Resistors are designed to limit the current flowing through an electric circuit, so semiconductor materials are used to serve this purpose. When current passes by a resistor, it faces a resistance, which produces heat over time, but if the load on the resistor increases, the heat increases, leading to the resistor being burnt out. So, how to tell if a resistor is burnt out?
How To Tell if a Resistor Is Burnt Out?
A burnt-out resistor will not be able to resist the current flow which is generated by the excessive voltage; as a result, the resistor will break down. However, the current flowing through the resistor will face no resistance, making the total current passing through the circuit not affected and unchecked.
The excess current passing can damage the components connected to the circuit through the circuit. For example, when a resistor is overloaded by an excess voltage more than its rating, the resistor temperature will increase, and its body will be too hot to touch. As a result, the resistor color will darken and may meltdown starting a fire.
However, when a resistor has these signs, it may still be working, but its resistance will be affected and can decrease, which increases the current passing through.
How To Tell if a Resistor Is Overheating?
When the voltage approaches the limits of a resistor’s power rating, the heat resulting from the resistor will increase, and it will be higher than usual. This is because the source’s electrons or current have more pressure from the voltage source, which applies more pressure on the resistor.
Each resistor has been designed for a certain amount of current to pass through it; when this amount is exceeded, the resistor becomes hotter and maybe untouchable, and marks of burning can be detected. When the resistor components; pigment of the color code, the carbon starts to burn.
There will be a burning odor, which can be a warning sign for you that the resistor is overloading, and the problem needs to be fixed before the resistor is completely burnt.
How To Tell if a Resistor Is Normal?
A typical resistor will be working under its limit power rating, which means average voltage load; this load must not exceed its limit and stays under it or, in some cases, be the same as its limit. In addition, the resistor will be touchable, as it produces a low average amount of heat like any other semiconductor component.
The semiconductors allow only a certain amount of current or electrons to pass through; when these electrons pass through the semiconductor, they face resistance, producing heat. Any resistor is designed to disperse the heat produced from the flowing of the current or electrons, which protects the resistor material.
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Can a Burnt Resistor Be Replaced?
Yes, you can replace any burnt or defective resistor in an electric circuit, and an advantage that resistors have is that they can be measured even if the circuit is turned off. To replace the burnt resistor, you can follow the following steps:
- First, calculate the value of the defective or burnt resistor.
- Use the multimeter to calculate the resistor’s value by measuring the resistance from the burnt side to both ends of the resistor.
- Count the colored circles around the resistor body to know its value; you can follow this method if the circles around the resistor’s body are still intact.
- Remove the burnt resistor from the board by using diagonal cutters to remove the resistor’s terminals from the board.
- Use the soldering iron to melt down the leads connecting the resistor to the circuit board, and use the diagonal cutters to help you remove the resistor after the solder has melted down.
- Bring a new resistor that has the same value as the burnt one, use leads and a soldering iron to fix the new resistor in the same place as the burnt one. Resistors don’t have polarity, so that you can fix any end in any pad; it doesn’t make a difference.
- Measure the new resistor’s value after fixing it in the circuit to ensure everything is working correctly.
How To Know the Value of a Burnt Resistor?
You can find the value of any burnt resistor using four simple methods. When repairing, troubleshooting, or designing electronic and electric circuit boards, you may need to replace a burnt resistor. Therefore you need to find its value before replacing it.
First Method
- Remove the external coating of the resistor body.
- Find the burnt section of the resistor and clean it.
- Grab a multimeter and measure the resistance from one resistor’s ends and the burnt section.
- Measure the resistance from the burnt resistance and the other end of the resistor.
- Add the first value to the second value using any calculator.
- The result will be the approximate resistor’s value.
- You can add a small amount to make the value more accurate; for example, if the value was 470 Ω, you can 30 Ω to make it 500Ω.
Second Method
- Prepare your multimeter on voltage mode.
- Use the multimeter’s red and black probes to measure the voltage.
- Measure the voltage across the burnt section.
- Use the multimeter to measure the current passing through the resistor.
- Multiply the voltage value by the current value to know the wattage.
- The wattage of the new resistor needs to be higher than the wattage of the burnt resistor.
Third Method
This method can be helpful only if you know the circuit’s expected voltage and have another resistor of the same wattage as the burnt or damaged resistor. Therefore, these two conditions must be available to use this method.
- Adjust the multimeter to a high value of resistance to start with, and instead of the burnt resistor, connect the one with the same wattage.
- Use the multimeter to measure the voltage; if the measured voltage is the same as you expected, then the value of the burnt resistor is the same as the one you used.
- If you can’t remember the circuit’s voltage, you can start with high resistance and then decrease the resistance until the circuit is working correctly. The resistor that will replace the burnt one should have the same resistance that makes the circuit function properly.
Fourth Method
In some printed circuit boards, the value of each resistor in the circuit can be found printed around the resistor. Therefore you can look around the burnt resistor to see if its value is printed beside it. Unfortunately, this doesn’t apply to every circuit, it depends on the circuit manufacturer, so if it doesn’t work for you, you can follow previous methods.
Conclusion
To sum up, you can tell if a resistor has been burnt out, which happens when the voltage approaches the limits of a resistor’s power rating; the heat resulting from the resistor will increase, and it will be higher than usual. As a result, the resistor temperature will increase, and its body will be too hot to touch.
As a result, the resistor color will darken and may meltdown starting a fire; this could affect near components in the circuit, not only the resistor. In addition, the excess current passing can damage the components connected to the circuit through the circuit, and the fire could reach the components.
A burnt-out resistor will not be able to resist the current flow which is generated by the excessive voltage; as a result, the resistor will break down. However, the current flowing through the resistor will face no resistance, making the total current passing through the circuit not affected and unchecked.
