Background/Tutorial/FAQ/Refrences

Background Information:
        An AC generator consists essentially of a long loop of wire called an armature that rotates between the poles of a magnet. The armature is rotated between the poles by the shaft of a fuel powered engine. As the armature rotates it cuts through the magnetic field that exists between the poles of the magnet, thus inducing a current of electricity in the armature. The armature supplies current to an external circuit through slip rings and brushes. DC generators operate according to the same electromagnetic principals as the AC generator. The major difference between the two is the way in which the induced electromotive force is collected and transferred to an external circuit. Our design consists of a AC current, generated by the magnet moving up and down inside a tube. A copper coil is attached to outside of the tube, to pick up the change in the magnetic field and generate charge. The charge is led from the coil into a rectifier. The rectifier converts the raw AC current into a manageable DC current. From there it travels into a capacitor to provide a constant flow into rechargeable batteries. A USB adapter is connected to the batteries with a switch in the middle to prevent constant energy drain.

Tutorials:

E-How's DIY Induction Powered Shake Flashlight
       This tutorial porivdes the basic foundation of generating and storing electricity using a coil and a magnet. It helped us identify the fundamental principals of electromagntism and figure out components needed to build our own source of electricity.
http://www.ehow.com/way_5371860_diy-shake-flashlight.html

 Laser Pointer Forum's DIY Solar Cell Phone Charger
      The tutorial posted in the forum below basically creates a solar powered cell phone charger and describes the components needed to make one. Our inspiration fro this project came from this tutorial however, we decided to use current generated by induction to charge the phone unlike the forum poster who uses solar energy.
http://laserpointerforums.com/f60/diy-10-solar-cell-phone-charger-76550.html

FAQ:

Q.1 How to convert from AC to DC?

First, the AC input voltage should be determined what it is. Second, find the needed amperage and voltage to power the components of the device. After that, a transformer should be used to step down the output from high-voltage AC to low-voltage AC. Then, a rectifier should be used so that the low-voltage AC could run through it. After that,  a large electrolytic capacitor should be used too to smooth out the voltage. Finally, pass the output of the smoother through a regulator. 

For the purposes of this project, a bridge rectifier was constructed. Here is a detailed video about constructing a bridge rectifier. 

         

Q.2 How to charge a pair of NiMH batteries?

          In order to charge a pair of NiMH batteries, a current of C/10 is needed where C is the battery's capacitance. A current that is at least 10% of the battery's capacitance is needed to start charging a battery. For example, a 2000 mAH battery would need a current of 200 mAH over a period of 10-15 hours in order to become charged. To preserve battery life, make sure to not to overcharge the batteries for a period longer than 10-15 hours.

Q.3 Does "sticking" magnets together increase their strength?

       Different magnets behave with different results. Some magnets double their pull strength, some increase it by a factor, others don't at all. Neodymium magnets increase their strength most efficiently when you attach the opposite forces forcefully.

Q.4 Why use rechargable batteries instead of capacitors; don’t they do the same thing?

                  While it is true that both capacitors and batteries are used to store charge, and both are certainly capable of charging a cellphone in a DC circuit, there are benefits that each one provides that the other does not.

                  Capacitors are comprised of two plates separated by a small distance with an insulating material between the plates known as a dielectric. The capacitance of a capacitor is its ability to store charge, which is directly related to the potential difference between the plates by the following equation:

 where Q is the charge stored in the plates and V is the potential difference across the plates. The capacitance itself, C, can be found by using the following equation

Where κ is the dielectric constant of the material between the plates, ε is the permittivity of free space, A is the area of each plate, and d is the distance between the plates. Increasing the area of each plate, decreasing the distance between the plates, or using a material with a higher dielectric constant can increase the capacitance of the capacitor, allowing it to store more charge.

                  Like capacitors, batteries are used to store charge to be used. Batteries, unlike capacitors, can store much more charge at the cost of a slower discharge rate. In our application, the ability to store charge is significantly more valuable than the ability to transfer it quickly, especially given the fact that we only require .5A of current to charge a smartphone.

Refrences:

-http://www.iphoneforums.net/forum/iphone-help-15/how-many-amps-necessary-charge-4s-26319/
-http://en.wikipedia.org/wiki/Neodymium_magnet

- http://www.ehow.com/way_5371860_diy-shake-flashlight.html

- http://laserpointerforums.com/f60/diy-10-solar-cell-phone-charger-76550.html

- http://www.china-magnet.net/info/2011-6-23/stacking-magnets_1.html

- http://www.wikihow.com/Convert-AC-to-DC

-http://www.candlepowerforums.com/vb/showthread.php?103675-NiMh-batteries-maximum-charge-voltage

-https://discussions.apple.com/docs/DOC-3511

- http://physics.bu.edu/~duffy/py106/Capacitors.html

- http://www.youtube.com/watch?v=O6_mFyDh8Z8

- http://www.youtube.com/watch?v=S0wbEl7caTY