DIY Bicycle Dynamo USB Charger for Smartphones and Battery Packs

Posted on Aug 4, 2013
488 101

Posted on Aug 4, 2013

488 101
Reading time: 7 min

In this post I describe how I made a DIY bicycle dynamo USB charger for smartphones and battery packs. The idea came from multiple sources, including Mr. Howdy,, and Peter. But they assume the person making the charger knows how to read a circuit diagram. I cannot understand a circuit diagram. If you’re like me, then this blog post is for you.

Last updated Oct 13, 2018

Cost and Specs

Total cost: approx. US$15 (parts only; you need tools such as soldering iron etc.)
Weight: 29 grams
Weatherproof: Yes
Output: 5 volts DC (USB standard)
Input: 6 volts AC
Efficiency: Will charge a Sony Experia Z smartphone at a rate of approximately 1% per 1km (with the smartphone turned off).
Charge start:  5.5km/h


DIY Dynamo USB Charger for a Bicycle | 自作の自転車用のダイナモ充電器(USB)

What this device does

When charging your smartphone using a wall charger or your laptop’s USB, the electricity going into your phone is direct current (DC) at 5 volts. A bicycle dynamo hub, however, usually creates electricity in the form of alternating current (AC), at 6 volts. So, we’ve got to change the electricity created by the dynamo hub (6V AC) into the same type as what comes out of your smartphone wall charger or your laptop’s USB (5V DC). That’s what this device does.

Disclaimer: I know nothing about electronics. This charger has worked well for me so far (about 1,000km of cycle touring), but it may turn on you and eat your smartphone’s innards alive, rendering it a useless shell. Also, note that in very hilly terrain where constant high cycling speeds are expected (on the downhills), the charger may not cope with the high voltage output from the dynamo (voltage output often varies depending on speed) (thanks to commenter Prashant for the real-world observation). This may mean a need to unplug the charger on long, fast downhills. If you’d rather let someone else take the responsibility for your delicate electronics, check out the Bright-Bike Revolution (amazing value for a solid charger) or the Busch & Mueller Luxos IQ2 headlight with USB charging built in, or the Tout-Terrain Plug II.

What you need

  • Parallel stripboard (example)
  • 5 Volt Regulator LDO LM2940 (example – max input voltage 26V) (changes 6V to 5V)
  • Capacitor 1 (Tantalum bead, 16V 22µF) (example)
  • Capacitor 2 (Tantalum bead, 35V 0.47µF) (example)
  • Capacitor 3 (Electrolytic capacitor, 25V 2200µF) (example)
    • The capacitors help keep the flow of electricity steady as you slow down and speed up on your bike (see Wikipedia for more).
  • Bridge Rectifier, 1.5A, 100V (example) (changes the input from AC to DC)
  • Micro-USB terminal (example; you’ll cut off the big USB end and keep the small end, to plug into your device)
  • Wire and terminals to attach to dynamo outlets
  • A case of some kind to hold the electronics
DIY Dynamo USB Charger for a Bicycle | 自作の自転車用のダイナモ充電器(USB)

How to Make it

Step 1

Cut the veroboard (stripboard) into an oblong, 4 holes wide by approximately 25 holes long. I did this by scoring the board with a craft knife on both sides and then snapping it.

Step 2

Start to populate your board. On the capacitors, the long leg is positive. Click on the photos for a larger version.

DIY Dynamo USB Charger for a Bicycle | 自作の自転車用のダイナモ充電器(USB)
DIY Dynamo USB Charger for a Bicycle | 自作の自転車用のダイナモ充電器(USB)
DIY Dynamo USB Charger for a Bicycle | 自作の自転車用のダイナモ充電器(USB)
DIY Dynamo USB Charger for a Bicycle | 自作の自転車用のダイナモ充電器(USB)

Step 3

This step can be tricky…aligning the bridge rectifier in place. Note the polarity (positioning of the negative and positive legs).

DIY Dynamo USB Charger for a Bicycle | 自作の自転車用のダイナモ充電器(USB)

Looking from the top, your board should now look something like this.

DIY Dynamo USB Charger for a Bicycle | 自作の自転車用のダイナモ充電器(USB)

You can now go about carefully soldering the parts in place at the rear of the board. Take care not to overheat the parts, and make sure not to ‘connect’ any of the copper strips on the stripboard with stray bits of solder.

Post-soldering should look something like below. Ignore all the drill-marks, except for the one at the bottom. You need that one to stop current going directly to the regulator (LM2940). Holes can be made by hand-turning a 5mm drill bit.

