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Building a simple Dc generator? Answered


We have a school project and we must a build a DC generator, and I want it to be D.I.Y., but I have a problem, I don't know if the generator I am planning to build can make enough power to make small loads work.

My armature is made of several laminated "I" core with winding of AWG#24and1/2, that's my plan, but how many turns shall I wind? is the laminated Iron core enough or should I use iron core instead?, do I need a strong magnet?

Thanks in advance!

5 Replies

argha halder (author)2013-04-20

for easier way ,get a dc motor which is of 6-12v.then get a toy wheel and attach it to the rotor of the motor.then attach the ends of the motor to a voltmetre and when you spin the wheel very fast you will see the metre jump to 4-6volts which is enough to light an led or even another motor.if you use a led use the green ones because they use less energy.good luck to your project.

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Jack A Lopez (author)2012-07-26

Technically the open circuit voltage induced in a coil by a changing magnetic field, depends on three things:  the number of turns in the coil, the strength of the magnet, and how fast the magnet is moving past the coil.   This is just Faraday's law:  V = N*(dΦ/dt) where N is the number of turns, Φ is the magnetic flux enclosed by the coil, and dΦ/dt is the speed at which Φ is changing.

I have tried building my own generator toys before, and in doing this I have found that it seems to take a very large number of turns to get just a few volts of potential across the coil. 

As sort of a shortcut for building the coil, I suggest starting with a coil pulled from something else, which already has a huge number of turns off very fine wire.  I suggest two places to find such a coil. 

One place is a clock which runs from a single AA battery.  The motor for such a clock is the World's most simple stepper motor; i.e. it is a stepper motor with just one coil. A picture of such a coil is attached.

Another place to find your coil with many-many turns of wire, is in one of those little solar dancing flowers.  The coil itself is shaped sort of like a coin (a cylinder with a radius much larger than its height).  A picture of such a coil is attached, but it is kind of hard to see.  It is the copper colored thing on the left side of that big white rotor thing there.

Note the minimum voltage needed to light a red LED is about 1.8 V, and the minimum voltage needed for a blue (or white) LED is about 3.6 V. 

So you can maybe test the open-circuit voltage on your coil using a multimeter or oscilloscope, and if that indicates a voltage less than 1.8 V, then that means your coil doesn't have enough turns, or you need a way to make the magnetic flux change faster; i.e. a bigger, faster moving, magnet.

Also note that a simple generator like this ( a coil placed near a moving magnet) will give you AC instead of DC.  To get DC you either need a rectifier, made from diodes, or a commutator, and a commutator is a switch that flips the output of the coil in sync with the pulse produced by the moving magnet.

Note that for a rectifier circuit there is some small voltage needed ( about 0.6 V for silicon) just to forward bias the diode.

In the case that you build your generator from an existing permanent magnet DC motor, then you get a commutator already built in, and that's convenient. 

If you build your generator from something like an old cordless drill,
then that comes with a permanent magnet DC motor, and it comes with gears to increase the speed at which the rotor turns, and that helps a lot too.

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Dang! I forgot the link to the solar dancing flower:
Anyway, you've probably seen those before.

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rickharris (author)2012-07-26

Alternatively use a small permanent magnet motor and an LED to show current being generated./

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frollard (author)2012-07-26

any of the above should work so long as you follow the rules of getting the power out from the armature (or spin the magnet and have a wound stator).

The more turns, the bigger the voltage
The bigger the wire, the more amperage it can supply.
The stronger the magnetic field (closer magnet + stronger magnet) the more overall power.
The faster the rotor, thus faster change in magnetic field, the higher the voltage & higher the power generated.

so, yes. more in all accounts is merrier.

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