Quick and dirty dynamo powered bike USB charger

One day a biker friend of mine asked me to give him a solution for charging his phone from the bike's dynamo while on longer trips. Sounded pretty simple and a nice challenge for a low cost solution to be found.

His bike has a Shimano HB-NX70 dynamo that's nothing more than a alternating current generator rated for 6V and 3W. That voltage rating is an estimative figure though as it all depends on the wheel's speed so you can have much less when cycling slow or much more when speeding.

That being said, the solution? Whatever I had laying around as left overs or in the junkbox. A small plastic case, small piece of prototype PCB, a PC bracket with two USB connectors, a DC/DC converter (a.k.a. BEC in RC hobby world), and some discrete components: a rectifier diode bridge, a big fat filtering capacitor and a little protection with a zenner diode.
 

On the bike's original electrical instalation, the dynamo powers a head light together with a tail light. I had to open the head light anyway because it wasn't working so I pulled the AC from there.

 The BEC starts operating at 6Vdc and goes all the way up to 23Vdc. I put it all together in a hurry and didn't give the time to pull up a schematic or do some multimeter work on the dynamo's output and how all things work together.

All I can say is that when the time came and we gave the charger a test spin, it worked, charging a phone with 600mA which is decent enough.

Bicycle Handlebar Mount Holder review

Taking the time to talk again a little bit about the cheap little things one can find over ebay. Got this gizmo for 5$ with free shipping from China all the way to Europe.

It states to be a clamp for bike handlebar mounting of a photo digital camera but I'd  think more at something like a lightweight GoPro, ContourROAM or these type of action camers. Anyway, my real interest for this thing was as a studio clamp for holding flashes or other accessories.

The clamp has a standard camera screw of 1/4-20 BSW so it can theoretically connect to anything that's light enough. The construction is not as bad as I expected it to be in this price range. Of course it's mostly plastic but good enough to get the job done.

The jaws are padded with rubber for extra grip and can open wide enough to clamp even on my Giottos MT8350 center column. You have a screw with which you set your opening and then a lever that grips the jaws on the support. Once fixed into position you now have 2 axes of control for your "payload". One is for tilting done with a screw while the other is for rotation through a rather ingenious spring loaded teethed coupling between the actual clamp and the mounting plate. The spring is quite strong and great for impressive static loads but can't deal with any bumps and vibrations given by any bike riding on anything but ideal tracks. The mounting plate has a metal screw with a nut that helps to further lock the payload. The nut is also doubled with a rubber washer for extra grip.

As I've said, I've done some testing on my Giottos MT8350 as a support and a Canon 580EX II as a payload. It's doable without much effort even horizontally with the flash extended but it's obvious the mounting plate junction is under excessive effort for it's capability.

In the end, it's 5$ that weren't spent for nothing, I have a clamp that works if taken to appropriate use but it must not be mistaken with the whole different world of metal clamps like the ones from Manfrotto or even the way cheaper CoolLCD's Super Clamps.