http://www.instructables.com/id/USB-Bike-Generator/

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USB Bike Generatorby dbc1218 on June 15, 2010

Table of Contents

USB Bike Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Intro:   USB Bike Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Step 1:   BikeGen Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

File Downloads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Step 2:   The Tools and Parts you will Need . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Step 3:   Build the Electronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Step 4:   Build the Generator Mount . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Step 5:   Final Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Related Instructables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

http://www.instructables.com/id/USB-Bike-Generator/

Author:dbc1218I enjoy building things more than actually using them.

Intro:  USB Bike GeneratorThe USB Bike Generator is a small bike mounted electricity producing device optimized to provide power for two USB ports.  There are so many small electronics thatcan be powered or charged from a USB connection it only makes since that people might want to do this while riding a bike.  The basic idea for the USB Bike Generatoris to use a suitable stepper motor as a generator and a voltage regulator circuit to maintain the 5 volts needed for the USB ports.  In this instructable I will show you howto build this generator and through testing show that it is 70% efficient at converting the power from the generator to the power needed for the USB port. 

This is the third revision of my bike generator project, the first two can be found here http://www.instructables.com/id/Bike-Generator/ and herehttp://www.instructables.com/id/BikeGen/ I would strongly recommend that if you plan on building this USB Bike Generator you at least look over how these past toversions went together.

This third rendition of my bike generator project came about after reading some of the comments made about my previous methods. Specifically, one comment frommember ac-dc stated that my decision to use a linear regulator to go from 30 volts from the generator to 3 volts to power the light was at best 10% efficient. Now sinceone of the interests I've had listed on my profile since I joined this site has been efficiency I decided to read the rest of his comment after wiping the tears from my eyes.Ac-dc suggested that buck switching regulator would be better suited for a bike generator like mine. I had no idea what a switching regulator was so I started to do someresearch and found out that ac-dc was right and that I could significantly increase the efficiency of the electronics I was using.

In my searching for switching regulators I came across this reference from Dimension Engineering, http://www.dimensionengineering.com/switchingregulators.htm.  Theyoffer a good explanation of the switching regulators and even sell them. 

Image Notes1. The u-bolts I made in the BikeGen instructable were used again here.2. Two 8-32 machine screws and nuts hold the flat to the angle.3. The Spring

http://www.instructables.com/id/USB-Bike-Generator/

Image Notes1. I think this will be the most convenient spot for the connector, because youcould keep what ever you are powering in you pocket or rear pannier.

Step 1: BikeGen TestingIf you only want to learn how I built the USB Bike Generator and not why the BikeGen system wasn't the best, you can skip this step.

In order to set a bench mark for the efficiency of BikeGen system I decided to do some testing.  In my searching for switching regulators one of the best resources I foundwas this article http://www.dimensionengineering.com/switchingregulators.htm It explains how switching regulators work and how you can calculate the power lostthrough heat generation.  The power lost to heat can be calculated using this equation:

Power lost = (Input voltage – output voltage) * load current

So in order to find the power lost you need to know the input and output voltages as well as the load current.  Luckily, I already had the tools for this job which required 3digital multimeters and a small drill press.  

The test setup was fairly simple, I tightened the drill press chuck onto the shaft of the stepper motor and loosely clamped the motor in a vice.  This was the same steppermotor that I have used for both the Bike Generator and and BikeGen Instructabes.  This actually works out really well for two reasons.  First the speeds that the drill presscan spin are labeled and from these speeds I calculated how fast I would need to ride the bike based on how fast the generator is spinning.  So using the tire size, rimsize and the diameter of the small wheel mounted on the stepper motor for the BikeGen instructable I calculated the following speeds:

Drill Press RPM            Bike Speed (MPH)         620                                     4.7        1100                                    8.3        1720                                   13.0        2340                                   17.7        3100                                   23.4

This range of bike speeds seems very reasonable.  The second reason that using the drill press is a good representation of a bike rider is the power rating of the drillpress motor.  This drill press is rated at 1/3 horse power which is roughly 250 watts, this is attainable by an average person while riding a bicycle.  

