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Ballast Resistor – Maintain Circuit Stability

Any electrical device requires a stable current and voltage supply. Otherwise, if the current changes abruptly, it will affect its functioning. For instance, applying a low current to a fluorescent lamp will dim it, and Similarly, using an extra voltage to a fluorescent light will damage it. Therefore, having stability in electrical circuits is significant. A ballast resistor is a component that facilitates the achievement of peace in electronic devices. We are going to look at how a ballast resistor works and other critical insights about it. Hence, keep reading for further enlightenment. 


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What is a Ballast Resistor?


An Engineer Checking a Circuit Board

Figure 1: An Engineer Checking a Circuit Board


A resistive ballast is a component that will protect a circuit from current faults by reducing the current. When the recent increases to a particular threshold, the electrical ballast springs to action, increasing the electrical resistance and decreasing the current. 

Essentially, electronic ballasts will improve the circuit's stability. Thus, with electronic ballasts, the electrical circuit cannot experience current faults. 

Also note, in all circuits, the electronic ballasts are parallel to the load. Hence, an electrical ballast will manipulate the current levels throughout for a stable current flow, and it realizes this by decreasing the circuit's resistance. 


Types of Ballast Resistors


Resistor electronic components mounted on a motherboard

Figure 2: Resistor electronic components mounted on a motherboard


Primarily, there are two types of ballast resistors. They include the following: 


  • Fixed Resistors


A Neon Light Sign

Figure 3: A Neon Light Sign


They do not allow a variation of the resistance hence the term fixed resistors. Often, they are in an exceptionally high resistance level for the current control. Thus, during operation, they will produce a low current supply. Therefore, they help run low-current circuits such as in a LED lamp, which is also helpful in a neon lamp

Another common application is in the control of a ventilation fan speed.  A fan speed selector switch utilizes the principle of fixed resistance in all fans, and the resistor will not be operational at a low rate while fully functional at high speed.

The above process is imperative in current control, which determines the maximum and minimum fan speed. 


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    Self Variable Resistors


Incandescent Light Bulbs

Figure 4: Incandescent Light Bulbs


The type of ballast resistors alters the resistance according to the current changes. Thus, unlike the aforementioned electric ballast, the self variable resistors lack a fixed resistance point. Instead, an increase in the circuit's current will prompt a decrease of resistance and vice versa. 

You'll mostly find them in incandescent lamps. When the lamp's current increases during use, its ballast resistor's resistance will also increase due to heating. As a result, there will be a voltage drop increase. 

Similarly, as the current decreases, there will be lesser heating of the ballast resistor. Thus, the ballast resistance will decrease, and consequently, the voltage drop will decrease. 

The essential advantage of the type of ballast resistors is improvement in current control, and they are more accurate and precise than the aforementioned fixed resistor. Also, there is significantly lesser ballast loss of power in the self variable resistors than in fixed resistors. 


Ballast Resistor – Applications


Let us delve into the critical applications of ballast resistors. 


Ballast Resistor in Fluorescent Lamps


Fluorescent Tubes

Figure 5: Fluorescent Tubes


Fluorescent lighting is among the familiar, reliable light sources, and it is the technology behind the working of fluorescent office lamps. Nonetheless, while it's popular, it also has an apparent downside. When you connect a fluorescent bulb directly to a voltage source, it'll heat up. 

In such a connection, there is an apparent draw of high current, prompting the heating of the fluorescent bulb. Nonetheless, the issue is solvable by connecting a ballast resistor to the circuit, and it will prevent the excess current drawn by current and filament voltage regulation. 

However, note that the lighting of the lamp is reliant on the establishment of an arc between two electrodes. Thus, there is an apparent need to supply a high starting voltage that equals the supply voltage. Otherwise, the standard operating voltage cannot start fluorescent lamp fittings. 

The ballast resistor acts as the starter motor in facilitating the above operation. It will first provide the high voltage, which is paramount in the starting of the bulb. Next, it'll induce a drop in voltage when the lamp switches on in addition to lamp current control. 

The lamp efficiency will depend on the above process. Note that in fluorescent lamps, you'll need to connect the light in series with the ballast. 


Ballast Resistor for Automotive Applications


Car Ignition

Figure 6: Car Ignition


You'll also find the resistors in the starter motor of a gas-powered engine. The ballast will be an ignition ballast resistor during such application since it'll control the starting process. The fundamental need of using the resistor in this process is to improve the ignition coil life. 

The ballast resistor will control the coil voltage and coil current. Therefore, it will prevent heating of the coil, which results in extended life of the component. 

Nonetheless, like in the above application, a high voltage is necessary for the electronic switch ignition. Ideally, the primary voltage source will be sufficient to facilitate the ignition process. To achieve this, there is a jumper wire which will deliver the high voltage to prompt ignition. 


Ballast Resistor in a LED Circuit


Car Ignition

Figure 7: A LED Light Bulb


Another application is in an LED light bulb. The principle of the ballast resistor application is that such a light bulb is the same in the above applications. 

For efficient lighting, the primary voltage source should not exceed the requirements of the lamp type. Therefore, a ballast resistor limits the supply voltage to the average operating voltage in the electronic lamp circuit

As a result, the connection yields a voltage that is equivalent to the necessary lamp load. You can also calculate the value of the necessary ballast resistance. Here is the formula: 

Resistance= (Voltage Source - LED's forward voltage) / (LED's forward current) 


How to test Ballast Resistor?


A Digital Multimeter

Figure 8: A Digital Multimeter


It's imperative to test if your current vehicle features a ballast resistor on the ignition coil. It'll save you from expensive repairs of the ignition engine. An ignition with a resistor is also energy efficient. In many of the late-model vehicles, the resistor is present. But you may want to test if it exists. 

In two main processes, you can find if your car features the critical resistor. First, place the red probe of a multimeter in DC mode on the coil. At the same time, ground the negative probe. Your multimeter reading should be 12V irrespective of whether the ballast resistor kit exists or not. 

While still maintaining the above connection, earth the opposing end of the coil temporarily. The outcome should be a voltage drop. Suppose the depth is less than 9V; the ignition circuit certainly has a lock, and if it doesn't, it is probably absent. 

As a precaution, after testing for ballast resistive properties of the coil, unearth the negative. 


If the Ballast Resistor fails, what happens?


Car Key in Ignition Lock

Figure 9: Car Key in Ignition Lock


When your car ignition system's ballast resistor fails, several things will happen. First, the car may start and go off immediately, and in some cases, it may not start at all.

If that happens, engage a professional to fix the problem. The expert will advise if a ballast resistor replacement is necessary. Don't try to jump the resistor, as doing so will probably damage the points permanently. 




We have outlined the workings of a ballast resistor and all the critical insights of the component. And we advise you never to run an electronic device requiring a ballast resistor without it. 

We also have plenty of insights on other electronic parts. Contact us for any queries by visiting our website. We'll get back to you immediately. 



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