This is a step by step guide on creating your own USB compatible charger using your bicycle’s hub-dynamo as the power source.
It’s a work in progress and I will update this post along the way.
All images link to full resolution originals.
- Soldering iron + tin
- (optional) Multimeter
- (optional) Soldering clamp
- (optional) wire stripper
- Parallel Strip Veroboard (€ 8,22) )
- USB-A Receptacle (optional, a direct usb cable with micro or mini usb is also possible)
- 5Volt Regulator LDO (Low Dropout) LM2940 (CT) ( € 1,31)
- Heatsink for LDO (optional) (€ 0,5)
- C1 2200uF 16v (€ 0,65)
- C4 .47uF Tantalum bead (€ 0,22)
- C5 22uF Tantalum bead (€ 0.43)
- Bridge Rectifier, 1.5A, 100V (€ 0,5)
- Heat-shrink tubing (optional)
- ABS Case / housing (optional) (€ 1.17)
- Cable Gland Locknut (optional) or: a Grommet:
- hub dynamo connector (€ 2,- ?)
Note that these prices are ex FAT and I ordered them in larger volumes, ymmv.
Step 2: Solder the two tantalum bead capacitors on the voltage regulator. Be careful to not overheat the components, polarity is essential. Long leg is positive.
Place the 22uF Capacitor on the right, the .47 uF on the left. Negative polarity combined in the middle.
Step 3: prepare capacitor C1 with the heat-shrink tubing, bend the pins (long leg = positive) as seen in the photo. Keep the legs as long as possible for flexible placement of this component inside the ABS case.
Step 4: place the components on the veroboard:
Looking at the first picture below; the middle three parallel stripes on the board serve as the main electrical paths for the components. The stripe on the left corresponds with the positive side on the diagram.
- C1: the long leg (+) should be placed on the left of the three middle stripes. The short leg should go in the middle. (in reference to picture 1)
The bridge rectifier output legs should be placed as follows: The + (as indicated on the component) should go on the left of the three middle strips.
The – (negative) output should go in the middle. The AC input legs can be placed on the outer stripes of the board. (left and right in reference to picture 1)
And finally solder the voltage regulator as well.
Before going any further, check to see if it’s working properly.
Prepare the cable that runs to the dynamo, and connect it on the input legs of the bridge rectifier. Polarity is of course of no concern as we are dealing with an alternating current. Connect the dynamo to this kit, swing the wheel and measure the output voltage on the + (Vout) and – leg of the output regulator.
We should measure around 5 Volts
If it doesn’t work, carefully check the polarity of the capacitors and other components.
We can now safely cut the remaining component legs form the veroboard, and bend C1 to fit inside the ABS case.
I connected the heat-sink using a blind rivet this is ideal as it does not need any additional space (especially height).
Before connecting the cables, drill a small hole for the Cable Gland Locknut, connect the Cable Gland Locknut and route the wires through it.
Next, connect the USB A receptacle or if you like a mini or micro USB cable directly to the voltage regulator output legs. Connect the dynamo cable to the bridge rectifier.
In order for this whole package to fit inside the box, I had to saw one of the corners from the veroboard.
When using the same ABS case as listed in the requirements section, be sure to cut the two screw holes at the bottom of the case for more room.
That’s pretty much it. I will seal the case of with a polymer resin, to make it water proof. Be sure to only do this after you are absolutely sure everything works.
Revision 2 with grommets
That’s it! Let me know if you take on the challenge to build one yourself, or if I need to explain anything in more detail.