The next step was to connect 3 digital multimeters into the circuit.  I had cut some of the wires and use a few sets of alligator clips to make this happen.  Check out thepicture or the Test Setup pdf to see how I connected the meters.  Basically the current meter was placed inline between the regulator and the charging circuit and thevoltage meters connected after the diodes and after the regulator and were grounded at the same spot.  This measures the values I need to calculate the power lost.

Once everything was ready I plugged in the drill and turned it on.  I tested the generator at every speed the drill was capable of and found out that at the first 3 speeds(620,1100,1720 RPM) there was not enough power to consistently charge the batteries.  This was confirmed by the blinking LED on the charger.  At 2340 RPM and 3100RPM enough power was provided by the generator to charge the batteries.  The values I measured at these two speeds are listed below:

Motor RPM                  2340       3100Input Volts                    15.2        20.2Output Volts                   13        12.68Output Amps                0.29        0.28Power Lost (W)           0.638     2.106Output Power (W)       3.770     3.550Total Power (W)          4.408     5.656Efficiency                      85.5%    62.8%

The power lost was calculated from the equation I showed earlier, the other values were calculated from the following equations:

output power = output voltage x output currenttotal power = output power +  power lostefficiency = output power / total power

RESULTS

So looking at these results I think there is something to be desired.  First there was not enough power to charge the batteries until 2340 RPM which is 17.7 mph on thebike.  This is a high speed and doesn't seem reasonable for a casual bike ride.  Of course this speed is attainable but it would be a lot of effort to maintain the speed foran extended period of time.  The efficiency  seems very good at 2340 RPM (85%) but it drops to 62% at 3100 RPM.  This is because the input voltage goes up at higherspeeds which means more power is lost to heat.  So unless I want to ride the bike at and average speed of 18mph everywhere I ride I will not achieve the best efficiencypossible.    

http://www.instructables.com/id/USB-Bike-Generator/

Image Notes1. The stepper motor mounted in the drill press for testing

Image Notes1. This digital multimeter reads the input voltage to the regulator from thegenerator2. This is the output voltage from the regulator3. This is the load current

Image Notes1. The batteries and the charger circuit

File Downloads

Test Setup.pdf ((792x612) 92 KB)[NOTE: When saving, if you see .tmp as the file ext, rename it to 'Test Setup.pdf']

Step 2: The Tools and Parts you will NeedBelow is a list of most of the tools and parts I used to build the USB Bike Generator.

Tools

Soldering IronSolderSolder SuckerDesoldering BraidDigital Multimeter (3 of these were used in testing)

HacksawDrillDrill BitsFile

http://www.instructables.com/id/USB-Bike-Generator/

Tap (8-32 screw size)Tape MeasureSharpieDremel

Parts

WireUSB Car Power Adapter (read more about this in the next step)Stepper Motor1N4001 Diodes (8 diodes are needed)

1-1/4" x 1-1/4" x 1/16" Aluminum Angle1/2" x 1/8" Aluminum Flat8-32 Machine screws and nuts

Image Notes1. This is the USB car adapter I got for one dollar

Image Notes1. This is the stepper motor I used as a generator for the last two versions of mybike generator2. This is the new stepper motor

Image Notes1. Old2. New

http://www.instructables.com/id/USB-Bike-Generator/

Step 3: Build the ElectronicsThere are three major parts to the electronics of the USB Bike Generator, the stepper motor, the rectifier and the voltage regulator. 

Stepper Motor

The USB Bike Generator uses a stepper motor as a generator to produce the electricity.  In general any electric motor can be used as a generator but not all motors arewell suited as generators.  The stepper motor I used in my last two instructables came from an old printer and was rated at 24 volts.  Through testing I found that thismotor provided up to 48 volts when unloaded and spun at 3100 rpm.  People new to electronics should understand that high voltage doesn't always mean high power.  Inorder to reduce this voltage to the 12 volts needed for the BikeGen instructable the regulator just burned off the extra voltage as heat.  This meant the regulator wasinefficient.  

