I teach 6th grade physical science. My electronics knowledge is limited. I have a bike powered generator from windstream power, and I have it hooked up to a board with light sockets so students can feel the difference between different kinds of bulbs. The students easily generate 120 volts, and can sustain .5 amps to power 60 watts of bulbs.
Problem one: I'd like to be able to have LED bulbs in the mix (Philips 12.5 watt, 110 volt edison base), but the voltage is too unpredictable. My understanding is that fluctuating voltage will damage them. The generator is capable of producing 150+ volts. Am I looking for a voltage regulator? Does it need to regulate minimum and maximum?
I also have a battery pack with an inverter from the same company, but it's giving me problems and I'd rather dispense with the battery altogether. I don't want to deal with the maintenance issues, and the battery seems to make it harder for the students to understand the whole system.
Problem two: What's the best way to build an array of LED lights that could be run continuously off of the generator. I'd like to have enough storage (in a capacitor maybe?) that the lights would stay on for a few seconds while one student gets off the bike and another gets on. I'd rather not have a battery. The purpose of this is to "light" the room for a day while teaching about other subjects. I put that in quotes because 60 watts of even the most efficient LED's is a little dim for my classroom. The lesson for the kids is to gain an awareness of how much power we're consuming regularly. I can't use incandescents for this purpose because my room has no windows and it would be too dark. I'm looking for bright white LED's as the most efficient lighting source. The reason I'd like to have the lights stay on while the students switch on and off the bike is because otherwise it will be too dark in the room.
Best Answer
For Problem 1:
A string of LEDs hooked up in series with a current regulator like SuperTex CL220 would do the trick: The component is a simple a 2-terminal device (like a diode) and needs no additional components or configuration. It allows 20 mA (+/-10%) current to pass through as long as there is sufficient voltage headroom: 5 volts above the total forward voltage of the LEDs is sufficient. This current regulation is stable up to 160 volts, enough for your purposes.
Note that LEDs are current-dependent rather than voltage dependent devices. They glow at essentially the same brightness as long as the current is constant.
For your application, if the LEDs need to start glowing from around 60 Volts, half the 120 Volts your students generate, then a string of 25-30 standard 5-mm red LEDs would be optimal. They would glow without intensity change till your maximum voltage.
Too many LEDs = they won't glow till a higher voltage.
Too few LEDs = the CL220 device would overheat in dissipating the surplus voltage.
For Problem 2: The extent of energy storage required to keep a string of around 25 LEDs (from above section) glowing for even half a minute, is pretty high. Capacitors would not be the way to go, unless you have access to big power-line capacitors through surplus channels.
I hope this helped.