A capacitor is a component that stores electrical energy and releases it when needed. It consists of two conductive plates separated by an insulating material (the dielectric) and accumulates charge as an electric field. Unlike a battery, it charges and discharges very quickly. In circuits it serves several functions: it stabilises voltage, filters noise, blocks direct current while letting alternating current through, times signals and helps start motors. It is one of the most widely used components in electronics and electrical engineering. In power systems, film capacitors are used — such as those manufactured by ICEL in polypropylene and polyester.

A capacitor works by accumulating opposite charges on its two plates. When connected to a voltage source, positive charge gathers on one plate and negative charge on the other: an electric field forms between them, but the charges cannot cross the insulating dielectric that separates them. The energy stays stored until the circuit needs it; once power is removed, the capacitor releases it. The amount of charge stored (Q) depends on the component's capacitance (C, measured in farads) and the applied voltage (V), according to the fundamental formula Q = C × V. Capacitance increases with larger plate area, smaller distance between the plates and the properties of the dielectric — an area where plastic films deliver exceptional performance in insulation and stability.

A capacitor is made of two conductive plates separated by an insulating dielectric. The plates are usually metallic (aluminium) and collect the electric charge; the dielectric is the insulating material between them, which prevents direct current flow and largely determines performance. The dielectric type gives the capacitor its name: ceramic, electrolytic, plastic film. In film capacitors the dielectric is an extremely thin film of polypropylene or polyester, often metallised directly on its surface. The plates, therefore, are hardly ever thick, separate metal foils, but rather a metallised film. Through a vacuum-evaporation process, a microscopic layer of metal — typically aluminium, zinc or an alloy of the two (Al-Zn) — is deposited directly onto the dielectric surface. This specific construction technology ensures extremely low losses, high long-term stability and the self-healing property: in the event of an internal micro-discharge, the thin metal layer around the defect evaporates instantly, isolating the short circuit and allowing the capacitor to keep working — features that make film the typical choice for power electronics.

Capacitors store electrical energy in the form of an electric field. They do not store current but charge: by separating positive and negative charges on the two plates, they hold energy that can be released almost instantly. This is the key difference from a battery, which stores energy chemically and releases it slowly. The stored energy grows with capacitance and with the square of the voltage (E = ½ × C × V²): that is why power applications use capacitors rated for high voltages and currents. Their ability to deliver energy very quickly makes capacitors essential for stabilising and filtering the supply in converters and inverters.

The main types of capacitor are distinguished by their dielectric: ceramic, electrolytic and plastic film are the three most common families, joined by tantalum and supercapacitors. Ceramics are small and cheap, suited to high frequencies; electrolytics offer high capacitance in little space but are polarised and shorter-lived; film capacitors offer low losses, great stability and long life, ideal for power and high voltage. There is no single "best" type: the choice depends on the application. ICEL specialises in film capacitors made of polypropylene and polyester for power electronics.

The three most common types are ceramic, electrolytic and plastic film capacitors. Ceramics use a ceramic dielectric, are compact and work well at high frequencies, though their capacitance varies with voltage and temperature. Electrolytics use a microscopic layer of metal oxide as dielectric combined with a conductive liquid or gel (the electrolyte) to reach very high capacitance: they are polarised (must be connected the right way) and suited to smoothing in power supplies. Film capacitors use a plastic film and stand out for stability, very low losses and long life, with no polarity. They are the natural choice where reliability, high voltage and high currents are needed — such as the inverters and power converters where ICEL products are used.

The difference lies in the dielectric and therefore in performance. Ceramic is small, cheap and fast, but its capacitance is unstable and not ideal for power. Electrolytic offers very high capacitance in a small volume, yet it is polarised, has higher losses and a life limited by electrolyte dry-out (often a few thousand hours). The film capacitor, based on polypropylene or polyester films, is non-polarised, has very low losses, excellent stability and very long life, and withstands high voltages and currents. That is why, where long-term reliability matters — inverters, converters, power systems — film often replaces electrolytic. This is ICEL's field.

