Are you able to properly choose your capacitor?
If you have landed here, it is probably because you have enjoyed playing with our ICELOMETER: a symbolic tool we have designed to make you reflect on certain characteristics that are not always considered when choosing a capacitor.
Follow the trail of questions below and find out if your answers find the ‘’approval‘’ of our capacitors...
In order to choose the right capacitor, is it important to know the operating conditions in detail of the specific application?
Correct! Choosing the right capacitor is not as simple as it might seem. Pay attention to the data as they are provided and to the reference conditions (temperature, voltage, frequency, etc...): different manufacturers may make different choices regarding the references adopted.
It is up to the user to relate all data to the actual working conditions of his application.
This is a wise approach that can lead you to a reliable and long-lasting design.
Be careful! Knowing the general characteristics and electrical ratings is certainly important, but don’t underestimate all those factors that can have a significant impact on the performance of capacitors, such as the layout of the circuit, the environmental conditions, any possible external sources of additional stress: in general, everything that helps to define the operating conditions of the application as completely as possible.
No way! Each component of a circuit deserves equal importance, including capacitors.
Don't forget that, despite the best that is foreseen and adopted in terms of protection and safety on the level of capacitors design and construction, in the event of serious problems and failures, the failure of capacitors can damage the entire apparatus, also in a devastating way (explosions, fire, meltdown, etc.).
And you don't want that to happen, do you?
What measures should be taken for a good mounting layout to ensure correct dissipation and mechanical stability?
Very good! It’s essential not to install capacitors in contact or very close to other components but with enough distance to allow proper airflow and cooling: contact with other components can cause mechanical stress under vibration, shocks or due to thermal settlements.
Dimensional tolerances must also be taken in consideration when designing capacitors fitting on PCBs and in the equipment.
As a general indication, the suggested minimum distance between side by side elements should be at least about 1/12 of the diameter or thickness in case of axial terminals components and at least about 1/8 of the thickness in case of radial terminals capacitors and capacitors in box with lug terminals (on all the components faces).
Particular attention shall be paid to possible body deformations when capacitors are used in high humidity environments.
Not exactly… certainly where environmental conditions are particularly stressful, correct positioning and layout becomes increasingly crucial.
It’s also a fact that, generally speaking, the larger the capacitor is and the more it is stressed by voltage, current or temperature, the more important the correct layout design is.
However, it is strongly advisable to consider all the necessary precautions: in fact, even in case of a not particularly demanding application for the capacitors, unexpected or exceptional conditions can still occur which can put the entire system to the test.
“Better safe than sorry”.
No, dangerous! It is always necessary to size the capacitor starting from the operating conditions and the actual stress expected in the application in order to guarantee reliable design.
In short, never "save the choice of capacitor for last", otherwise the risk is being forced to choose an undersized component because there is not enough space available in the apparatus.
Capacitor manufacturers are very good guys, but they can't work miracles: you can't fill a half-liter bottle with 5 liters of liquid, right?
Reliability means long life expectancy with the lowest possible failure rate, commensurate with the expectation of the application: what can be done to minimize the potential risks related to the choice of capacitor?
Good answer! Capacitors used in power applications are typically exposed to relevant stresses level and possible failure may result in very serious consequences.
For this reason, the keeping of a wide safety margin (suggested about 25÷30%) compared to ratings is a wise and long-term profitable approach.
Wise, but not enough! One might be led to think that scheduled maintenance, calibrated with the capacitors maximum guaranteed lifetime as per specification, allows to maximize the performance of the capacitors, without running particular risks.
However, it is often forgotten or underestimated that the concept of lifetime expectancy is purely statistical and strongly correlated to the failure rate. In other words, given a certain number of capacitors operating in the field, it cannot be expected that all of them will reach the end of their expected life without any failure, nor that they will all fail immediately afterwards.
The aging process can easily be uneven and more rapid the closer the operating conditions get to the nominal ratings.
For this reason, it is necessary to keep in mind, during the design phase, the state in which the capacitors may be near the end of their life, because they can’t stay always "as new".
Nice try… but no! Of course, manufacturers consider safety margins when drawing up capacitor specifications, to take into account all the tolerances involved, from the material to production tolerances.
However, they cannot in any way predict or simulate all the specific uses of a certain type of capacitor in the field, and related stresses they will face, which can be almost infinite.
As far as we are concerned, what we believe is right and professional to declare in the specification is the reliability of the components in the worst possible conditions, among those allowed and specified reference parameters, of course.
How to say: “it can only go better than this!”
Can the reliability of capacitors depend somehow also on potential external factors, as additional stress sources, including for example environmental ones?
Yeah, music to my ears! We don't have much to add, but just few examples.
The possible presence of relevant humidity levels may critically increase the global stress and accelerate the aging of the components, so it is essential to choose capacitors designed with specific technologies and materials for harsh environments.
Capacitors shall be placed away from any source of heating to prevent high temperatures to compromise design reliability. Extra heating can also be consequence of strong magnetic fields inducing currents in metal part.
Capacitors shall be in safe distance from heavy current conductors and, in general, the influence of other components must always be carefully evaluated.
Note that also leads, especially large section lugs, dissipate heat but can also transfer heat into the capacitor: it is necessary to keep the connections cooler than the capacitor.
You can’t get off that easy! An appropriate ventilation system can help dissipate excess heat more effectively.
However, it is necessary to size the capacitors in steady-state conditions without ventilation.
In fact, even in the presence of ventilation, the internal temperature of the capacitor (its core, basically) depends mostly on the operating conditions, which if very stressful would only be masked from outside by the ventilation, even if the capacitor itself will still suffer overstresses.
Regarding humidity, however, ventilation may not be helpful at all as it may not have the effect of making the air drier, but of creating a flow of humidity particles on the capacitor.
It would be nice, but no. The technological level achieved certainly guarantees exceptional performance and resistance to various stress factors. However, it is not and cannot be sufficient.