Avoiding Common Errors When Selecting Resistors and Capacitors
Selecting the correct components for a circuit can be the difference between a high level of performance being achieved, and potentially catastrophic consequences. This is no less the case as far as resistors and capacitors are concerned.
You might be reading this as someone building an Arduino project for the first time, or perhaps prototyping a power supply, or even repairing vintage hi-fi gear.
Regardless, you won’t want to pick the wrong capacitor or resistor for your project. Opting for the incorrect type of component or an unsuitable tolerance, or even just misreading a particular part’s value, can lead to flickering LEDs, overheating components, unstable oscillators, or distorted audio. In the worst cases, your circuit could even start smoking.
So, in this article, we’ll lay out some of the most frequently committed mistakes among hobbyists and engineers seeking to choose the right capacitors and resistors for their needs. It’s very much about making sure you get your choice right at the first attempt, instead of being forced to learn “the hard” (and unpleasant) way.
Common Errors in Resistor Selection
- Ignoring The Power Rating
Many beginners choose a resistor solely on the basis of its resistance in ohms. However, it is also crucial to pick a resistor that will dissipate heat safely. A standard ¼-watt resistor can be prone to failure if used in a high-current application.
This is why you should always verify your wattage, using the formula: P = I2 x R. In this, P refers to power dissipation, I to current, and R to resistance.
- Misjudging Tolerance
As you will know if you have been using a resistor colour code table – such as the one on the RS website – to identify resistor values, a silver band on a resistor denotes a 10% tolerance.
Choosing a resistor with such high tolerance, though, means it can vary significantly from its nominal value. So, if your given application requires precision timing or audio gain, you should be seeking to use parts with 1% or even 0.1% tolerance to ensure stability.
- Overlooking Temperature Coefficient
Resistance is liable to change amid fluctuating environments. If, then, your project will sit in a hot enclosure, you should be looking for a resistor with a low temperature coefficient of resistance (TCR) to combat the risk of circuit drift.
Common Errors in Capacitor Selection
- Under-rating Voltage
You should never run a capacitor at its exact rated voltage. An industry “rule of thumb” is to choose a capacitor with a voltage rating at least 20% to 30% higher than the peak voltage of the given circuit, to prevent catastrophic failure.
- Paying Insufficient Attention to Equivalent Series Resistance (ESR)
Equivalent series resistance is the total non-ideal internal resistance in a capacitor, modelled as a resistor in series with the ideal capacitor. It represents energy lost as heat, impacting on performance in high-frequency circuits by increasing ripple and lowering efficiency.
ESR needs to be one of your major considerations when choosing a capacitor. Higher ESR leads to greater power loss and heat, thereby diminishing the lifespan and stability of the component.
The use of low-ESR ceramic capacitors is standard practice for decoupling high-speed digital integrated circuits (ICs). This is because such capacitors offer quick delivery, effectively filter high-frequency noise, and have low inductance. Users can be assured, then, that these capacitors will prevent voltage drops and ensure stable power for sensitive components.
Don’t Forget How the Right Online Tools Can Make Your Life Easier
When you, for instance, Google “resistor colour code calculator” or a similar term, you can soon expect to find online tools enabling you to rapidly interpret the colour bands on whatever resistor you’re considering using. This, in turn, can help speed up your work and ensure optimal precision and performance.
We wish you all the best in your efforts to build projects that deliver the most impressive results!