How Does a Starter Generator Work?

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Starter generators are found on lawn tractors.

A starter generator is a combination of two different engine components. The component can be found in lawn tractors, garden tractors and aircraft. The starter component generates the initial ignition, starting the vehicle, and the generator maintains the voltage while the vehicle is being operated.



The starter generator initially engages because of the direct current voltage sent from the battery of the vehicle or equipment. Once the ignition switch is turned, it closes the contactor or electrical connection, sending voltage to the starter of the component. After voltage gets sent to the starter, the component acts as a small motor. The starter turns, tripping or turning the engine. Voltage is simultaneously being sent to the spark plugs, which ignites the fuel inside the engine cylinder or turbine.


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The starter part of the component is composed of a stator, windings, armature and brushes. The armature is connected to wires wound in a circular motion making a field coil. Voltage is sent to the coil, then into the brushes and to the armature. As the voltage flows through a series field, a magnetic field is created. The voltage runs through different parts of the coil, changing the magnetic fields created. As the magnetic field rotates around the coil, the stator turns, engaging the engine.



The generator portion of the starter generator components provides voltage to all the electrical components of the vehicle. Each electric feature of a vehicle requires some amount of voltage to operate. The lights, PTO, emergency shutoff components, computer systems and other electronics found on aircraft or tractors must be powered. The generator sends the correct amount of voltage to each component, while maintaining enough voltage to operate all the components simultaneously.



The starter generator has common problems that can develop with these assemblies. The component can generate a certain amount of current, because it has one coil, which can limit the features available on a vehicle. Regular automotive and tractor generators have cooling fans on the components, but the starter generator is enclosed, which can cause it to overheat. If the brushes wear too much and the internal components get out of round, the brush can bounces, cause a break in the electric flow. If electricity is interrupted, the electronic component will work intermittently. Bearings and other components can wear prematurely if the starter generator begins to overheat.



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