In my searching for a new stepper motor I looked for two important aspects.  First, the voltage rating of the motor need to match the 5 volts required by the USB ports.Second, the amperage of the motor needed to be higher, meaning there was more power potential in the motor.  I found a somewhat local electronics surplus store thatsells stepper motors and searched their website, http://www.electronicsurplus.com/home.cstm.  They had a stepper motor listed at 5 volts and 3.3 amps, this seemedperfect.  I went to the store and after looking at everything they had I got the motor.  I would recommend finding a local surplus store in your area if you plan on buildinganything electronic, they are a great resource.  

Rectifier

In basic terms a rectifier changes Alternating Current, AC, to direct current, DC.  The coils inside the stepper motor are energized as the motor spins causing the currentin the coils to alternate.  This is the alternating current.  The 5 volts need for the USB port need to be direct current.  The rectifier, which is just 4 diodes, changes thealternating current from the stepper motor to the direct current needed for the voltage regulator.     After doing the testing on the BikeGen regulator circuit I realized that the zener diodes I was using were getting very hot.  One of them even failed because it overheated. I wanted to use a more suitable diode for this project and after checking back to the instructable that inspired this whole project for me, http://www.instructables.com/id/personal-powerPlant/, I decided to go with a 1N4001 diode which is rated at 50V and 1 Amp.  I got the diodes in a variety pack from RadioShack.

Voltage Regulator

The voltage regulator is a switching voltage regulator as opposed to linear regulator.  At first my searching led me to the LM2575 switching regulator and I was planningon building the circuit myself.  Just search "LM2575" and the data sheet will show up.  On the data sheet the recommend circuit for a 5 volt output is shown withrecommendations for all the components.  I continued searching and found the exact circuit I needed from Lightobject, http://www.lightobject.com/LM2575-High-Input-6V60V-Switching-5V-Power-Module-Regulator-P417.aspx.  This seemed to be a better option for me because I didn't want to have to buy all the components in muchhigher quantities than I needed from a electronics distributor.  

As a last resort I went to the local dollar store because they always seem to have the things I need.  To my complete surprise they had 12 volt car adapters with power fortwo USB ports.  So I bought two and went home to take them apart.  They had a switching regulator circuit already!  It uses a MC34063 regulator IC and has all thesupporting components.  All of this for a dollar, you can do much better than that.

Follow through the notes on the pictures to see how I connected all the parts together. 

              

Image Notes1. Here is the guts of the regulator, the MC34063 is the 8 pin IC, there is an LEDpower indicator, and 2 USB ports2. This is the negative side or ground for the power input3. This spring is the positive side of the power input

Image Notes1. These are the specs for the stepper motor

http://www.instructables.com/id/USB-Bike-Generator/

Image Notes1. I built this rectifier circuit to test the new stepper motor

Image Notes1. I soldered the diodes directly together to build each rectifier,2. The side of the diode with the line is the cathode and the other side is theanode. Start by soldering two diodes together cathode to anode. You will need4 sets.

Image Notes1. Take two sets and solder the cathode, line sides, together

Image Notes1. Then solder the anode, non-line sides together

http://www.instructables.com/id/USB-Bike-Generator/

Image Notes1. This is a completed rectifier2. The stepper motor has 4 wires which connect to the ends of 2 coils inside themotor. You can tell which two wires are connected to the same coil by measuringthe resistance between the wires. The two wires from each coil in the motorconnect to these two junctions in the rectifier3. This junction is the positive output of the rectifier4. This junction is the negative output of the rectifier

Image Notes1. I soldered a 4 conductor wire to the rectifiers. Then wrap the connection withelectrical tape so the junctions won't touch and short the circuit2. I soldered these junctions together to have one positive output from therectifier3. These junctions were soldered together to form the negative output of therectifier

Image Notes1. The positive and negative outputs of the two rectifiers

Image Notes1. The spring and clip were removed and the wires were soldered in their place

http://www.instructables.com/id/USB-Bike-Generator/

Image Notes1. The 4 conductor wire was then soldered to the 4 wires coming from thestepper motor

Step 4: Build the Generator MountTo mount the stepper motor to the bike I used a method very similar to the BikeGen instructable.  A small wheel was attached to the stepper motor and the motor wasmounted perpendicular to the bike wheel on the rear rack.  The small wheel on the stepper motor rubs against the braking surface of the bike wheel to spin the motor.  A spring was used to force the stepper motor toward the bike wheel to ensure constant contact between the two wheels.  

