My cycle dynamo USB charger - design and principle

Much awaited dream of getting my own mountain bike becomes true last month. :) Last month I bought KHS Alite 500, 2012 model from Pedals and Wheels Malleshwaram. Odo reads around 300 Kms and am loving the rides! First I fell in love with Bullet, then I fell in love with Biking as its even more adventurous and fun. A lot of people get this silly idea in their minds that he is doing a vain attempt to save environment, some say he is over-doing a workout and getting thinner, some even kindle the way I look wearing my cycling attire. But I don't care for what people think because more than all that stuff, I bike just for my own enjoyment :)

Coming back to my original title - USB charger using cycle dynamo. This was my last weekend's plan which I got executed this whole week. My room had become a electronics workshop for a while with smell of burnt solder and also a generator room with the sounds of dragging dynamo over the tire treads. I burned a little of  midnight oil during weekdays in completing this project.

The basic drive for coming up with this charger is to charge my Phone/Camera/GPS device on long touring.
All feature-rich-smartphones have got a weak battery life. Mine is Motorola Defy BF5X 3.7V, 1500mAh which lasts for about max 2 days with CPU underclocking governors of 300MHz and 600MHz in action!

Recently bought a MINI DVR 80, sports camera to shoot my biking adventures which will now be usable if have a all-time-charger on the go!


Having worked on basics of 12V electricals in Bullet it was a pretty easy job to design battery charger for my cycle dynamo. Principles involved are the same and anyone can design it in minutes if you had attended your high school class about non-linear circuits.

AC supply from dynamo -> Full wave rectified (double the AC frequency, using 4 diode bridge-rectifier) pulsating DC -> Apply a capacitor as filter to smoothen out the DC output -> Limit the current by a shunt resistor (simplest electric ballast) -> Regulate the fluctuating DC by putting a IC regulator to appropriate voltage (IC78XX series).

This simple circuit below will explain a lot more:

> The output current varies from 0-1A based on the speeds of the cycling. IC7805 starts to give the output at speeds of 6-7Kmph as the input unregulated DC supply should be more than 8V for IC7805 to kick off.

> The power of dynamo itself restricts the capacity of current it can drive to the IC and thus a decent shunt resistor of rated around 2-3W should be sufficient.

> Capacitor could be more better if its rating is something like 25V, 0.1F. More-the-better. Will hold more charge and thus keeps charging for a while even though you stop for a while during the ride.

> This is not a very efficient circuit but just works for me. I saw better designs on web doing similar stuff. Output current should be ideally 1/10th the Ah rating of the battery being charged from the USB, as there will be chances of over charging and also lessens the life of rechargeable Li-ion batteries. You will need to add voltage comparator and make current trickle when fully charged. Then circuit becomes more complex. But to avoid this I usually connect the USB output to a portable battery power which has got protection inbuilt to cut-off the supply when its fully charged. (Note that, this portable battery power can be charged by other power outlets as well)

Further upgrades would be to put a high rated capacitor like 1F and put some 3W LED lighting for the front and the rear which could lessen the value of current limiting resistor.

Things you need:
1. I found the circuit of full wave bridge rectifier in a damaged wall charger adaptor unit of my WIFI modem at home. It had real good diodes IN5400 which can rectify upto 50V, 3A. A cycle dynamo can never reach that power rating to burn them!
2. Regulator IC costs some 8 Bucks (Courtesy: Famous SP road of Bangalore)/ Or you can find it in some old radios/ Or go to local TV repair shop.
3. Most important of all! Bottle dynamo, Just the generator coil with strong neodymium magnet will cost INR 80. (Hub dynamos will be better as there wont be drag/tire wear)
4. A USB Type A socket (Female pin). (A cheap USB adapter cable which was unused at home)
5. Soldering gun + solder paste + solder wire. (You can get soldering done in nearby electric shop if you are not good at working with PCB)
6. Insulated wires (About 2 meters)
7. A Heatsink(+ metal paste) for regulator. I made my own heatsink with several folds of Aluminium foil as the power dissipation will be less if cycling speeds are around than 20kmph ;) And I don't expect to reach constant speeds of 40kmph during touring.
8. Alligator clips for clamping at the dynamo output terminals. (I use them as its flexible for removal. Saddle bag can hold all of the charger circuit when I want to remove)
9. A digital multimeter to verify that circuit is behaving as expected. (An oscilloscope would be better to view it graphically :P)

With an overall cost of around INR 250 anyone can build this circuit.