DIY Dynamo USB Charger for a Bicycle | 自作の自転車用のダイナモ充電器(USB)

Step 4

Prepare your micro-USB connector by butchering a cheap USB to micro-USB cable, discarding the big USB end. We will attach this to the circuit-board, and it will plug into your smartphone. Frustratingly, USB cable inner wire colors are sometimes different (like, green for negative). But most of the time, they will be red (positive), black (negative) and white (data). You won’t be needing the white wire, so you can cut it short.

Micro USB inner wire colors (positive, negative, data)

Step 5

Before attaching the micro-USB cable to the circuit-board, a suitable case needs to be found. I happened to have an old fish-tank PH level tester container hanging around that was a perfect size.

DIY Dynamo USB Charger for a Bicycle | 自作の自転車用のダイナモ充電器(USB)

Step 6

Container sorted, time to thread the cables through the openings and solder them to the circuit board. I first attached the micro-USB cable. Red on the positive line, black on the negative line.

DIY Dynamo USB Charger for a Bicycle | 自作の自転車用のダイナモ充電器(USB)
DIY Dynamo USB Charger for a Bicycle | 自作の自転車用のダイナモ充電器(USB)

Next, attach the wires that will run from the dynamo hub. The polarity (negative and positive direction) here doesn’t matter at all; the bridge rectifier has magic fairies inside that sort all that out.

DIY Dynamo USB Charger for a Bicycle | 自作の自転車用のダイナモ充電器(USB)

Step 7

Install the circuit board in a suitable container. Before sealing the container up properly, now may be a good time to hook the unit up to a dynamo hub and smartphone to check that everything is working.

DIY Dynamo USB Charger for a Bicycle | 自作の自転車用のダイナモ充電器(USB)

Step 8 (optional)

This step is not essential, but I wanted to make this unit as weather-proof as possible. Using a couple of different size heat-shrink tubing, I covered the whole thing up, making it very weather-proof.

DIY Dynamo USB Charger for a Bicycle | 自作の自転車用のダイナモ充電器(USB)
DIY Dynamo USB Charger for a Bicycle | 自作の自転車用のダイナモ充電器(USB)

Step 9

I wanted to be able to easily attach and remove the charger from my bike. The only time I use it is when I am cycle touring (about twice a year). This was easily done by using simple male/female connectors. The wire running from my hub to the female connectors is on my bike all the time, and I can just connect the charger when I need to.

DIY Dynamo USB Charger for a Bicycle | 自作の自転車用のダイナモ充電器(USB)
DIY USB dynamo charger for a bicycle - B+M Lumotec auxiliary power outlet (near Nanporo, Hokkaido, Japan)
DIY USB dynamo charger for a bicycle - handlebar mounted plugs (near Nanporo, Hokkaido, Japan)


Performance in the real world

This is the second charger I have made (using the exact same circuitry). The first one ended up in a PVC pipe casing, which is ugly and bulky. It works exactly the same as this new slick-cased version. Using the PVC-pipe-case version, I was able to get around 1% charge for every 1km pedaled on a laden, flat-terrain four-day cycle tour (with the phone powered off). That was charging a Sony Experia Z smartphone, which has a very large battery (2330mAh). With an iPhone, with its smaller 1440mAh, this might be more like 2% charge per 1km.

In any case, with the phone powered off, it will charge fully over a full day of cycling. It does not put out enough charge to keep up with intensive computing tasks like Google Map Navigation. That is, with the screen on all the time, plus the GPS running, the battery will still run down even while charging.

DIY USB dynamo charger for a bicycle (Hokkaido, Japan)

DIY USB dynamo charger for a bicycle, charging a Sony Xperia Z (near Ebetsu, Japan)

DIY USB dynamo charger for a bicycle - charging a Sony Xperia Z (near Nanporo, Hokkaido, Japan)

My wife has claimed this new version as her own, so I am still stuck with the PVC pipe version. On her bike, this is the set up we have at present (she doesn’t use a handlear bag). Here, the charger is attached using a cable tie, in the photo at the top of this post, we have attached a velcro strap, which will make attaching/removing the charger easier.