I started by cutting two 6 in. pieces of 1-1/4" aluminum angle.  One of these pieces mounts to the rear rack and the other mounts directly to the motor.  Two sections ofeach piece were cut out to allow for clearance between the motor, rack and wheel.  I reused the home made u-bolts from the BikeGen instructable to mount to the rack. Two short pieces of the 1/2" aluminum flat bar were bolted to the angle aluminum to hold the screws that retain the spring and the motor.  The small wheel attached to themotor started out as a few parts from Servocity,  http://www.servocity.com/.  They sell very nice shaft connectors and wheels that make mounting anything to a motorvery easy.

While I can't offer exact dimensions for any other mounting situation I do believe this to be a fairly universal method of mounting a stepper motor to any bike with a rearrack.  I have considered many other mounting options for my bike it all my ideas seem to work back to this one.  The parts were fairly easy to make and the precisionrequired was not that high.  I made all of the cuts with the hacksaw and drilled all the holes with my battery drill or the drill press.  Simple tape measure and sharpie tomark everything and a center punch to get all the holes right was enough.  

If anyone has any fresh ideas on the mounting of the stepper motor I want to hear them.  I would like something more permanent and rigid, while still maintaining wheelserviceability.    

Image Notes1. Cut two 6 in. long pieces2. I used a C-clamp to hold the aluminum to the table and then cut it with thehacksaw.

Image Notes1. The u-bolts I made in the BikeGen instructable were used again here.2. Two 8-32 machine screws and nuts hold the flat to the angle.3. The Spring

http://www.instructables.com/id/USB-Bike-Generator/

Image Notes1. Once the pieces are cut your going to want to file the edges smooth, they getpretty rough from being cut with a hacksaw.

Image Notes1. These sections are the ones that need cut off.

Image Notes1. This section is gone. To do the other side I just clamped the piece to the othercorner of the table

Image Notes1. The two sections have been removed from this piece and a small notch wascut in it to allow clearance for the motor shaft

Image Notes1. These two marks are for the holes to be drilled, to mount this piece to themotor

Image Notes1. This piece mounts to the bike rack. The line represent the bars on the rackand the dots are the marks for the u-bolts used to mount this piece

http://www.instructables.com/id/USB-Bike-Generator/

2. Use a center punch and hammer to make it easier to drill the holes in the rightspots

Image Notes1. A 3-1/2" hole saw was used to make the small wheel that attaches to thestepper motor from 1/4" ply wood

Image Notes1. This is the plywood wheel2. This is the clamping shaft coupler from servocity.com

Image Notes1. I wrapped the plywood wheel with electrical tape and some thin foam paddingto ensure good grip on the braking surface of the bike wheel

Step 5: Final ResultsBefore I did the final assembly of everything I tested the performance of the new stepper motor, diodes and switching regulator.  I used a dead 5V 1000maH battery as aload and measured the current and voltage input and output of the regulator.  I used the drill press again to turn the generator at its 5 different speeds. The results arelisted below.

RPM                           620     1100      1720     2340     3100Vin (volt)                    5.81      6.61       7.15      7.43       7.67Ain                              0.15      0.26       0.34      0.38      0.40Vout                            3.70      4.21       4.55      4.78      5.05Aout (Amp)                0.15      0.28       0.37      0.42      0.44Input Power (W)       0.87      1.72       2.43      2.82     3.07Output Power (W)    0.56      1.18       1.68      2.01     2.22Efficiency                   64%       69%      69%      71%     72%

As you can see the regulator is right at 70% efficient between 1100 and 3100 rpm.  Also it generated enough power for the USB ports even at 620 rpm.  I also increasedthe size of the wheel mounted to the generator to slow it down compared to the old BikeGen stepper motor. 

