Make_ Projects - Pedal-powered phone charger

Make: Online : Make: Projects - Pedal-powered phone charger
8/30/09 10:34 PM
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by Alastair Bland
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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.
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Electronic parts
1.
2.
3.
4.
circuit board (i.e. Radio Shack part no. 276-148)
bridge rectifier, 100 V, 1.4 A (i.e. Radio Shack part no. 276-1152)
capacitor, 1000 micro Farad, Radial-Lead Electrolytic, 35 V DC (i.e. Radio Shack part no. 272-1032)
voltage regulator, 7805, +5 V DC, 1 A (i.e. Radio Shack part no. 276-1770)
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Tools
1.
2.
3.
4.
5.
6.
7.
8.
9.
soldering iron
nose pliers
diagonal cutters
wire stripper
hookup wire
speaker wire
mounting pins
electrical tape
zip ties (optional)
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Other components
1. cell phone charger
2. 12 V 6 W bicycle headlight generator
3. bicycle
Circuit diagram:
http://blog.makezine.com/archive/2009/06/how-to_pedal-powered_phone_charger.html
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Make: Online : Make: Projects - Pedal-powered phone charger
8/30/09 10:34 PM
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.
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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.
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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.
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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.
http://blog.makezine.com/archive/2009/06/how-to_pedal-powered_phone_charger.html
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Make: Online : Make: Projects - Pedal-powered phone charger
8/30/09 10:34 PM
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).
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.
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Step 7: Plug in your phone and start pedaling! The phone should react just as if it were charging from a wall outlet.
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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.
http://blog.makezine.com/archive/2009/06/how-to_pedal-powered_phone_charger.html
Page 3 of 5
Make: Online : Make: Projects - Pedal-powered phone charger
8/30/09 10:34 PM
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!
Related:
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Posted by Sean Michael Ragan | Jun 8, 2009 07:00 AM
Bicycles, DIY Projects, Electronics, MAKE Projects, Transportation | Permalink | Comments (7) | Email This |
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Posted by: MarceloR on June 8, 2009 at 7:26 AM
Nice Surly Cross-Check. Early pea-green ones were Reynolds 531, definitely a keeper.
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Posted by: AndyL on June 8, 2009 at 5:11 PM
Regenerative braking possible?
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?
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I think about this every time I brake all the way down a hill, or every time I replace the batteries in my headlamp.
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Posted by: HJ Schmidt on June 10, 2009 at 8:58 AM
AC from generator?
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
Reply to this comment
Posted by: Sean Michael Ragan on June 10, 2009 at 12:05 PM
http://blog.makezine.com/archive/2009/06/how-to_pedal-powered_phone_charger.html
Page 4 of 5
Make: Online : Make: Projects - Pedal-powered phone charger
8/30/09 10:34 PM
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.
Reply to this comment
Posted by: Anonymous on June 12, 2009 at 6:37 PM
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.
Reply to this comment
Posted by: Karla on July 28, 2009 at 7:50 PM
Hi Alistair,
This is an awesome post, I wrote about your experience today in my blog post at www.mobileapptitude.com Thank
you for sharing! Karla
Reply to this comment
Posted by: Charles on August 20, 2009 at 2:02 PM
generator
this is pretty great
how about using a 6V generator to reduce the friction during the ride?
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