How to Charge Any USB Device by Riding Your Bike

To start off, this project was started when we received a grant from the Lemelson-MIT Program. (Josh, if you're reading this, we love you.)
A team of 6 students and one teacher put this project together, and we have decided to put it on Instructables in hopes of winning a laser cutter, or at least a t-shirt.

What follows, is a compilation of our presentation and my own personal notes. I hope you enjoy this Instructable as much as we did.

I'd also like to thank Limor Fried, creator of the MintyBoost circuit. It played an key role in our project.


Jeff Brookins
Divine Child InvenTeam Member

Step 1 Our original intention...

Our original project was to develop a product that used the Faraday Principle to allow runners to charge their iPods while they run. This concept would generate electricity the same way those Faraday flashlights do.
However, we had a problem. To quote my team mate Nick Ciarelli,

"At first we considered using a design similar to one of those shake-up flashlights and converting it so that a runner could strap it on for a run and have energy to charge their iPod or whatever device they use. The shake-up flashlight gets its energy from the interaction of the moving magnetic field of the magnet in the flashlight and the coil of wire wrapped around the tube the magnet slides through. The moving magnetic field causes electrons in the coil to move along the wire, creating an electric current. This current is then stored in a battery, which is then available to use for the flashlight bulb/LED. However, when we calculated how much energy we would be able to get from a run, we determined that it would take a 50-mile run to get enough energy to charge one AA battery. This was unreasonable so we changed our project to the bike system."

We then decided to use a bike-mounted system instead.

Comments

[emihackr97]

I don't understand, why regulate down the voltage to then boost it up, it's nonsense!

[lmaclean]

I have looked at the circuit and I can't see where to put the 140f supercapacitor. Can someone please help me?

[importsonly]

JeffB you should try marking this item, make to usb ports one for a Ipod and one for the mobile phone, I know heaps of people that would buy a simple idea like this.. Good Job :)

[joshnosh]

not at over >$280 they wont you would be a moron to buy this lol

jeffB considering you have used a ridiculous motor for this project i think the constructive criticism off kagetsujki is quite apt.
if you don't want people to sit on top off a mountain criticizing then don't give them such a big mountain

[griteck]

that is cool would you be able to power a bike light

[lovetoride]

I always wondered about charging my devices (I have a lot of them) while riding my bike.

I bought the Cycle Charger from www.econvergence.net/cyclech.htm because it has a USB port. It works well and starts charging at pretty slow speeds - around 8 mph.

I use it primarily to charge my Blackberry for work.

[zoltzerino]

Why not use a smaller, cheaper, lower power motor and use a gearing system to increase it's RPM from the wheel rim? Similar to those wind-up torches with the handles. :-) Nice one anyway, but pricey.

[zoltzerino]

The torch in question (one that I've dismantled) has a simple 4 diode AC-DC rectifier with a smoothing cap, this is somehow rut through a transistor, this seems to be enough to charge a little 3v button cell. With something a little more flashy, could this be notched up to 5v directly? With or without a Minty Boost.

[rapidprototyping]

hey look at what was done in the early seventies in this work on the pancake motor i'm trying to clean up the images but new to that line work

[rapidprototyping]

here is gimp photo of a pancake motor

[kerembasaran]

A 140F capacitor is just crazy.

[ReCreate]

i have seen 300 Farad caps

[uberdum05]

I've seen a 3000F supercapacitor on http://www.wima.com/EN/supercap_r_2.htm

[agent harmsy]

add a transformer, hook it up to a coilgun and watch it blow up a HOUSE! :D

[qwerty156]

Bad circuit, good idea. Take a 2 of those caps in series to make a ~5v Cap. so- Motor gives electricity 5v regulator gives 5v to Super caps. Caps give to deveice

[adeb2]

I agree with dirty valentine, a low dropout 5v regulator is much more efficient. I've build a unit to output 5 Volt 500 mA on USB cable to charge my Phone / GPS / PDA from a 6Volts, 3Watts HUB dynamo using just that. Of course with an additional bridge rectifier and a couple of capacitors. Have a look: http://www.arenddeboer.com/bike-mounted-usb-charger/

[Stubloke]

Hiya, i want to replicate this circuit for use on my bike, but im a bit confused. The step by step instructions mention components that are not on the circuit diagram, and also the circuit diagram doesnt show the ultracapacitor on it. Could you just clarify what components are needed in your circuit (not the mintyboost circuit). By the way im going to be using the mintyboost v2.0.

Any help would be much appreciated.

Thanks in advance

[jevoncarlson]

The supercap post ride charge is a fun idea but who would actually leave their ipod on their bike while not riding? security issues.

[Algag]

 if you are talking about how it charges even if you are not moving thats so if you are stopped it still charges, not to leave it on there when you are done

[gamal kotp]

i am habye thank fo all

[jenninstructables]

I've got the added task of recifying the output of the source, as it's actually an AC alternator, as opposed to a DC generator, or dynamo - which seems to be the subject of this instructable.

At least a couple of companies (Shimano being one of them) make these alternators which are built into the hub of the front wheel. Mine puts out a fairly steady 6vac at speed, but is slews to 0v at stop.

Has anyone addressed this previously?

[jenninstructables]

.... this supercap is hard to find... does anyone know of a source that will sell ONE ultracap at a time?

[harpleblues]

 I found the capcitor available in quantites of one at www.tecategroup.com/store/index.php

[jenninstructables]

man... SO long it took me to locate these

BCAP0150 - 150F ultra-capacitor Mouser Electronics - yay!

i'll post more later.

