# Film vs Aluminium Electrolytic Capacitors: Choosing for DC Link and Bulk Storage

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Technical comparison between **Film Capacitor** and **Aluminium Electrolytic** by [Novapart](https://novapart.co).

## Overview

On a DC link the choice between film and aluminium electrolytic is a trade between capacitance you can afford and lifetime you can rely on. Everything else follows from that.

An aluminium electrolytic stores charge across an oxide layer grown on etched foil. The etching multiplies the effective surface area enormously, which is why the part offers more microfarads per euro and per cubic centimetre than any other family. The price is a liquid electrolyte, and liquids escape. The electrolyte diffuses out through the end seal over the working life of the component, capacitance falls, ESR climbs, and eventually the part stops doing its job. Manufacturers quote this as a life in hours at the maximum rated temperature, commonly 2,000 or 5,000 hours at 105 °C, and the useful rule is that life roughly doubles for every 10 °C cooler the part actually runs. A 2,000-hour capacitor sitting at 65 °C is good for something near 32,000 hours. The same part pressed against a hot heatsink is good for a fraction of that, and it is usually the capacitor that ends the life of the equipment.

A film capacitor has no electrolyte. It is a metallised plastic film, wound or stacked, and there is nothing in it to dry out. Its ESR is very low and stays low when cold, which matters because an electrolytic's ESR can multiply several times at −25 °C and take the ripple performance of a supply with it. Film parts are non-polarised, so they handle reversal and true AC, and they tolerate the fast dV/dt that a snubber sees.

The property with no equivalent on the other side is self-healing. When a metallised film part suffers a dielectric fault, the fault current vaporises the thin metallisation around the defect and isolates it. The capacitor loses a sliver of capacitance and carries on. That is why film degrades gracefully, drifting down over years, while an electrolytic tends to reach a threshold and then vent. In equipment where an abrupt failure is expensive, that difference is worth more than the capacitance you gave up.

What film cannot do is be cheap in bulk. If a design needs 4,700 µF at 400 V on a DC link, the electrolytic bank is a handful of cans and the film equivalent is a box. This is the entire reason electrolytics remain in mainstream power supplies: for pure energy storage at low frequency, nothing competes on cost or volume.

Two applications admit no argument. Anything across the mains, X class between line and neutral or Y class to earth, must be a safety-rated film capacitor, because the failure mode is a safety matter and electrolytics are not permitted there. And any snubber across a switching device must be film, because an electrolytic is too slow and too lossy to absorb those edges.

In practice, high-reliability and long-life designs increasingly use both: a film capacitor sized for the ripple current and the high-frequency work, backed by a smaller electrolytic bank for bulk energy. The film part takes the heating that would otherwise age the electrolytic, and the electrolytic supplies the microfarads the film part cannot afford.

## Comparison Parameters

| Parameter | Film Capacitor | Aluminium Electrolytic | Recommendation |
|---|---|---|---|
| Capacitance per unit volume | Low. Microfarads occupy real board area. | High. Thousands of µF in a modest can. | right |
| ESR | Very low, a few milliohms, and stable with temperature. | Tens to hundreds of milliohms, rising sharply below 0 °C. | left |
| Ripple current per µF | High. Low ESR means little self-heating. | Lower per µF, but the sheer capacitance compensates. | left |
| Polarity | Non-polarised. Handles AC and reversal directly. | Polarised. Reverse voltage destroys it, often violently. | left |
| Wear-out mechanism | None in normal use. Self-heals around dielectric faults. | Electrolyte dries out. Life rated in hours at 105 °C. | left |
| Failure mode | Degrades gracefully; capacitance falls as sections clear. | Goes high-ESR, then vents. Can fail short in some constructions. | left |
| Temperature behaviour | Stable across the range. No cold-start ESR problem. | ESR can multiply several times at −25 °C. | left |
| Voltage derating needed | Modest. Many parts run near rated voltage. | Significant. 20% headroom is common practice. | left |
| Cost per µF | High. | The cheapest bulk capacitance available. | right |
| Suitability across mains (X/Y class) | The only option. Safety-rated X and Y parts are film. | Never. Not permitted across mains. | left |
| Suitability for snubbers | Designed for it. Low ESL and high dV/dt tolerance. | Unsuitable. Too slow, too lossy. | left |
| Catalogue depth at Novapart | 24,425 active film references, 39% in stock. | 19,734 active aluminium electrolytics, 47% in stock. | None |