DIY Dynamo USB Charger for a Bicycle | 自作の自転車用のダイナモ充電器(USB)
DIY Dynamo USB Charger for a Bicycle | 自作の自転車用のダイナモ充電器(USB)

Update (2014/06/08)

Thanks to commenter Prashant, I’ve just found out that you can buy a perfectly good charger for only US$30 or so: The Biologic ReeCharge Dynamo Kit. See the demo on Youtube, and looks like you can get it on Amazon: For that price, the only reason you’d ever need to make your own device is if you’re really into DIY! Official page for the kit here:

Update (2014/09/21)

Note Viktoras’s comment that the Biologic Reecharge may not give enough output for some devices.

Comments | Queries | Discussion

101 thoughts on “DIY Bicycle Dynamo USB Charger for Smartphones and Battery Packs”

  1. Hi! Thanks for schematics. I installed USB A-socket directly to the veroboard. It’s working now. I checked quickly today. Better test will be done after I build my new wheel with better parts.

      1. I built my new wheel. Usb charger is now working properly with my old ZTE smartphone. But it’s old and tired and should be replaced. I borrowed one Samsung Galaxy Trend and tried. It did not load anymore. I switchednback to old smartphone and it worked.

        So I hsve to find a phone which can be loaded. Itmcan be hard. Maybe most clever solution were to buy s usb battery pack.

        1. Now I have shorted the data pins in the socket. Both smart phones started to load immediately. I did my tests in my kitchen. Tomorrow will be the real world testing.

          Shorting the data pins did the trick!

          1. Very interesting! Great to hear it is all working. I’d be keen to hear the long-term results (i.e., will your phone battery last OK?).

  2. I’m using a 6V AC – 3W dynohub
    and it works fine for my old HTC smartphone.
    gives perfect 5V and charges my phone.
    So I tried it out with my Samsung Galaxy S3. The charging connects, so my phone thinks it’s charging, but in reality it is not. It is still using energy and won’t charge at all.
    I’ve read a lot about this problem for iJunk (as i like to call it) and they need a voltage reference on the data lines for it to charge at different speeds. All i can find about this for a galaxy is shorting the data lines instead of leaving them to float. Now shorting the data lines will tell the phone it is plugged into the wall and can take as much power as it wants. So i’m afraid that if I do this it might blow the 7805 or another part of the circuit.
    Or is my smartphone smart enough to take the max amount of current available? (while watching the Vcc usb so it doesn’t fall under lowest limit.)
    Or what should the voltage reference be for my phone so it takes 500mA

    1. To be honest, I have no idea. I had heard of some phones being more sensitive to fluctuations (i.e., they shut off the power source more readily than others). Perhaps the Galaxy is one of those phones?

    2. Blowing out 7805 is not likely to happen as maximum current drawn from your dynamo hub will be around 500mA (P = I*U and U = 6V and P = 3W so I must be 0.5A) and 7805 is designed for up to 1.5A (with proper cooling) and even without the cooling it has built-in overheat protection. So shorting data pins is not dangerous:) Or at least shouldn’t be.

    1. I would imagine you might need a different voltage regulator, but I’m really not sure what other modifications you’d need.

      1. Hi everyone! It’s not written here so I will do this:).

        You can use this circuit, with all the components, but the problem is, that linear regulators (such as LM2940CT-5.0 in this project) will behave like a regulated resistor to match output voltage of 5V. That means that when using 6V dynamo you will lose this 6V – 5V = 1V extra volt (times current drawn) as a heat. When you use the same circuit but with 12V supply, you will lose excess 12V – 5V = 7V (times current) as a heat. And despite the poor efficiency of such solution, without any radiator this component will surely overheat.

        For 12V supply it would be best to use some electronic step down converter ( or even a small transformer (as we have AC on the input side, and AC can be transformed down to around 6V) and then rectifier bridge, regulator (the same LM2940CT-5.0) and filtering capacitors.

        Using different voltage regulator will simply change output voltage, and different voltage is not wanted here.

  3. This is an amazing guide. Clearest I’ve seen yet for those of us with no electronics background. I’m going to have a go at this.

    Am I right in thinking the stripboard is standard pitch (0.1 inch), so the board you cut off is less than half an inch wide?

    And, other than for size, is there any reason why C3 isn’t a capacitor rated higher than 25v?

    Finally, did you need a special soldering iron with a fine tip?


    1. Thank you very much! The stripboard is indeed standard pitch, and yes, the bit I cut off is super narrow. As for the C3 rating, I did see some comments about capacity on another webpage describing the same design. Someone commented it should be a higher rating…I’m not sure what the ‘correct’ answer is.

      My soldering iron has a fine-ish tip. That’s not very helpful, I know. But it was just a standard electronics soldering iron.

      I hope this helps!

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