Phone Charger for Bikes

I recently wondered about those hub dynamos: They are always generating engery while riding your bike but we actually just use that energy to power our little lamps when it is getting dark and while it is bright outside we just waste the precious energy which we toughly "generated". So, my thought was to basicly use that wasted energy for something useful. There are a lot of possibilitys: First of all you could power some lights with that energy or maybe an electrical bike bell or even as you read it in the title a portable mobile charger. I know you could maybe charge your phone faster if you use a proper solar panel or a power bank but my intention was it just to make use out of this precious waste.

Those are the things we need:

-obviously a bike

-a "FULL BRIDGE RECTIFIER" (made of 4 diodes)

-transformer (single phase step down 8.8 turns ration (salvaged from a CD Player)

-a step up converter (up to 5V and additionally with an USB port as output)

-some long wires and tools to handel them (solder iron, ...)

-3D printer to print a case or a cheap plasic case

-some zip ties to mount the case to any bike

The very precise circuit above shows who things work: The dynamo on my bike is supposed to spit out at leat 3W and 6V (this is at least a norm in Germany). For our step up converter we need a lower operating Voltage (<5V) so it is actually good that the FULL BRIDGE RECTIFIER draws some of that but still the output of our bike is very likely much higher (up to about 30V) so we need something better to reduce Voltage --> a transformer! Mine was a little bit to overkill because it converts the input from the bike down to something around +0,1V which is not the best outcome but it would still work if the bike is fast enought (my minimum speed to activate the USB charger was 21km/h which is not that slow) So my suggestion is to use the second circuit (which I couldn't cause I hadn't had a step down converter at hand) or to simply use a transformer with a smaler turns ratio (mine should be 8.8). In addition you could add a capacitor after the full bridge rectifier to smooth the output (I solderd first and then thought so I do not have this feature). Isolate the exposed wires because it is going to be safer as soon as you put everything together

After all the parts are soldered together, it would be advantageous to have a case to keep all the parts together and to offer them a little bit of protection (at leat to the soldered wires which would rip of easily if not protected). I designed my case in Autodesk Inventor Professional (I got a license from my school if you are not a student anymore you could use Fusion or FreeCAD).

The design is very simple the holes at the bottom are for the zipties for mounting the case on any spot on your bike and the holes on the sides are for the USB charger Output and the AC power input. On top there are holes for some screws (diameter of about 2mm) if you don'T have screws in that size you could use hot glue or salvage them from an old laptop (as I did). Print those two files with a suggested infill of at leat 20%. If you don't have a 3D printer: There are little plastic boxes in various sizes buyable in online stores like Ebay.

It was planned to make a advanced case which is a bit dust proof and which looks a bit better and is more stable but my hollidays are over now and I had to finish this project before school starts again (I might soon upload a Version 2).

Watch Out!: You parts might differ from mine when it comes to sizes --> make sure that your parts fit into my box or modify the .ipt files in Inventor or Fusion (or just give me your sizes and I'm going to try to modify it for you).

First you have to find the Output of your dynamo. I found mine directly attached to the front light of my bike and because I actually never ride my bike in darkness I just attached the wires from the dynamo directly to the input of our "charging box" (see "not optimal way" grafics). If you still want to use your light you could use a switch to switch between the the outputs or simply just join them all together. I then mountet the box right at the steering wheel (see image and grafics 2) with a zip tie but every bike is different so you probably should change the location.

Attention: In some countrys it is illegal to ride a bike without working lights (also in Germany) so make sure that you eighter use the connection circuit above or that you mount an other lightsource on your bike (light with battery for instance)

For me it worked well and I'm going to invest more time in this project. I'm sure that this is a nice upgrade to my bike and hopefully as well to yours.

Hope you liked it and got your very own phone charger. IF you got any suggestions or questions just ask and I'm happy to replay