Bicycle USB charger using a hub dynamo (update)

June 1st, 2010 by Arend Leave a reply »

This is an update on my previous post about a hub-dynamo driven (USB) charger.
A step by step guide is posted here

The latest incarnation is a stripped down version of the original. I left out the input tuning C2, C3, R1 (see original post for the diagram) and replaced the 4 Schottky diodes with an integrated bridge rectifier. The Schottky diodes  are more efficient due to the lower forward voltage drop, but require more soldering and space.  This version now fits into a small ABS case. I hope to replace the fixed USB cable with a USB A receptacle (if it fits).

usb dynamo case

usb dynamo case layout


  1. Adam says:

    Hi! How interesting that you updated this post today as i found your original just yesterday! Is there any chance of getting a little bit more information about the updated parts/schematic and how your updated charger is working?

    Thanks in advance,

  2. Arend says:

    Yep, I was triggered by a comment yesterday on the original post. And of course the arriving summer in the northern hemisphere. I will look it up. It’s been a while and I don’t remember the exact changes by hearth.

    • Adam says:

      Wow, pretty cool that two people happened upon your original post at the same time! Can’t wait to hear about your new modifications.

  3. Arend says:

    I finally got some time to test it out on my HTC Desire which uses a micro usb B connector.
    I was able to charge with a max current of 400 mA. This was not on my regular bike so I have to test this out at home to see if I can squeeze out a bit more mAmps.

    In this version I left out the input tuning circuitry (C2, C3, R1), you then have to connect the dynamo input between D2 and D4. But I also changed the 4 diode bridge rectifier with an integrated bridge rectifier for space. These are some of the parts I used, from Farnell:
    Bridge rectifier:
    Capicitor C5:
    Capicitor C4:

    The ABS case:

    The details of this modification are explained in this post:

  4. Arend says:

    I just checked the rating on the dynamo and this test was on a 2.4 Watt, while at home I use a 3 Watt hub dynamo.

  5. Jay` says:

    How has the design faired over the past few months? Anyway to get the full 500mA needed for USB most devices?

    • Arend says:

      To be frankly, I haven’t had (/created) much opportunity to work with the charger. However it can keep up pretty well. You will have to limit the power drain a bit with idle timeout, disabling 3g data connection and perhaps limit the brightness of the display.

      I think it’s the hub dynamo that makes it hard to get the desired 500mA, especially since the efficiency drops because of the AC-DC conversion.

  6. Caveman A says:

    Hello, I need to update the system I built a few years ago so I thought I would do a search and see if anybody has come up with anything new. This is when I came across your site. Thanks for the parts list.
    I did something similar a few years back, but now I can’t remember how I came up with the parts I used. Too much tinkering/researching not enough writing/recording. oops.

    I will mod your design with mine to have a box with a switch and batteries charge the batts or run the lights, then discharge the batteries with the devices. It’s nice to have a USB powered GPS on this circuit. Thanks for your post.

    With a crude design I get about 2000-2500 miles out of four AA batteries. You have to mind how much you charge the batteries with a simple circuit, but it’s really not very hard once you understand the draw of your devices and average speed.

    I like the idea of going through the batteries to chage devices since this levels out any left over waves and noise from the straight AC Generator.

  7. Eduardo Lindenmeyer says:

    Hey guys!! That’s excellent design!! Congratulation! I want to build it my self in the next month for my SON 28 dynamo!
    I Heard thin dynamo may put up very high voltages at high speeds, will this take it without problem? I mean, 100V seams to be very high.
    Anyway, I was thinking of adding two 18650 batteries to my project, so they would feed my gps data logger and tracker while not riding my bike.
    How would be the best way to add the circuitry to this project so the battery would act as a big buffer ?
    Thanks guys!

  8. Mathieu says:

    could you please detail what was the function of C2, C3, and R1? What do you mean under “input tuning” ?
    Thanks for commenting, that would be useful in my self-teaching of electronics.

    • Arend says:

      Hi Mathieu,

      A bit late, but better than never:
      Straight from Simon Galgut own post (he came up with this schematic/design):
      “You can leave out C1, C2, C3 and R1 if you wish, though C1 is quite useful to smooth the rectifier output. If you leave out the input tuning circuitry (C2, C3, R1) then connect the dynamo input between D2 and D4.”
      So this pretty much stabilizes the input current to the LM2940 LDR. (

  9. what happens if this arragement use a 12v 6W bottle dynamo and not hub dynamo?

  10. Mohee says:

    Hi Arend . Good idea .There are some renowned brand such Nokia bicycle charger . I think you must creativity beyond them . Of course you started in 2010 .Did you Patented your ideas ?. Any income from them ?. I am an amateur innovator too . where do you live ?. I need your guidance . you can find me in Youtube . Paraplegic gunmaker ! . Thankx

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