Ballast Resistor

According to the English dictionary, “ballast” means something that gives stability. Thus when referring to an electrical ballast, we mean an electrical device that plays an important role in maintaining the stability of the electrical circuit. However, the question you may have is how does it provide the stability? Some electric ballasts limit current while some limit voltage, depending upon the circuit in which they are used. By doing so, they reduce the risk of either over voltage or over current in the circuit and thereby enhancing the stability of the system. Electric ballast varies greatly in complexity. It can be as simple as a resistor, capacitor, inductor, combination of these or it can be as complex as the electronic ballast used in the florescent lamp. Here in this article, we shall discuss about simple electric ballast, the ballast resistor. What is a Ballast Resistor? A ballast resistor is used in a circuit to limit the current and hence prevent it from over current faults. Here, as the current in the circuit varies and increases above a particular threshold value, the resistance also starts to increase. This in turn decreases the current and protects the circuit from over current faults. Thus, maintaining the stability of the circuit. These devices are mostly connected in parallel with the load of the circuit. So we can define a ballast resistor as: “A resistor limits the current in a circuit by increasing the resistance as the current increases above a certain value.”   Now let us discuss some of its areas of application. Ballast Resistor – Uses and Applications Now let us discuss some of its areas of application. Ballast Resistor in Fluorescent Lamps As we know, fluorescent lighting is one of the popular and efficient lighting system. However, there is downside to this type of lighting system. It gets heated very fast when directly connected to the voltage source. This happens due to the uncontrollable current draw by the lamp, as soon as it is switched on. In order to avoid the overheating due to the excessive current draw, a ballast resistor is used in the circuit, mostly connected in parallel with the lamp. So what does a ballast resistor do? It simply regulates the current and reduces the voltage. However, for the lamp to light up, it needs to establish an arc between its two electrodes. For this, a high starting voltage almost equal to the supply voltage is needed. The ballast resistor, supplies the needed voltage during the start up, and then immediately after the arc is established, it reduces the voltage in addition to regulating the current flow. The figure below shows a florescent light tube connected with a ballast resistor and a starting switch.   Ballast Resistor for Automotive Applications The ballast resistors are often included in the ignition kit of automotive machines such as car engines. Due to its application, such devices are called Ignition Ballast Resistor. Use of this device reduces the risk of coil failure. It is installed in the circuit between the primary voltage source for the ignition coil and the coil stud. This helps to reduce the coil voltage and coil current, therefore with the addition of the same, the coil does not get as heated as it would without the same, thus increasing the life of the coil. However, during the starting of the ignition engine, a high voltage equal to the primary voltage source is needed. Therefore a jumper wire is often connected with the ballast resistor. This jumper wire provides the necessary voltage to make the engine start. The figure below shows...
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