WEBVTT - How does a magneto work?

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<v Speaker 1>Welcome to Brainstuff from how stuff Works dot com where

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<v Speaker 1>smart happens him Marshall Brain with today's question, how does

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<v Speaker 1>a magneto work? Most small lawnmowers, chainsaws, string trimmers, and

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<v Speaker 1>other small gasoline engines don't need a battery. Instead, they

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<v Speaker 1>actually generate the power for the spark plug using a magneto.

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<v Speaker 1>Magnetos are also used on many small airplanes. For example,

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<v Speaker 1>the session of one fifty two seen in the article

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<v Speaker 1>how Airplanes Works uses magnetos because magnetos are incredibly reliable.

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<v Speaker 1>The idea behind any ignition system is to generate an

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<v Speaker 1>extremely high voltage on the order of twenty thousand volts

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<v Speaker 1>at exactly the right time. The voltage causes a spark

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<v Speaker 1>to jump across the spark plug gap, and the spark

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<v Speaker 1>ignites the fuel in the engine. The idea behind a

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<v Speaker 1>magneto is incredibly simple. It's basically an electrical generator that

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<v Speaker 1>has been tuned to create a periodic, high voltage pulse

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<v Speaker 1>rather than continuous current like a normal generator would. An

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<v Speaker 1>electrical generator, or a magneto is the reverse of an electromagnet.

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<v Speaker 1>In an electromagnet, there's a coil of wire around an

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<v Speaker 1>iron bar called the armature. When you apply current to

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<v Speaker 1>the electromagnets coil i e. With a battery, the coil

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<v Speaker 1>creates a magnetic field in the armature. In a generator,

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<v Speaker 1>you reverse that process. You move a magnet past the armature,

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<v Speaker 1>and you create an electric current in the coil. A

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<v Speaker 1>magneto consists of five parts. It has an armature and

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<v Speaker 1>a primary coil of wire that's wrapped around that armature.

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<v Speaker 1>It might be two d turns of thick wire wrapped

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<v Speaker 1>around the piece of iron. Then it has a secondary

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<v Speaker 1>coil of perhaps twenty thousand turns of very thin wire

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<v Speaker 1>wrapped around that primary coil. And then it has a

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<v Speaker 1>simple electrical control unit that commonly goes by the name

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<v Speaker 1>electronic ignition. That's a set of breaker points and a capacitor,

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<v Speaker 1>and it has a pair of strong permanent magnets embedded

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<v Speaker 1>in the engine's flywheel. When those magnets fly past the armature,

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<v Speaker 1>they create a magnetic field in the armature. This field

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<v Speaker 1>induces some small amount of current in the primary and

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<v Speaker 1>then the secondary coil. What we need, however, is extremely

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<v Speaker 1>high voltage. Therefore, as the magnetic field in the armature

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<v Speaker 1>reaches its maximum, a switch in the electronic control unit opens.

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<v Speaker 1>This switch breaks the flow of current through the primary

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<v Speaker 1>coil and causes a voltage spike perhaps two hundred volts.

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<v Speaker 1>The secondary coil, having a hundred times more turns than

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<v Speaker 1>the primary coil, amplifies this voltage to approximately twenty thousand volts,

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<v Speaker 1>and this voltage feeds to the spark plug. Many writing

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<v Speaker 1>lawnmowers do have a battery if they have accessories like

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<v Speaker 1>headlights and electric starting. Even so, the engine may still

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<v Speaker 1>use a magneto because the magneto is so simple and reliable.

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