Most small garden mowers, chain saws, trimmers and different small gas engines do now no longer want a battery. Instead, they honestly generate the electricity for the spark plug the usage of a magneto. Magnetos also are used on many small airplanes (for example, the Cessna 152 visible in How Airplanes Work) due to the fact they're extraordinarily reliable.
The concept at the back of any ignition device is to generate a very excessive voltage -- at the order of 20,000 volts -- at precisely the proper time. The voltage reasons a spark to leap throughout the spark plug`s gap, and the spark ignites the gasoline withinside the engine. See How Car Engines Work or How Two-Stroke Engines Work for details.
The magneto is the white block withinside the following photo (that is the magneto for a series saw):
The concept at the back of a magneto is easy. It is largely an electrical generator that has been tuned to create a periodic excessive-voltage pulse in place of non-stop contemporary. An electric generator (or a magneto) is the opposite of an electromagnet (see How Electromagnets Work for details). In an electromagnet there may be a coil of twine round an iron bar (the armature). When you follow contemporary to the electromagnet's coil (e.g. with a battery), the coil creates a magnetic subject withinside the armature. In a generator, you opposite the process. You circulate a magnet beyond the armature to create electric powered contemporary withinside the coil.
A magneto includes 5 parts:
An armature. In the above magneto, the armature is formed like a capital "U". The ends of the U factor in the direction of the flywheel.
A number one coil of possibly 2 hundred turns of thick twine wrapped round one leg of the U
A secondary coil of possibly 20,000 turns of very skinny twine wrapped across the number one coil
A easy digital manage unit that typically is going via way of means of the name "digital ignition" (or a fixed of breaker factors and a capacitor)
A pair of robust everlasting magnets embedded withinside the engine's flywheel.
When the magnets fly beyond the U-formed armature, they result in a magnetic subject withinside the armature. This subject induces a few small quantity of contemporary withinside the number one and secondary coil.
What we want, however, is extraordinarily excessive voltage. Therefore, because the magnetic subject withinside the armature reaches its maximum, a transfer withinside the digital manage unit opens. This transfer breaks the waft of contemporary thru the number one coil and reasons a voltage spike (of possibly 2 hundred volts).
The secondary coil, having a hundred instances extra turns than the number one coil, amplifies this voltage to about 20,000 volts, and this voltage feeds to the spark plug.
Many using garden mowers do have a battery in the event that they have add-ons like headlights and electric powered start. Even so, the engine might also additionally use a magneto due to the fact the magneto is easy and reliable.
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