A film capacitor is a capacitor that uses a thin plastic film as dielectric, typically polypropylene or polyester. The film can be surface-metallised, which gives a valuable property: self-healing, the ability to automatically isolate small defects without failing. The advantages are very low losses, high capacitance stability over time and temperature, no polarity, good handling of high voltages and currents, and a very long service life. These strengths make film capacitors the typical choice for power electronics: DC-Link, snubber, AC filters. ICEL manufactures them in polypropylene and polyester.

Polypropylene (PP) and polyester (PET) are the two most-used film dielectrics, with complementary characteristics. Polyester has a higher dielectric constant, so for a given capacitance it takes up less space and costs less. It also offers excellent resistance to high temperatures (up to 125°C): it is the ideal choice for general DC applications, coupling/decoupling circuits and where board space is limited.

Polypropylene stands out for extraordinarily low dielectric losses (very low dissipation factor) and excellent stability as frequency and temperature vary. It withstands high pulse currents (dV/dt) without overheating. This makes it the material of choice for power electronics, AC applications, resonant circuits, snubbers and DC-Links.

In short: polyester for compactness and economy, polypropylene for performance and reliability in power. ICEL manufactures both families — polypropylene and polyester — to cover every need.

Capacitors are used in almost every electrical and electronic device. They are found in power supplies, where they smooth the voltage, in electric motors, where they provide starting torque, in lighting, audio, telecommunications and consumer electronics. In industry and energy their role is even more critical: solar and wind inverters, uninterruptible power supplies (UPS), motor drives, welding machines, battery chargers and railway traction systems. In these power contexts, film capacitors are used, chosen for reliability and durability. ICEL supplies film capacitors precisely for these industrial and power applications; you can explore the series with the parametric search.

The main applications of capacitors are filtering, energy storage, decoupling, timing and phase-shifting. They filter noise and smooth voltage in power supplies; store energy to be released quickly in converters; decouple the stages of a circuit; create delays in timing circuits; shift the current to start single-phase motors. In power electronics they play specific roles such as DC-Link (stabilising the DC bus of an inverter), snubber (protecting semiconductors from spikes) and AC filters. These are the applications ICEL specialises in with its film capacitors: each product family is optimised for one of these functions.

In an electrical circuit a capacitor mainly serves to stabilise and filter. Placed in a power supply, it smooths the rectified voltage by removing residual ripple and supplying current at peak moments. It blocks the DC component while letting AC through, useful for coupling different stages. It decouples circuits, absorbing noise near sensitive components. Combined with a resistor it creates time constants for delays and oscillators. Finally, in power electronics it stores energy on the DC bus and protects the power semiconductors. Its concrete function depends on where it sits: the same component, placed differently, filters, couples or protects.

In a single-phase electric motor, the capacitor is the key component for creating the electrical phase shift needed to start and keep the rotor turning.

Unlike three-phase systems, a single-phase motor powered from the ordinary mains generates a purely pulsating magnetic field, which on its own cannot impart an initial rotation (the motor would merely vibrate). By shifting the current by 90°, the capacitor feeds an auxiliary winding: the combination of the two magnetic fluxes finally produces the rotating field needed for starting.

There are two kinds: the start capacitor, engaged only at start-up to give high torque, and the run capacitor, which stays in operation to optimise efficiency and quietness. The run capacitor is typically a film type, chosen for long life in continuous service. For industrial motor drives and motor control, ICEL offers dedicated film capacitors.

A capacitor's values are read from the markings on its body: capacitance, working voltage and tolerance. On large components the data is often written in full (e.g. "10 µF 400 V"). On small ones a three-digit code is used: the first two are the significant figures, the third is the number of zeros, with the result in picofarads. For example "104" means 10 followed by 4 zeros = 100,000 pF = 100 nF = 0.1 µF. A final letter indicates the tolerance (e.g. K = ±10%). Maximum voltage and temperature range may also appear. For ICEL film capacitors, the full technical data and all useful information are in each series' datasheet and in the "General Technical Information" document.

µF stands for microfarad and is the most common unit for measuring capacitance. The farad (F) is the base unit, but it is enormous: in practice its submultiples are used. A microfarad (µF) is one millionth of a farad; a nanofarad (nF) is one billionth; a picofarad (pF) is one thousandth of a billionth. The useful equivalences are: 1 µF = 1,000 nF = 1,000,000 pF, so 0.1 µF = 100 nF. Ceramic capacitors are often measured in pF and nF, while film and power capacitors are in nF and µF. Knowing these conversions is essential to read datasheets correctly and choose the right component.

