I'm trying to make my own simple magnet generator project Like these: http://amasci.com/amateur/coilgen.html http://www.wikihow.com/Make-a-Simple-Electric-Generator with the following materials: 2 1.5X1.5X1/8" square magnets https://www.amazon.com/gp/product/B011FNB7WK?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00 Copper wire (gauge shouldn't matter right?) https://www.amazon.com/gp/product/B007TUQW1K?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00 Blue LED (that requires 3-4.5 volts) https://www.amazon.com/gp/product/B004UZCADG?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00 I have a small cardboard box with no bottom or top. Inside is a magnet connected to a rod that sticks out of the box. I can turn the rod to spin the magnet. I wrapped the copper wire around the box and will attach the ends to a light bulb. Assuming this works (and if you believe I am missing something please do tell), I can spin the magnet to induce a current in the coil and to the light bulb, thus powering a light bulb without a battery. My question is, how do I know how many turns/wrapping of copper wire around the box I need? I don't have a voltmeter and the copper wire is thin like human hair, so I might accidentally rip the wire if I take off the insulating material for testing. In other words, I only have one try to figure out how many times I need to wrap the wire and make it so it can supply 3-4.5 volts. I attempted using Faraday's law: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html Voltage = - (Number of turns)(Change in Magnetic Flux over time) or Voltage = -(Number of turns)(Magnetic Field Strength)(Surface Area of Magnet)/ (time) I used an app on my phone to get a general idea of the magnetic field (it read 200 micro teslas). B = 200 * 10^-6 Teslas Magnet surface area is 1.5X1.5" so in meters is: 0.0381 ^2 meters or 0.00145161 square meters A = 0.00145161 m^2 Voltage needed = 4.5 Volts Time = I felt this would be an arbitrary number, but would be in the range of 2 - 10 seconds. I wouldn't want to spin the magnet forever. So N (number of turns) should equal to = Volts * time / B*A = 4.5 Volts * 10s / 200*10^-6 Teslas * 0.00145161 m^2 = 155000310.001 I'm really hoping I made a mistake. Please help me figure this out. Thank you!