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

[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.

[BC-45]

would a 3000 farad cap work?

[PCfreak]

7.2v RC Battery is Lightweight and ive used one in many applications

[name101]

The way I see this design, The Supercapacitor was not meant to store "Large" amounts of energy but enough to keep the power consistent if the rider was to slow down or stop for a short period of time.. I agree a battery would be able to store a lot more energy than a Capacitor. but the capacitor is short term. Correct me if I'm wrong. ~Name101

[ac-dc]

Of course, a supercap is short term. The problem is, a supercap doesn't have enough capacity to *buffer* for regular riding. That means that once the supercap is charged the voltage in the system rises and creates even more heat and loss with the linear regulator.

Let me put it another way. I don't revel in wasting energy but it's not so much a concern when something is AC wall powered. When you are peddling on the other hand, and a design has multiple forms of loss, energy conservation is really good, worth the time to do it right.

The problem was they didn't look at how to get from point A to point B, point A being a human being producing linear movement of a wheel, and point B, producing the desired charge, then finding the best way to get there.

Instead, they reused a design not just suboptimal for the purpose but contraindicated for the input and output.

The way this is set up it would be far better to just strap a battery pack onto a bike to recharge something, or of course to use a proper bike generator, a switching supply circuit that accepts (uses) input over the voltage variations that result from a bike generator, and and output with current regulation and the associated charge control chip complimentary to the battery type being recharged.

I appreciate this is beyond the ability of someone starting out, but at the same time this is what is great about technology today that we have ready-made ICs to do things difficult or lengthly to do with discrete parts. It is good to experiment but it is also good to see when it is redundant work, that each part of the problem can be seen modularly as how to get from point A to point B and that today we have great custom ICs to do these jobs (since when broken down into units, none of the things being done are new electronically).

I think it's great if they had no hands-on experience, to learn from building something like this, BUT to put it out there for others as an example of how to get something done, it is a poor one.

[name101]

Well Personally am new to electronics.

I see that stepping down then stepping the voltage up again is a waste of energy. but when the power supply is so close to a LDO linear regulator I thought Providing consistent energy would be a problem.

You said "supercap is charged the voltage in the system rises and creates even more heat and loss with the linear regulator."

How is this so? I would like to learn from this experience.

I would like to learn how to make this as efficient as possible.

(I'm sorry about the short comment I wrote a big one but pressed cancel instead of post =( )

~Regards
Name101

[ac-dc]

To make it as efficient as possible, to start you would approximate an efficiency, perhaps 80% pulling numbers out of air. Next determine the required charge current for the device, and divide that by 80% or 0.8. Next determine the minimum dropout voltage for the regulation stage, some working familiarity with switching regulator designs helps a lot here, but just to pick a number a run with it until something more is known experimentally let's say 3V dropout across regulation stage. With this much info we know the minimum output voltage a generator will need, and can begin testing generators loaded to the desired output power (current times pre-dropout voltage) to see if they are sufficient. Once one at least capable of this output power is selected, the max and minimum voltage during riding with it powering the same load level will tell us the voltage range the switching subcircuit will have to accept. Next go to a website like Digikey if you don't have a regulation controller in mind yet. Browse through their offerings for a regulation chip capable of the input voltage variations and either fixed output for the device charging, or variable output with components you add to select the target voltage. Study the regulators example datasheet circuits as they provide the basic topology as well as reading any datasheet notes about precautions and requirements for it's rated functionality. Then you are ready to convert a rough sketch of circuit logic blocks into a schematic of electronic component values, and generate a PCB layout. Prior to that you probably also want to have selected a chassis for the circuit board, a vibration resistant mounting, and have therefore determined the dimensions of the PCB and keep-out zones for mounting hardware so you can plan the circuit layout around these dimensions. Obviously there's a bit more to it than described, but it is a start.