## Verdict & Recommendation

Bulk energy storage where cost and volume decide, and the operating temperature is under control: aluminium electrolytic. Nothing else buys microfarads that cheaply. Derate the voltage by around 20%, keep the part away from heat sources, and do the lifetime arithmetic at the temperature it will actually see rather than at the rating.

DC link duty with heavy ripple current, a cold operating environment, or a service life measured in years rather than warranty periods: film. The low and temperature-stable ESR, the absence of any wear-out mechanism and the self-healing behaviour are what you are paying for.

Across the mains, line to neutral or line to earth: a safety-rated X or Y class film capacitor, with no exceptions. An electrolytic is not an option there.

Snubbing a switching device: film, for the low ESL and the dV/dt tolerance.

Where the budget allows, the strongest DC link designs combine the two, letting the film part absorb the ripple heating that would otherwise dry out the electrolytic bank. That arrangement costs more in parts and usually less over the life of the equipment.

## Relevant In-Stock Components

| SKU | Name | Manufacturer | Price | Stock |
|---|---|---|---|---|
| [EEUFR0J102](https://novapart.co/products/EEUFR0J102/electrolytic-capacitor-1000-f-63-v-20-radial) | Electrolytic Capacitor, 1000 µF, 6.3 V, ± 20%, Radial Leaded, 6000 hours @ 105°C, Polar | PANASONIC | €0.1440 | 1000+ |
| [R82DC3100DQ50K](https://novapart.co/products/R82DC3100DQ50K/general-purpose-film-capacitor-metallized-pet) | General Purpose Film Capacitor, Metallized PET Stacked, Radial Box - 2 Pin, 0.1 µF, ± 10%, 40 V | KEMET | €0.0520 | 1000+ |
| [MCKSK400M4R7G13S](https://novapart.co/products/MCKSK400M4R7G13S/electrolytic-capacitor-47-f-400-v-20-radial-leaded) | Electrolytic Capacitor, 4.7 µF, 400 V, ± 20%, Radial Leaded, 2000 hours @ 105°C, Polar | MULTICOMP PRO | €0.1340 | 1000+ |
| [R82DC3150AA60J](https://novapart.co/products/R82DC3150AA60J/general-purpose-film-capacitor-metallized-pet) | General Purpose Film Capacitor, Metallized PET Stacked, Radial Box - 2 Pin, 0.15 µF, ± 5%, 40 V | KEMET | €0.0580 | 1000+ |
| [F841DM154M330L](https://novapart.co/products/F841DM154M330L/film-capacitors-150nf3plus-20perv) | FILM CAPACITORS 150NF3PLUS-- 20PERV | KEMET / PARTNER STOCK | €1.1200 | 1000+ |
| [82EC1100KI50J](https://novapart.co/products/82EC1100KI50J/general-purpose-film-capacitors) | GENERAL PURPOSE FILM CAPACITORS | KEMET / PARTNER STOCK | €0.0390 | 1000+ |
| [MCGPR35V106M5X11](https://novapart.co/products/MCGPR35V106M5X11/electrolytic-capacitor-10-f-35-v-20-radial-leaded) | Electrolytic Capacitor, 10 µF, 35 V, ± 20%, Radial Leaded, 2000 hours @ 85°C, Polar | MULTICOMP PRO | €0.0140 | 1000+ |
| [MCRH25V227M8X11](https://novapart.co/products/MCRH25V227M8X11/electrolytic-capacitor-220-f-25-v-20-radial-leaded) | Electrolytic Capacitor, 220 µF, 25 V, ± 20%, Radial Leaded, 2000 hours @ 105°C, Polar | MULTICOMP PRO | €0.1080 | 1000+ |
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