All of the work comes to this final point. The USB Bike Generator can power two USB ports as you ride your bike, to charge your electronics.  The electronics ofthe system are 70% efficient above 12 mph bike speed and can generate adequate power at 7 mph.  I have tested a rechargeable battery, handheld GPS and anEton radio with the USB Bike Generator and they all work.  I have also tested a Ipod touch 3gen and have found its is possible to charge but because of the variability ofthe power source and the pickyness of the Ipod its not very reliable.

I welcome all comments, questions, and suggestions. Thanks 

http://www.instructables.com/id/USB-Bike-Generator/

Image Notes1. I think this will be the most convenient spot for the connector, because youcould keep what ever you are powering in you pocket or rear pannier.

Related Instructables

Bike Light 2011by hydronics

Bicycle DynamoUSB Charger bysmrtcar

Bike Dynamo byFat Bagel Dynamo

powered LEDbike lights bykptBurek

Contactlessdynamo bikewheel lights byvbnicolau

A simple water-proof LED lightcase for bicycle,easy installationand adjustable.(Photos) by iwico

Comments

36 comments Add Comment

 thegodfather279 says:  Oct 7, 2010. 6:30 PM  REPLYcould you use a car outlet power supply that has an AC plug and a USB plug instead of the dual USB power supply?

 zogworth says:  Jan 19, 2011. 1:07 PM  REPLYYou mean an inverter?

Most things that you could run off a small dynamo would be DC anyway, so you'd be inverting up to 110/240 VAC then recifying down to DC for yourphone/satnav/what ever charger with associated wastages.

 traeblain says:  Jul 6, 2010. 4:02 PM  REPLYLast question...but why did you choose to abandon the intermediate battery approach you used on your previous generation? I would think the battery couldtake the flaky charge gracefully, then you'd have clean output power to your devices and would correct for issue with the ipod charging reliability?

 dbc1218 says:  Jul 6, 2010. 4:37 PM  REPLYI think a battery could be used but I would want something to protect it and whatever device I'm using. I wouldn't want to over charge it or drain it to low.That would require another circuit to control everything, which I might try in the future.

 brickbreaker says:  Dec 2, 2010. 1:15 PM  REPLYWell obviously more research is required before you start building a battery addon for this build but I would like to point out (if its not too obvious) thatmodern devices with lithium batteries have a set up that prevents over charging. Maybe hacking an old device to be your bike-battery would be easierthan building your own circuit? Just a thought.

http://www.instructables.com/id/USB-Bike-Generator/

 tomtortoise says:  Jul 6, 2010. 4:29 PM  REPLYcan you please make a simple schematic to better explain the rectifier wiring.

 dbc1218 says:  Jul 6, 2010. 8:12 PM  REPLYWill this do?

 tomtortoise says:  Nov 15, 2010. 1:53 PM  REPLYthanks sorry for the late reply but i needed to make a mount first and get parts but i needed to use a different motor for my mount but the wires areweird. from the motor the order is orange, yellow, brown, green but when it goes to the white PCB mount plug it is yellow, orange, brown, greenshould i hook up the rectifiers in motor order or PCB plug order

 dbc1218 says:  Nov 16, 2010. 5:38 PM  REPLYYou should check the wires to find out which ones are connected to the same coil inside the motor. Get your DMM and set it to resistance thantouch the probes to two wires. If you see a few ohms of resistance than those two wires are connected to a single coil in the motor. These are thetwo connect to one of the rectifiers. There are two coils in the motor that's why you have four wires. Don't go by color or connectors just measureand find out what it actually is.

 mobby666 says:  Nov 7, 2010. 7:44 PM  REPLYWith the right regulator you should be getting over 90% efficiency. Using a solar cell setup & a boost regulator should give you power to supliment yourgenerator & reduce it's drag on your wheel. Look at BEAM robotics sites for other ideas about harvesting solar power. Nice

 proelectron says:  Oct 16, 2010. 11:23 PM  REPLYGreat project! I might try this, but with a smaller wheel giving the required alternator speed. Surely the output of the stepper motor is pulsed and thereforecould be stepped down using a small transformer?

