Capacitors are hugely important components in electrical circuits. Consisting of two conductors in close proximity that are also insulated from each other, capacitors store and release electrical energy, similar to a temporary battery.
So, when it comes to such functions as filtering, timing, and energy storage, it is essential to use these components in an appropriate, responsible, and safe manner.
One thing you will not want to do – whether you are working with capacitors in series or parallel configurations, or both – is make avoidable mistakes. Otherwise, such consequences as inefficiencies, circuit failure, or even component damage could follow.
What, then, are some of the most frequently made mistakes with capacitors in series and parallel arrangements, that you should steer clear of when trying to design reliable circuits?
Below, we’ve picked out five of them.
Misunderstanding Capacitance in Series and Parallel Configurations
You won’t want to get your numbers wrong when it comes to calculating total capacitance in series or parallel circuits.
Remember that as far as capacitors in series are concerned, you’ll need to use this formula to figure out total capacitance (Ctotal): 1/Ctotal = 1/C1 + 1/C2 + 1/C3 + … This means the total capacitance will always be less than the smallest individual capacitor.
If, on the other hand, you need to know the total capacitance for capacitors in parallel, the relevant calculation will be: Ctotal = C1 + C2 + C3 + … Yes, that’s right – the total capacitance will be simply the sum of the individual capacitances.
However, some people may apply the wrong formula from time to time. In other words, they may add capacitances in series or use the reciprocal method for parallel circuits.
A mistake like this can bring about undesirable circuit behaviour, such as improper timing in an oscillator circuit.
Ignoring Voltage Ratings
Any given capacitor will have a voltage rating, which is the maximum voltage it can safely handle. If a voltage higher than this rating is applied to the component, it is likely that the capacitor’s dielectric (insulating material) will be damaged. This, in turn, could lead to failure and a short-circuit.
Nonetheless, some people make the mistake of connecting capacitors in series or parallel without considering how the circuit configuration will affect voltage distribution.
In a series arrangement, the voltage across each capacitor divides, inversely proportional to capacitance; however, the circuit’s total voltage rating doesn’t simply add up. In a parallel arrangement, though, all capacitors experience the same voltage, which can exceed the rating of lower-rated capacitors. The evolution of capacitors has wiimproved the voltage ratings.
Using a 16V-rated capacitor in a 20V parallel circuit, then, could result in the dreaded dielectric breakdown. This might mean the capacitor fails or even explodes.
Overlooking Capacitor Tolerance
The tolerance rating of a capacitor indicates how much the component’s actual capacitance value can deviate from its marked, or nominal value, due to manufacturing variations and other factors. It is often expressed as a percentage, such as ±10%.
A frequent error is assuming all a given circuit’s capacitors have their exact labelled capacitance; this oversight can lead to unexpected circuit performance.
For example, in a timing circuit, a capacitor with a high tolerance could bring about significant deviations in frequency.
Neglecting Parasitic Effects
Capacitors are by no means perfect components; they show certain parasitic effects (in other words, unintentional effects that arise in real-world circuits).
One common parasitic effect is equivalent series resistance (ESR). If, for instance, high ESR occurs in a parallel capacitor bank for a power supply, this can cause excessive heat, thereby shortening lifespan.
Ignoring these effects, then, is not a mistake you will want to make when designing high-frequency circuits, such as those used in telecommunications or audio equipment.
Incorrectly Mixing Capacitor Types
These components come in a range of types, such as ceramic, electrolytic, and tantalum capacitors. Crucially, each of these types has certain characteristics, rendering it suitable for particular applications.
Unfortunately, mixing incompatible types of capacitors in series or parallel circuits, without giving much thought to their respective properties, is another all-too-frequent error.
Consider the example of electrolytic capacitors, which are widely used in UK power supplies. Capacitors of this type offer high capacitance, but poor high-frequency performance. So, pairing these components with ceramic capacitors in a parallel filter circuit could result in unexpected frequency responses.
It’s Well Worth Taking the Extra Care When Using Capacitors
With such factors as capacitance calculations, voltage ratings, parasitic effects, capacitor types, and tolerance all necessitating close attention by those designing and honing circuits, it is fair to say a little care can go a long way.
Don’t forget, too, that a reputable capacitor calculator – such as the one on the website of electrical components supplier RS – can help you streamline your design process, verify the accuracy of your manual calculations, and avoid common mistakes.
