Home-made AC-generator

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  • #1
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I have tried to make an AC-generator to create a voltage over an LED. The circuit diagram can be seen in the attached figure. It consists of four coils attached in series and a rotating magnet in the middle. I first tried with only two of the coils on either sides of the magnet, and got 1 volt. I then tried adding the other two coils and also got 1 volt, but I need at least 2 volts to make the LED work. I suspect this was caused by a phase shift of the voltage of the two other coils, which gives 0 volts when the first two give 1 volts.

I suspect that adding a capacitor should make a phase shift and add the voltages from both pairs of coils so I can get 2 volts. I am just woundering if I am going in the right track. Will adding a capacitor as indicated in the circuit diagram give me the result I want of giving the same phase to both pairs of coils?
 

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  • #2
hutchphd
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For the time being stay with two coils and no capacitor. With a strong (rare-earth) magnet you should have no trouble lighting the LED. Do your coils have an iron core? They should Series is correct but all the turns should be in the same direction when you connect the two.coils. It should work fine. If not we will need detailed info.
 
  • #3
Baluncore
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You should put a reversed power diode in parallel with the LED to limit the reverse voltage across the LED. Take a look at the reverse voltage specification for the LED you are using.
 
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  • #4
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For the time being stay with two coils and no capacitor. With a strong (rare-earth) magnet you should have no trouble lighting the LED. Do your coils have an iron core? They should Series is correct but all the turns should be in the same direction when you connect the two.coils. It should work fine. If not we will need detailed info.
No I don't have access to any iron core. Maybe that would do the trick.

As mentioned earlier, I only get 1 volt when trying with only the two coils. I can't make them larger because they won't fit in the required space, that is why I'm using four coils instead.

But theoretically speaking, could the construction with the capacitor work?
 
  • #5
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You should put a reversed power diode in parallel with the LED to limit the reverse voltage across the LED. Take a look at the reverse voltage specification for the LED you are using.
I don't think that is a problem since I don't get a high enough voltage to break the diod.
 
  • #6
Baluncore
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No I don't have access to any iron core. Maybe that would do the trick.
You have a circuit to conduct the electric current. Now you need a magnetic circuit to guide the magnetic field through the coils. That might be an iron sleeve that surrounds the coils with the PMs in the middle.
I don't think that is a problem since I don't get a high enough voltage to break the diod.
Maybe not now with 1 volt, but check it out. The reverse breakdown voltage is often less than the forward voltage needed to light the LED.
 
  • #7
Baluncore
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An AC generator is called an alternator.

If you only have one bar magnet = 2 poles, you only need two coils.

If you double the number of turns on the coils, or you double the RPM, you will double the voltage produced. If you do both, you will get four times the voltage.

Maybe a picture of your alternator would help us identify the easiest way to improve the performance.
 
  • #9
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You must drive an led with either a current source, or a voltage source plus a series resistor. Do not put an led directly across the generator output unless the regulator is used to maintain constant current.

Claude
 
  • #10
Tom.G
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What voltage do you get from the alternator (AC-generator) without the LED connected?

Also, if you have any resistors around, pick one around 200 Ohms (any value from 47 to 330 will do) and measure the alternator voltage with just the resistor connected to the alternator. Report the resistor value and the voltage you measure.

Oh, and what is the part number of the LED?
 
  • #11
Baluncore
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You got off to a good start by building something that can be optimised.

1. What is the outer perforated tube made from, aluminium, stainless steel or?
The perforated outer housing that is full of holes looks good, but should be a plain iron tube. Iron pole-pieces, in the middle of each coil should be attached against the outer housing and should reach close to the moving magnet poles. That will support the coil and form a magnetic circuit through the coil.

2. What is the flat material between the coils, clear plastic, or aluminium, or?

3. How is the rotating magnet supported?
If the magnet rotates inside a fixed metal cage, the holes in the cage will act as single shorted coil turns, so the backward eddy currents in the cage will generate a magnetic field that cancels most of the rotating magnetic field that you intended for the wound coils.
 
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