Even Nokia has come up with bicycle charger kit but at a whooping cost of INR 1500!!
http://thegadgetfan.com/gadgets/nokia-dc-14-bicycle-charger-now-available.html

http://europe.nokia.com/find-products/accessories/all-accessories/power/chargers/nokia-bicycle-charger-kit/specifications

Some pics of my project:

Final housing of all wiring with charger inside saddle bag.

Had kept my cycle upside down for Pedalling, thus the dynamo reversed!

In my first attempt heat sink was bigger than PCB :P

Rectifier circuit

Constant voltage output of regulator with any output load

Avg output current, 440 mA

USB adaptor PIN

My funny packaging in a organic tea box :P

I shall call this device as Organic USB Charger to Go Green :)

Charging in action, Device getting charged while pedaling

Housing of all cables below the seat.

With just about 20 Mins of cycling at 15kmph you could easily recharge the phone for about 30 mins of talk time / 20 hours of standby time! You can disengage the dynamo from wheel by pulling and pushing a lever when you want to stop charging.

Disadvantages:
1. Drag when the dynamo is in action. (Quite a humming sound at rear which makes the nearby street dogs chase you at times! :P)
2. Tyre wear (I don't think much as MTB tyres are built for more worse terrain)
3. Weight of dynamo (around 200 gms). Wont be much of effort to pull that weight along on an Aluminum frame bike.

Gurubhyo namah!

Lots of people have touched my life without whom I wouldn't be in exactly in the same position as now I am in this society. I call all of them as gurus because they have taught me how to have a living.

To start with as one of the Sanskrit sloka says "Maathrubyo namah, Pitrubhyo namah, Archaryebhyo namah", parents are the first gurus who have taught us how to behave and respect others. Some qualities come from genes and some are cultivated in us when we are young which of-course don't remember now.

The third and most important of all the "gurus" is the acharya, or the teacher. A teacher is a person who comes in many forms. Most of us having not studied in "gurukul" system of study we never have opportunity to see the guru-shishya(teacher-student) relationship. Having studied in convents where medium of instructions were in English no wonder we even ever heard of gurukul way of earning knowledge.

But, in-spite of saying the above I have seen few teachers in my schooling days who really inspire students to get motivated to do things on their own. I would like to dedicate this post to all those Archaryas.

First of all I would like to credit my primary school teacher, Mrs. Mythili, who taught me basics of math without which I wouldn't be good at quantitative aptitude and not even close to studying computer science.

Secondly, I am grateful to my language teachers(English and Kannada) at high school who developed my interest in books and literature without which my grammar would be so bad that you couldn't have even made out what I have written in this post. (First of all I would have not dared to write any :P)

Thirdly, the credit goes to lots of books which provided me knowledge, taught me different words and there usage increasing my vocabulary day-by-day.

Fourth, My favorite lecturers of all time... Awesome foursome.. Mr. Gururaj sir, Mr. Divakar Bhat, Mr. M N Laxman, Mr. Sheshachalam (Who took majors PCMB, in order) Who made me burn the night oil and churn out my best in the entrance exams for Engineering without which I wouldn't have secured ranking of 176 in Karnataka, Common entrance test.

I appreciate the friendly lecturers at graduation who exactly knew our brilliant capability to perform in tests and allowed us to be free during class hours.. helping us to prepare for CAT, GATE and other entrance exams for Masters. One of whom I remember the most is Mrs. Padmashri madam, who stressed the importance of practical learning and application than theoretical study for the sake of exams.