 texasclodhopper says:  Jul 8, 2010. 1:00 PM  REPLYI still don't see how you have found a place to ride that doesn't require any stopping! As soon as you stop, everything starts dying! ;) A battery is the onlypractical way to store energy in your design. All of your electronic gadgets will see a steady voltage all the time. All you've done is present part of the project... now get busy and make it practical with some energy storage!

 pteranosaur says:  Aug 17, 2010. 12:52 PM  REPLYClod Hopper-More research,you need MORE RESEARCH...lol

 watermelonhead says:  Jul 18, 2010. 1:28 PM  REPLYActually, in the second rebuild of this project, he did just that... instead of directly powering the headlights, it recharged its batteries. He also says that thisis not to power, but "The USB Bike Generator can power two USB ports as you ride your bike, to charge your electronics."

 varunmehta says:  Jul 19, 2010. 8:51 AM  REPLYRather than dismantling the whole male plug system (car style) on the USB charger and connect the wires, how about making a female receiver, like that inthe car. You can plug this USB drive charger into it + if tomorrow you make a new enhancement or want to connect something new to it, you can reuse thesame stepper motor and circuit to achieve it!

 laznz1 says:  Jul 10, 2010. 1:38 AM  REPLYhttp://www.nzherald.co.nz/technology/news/article.cfm?c_id=5&objectid=10657566 epic win!

 traeblain says:  Jul 6, 2010. 3:58 PM  REPLYI know this is why your previous generation motor didn't work, but I think there could have been better options than moving to a new motor (although I havenot built this and don't know the ins-and-outs of your work). My first question is why not try a new wheel for the previous stepper motor? My calculations(assuming you're using a 700x23 wheel and tyre) simply using an aggressive inline skate wheel (47mm) you could move your target down to 12.9mph whichis pretty good for casual riding. Not sure your target speed though. It may help to understand as I believe you got the last motor from an old printer? Wherethis one may cost a bit more money.

http://www.instructables.com/id/USB-Bike-Generator/

 dbc1218 says:  Jul 6, 2010. 4:30 PM  REPLYThe main reason I didn't want to reuse the stepper motor from the printer was that its voltage output was to high, which caused the regulator to becomeinefficient. I think the goal should be to first create the voltage you need, in this case 5v, and then try to develop as much current as you can at thatvoltage, to get the most power and efficiency. As far as a speed target, I wanted something that would maintain high efficiency over a large speed range.I didn't want to have a really high efficiency at one certain speed because then I would have to ride at that speed all the time to get the best performance.As far as the cost goes, I spent $10 on the new stepper motor from electronics surplus.com They have that same motor on sale on-line for $10 as well.

 retasker says:  Jul 8, 2010. 3:13 PM  REPLYAh, but that is the whole point of using a switching regulator. I don't know what is actually in your $1.00 USB convertor, but a properly designedswitching regulator would allow you to transfer power efficiently and get more current out than you put in by operating with a higher input voltage.That is, with the proper switching regulator design including an input storage capacitor, you could use a higher voltage stepper motor to generate 12Vfor your convertor which would then step the voltage down to what you need. You see a tiny bit of that at the higher input voltages where you getslightly more current out than you are putting in. However, as it is now, you are barely getting enough voltage to make the switching regulatornecessary. Based on the output voltages you list you would actually now be better off with the linear regulator - especially at the lower speeds. Isuggest you try the old stepper motor with the higher voltage output with your new switching regulator. If you do this, make sure you don't get somuch voltage that you destroy the switching regulator - I don't know what the input rating is although it is at least 15V if it is designed to operate in acar and probably more. Or try your new stepper motor setup with your older linear regulator. Additionally, you could get more efficiency by usingschottky diodes for your rectifiers since they have a lower voltage drop than the 1N4001 diodes (0.4V vs 0.7V each)

 dbc1218 says:  Jul 9, 2010. 8:14 PM  REPLYUsing the old stepper motor will not work, I know because I fried two of the regulators during testing. The MC34063 is rated at 40V and the newstepper motor puts out 30V unloaded at 3100 rpm. I think the high load of the dead battery is what caused the voltage to stay around 7V for thenew motor, but I'm not quite sure how this works. At lower loads or lower output power the voltage will go up and the input current will decrease,right? But won't a higher load cause the voltage to drop even further because it can't compensate for the load? I guess my real question is whatconditions are needed for max power output and what conditions are needed for max efficiency? Are they the same or is it a trade off.

