Bicycle Dynamo USB Charger




Introduction: Bicycle Dynamo USB Charger

I've looking for a way to charge my electronics while I excercise on my bike. I couldn't find dynamo powered USB charger so I decided to try and make one. I used what I could find and cobbled it together based on information from Instructable and other on-line sources.

Step 1: Installing the Dynamo

This was not complicated. I just followed the instructions that came with the dynamo. I tested the voltage coming from the dynamo and soon realized it exceeded my listed specs. The specs specified a 6 volt output but my testing confirmed not only was the voltage AC instead DC (which I expected) but the output could acheive up to 13 volts.

Step 2: Rectifying and Regulating the Voltage

I found an Instructable explaining the creation of a Rectifying Bridge using common diodes. A clear example is also available on Wikipedia here. So I built my rectifying bridge and testing it. It worked as described.

I then had to regulate the voltage and amperage to an USB standard rate of 5.5vdc and 500Ma. I found it easier to recycle a car lighter USB device to do the work for me rather that building something. Safer for everyone involved. :)

The output for the car lighter USB device says it should be 5.5vdc and 700Ma but testing both in the car and on the bike showed 5.5vdc and 950Ma. Since I've used this device a lot in the car, I'm accepting these figures as safe and fine. If you think otherwise, please let me know.

Step 3: View the Video

I tried posting this video to but it is too big so it's on

Please feel free to comment. I'd be interested in what you might have to say about my project.

Cheers and Thanks!



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    16 Discussions

    Nice prototype. I like how you cobbled it by reusing things that were meant for other purposes. Nice work.

    3366carlos, you are totally right. I measured the voltage without load and it goes up to 30V if running fast! When the load (i.e. lights) is connected, it goes down to 6 or 7V.

    If you want to go a step further and build the electronics yourself, you can check this guide

    very nice. where did you get the dynamo? also, its probably 13VAC because it's not loaded, once you load it, it comes down to 6Vac

    Hi I wanna to see do you know how to make it to recharge a battery? so instead of USB I want to charge batteries.

    yes mate fantastic, I was wondering if a car usb thing would work, as I have not got the 40 odd quid to buy a kemo thingy, I keep getting lost in london so I wantbto take my sat nav , which crys its battery is flat as soon as I turn the ignition off. Poundland even do the 12v to usb. Mounting and Making my satnav waterproof will be interesting.

    How does the output vary with speed? I'm thinking of doing this just for lights, so even at low speeds the output needs to be pretty close to spec.

    2 replies

    Hi, from what I recall, the output is maxxed out by the lighter USB voltage regulator. You still need a minimum effort of pedalling/speed to acheive a rate of output sufficient for charging anything or running lights.

    I'm wondering what that minimum is. I have a townie that I really only use in town. That means stopping couple of blocks for lights and net getting all that fast. I would use it for LED lights.

    The fact that the lighters are made to accept 12vdc makes me think that I would at least need a smoothing cap after the rectifier, and maybe a large cap and diode after the regulator to provide a minute or so light when stopped.

    PS: I was wondering how it would took like when I would buy dynamo USB phone churger like from link below. Deconstruct it... and just plug in instead of typical dynamo :)

    Can you plug in there more than 1 phone? (I know, sounds silly cause there is 2 less of power in it... but just askin)

    Oh I see.
    I though that you have just plugged all in same place :)
    Can you update some schematic about connection?
    Can you connect more than one device to this USB churger?


    Will it not burn USB in phone?
    Without any wattage regulation it probably will.

    Have you used any other electronic than short connection of dynamo and 12v USB car churger?
    Can we see any build up solution?

    1 reply

    I'm not sure I understand your question. This is a simple device that uses the dynamo to generate the voltage, the bridge to convert ac to dc, and the lighter adapter to regulate the output to the phone.

    The dynamo I purchased didn't come with instructions, how do I connect it to the circuit? Here's the one I bought: I think it's basically the same. My guess is the small metal stub on the bottom is the positive and the larger metal part is the negative/ground. Just feel I should check before trying anything.

    1 reply

    be sure to test the voltage and poles using a multimeter. I suggest doing that after installing the rectifying bridge since that is when you will have stable pos and neg leads.