a higher voltage than the level on the supercap.).

Only gotchas are; riding too slow and sudden or long descents when your speed picks up, when you might need to consider some form of voltage regulation, aka clipping zener(s) and large wattage resistors. the 6Volt output is really nominal. Too slow and you get nothing. Too fast and as many peeps can tell you you had a bulb popping moment and everything went dark.

Now, if you want to use this excess power to recharge some device, the device needs to accept DC and have the ability to regulate the provided voltage down to its needs. Depending on the device, you might not event need the supercap, just ttake the output from the cynamo , run it through

Keep in mind that 3Watts isn't that much to play around with, so stuff like Ac transformers and voltage regulators (lm39?? 7805, etc) are going to waste a significant proportion of that 3watts.

I'd suggest building a basic 4 diode bridge recitifier, adding a super cap and then connecting this to an old bulb light, plus a cheap multimeter set on voltage and mounted on the handlebars (GPS caddy?). Ride around with the light on and not the voltages sitting on the super cap. The idea is to work out what power your personal riding style puts out, then you can design from there. (I found that I ride so slowly, that I need a voltage doubler, sucks).