Speaker 1: Welcome to Brainstuff from how stuff Works dot com where
Speaker 1: smart happens him Marshall Brain with today's question, how does
Speaker 1: a magneto work? Most small lawnmowers, chainsaws, string trimmers, and
Speaker 1: other small gasoline engines don't need a battery. Instead, they
Speaker 1: actually generate the power for the spark plug using a magneto.
Speaker 1: Magnetos are also used on many small airplanes. For example,
Speaker 1: the session of one fifty two seen in the article
Speaker 1: how Airplanes Works uses magnetos because magnetos are incredibly reliable.
Speaker 1: The idea behind any ignition system is to generate an
Speaker 1: extremely high voltage on the order of twenty thousand volts
Speaker 1: at exactly the right time. The voltage causes a spark
Speaker 1: to jump across the spark plug gap, and the spark
Speaker 1: ignites the fuel in the engine. The idea behind a
Speaker 1: magneto is incredibly simple. It's basically an electrical generator that
Speaker 1: has been tuned to create a periodic, high voltage pulse
Speaker 1: rather than continuous current like a normal generator would. An
Speaker 1: electrical generator, or a magneto is the reverse of an electromagnet.
Speaker 1: In an electromagnet, there's a coil of wire around an
Speaker 1: iron bar called the armature. When you apply current to
Speaker 1: the electromagnets coil i e. With a battery, the coil
Speaker 1: creates a magnetic field in the armature. In a generator,
Speaker 1: you reverse that process. You move a magnet past the armature,
Speaker 1: and you create an electric current in the coil. A
Speaker 1: magneto consists of five parts. It has an armature and
Speaker 1: a primary coil of wire that's wrapped around that armature.
Speaker 1: It might be two d turns of thick wire wrapped
Speaker 1: around the piece of iron. Then it has a secondary
Speaker 1: coil of perhaps twenty thousand turns of very thin wire
Speaker 1: wrapped around that primary coil. And then it has a
Speaker 1: simple electrical control unit that commonly goes by the name
Speaker 1: electronic ignition. That's a set of breaker points and a capacitor,
Speaker 1: and it has a pair of strong permanent magnets embedded
Speaker 1: in the engine's flywheel. When those magnets fly past the armature,
Speaker 1: they create a magnetic field in the armature. This field
Speaker 1: induces some small amount of current in the primary and
Speaker 1: then the secondary coil. What we need, however, is extremely
Speaker 1: high voltage. Therefore, as the magnetic field in the armature
Speaker 1: reaches its maximum, a switch in the electronic control unit opens.
Speaker 1: This switch breaks the flow of current through the primary
Speaker 1: coil and causes a voltage spike perhaps two hundred volts.
Speaker 1: The secondary coil, having a hundred times more turns than
Speaker 1: the primary coil, amplifies this voltage to approximately twenty thousand volts,
Speaker 1: and this voltage feeds to the spark plug. Many writing
Speaker 1: lawnmowers do have a battery if they have accessories like
Speaker 1: headlights and electric starting. Even so, the engine may still
Speaker 1: use a magneto because the magneto is so simple and reliable.
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