Capacitance indicates how much charge a capacitor can store for every volt of applied voltage; the rated voltage indicates the maximum voltage it can safely withstand. Capacitance, measured in farads and their submultiples, determines how much energy the component stores at a given voltage. The rated (or working) voltage is the limit not to be exceeded continuously: beyond that value the dielectric risks breaking down. It is good practice to choose a capacitor with a rated voltage higher than the operating voltage, applying a safety margin. In power capacitors, ripple current, frequency and temperature also matter. To navigate the ICEL series you can use the Icelometer or the parametric search.

Tolerance indicates how much the actual capacitance may deviate from the nominal value. No capacitor has exactly its printed value: tolerance, expressed as a percentage, defines the acceptable range. A 10 µF capacitor with ±10% tolerance will have an actual capacitance between 9 and 11 µF. On components, tolerance is often coded with a letter: J = ±5%, K = ±10%, M = ±20%. The precision required depends on the application: in a power-supply filter a wide tolerance is acceptable, while a timing or resonant circuit needs a tight tolerance. In ICEL datasheets, tolerance is always specified for each series, along with the other electrical parameters.

Capacitors burn out or explode when stressed beyond their limits. The most common causes are overvoltage (above the rated voltage), overtemperature, excessive ripple current and, in electrolytics, reverse polarity. In these cases the dielectric breaks down or the electrolyte overheats and produces gas, up to the rupture of the casing. Ageing also contributes, especially in electrolytics. Plastic film capacitors offer markedly higher intrinsic safety standards. Thanks to the self-healing property, micro-short-circuits are isolated instantly by the evaporation of the surrounding metal. Moreover, for the most demanding power applications, some film capacitor series can adopt advanced technologies such as segmented metallisation (an internal micro-fuse structure) or, for large-size capacitors used in power-factor correction or AC applications, metal cases fitted with safety disconnectors that prevent the component from entering a destructive short circuit. The best prevention at the design stage remains careful calculation of the fundamental parameters, keeping wide operating margins on voltage, temperature and ripple current.

A faulty capacitor is recognised by visual signs and electrical measurements. Visually, especially in electrolytics, suspicious signs are bulging of the top, fluid leaks, burns or deformation of the casing. Electrically, capacitance is measured with a capacitance meter: if it is far from the nominal value (allowing for tolerance), the component is degraded. Another indicator is the equivalent series resistance (ESR), which rises with ageing. Indirect symptoms in the circuit are humming, high ripple, restarts or power-supply malfunctions. Film capacitors, being more stable and durable, fail far less often than electrolytics; when they do, they usually show reduced capacitance or lower insulation.

The right capacitor is chosen starting from the function and the electrical parameters of the application. The main criteria are: required capacitance, working voltage (with a safety margin), type of current (DC or AC) and, in power applications, ripple current, frequency and ambient temperature. The construction type also matters: film for reliability, stability and power; electrolytic for large capacitance at low cost; ceramic for high frequencies. Finally, size, mounting type and expected life must be considered. For industrial and power applications, ICEL film capacitors are selected by product family: the Icelometer and the parametric search help identify the right series.

Generally no: capacitance must be respected, because many circuits depend on its precise value. In a filter, or in a timing, resonant or phase-shift circuit, changing the capacitance alters behaviour: a different value shifts cut-off frequencies, delays or a motor's starting torque. A small variation within tolerance is acceptable; a marked deviation is not. In some non-critical functions, such as smoothing in a power supply, a slightly higher capacitance may be tolerated or even improve filtering, but inrush current and size must be checked. The rule of thumb: replace with the same value, or check the datasheet before changing it. When in doubt, keep the original specifications.

Yes: using a capacitor with a higher rated voltage is safe and often recommended. The rated voltage is a maximum limit, not a target value: a 630 V capacitor in place of a 400 V one works without problems in the same circuit — in fact with a greater safety margin that extends its life. The only caveat is that, for the same capacitance, a higher-voltage component is generally larger and more expensive, so size must be checked. The opposite does not hold: choosing a voltage lower than the operating one leads to dielectric breakdown. For the ICEL series, the voltages available for each family are in the datasheets.