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  #1  
Old 04-21-2008, 04:26 AM
arthur92710 arthur92710 is offline
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Default Strange phenomanon with wind turbine!

So for my school science fair I decided to make a Savonius wind turbine. It works alright I would say, it out puts a measly 2vac when you spin it full speed with a hair dryer. It is enough to light an led. But I accidentally noticed something strange. Normally the led would light at 1.2vac but if you short the led with a drill bit the led needs alot less voltage to light, about .1vac.
If the bit is stationary the led wont light but if you move it around and spin the turbine with your fingers it will light.

What could this be?
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Old 04-21-2008, 04:49 AM
jpanhalt jpanhalt is online now
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First guess: you are interrupting the voltage with the drill as a short circuit. Visual persistence makes the LED look to be continuously on, but it really isn't. Your voltmeter works differently and does not respond quickly to the on periods, so it reads a lower voltage. Simply put, the LED is responding to the peaks, the voltmeter to the valleys, and your eyes can't tell the difference.

John
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Old 04-22-2008, 12:15 AM
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mik3 mik3 is offline
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Quote:
Originally Posted by arthur92710 View Post
So for my school science fair I decided to make a Savonius wind turbine. It works alright I would say, it out puts a measly 2vac when you spin it full speed with a hair dryer. It is enough to light an led. But I accidentally noticed something strange. Normally the led would light at 1.2vac but if you short the led with a drill bit the led needs alot less voltage to light, about .1vac.
If the bit is stationary the led wont light but if you move it around and spin the turbine with your fingers it will light.

What could this be?
When you spin the bit you short and unshort the led so the led lights only when it is unshorted. Also the voltmeter measures RMS values and not peak values. So the RMS value of the short time the led is not shorted is 0.1 V (the voltmeter calculates the RMS by taking into account this voltage spikes) rather than 2 V when you dont short it with the bit and the voltmeter calculates the RMS by using all the continues AC voltage.
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Old 04-22-2008, 07:48 PM
arthur92710 arthur92710 is offline
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what can I do that will make the led light at lower voltages, with out the drill bit?
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Old 04-22-2008, 09:35 PM
jpanhalt jpanhalt is online now
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I don't think you can make the LED light with less voltage directly. Its voltage is determined by physics. However, you can make a simple amplifier that will allow much less voltage to be amplified and make it light. Here is a simple schematic. I picked a 9V battery, as they are common. You can use other batteries, but will need to adjust the size of the resistor so as to not destroy the lED. I assumed you had something like a 1.2 V/10mA LED. In any event, you can play with the resistor and battery values to see what works.

John

Last edited by jpanhalt; 03-05-2011 at 11:31 PM.
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Old 04-22-2008, 10:09 PM
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kubeek kubeek is online now
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Ive seen somewhere an oscillator or maybe it was more like switched boost converter, with one or two transistors, which powered a led from 1.2V battery.
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