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Final product.JPG

This winter, my dad and I took up the project of building a simple pedal-powered cell phone charger to mount on my bicycle. Cell phones are small potatoes in the big picture of energy consumption, but the apparatus we built could be a very practical concept for those on self-supported bike tours or those living temporarily in situations without electricity. Just unplug your phone from the wall, and in the time that it takes for you to rig up this gizmo your phone will be out of juice and you’ll be due for a long ride!

A couple visits to the local hardware store and Radio Shack secured all the parts we needed for the job.

What you’ll need:

Electronic parts

  1. circuit board (i.e. Radio Shack part no. 276-148)
  2. bridge rectifier, 100 V, 1.4 A (i.e. Radio Shack part no. 276-1152)
  3. capacitor, 1000 micro Farad, Radial-Lead Electrolytic, 35 V DC (i.e. Radio Shack part no. 272-1032)
  4. voltage regulator, 7805, +5 V DC, 1 A (i.e. Radio Shack part no. 276-1770)

Tools

  1. soldering iron
  2. nose pliers
  3. diagonal cutters
  4. wire stripper
  5. hookup wire
  6. speaker wire
  7. mounting pins
  8. electrical tape
  9. zip ties (optional)

Other components

  1. cell phone charger
  2. 12 V 6 W bicycle headlight generator
  3. bicycle

Circuit diagram:

CircuitDiagram.jpg

Step 1: Mount the generator onto your bicycle as directed on the package. It will work on either the rear or front axle. I mounted mine on the rear. Cut the cord off of your cell phone charger. Strip the insulation from the cut end to expose about a half-inch of both the positive and negative wires.

TheGenerator.JPG

Step 2: Assemble the circuit, as shown below. Push the wires from the components through the holes in the circuit board. Use mounting pins to connect to the electronic components when necessary, and connect from pin to pin with the hookup wire.

MakingConnections.JPG

Step 3: Solder the two cut, stripped leads from the cell phone charger to the mounting pins connected to the voltage regulator. The wire going to the center of the power jack is usually the positive/red one. Connect the wire coming from the generator to the AC terminals of the bridge rectifier. Check your work against the circuit diagram at the top of the page.

Soldering.JPG

Step 4: Protect the solder side of the circuit board with a layer of electrical tape. This will help protect the circuit from shorts due to accidental contact with conductive material, and from exposure to the elements.

ProtectBackWithTape.JPG

Step 5: You’re almost ready to go. You only need to secure the wire to the frame of your bike with tape (or zip ties) and position the circuit board somewhere out of the way (we placed mine at the base of the seat post).

PlacingCharger.JPG

Step 6: Where you place the charging cell phone while you ride is up to you. I keep a basket hanging from my handlebars, so I ran the wire along the length of the center bar of the bike such that the DC plug-in ended up in the basket, where the phone stays while I’m riding. Other options are to keep the phone in a tool bag under the seat or in a saddle bag on the rear rack.

Final Product Alt.JPG

Step 7: Plug in your phone and start pedaling! The phone should react just as if it were charging from a wall outlet.

How it works:

When engaged, the generator wheel rolls against the bike tire. The motion produces electricity, and the greater your speed, the greater the voltage output. The cord from the generator leads first to the circuit board’s bridge rectifier, which converts the AC to DC. In other words, the up-and-down, positive-to-negative current becomes a steady positive current. Then, the capacitor levels out the DC voltage, producing a steady voltage inflow to the voltage regulator. The voltage regulator is crucial, as the phone only needs five volts to charge, whereas fast pedaling can produce 30 volts or more, which is enough to fry the average cell phone. The regulator controls the voltage, putting a five-volt ceiling on the power entering the phone.

Results:

Starting with a dead cell phone, plugged in and placed in my basket, I spent approximately three hours and 25 miles riding in the streets of San Francisco to charge it back to full power. Much to my surprise, an easy speed of only four miles per hour was enough to keep the power production at the necessary five volts, and almost as soon as I rolled out the door, the phone lit up and beeped, indicating that it had begun to charge. Even in stop-and-go city cycling, my speed rarely dropped below charging speed, allowing the battery to juice up almost continuously.

The generator made riding significantly more difficult due to the friction of the roller against the tire, so you might want to disengage the generator on hard uphill climbs. Also, a lot of potential energy is wasted on long downhill runs, since voltage over and above 5V is lost as heat from the regulator. The system could be improved by installing a battery to catch and store the overflow energy for use when the output voltage drops below 5V, as when the bike is moving slowly or at rest.

The cost of the system is about $25.00, and the incentive – even the necessity – to ride the bike daily helps keep you in shape!

Alastair Bland

Alastair Bland is a freelance writer based in San Francisco. He writes frequently of food, science, and the environment. He travels frequently — often by bicycle — and his journeys can be followed at his blog “Off the Road” (blogs.smithsonianmag.com/adventure).


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Comments

  1. MarceloR says:

    Nice Surly Cross-Check. Early pea-green ones were Reynolds 531, definitely a keeper.

  2. AndyL says:

    I’ve always wondered, could something like this be set up to pull a more serious amount of energy from the wheel, but only when the front break is on?

    I think about this every time I brake all the way down a hill, or every time I replace the batteries in my headlamp.

  3. HJ Schmidt says:

    My experience with these bicycle generators has been that they put out DC current, not AC (as would be produced by an “alternator”). If this were the case, is the bridge still necessary? Would a diode be necessary in the circuit to prevent reverse voltage if the bicycle were rolled backwards?