[ac-dc]

With a variable input voltage (6V is not constant) an LDO will be a problem, but even if kept above the LDO regulated voltage it's still a very lossy circuit. With the supercap you are improving charging, but putting more drag on the rider to generate that charge, and by keeping the voltage higher it is continual drag instead of the voltage being allowed to drop below the critical level needed to power the rest of the circuit so the rider has no moments of relief. So it does improve the circuit but it does not meet a different goal in use on a bicycle, plus it adds a lot of weight. With a battery on the other hand, or really I mean a pack of series cells, they serve as a crude but effective enough form of regulation to keep the voltage at roughly the sum of the cells. There is some loss in doing this too, but not as much as use of an LDO. One thing that is not really clear is why either would be needed, charging doesn't have to continue at all moments necessarily. It could be good to even tweak the circuit such that applying the brakes bypasses a current limiter right after the motor so that during braking a higher % of power is produced and more motor drag, then less when not, but it would be a secondary issue, the primary one being that the better solution is none of these supercaps or batteries, to just use a wide input voltage, regulated output switching circuit. I'm not suggesting no capacitors are needed for that, but rather less capacitance, a smaller design with only the parts the regulation stage needs, also built more rugged (leaded parts like capactors don't like vibration much as you'd see on a bike, you can cement/glue/etc them in place or you can pick parts more immune to the environment).

[name101]

Personally. I want to charge my device a constant as possible(GPS device). Once the Supercap is fully charged the Circuit will only draw the current needed to maintain the charge on the device. Correct? When I was doing the Research with my basic knowledge Something similar to this was perfect. I was aware of the energy loss through heat and converting the voltages 2 times is excess but the way I saw it was the voltages(form power source to USB device) are too close to use the LDO linear regulator. IF the hub generator produced 12v for example having a single Linear regulator would be perfect. Simplifying the circuit drastically. If the supercap was replaced with a battery pack for example would the circuit charge the batteries and would the batteries act like a capacitor? From my understanding capacitors have the advantage of being able to charge or discharge incredibly fast while if a battery had the same current draw the battery it self would be damaged. I completely forgot about the environment with my research. I must thank you so much with helping me here. ~Name101

[ac-dc]

The generator voltage is not "close" to the LDO regulator necessarily, it depends on the load on it and of course gearing or friction wheel diameter, how fast it is spinning. A genuine 6V bike dynamo goes quite a bit above and below 6V even being designed for the task. That's why it's normally it's normally rated for wattage like 6W or 12W. I'm not saying it's terribly bad to have the supercap except it puts more drag on the bike at the worst possible time, getting started from a dead stop after having discharged. A constant charge isn't really needed, you only need to limit the max voltage and current within what the battery will accept. For example, suppose 20% of the time it wasn't charging, but the rest of the time it was charging at a high enough rate to compensate. The point that I'm attempting to keep drifting back towards is this needs to be seen as an accessory to bicycling, not the primary detail that matters so much as what factors are present while riding. Yes the batteries would charge like a capacitor, the point would mainly be that you can either: A) Have already charged them before the bike ride so they are a renewable portable power pack. B) Shut off the charging circuit before it drains them too much, then turn on again after having gotten up to speed so they aren't putting a high early drag on acceleration. You really don't want a linear regulator, not even an LDO. The voltage from a motor varies quite a lot, to always have it charging you will have to use something larger and create a great deal of heat as well as extra drag riding. The only way to have a small drop before the linear regulator is if you already had a wide input range switching regulator, but if you did then you wouldn't need the linear regulation stage at all. I have already outlined a much better way to do it, for good reason, that it should not be done a different way for bike powered use.

[name101]

Oh. I'm starting to understand. Haha. I suppose I'll keep this in mind when I'm designing future circuits. I did throw myself into the deep end by starting with this projects with very little prior knowledge. Ill Look into what I can do.

Seriously, Thank you so much. =]

~Regards
Name101

[mulan2015]

i'm curious to why the strap on shake-charger (original idea) didnt work?
Any help apprciated
thnx

[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

[thegriffy100]

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?