I would like to remember external guide at HP internship, Mr. Shyam, for providing me with a fair project for university and an insight to the industry.

But the learning doesn't stop after coming out of University courses! We are all "learners for life". Coming to the industry self-learning and sharing of knowledge was the need. Interacting with the senior most guys and getting to know what exactly we are in need of is been really challenging till-date because information is so cluttered among lots of people I find but no proper way it is put to communicate to a "new fish"! Knowledge is the motive to survive too in this industry for quite a long time till you get out-dated or technology is super upgraded! I thank all my colleagues and team leads for sharing valuable information and making my work easier, faster and me smarter ;)

I have great regards to my flute teacher for whatever minute drop of knowledge that I have in the ocean of Swaras!

Of-late I got to know a lot of things about my bullet due to my mechanic, Mr. Nandan, a skilled worker and well educated about the classic machine who even showed me machine drawings of fork suspension and explained why diesel engines are not good in bikes for the Madras IITian, who visited the workshop when I was getting my bike serviced. I am amazed at his dedication!

There are always other kinds of gurus whom you don't recognize as you take them for granted when it comes to learning from them. They are called "friends" :)
I wouldn't like to mention names here as it wouldn't be possible to mention them all in the post. But each of the wonderful kinship have a nice story behind them. It is like you explore yourself being in the company of others who think exactly alike as you do! Not surprising many of us have friends more of our age-group and that makes us feel secure and share our deepest feelings and inner thoughts which we wouldn't even share with some of our family members. We try to find qualities like trust, affection being close to someone as we always seek out for that someone who gives some nice company to fight against boredom, protection like elder brother, the care of a mother, being as respectable as a father, as kiddish as always torturing younger sibling (though we enjoy it within).

There are lots to learn even from you partner in a relationship about love, commitment and also from your kids who will have more IQ than what you had at their age!!!

Thanks for all those who have influenced my life in a positive way and I wish to see lot more gurus in life.
The fear(of vastness to learn), vinaya(Not being boastful) and bhakti(respect for guru's knowledge) are the most desirable qualities of a student no matter what he learns from his teacher.
Let me get back to learning! ;)
Adios!

Its hard to become a literate! but not impossible.

"The Illiterate of the 21st century will not be those who cannot read and write but those who cannot learn, unlearn and relearn"
-Alvin Toffler
I read this quote some time back and I still can't get it off my head as it made me really think a lot.

In this ever-new technological era, it seems to be so true. It is only the knowledge/innovation that keeps the people/industry moving ahead.

As a Software Engineer, I was wondering how does it apply to me! and without any surprise I realized that it impacts me, a very big time. In this time of recession with all the job cuts, only the really "talented literates" can survive in an industry.

The next question that I raised to myself was.. Am I one of them? I'm not productive yet at the new Co and I am very much in probation. I need to redeem myself that I am worthy for the given position. Of-course they saw something within me when they took the interviews and So its all up-to me to prove my ability.

Ramp-up in new technology domain, I feel like a child learning how to relate things to his previous experiences and coming to an understanding, though it may be wrong from its perception! (You can't teach a child about hotness of a flame until he himself experiences it!) Learning very new thing is something easier compared to unlearning deformed concepts in your mind. Really it is hard to unlearn something you strongly believe in and change it. All our learning is based on some rules. We create a map/network of ideas starting from accepted facts/axioms. Unknowingly this network becomes so huge that our brain cells gets so much wired-up and the rewiring takes its own toll!

Knowing half is more dangerous than knowing nothing. This is exactly what the current universities has done to many pathetic students. All the special thanks to my curricular books at university which taught me nothing practical about current technology! All the syllabus books start with organization of PC, 8085, then x86! learn basics of C, partial knowledge of system software and that's it.. I ended up in such a great position that I was no special to a graduate who passed out 10 years back!

Now having learnt everything the hard way, I refer to standards, specifications and Google/Wiki out latest information and that's the only way to get knowledge of current technology.
"Be flexible in process of being cognitive"