link to 6 gens page


The very simple generator described below is primitive but shows the basic operation. It has been deliberately left as simple as possible so that there is maximum scope for using it in imaginative designs and inventions. It can therefore form the basis for a more complex device as shown a little further on.

The generator is made from a coil of wire (about 1000 turns) wound around the last 3 cm, or so, of a large nail. When a spining magnet is placed near to the device it induces a voltage into the coil and this can then be used to light a bulb (or better still an LED see end for details) - generation of electricity can therefore be simply demonstrated.

nail gen

Diagram of simple generator

Step 1
Make up two cardboard circles about 3cm in diameter (1-2 mm thick). Carefully pierce a hole in the middle of the circles. Find a large (10-15 cm long, 6 mm wide) clean (unrusty) nail having a large head. Thread one of the circles onto the nail and push right up to the head.

Step 2
Cover the last 3-4 cm of the nail with a single layer of insulation tape (leave the nail head uncovered). Push the second circle onto the nail but only so far as the insulation tape. Add more tape onto the other side of the circle to fix the circle in place. You should now have a ready made 'spool' on which to wind the coil.

Step 3
Obtain some thin insulated copper wire (say 25m or so of 30SWG, aprox. 0.3mm diameter) leave about 20-30 cm free and start to wind turns onto the insulated part of the nail between the two circles. Wind 1000-1500 turns (the exact number does not matter much and will depending on how neat you can get them on before they spill over the restraining cardboard circles). Leave another 20-30 cm free at the end and then cut the wire. Tape up the whole assembly so that the wire does not come undone.

Step 4
Take the free ends of the wires and scrape off the insulation. Wire them to a bulb or to an LED. Bring a magnet close to the head of the nail and while holding it about 5mm or so from the head rapidly move the magnet from side to side. The Bulb or LED will light showing generation of electricity !!


A generator works by a magnetic field inducing a voltage into a coil of wire. Important points to note are that the voltage increases as the number of turns of wire on the coil, the size of the coil and the strength of the magnetic field increases. The magnetic field (or the coil) needs to be in constant motion to produce/induce the electricity into the coil. This can be done by moving the magnet or by moving the coil - the effect is the same. The coil (or the magnet) needs to move in such a way that the coil continually passes through the magnetic field.
The Iron nail is also important in our simple generator as it tends to concentrate the magnetic field. As the coil is wound around the nail it tends to draw in more magnetic flux into the area of the coil which boosts the overall efficency of the device and increases the voltage that is produced.
The type of wire in the coil is also important. For example, thick wire means there will be less power loss, but the down side is that the coil will get very large when a great number of turns is needed. In a practical generator some trade off has therefore to be found between the size of magnet, coil and the wire.

AC or DC
This simple generator is called an AC generator. This means that the voltage appearing at the two wires alternates between + and -, and - and + each time the magnet makes a complete revolution. As a result the generator can light a bulb or an LED without you having to worry about which way round the connections need to go (as they are effectively reversing all the time anyway). However, this simple generator is not good for running radios, calculators or other devices that need a direct current (DC) that is produced for example from a battery. You can have fun though connecting up speakers to the generator output, as you can hear the electricity alternating - but please don't use your parents best Hi-Fi Speakers !, try using walkman type headphones etc.


The photo below shows a simple hand cranked generator I built which used two of these nail-generators wired together (to give twice the power). This way both the N and S face of the magnet are used at once. One needs to get the wiring between the coils correct otherwise the voltage will cancel and you won't get any power from the gen! The coils are wired one after the other rather than one across the other (ie. a series circuit rather than in parallel). A simple wooden gear system was used so that you can comfortably generate electricity without having to turn the handle too fast.

nail gen I

A simple two nail generator with hand crank

nail gen II

Close up of the generator

click here for an even simpler generator

It may seem like common sense to use as low a voltage bulb as possible in this type of generator but actually a higher voltage bulb often works better. For example, a 1.5V (voltage) bulb often takes 0.25 A (amp - electrical current) to light while a 6V bulb can take as little as 0.05A. This simple generator can only supply a relatively small current (say 0.05-0.1A) and so consiquently the higher voltage bulbs tend to work better. By the way an LED (light emitting diode) works really really well in this design because they take very little current (about 0.01A). LED's can be obtained from Tandys or Maplins (almost any sort will do) or scrapped from an old radio or toy that contains one.

Click here for information about LED's

In general the stronger the magnet the better. Eclipse make all sorts of magnets and are generaly avaliable from most hardware stores. The 'crank handle' generator descrobed above used a E825 Eclipse magnet. Its is well worth trying other types of magnets but you might have to devise other ways of spinning the magnets to make sure the magnetic field is changing in the correct way with respect to the coil. Good generators can be made from button, bar, hourseshoe and cylindrical magnets - its just up to your imagination !

Cardboard from a cereal box for example
Iron nail with head (1/4" (6mm) diameter, ~6" (15cm) long)
Reel (aprox. 25m) of enamelled copper wire (30 SWG or ~0.3mm diameter)
E825 Eclipse Button Magnet
Torch bulb (6V, 0.06A) and holder or better still an LED
Hand drill (standard toolbox type)
Most of these parts can be obtained from a DIY store or from electronic shops such as Tandy or Maplins.

Books and articles:
Advanced Physics, Tom Duncan, 4Ed., John Murray, ISBN 0 7195 5199 4
nice section on generators and electricity.

Ideas for further work:
1) try varying the number of turns. Is it always true that the voltage goes up with number of turns for this simple gen ? What happens when the coil gets so large that mots of it is no longer very close to the nail ?

2) can you find a better iron former than a nail ?

3) how about trying other forms of energy to power the rotating magnet, eg. wind power, wave power (for example see the section building your own windmill)

goto 'build your own windmill'

4) can you build-in a moving switch to make the voltage direct (DC) instead of alternating (AC) - this is called a commutator

5) can you use the nail-coil (without the magnet) as a 'search' coil for detecting magnetic fields ? Try putting the nail-head coil near to a speaker playing load music, does the LED flash with the music ?
NOTE: never go near to mains powered devices of any kind with this apparatus


Web site information:
For details about the magnet used in this project :

click here for an even simpler generator

link to 6 gens page


Dr Jonathan Hare, The University of Sussex
Brighton, East Sussex. BN1 9QJ

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