 ian_eo says:  Jul 8, 2010. 10:04 PM  REPLYwhy not use a 5v regulator to regulate the voltage to 5v. its not efficient having some voltage changes during changes in speed. if you can get it to more than5v without a regulator thats not a problem.

 alzie says:  Jul 8, 2010. 5:10 PM  REPLYThe motorcycle people had this figured out Long ago. They use permanent magnet alternators very much like a 3 phase stepper. What they do to regulatevoltage, is short the windings with SCR's before the bridge rectifier. The SCR's are only triggered when the system voltage becomes high enough. Shortingthe windings is counter intuitive, but when you analyze the situation, a perfect inductor driven with a voltage source (induction) consumes No Real power. Inreality the windings do have a small resistance, which consumes small power when shorted. Also, core losses go way down. Unloaded, core losses are wayup. Your pancake stepper is Loaded with this! A hybrid stepper would do you way better. I ride a bent with a 3W 6V shimano hub gen up front. Had to makemy own spokes to fit. That should be an ibble! I use this for LED lighting. Ive been thinking of pulling the above trick for charging.

 rickpaulos says:  Jul 8, 2010. 1:06 PM  REPLYThere are some very nice front Hub Generators available. Not for cheap however. Schmidt ($300) & Shimano ($150) (plus wheel building labor, rim, spokes,etc if needed) make very good models that put out a nominal 6 volts/ 3 watts at about 20 kph. The huge advantage of these hub generators is you eliminatethe mechanical drag you get with any tire drive system. The only drag is the electro magnetic drag which is porportional to the power consumption of thedevice using the power. Another huge avantage of hub generators is you can use them all night long. Most high end bicycle lighting systems have battery lifelisted in just a couple of hours. When on, the drag is pretty much undetectable by the rider. 3 watts is far less than what we typically put out when pedaling.Oh, yeah, they are silent too. Adding a Zenor diode would protect against over voltage. That's what most generator specific head lights use to keep the bulbsfrom burning out at higher speeds. The "Switching Voltage regulator" in the schematic should do the same thing. Adding a large electrolytic capactor to thefull wave bridge circuit would help smooth out the 'dc' (direct current). Bicycle generators put out AC or alternating current. Seen on an oscilliscope, it lookslike a sine wave, swinging from positive to negative. The frequency depends on the speed of the bicycle and the number of sets of windings in the generator.The full wave bridge circut changes the AC to pulsating DC, Looks like a bunch of Gateway Arches (st louis), lined up end to end. The Capacitor smoothsthat out quite a bit. The size of the capacitor would depend on the expected power output of the circuit. More power consumption, and you need a largercapacitor. Some commercial generator specific lights use capacitors to keep the tail light lit when at a stop sign or traffic light. I have one that keeps a smallLED bulb going in the head lamp when stopped for a minute or so.

 martinator says:  Jul 7, 2010. 5:46 AM  REPLYThat is a HUGE generator!!!! Why not use a bicycle hub generator? Google: bicycle hub generator

 dbc1218 says:  Jul 7, 2010. 6:36 PM  REPLYAfter this third generator I think I've come to the realization the the hub would be a very good place for the generator. I'd like to get a dynamo just to dosome testing and see how it stacks up.