    Great article! thanks. hj

    1. Actually, I was under the same impression. I thought all bicycle generators were “dynamos,” i.e. that they generate direct current. Turns out that’s not true. Although there are bicycle dynamos in the world, most of the units sold today give alternating current, i.e. they are “alternators.” “Generator” is commonly used to refer to either a dynamo or an alternator, but in this case, where we’re dealing with nitty-gritty electronics stuff, we probably ought to be more specific. Thanks for pointing this out.

    2. Anonymous says:

      My experience with all the local bicycle shops is that they flat-out refuse to sell generators any more.

      All they stock is battery powered lights, and if you ask about a generator you get told that they are unsafe because the light turns off when you stop pedaling.

      1. Don't make stuff up please says:

        Almost all modern dynamo powered bike lights have a “stand-light” feature, pretty much just a huge cap, that powers it for 3-6 minutes after you stop *moving*. The dynamo is not powered by pedalling sir, so what you said is incongruous, unless it’s a fixie, in which case you would also not be moving.

  4. Karla says:

    Hi Alistair,

    This is an awesome post, I wrote about your experience today in my blog post at http://www.mobileapptitude.com Thank you for sharing! Karla

  5. Charles says:

    this is pretty great
    how about using a 6V generator to reduce the friction during the ride?

  6. Chris says:

    Could you hook this up to a USB port so you can not only charge your phone, but you can also power your arduino, music player, or other USB charged devices (I recently got video glasses for X-mas, but they must be charged with usb when you aren’t using them… But anyway…). Although, it would be very tedious to carry around, but that’s gonna be for V 2.0

    So I guess a USB port is a good idea… I’m gonna try it and tell you if it will work.

  7. ryan says:

    hi..im going to do my final year project and its a bit similar to this..may i know how much the minimum rotation speed to generate 12v 6w dynamo?? and i would like to attach the dynamo on the fan blade to generate the electricity..

  8. Hello, i tried this myself and have the identical generator and everything but i am having a problem. when i put the meter on the output i am getting the 5VDC but when i switch me meter to AC I also get 10.2VAC across the wires. The reason i check this is because when i plugged my device in to charge i notice it was charging but that i was also being slightly electrocuted while holding the device i was charging!
    I have checked and rechecked my circuit with your schematic and it all matches up but i still cannot figure out why I am getting shocked to the equivalent of putting a 9v battery on your tongue, in my hand.
    Is there supposed to be an extra ground to the generator or frame of the bike that i missed?

    1. Anonymous says:

      i’m wondering why this design is so simple. did you find out what is calling that ripple? is the capacitor wired backwards or something like that? i’m not a ee, just a tinkerer that sometimes uses a scope.

    2. Kurt Johanning says:

      You must be completing the circuit to receive a shock. You say your phone is charging. It should charge if it is insulated from you and/or the bike. If it does not then your body is providing the ground or return path for the charge. Hope this helps.

  9. I tried building one of these and it didn’t seem to work for my motorola droid, though I have to admit, this was my first attempt at electronic soldering. The plug in charger I still have is rated at 5V @ 850ma. I cranked the bicycle charger by hand and plugged in my phone and the phone immediately rebooted. All things considered, should the charger build described above work for my phone as intended?

  10. Qaiser Kundi says:

    i like your projects,i am student of Electrical Engineering,please keep sending me latest
    projects,related to my technology.I am in first semester and now i have made pedal powered charger………….thanks alot

  11. zeeshan ali says:

    plz help me ASAP…
    i want to make this for my coll project work . but can i attach this one to my motor bike , as it rotates faster than bycycle, about 60kms/phr on avg. . im thinking to make that using high conductors .
    IS THIS POSSIBLE??? coz i dont want to risk for my coll project

  12. Sean … this is a very interesting project. I’d REALLY like to share a presentation of mine with you and discuss the synergies. My email is falconian111@yahoo.com.

    I tried to connect with you on Facebook, but found it a bit difficult to find the correct Sean Ragan! Please connect with me there

    https://www.facebook.com/ianfalcon.bentley

    Many thanks!

    1. Sean Ragan says:

      This is not my idea. It really should be posted under Alastair’s by-line. I don’t have a contact point for him anymore, unfortunately,

  13. Ron says:

    I would love to have a 3-5 usb mini hub dashboard on my bicycle .. one to recharge my camera batteries, one for gps battery , & one for my roadlights . I already have a dynamo on the front wheel powering front & rear lights … Is this possible for you to manufacture? I’m sure you would become very rich very quickly with an invention like that. Don’t you? Is there such a thing already on the market ? I’ve never heard of it ..Yet!

  14. ananthamanikandan.s says:

    super

  15. Andrew R says:

    This is great. What seems like a good next step would be to generate power for a USB external battery. See if you could capture more of that downhill power, and the you could charge all kinds of devices. I started thinking of this when I saw a hand cranked USB charger and though, why not a pedal powered, or downhill powered.

  16. Masood Sayed says:

    Supar…! I want make a bicycle on solar system or electricals system. But how can i made this bicycle? I want made a battary charger when cycle is running, and energy stored in battary. Please help me if u found any idea about this concept. Thanks.

  17. I’m surprised that this worked since you ran your ground wire to the tail-light terminal of the generator. I suppose the 12v from the headlight terminal must’ve overcome the 2.5v but it definitely would have worked better if you had run the ground wire to the generator bracket.

  18. log home says:

    Its like you read my mind! You seem to know so much about this, like you wrote the book in it or something.
    I think that you can do with some pics to drive the message home a little bit, but other than that, this is wonderful
    blog. An excellent read. I’ll certainly be back.

  19. Hi there! This is my first visit to your blog!
    We are a team of volunteers and starting a new project in a community in the same niche.
    Your blog provided us valuable information to work on. You have done a wonderful job!