[dirty_valentine]

I really like this instructable, but the circuit is not optimal. Stepping down from 6V to 2.5V with a linear regulator such as the LM338 is inefficient. In this case only about 42% of the power from the generator will make it to the Minty Boost circuit. The Boost circuit will have further losses lowering the efficiency down even more. The circuit will no doubt work but it is not optimal.

If the generator really puts out 6V, then a simple 5V output Low Drop-Out (LDO) regulator such as the Linear Technology LT1963A (http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1040,C1055,P1879) could be used to drive pin 1 of the USB directly. In this case about 83% of the generator power would make it to USB device. The USB device would charge twice as fast, and the circuit cost and complexity is significantly reduced.

If the generator typically puts out less than 5V under load, a 5V output Buck-Boost converter could be used. This would provide for further efficiency improvement. I don't feel the added complexity and cost is justified if the generator can put out more than 5V under load though.

[rpvanpatt]

 I actually was thinking the same type of thing, but i am a newbie with all this stuff, I was wondering if a capacitor would be good tho, so that if the bike comes to a stop, the charging wont stop, i feel like that may hurt the battery to stop and go, is it?

[dirty_valentine]

I=C*dV/dt is the equation for a capacitor where I=current, C=capacitance and dV/dt is the change in voltage with time. rearranging the equation you get: C=I*dt/dV. If you are riding along and getting 6V out of the generator then suddenly stop, your capacitor will be charged to 6V. If a linear regulator is used as I suggested above It will start dropping out around 5V, and most LiIon chargers will stop charging around 4V. Thus best case you can only discharge the input capacitor from 6V to 4V (dV=2V). As for dt, that depends on how long you plan to be stopped. Lets assume you want to stop for 10seconds (dt=10s). Most LiIon chargers charge at 100mA or 500mA. I'll assume the best case (I=100mA). With this information we can figure out what size cap we need: C=100mA*10s/2V=0.5F. 0.5F is a REALLY big cap and would only buy you a best case stopping time of 10seconds.

Most likely any hand held electronics you buy today (cell phone, media player, etc) will have a LiIon type battery. LiIon batteries do not like to be overcharged. If overcharged they will start to loose capacity (best case) or can even burst into flames (worst case). The good news is that most quality electronics have built in protection circuitry that keep from overcharging the battery. I have not heard of any issues with starting and stopping charging. In fact some quality chargers do just that to measure the Equivelant Series Resistance (ESR) of the battery during the charging process.  Hope that helps. 

[rpvanpatt]

 thanks for the help...another idea...  if you havent already seen the 'contactless dynamo' bike light instructable, I was wondering if it would be possible to use that idea and your info to create a USB charger instead of with a motor...im not sure how much output voltage the contactless magent generator creates though, but I think this would be a better idea

[dirty_valentine]

Contactless induction can certainly be made to work. There are a lot of variables and I do not have much experience with this type of generator so I am not sure if the 'contactless dynamo' instructable will work in this application. My feeling is that the magnets turning at the rate of the wheel will be too slow and too far away from the coils to generate enough power.  FYI - it is really power that you are interested in and not voltage. My guess is that the peak voltage is probably high enough open circuit, but as soon as a load is applied (i.e. while charging) the voltage will collapse and charging will stop. To really make this work you will probably need an inductorless motor geared up off the wheel or chain to produce enough power to sustain charging.

[rpvanpatt]

gotcha...would they be good with just led lights tho? and maybe a stepper motor to charge?

[dirty_valentine]

Not sure, as I said I do not have much experience with generators, just a basic understanding of how they work. You would have to experiment or seek out knowledge elsewhere. Good luck.

[Ohnanka]

Yey, constructive criticism! : ) would've been nice to have some from ac-dc.

[Water Child]

I love this instructable, most likely ill be using it for life, anyway would it be illegal if i could use this fro my science fair project? there are no winners and no prizes its an elementary science fair for energy and i really lik this idea, i am a polite kid os i have to ask for your permission

[advante]

It's hard to find the materials in this country which is one of ASEAN countries.
Cause I lived in Indonesia... If I go to an electronic markets where the items are in so many kinds, the electronic stores are traditional electronic stores (dirty, old building, simple). It sells LEDs, Voltage stabilizer, UPS, antenna, audio devices (not exclusive), transistors, transformator, etc.

[advante]

I need 4.9 volt for my Sony Ericsson phone. Does it matter if over-voltage 0.1 volt? Cause 0.1 volt is matter for computer's processor. Please give a reply on [e-mail]

[Jodex]

You CAN always charge with a lot higher voltage than your battery needs. BUT if you use enough big voltage your battery MAY explode. But couple of volts doesn't matter.. Except LiPos may be bit different.. Sorry for the words written with BIG letters : D

[jules15]

no man, thats fine

[ctonks]

How do you handle surplus power?

[name101]

That's What the 140F capacitor was used for. In the graph explains that the surplus power is stored in the Ultra capacitor ~Name101

[ac-dc]

Such a capacitor would store power, but will not "handle" surplus. When the load current drops the input voltage will rise and the linear regulator will be dropping more voltage, resulting in a higher heat level. You'd need far more than a capacitor to store the energy, something like a battery of a capacity high enough that it never reaches full charge, and yet this would be an additional drag on the bike, it should not be used because the whole circuit is wrong in the first place.