 Nyckname says:  Jul 8, 2010. 12:12 PM  REPLYTake a look at the "Contactless dynamo powering bike safety lights" featured last year. Magnets attach to the spokes, coils on the frame, and youdon't lose energy to the friction of the generator pressing against the wheel. Always wore me out when I was a kid.

 uberwald says:  Jul 7, 2010. 4:04 AM  REPLYCouldn't you get higher RPMs on the motor by making the wheel smaller? just glancing at it, I think the bicycle wheel is probably around 4-6x thecircumference of your generator wheel, so every rotation of the bike wheel rotates the motor that many times. If you made the wheel half the size, you'd gettwice the RPMs on the generator motor and be able to get your output at lower speeds... right?

http://www.instructables.com/id/USB-Bike-Generator/

 dbc1218 says:  Jul 7, 2010. 3:37 PM  REPLYYes by making the wheel on the stepper motor smaller it could spin faster and that would mean more power. The other side to that is spinning the motorfaster means higher voltages are produced and when you only want to output 5v the higher voltage means less efficiency. Check out the equation on thetesting step. The wheel I currently have one the motor is 3-1/2" and the rim diameter is 24-3/8" that makes about a 7:1 ratio. I found through the testing Idid that I didn't need to spin the generator much faster than 2300 rpm to get decent power and efficiency. With the 7:1 ratio that means 27 mph on thebike which is fairly high speed for casual riding.

 uberwald says:  Jul 8, 2010. 11:25 AM  REPLYI was thinking much more along the lines of 8-12 mph being a "normal speed" for anything but a road bike, and so you should seek to optimize yourgenerator for those speeds, with the lower efficiency at higher speeds not making too much difference since you'll still be getting "enough." Thoughyou might be able to generate some sort of "overvoltage" circuit to run some other process or charge a backup set of batteries at the higher voltagesso that you're not just converting it all? hmmm... where's an EE when you need one?

 Analog1Jim2 says:  Jul 8, 2010. 11:22 AM  REPLYSpinning the stepper motor faster and generating a higher voltage will INCREASE efficiency, not decrease it. If you go back to your link to DimensionEngineering and re-read the page ALL the power loss calculations refer to use of a linear regulator, not a switching regulator. A switching regulatorhas essentially a negative input resistance. This means that for a particular output power the input current will DECREASE as the input voltageINCREASES to keep input power constant., and vice versa. For a switching regulator the "lost' power is the input power minus the output power. Lostpower = (input current x input voltage) - (output current x output voltage) The input current changes with input voltage to keep input power constantfor a fixed output power. Measuring the input current is a little tricky because the input current is in pulses, not a steady value. Using a True RMSdigital multimeter will give accurate readings, but using an averaging type meter (typical inexpensive meter) will give less accurate readings but willbe OK if you only want readings that are fairly close. The only limitation to spinning the motor faster is that the voltage might exceed the rating of theswitching regulator input. Check the maximum input voltage on the data sheet and keep below it for all operating conditions. The MC34063 has amaximum input voltage of 40V. To be safe, your design at the fastest bike speed should not go above 30V to give a good safety margin. I am anengineer and have been designing with switching regulators for many years. Your find at the dollar store was a great find as designing with aswitching regulator can involve custom coils and transformers. BTW excellent Instructable, I am impressed with the research you did for this project...... Jim

 lahtib says:  Jul 7, 2010. 11:34 AM  REPLYHave you considered the use of a capacitor? It might provide some stability while removing the concerns of a battery charge?

 gguillotte says:  Jul 6, 2010. 2:37 PM  REPLYHow does it handle rain, heat, storage? Would some sort of casing be feasible? How hot does the motor get? Would it work to charge a small battery andfeed the battery to USB ports to even out the variability?

 dbc1218 says:  Jul 6, 2010. 3:07 PM  REPLYI don't know about rain yet but I went out for a test ride last night. I rode about 4 miles and it powered my GPS, Garmin etrex Vista, for the whole ride.The motor does not get hot and I know from my drill press testing that the regulator IC can get fairly warm. The 5v battery I used for testing was aEnergizer Xpal XP1000 which could potentially be used to even out the output but I don't know how that could be done. Its easy enough to just chargethe battery and then charge whatever device you need with it. Some sort of case would be nice but I would like to make the stepper motor a morepermanent fixture on the bike first.

 gguillotte says:  Jul 6, 2010. 3:21 PM  REPLYThanks!

 anres321 says:  Jul 6, 2010. 2:08 PM  REPLYNice !! now a flatscreen and some speakers XD

 fungus amungus says:  Jul 6, 2010. 11:39 AM  REPLYNice work!