What Does a Ballast Resistor Do?

Written by sean kotz
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What Does a Ballast Resistor Do?
A ballast resistor, used with the car battery and starter, regulates electrical power during start up. (old engine image by John Sfondilias from Fotolia.com)

The process of starting a car involves more than simply turning the key to fire up your engine. Between the battery and the starter, a ballast resistor helps regulate the voltage.


WordNet Search defines a ballast resistor, most commonly found in an automobile ignition system, as a device "inserted into a circuit to compensate for changes, [such] as those arising from temperature fluctuations."


A ballast resistor helps regulate voltage flowing in an electrical system to avoid overloads or battery drainage.

Use in Automobiles

As the starter motor begins to crank the engine, it causes a significant drain on the battery. The ballast resistor allows the ignition system to operate at a lower voltage until the engine starts. After ignition, the alternator begins to recharge the battery, restoring the regular voltage. The ballast resistor then functions to regulate the voltage going to the ignition system to avoid additional wear on the system.

Additional uses

Low-voltage lighting systems, such as florescent, LED and neon lights, frequently contain ballast resistors.

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