Film power capacitors · Designed & built in the UK
We design and manufacture custom AC, DC-link, snubber, energy-storage and track-circuit capacitors in Great Yarmouth, matched to your voltage, current, envelope and terminations. Trusted in Royal Navy propulsion, on Eurostar and the London Underground, and at CERN.
Talk directly to the engineers who’ll design your part.
Precision windingGreat Yarmouth, UKMetallised PP film
In service with
Start here
Whether you’re designing something new, keeping a fleet running or specifying from a proven range, you deal directly with the engineers who design and build your capacitor.
New design
Bring us your ratings, envelope and environment. We’ll engineer a part to suit, from first concept to first article, with rapid prototypes and exclusive part numbers if you need them.
Start a design briefObsolescence
Mid-life refurbishment and the original maker has moved on? We engineer equivalents to parts from ICAR, NWL, EPCOS, TDK, Vishay, Electronicon and more. Most drop straight in.
Find an equivalentProven ranges
Six families of AC, DC, snubber, energy-storage, track-circuit and IGBT filter capacitors, each adaptable to your current, voltage, size, mass and terminations.
Explore the rangesCapacitor ranges
Every range starts from proven designs and is matched to your application: current, voltage, size, mass and terminations. You’re never limited to a catalogue.
For harmonic filtering, power-factor correction and voltage smoothing in drives, rail and power transmission.
Stabilise DC links, store energy and replace electrolytic banks in converters, inverters and HVDC systems.
Protect GTO, IGCT, IGBT and thyristor devices from voltage spikes and ringing during switching.
Pulse power: store energy and release it in fast, high-power discharges for research, defence and test.
Adjustable feed and relay-end capacitors, plus fixed capacitors for jointless track circuits in railway signalling.
Cut the ripple current from IGBT inverters for a cleaner, more stable output in drives and servo systems.
Can’t see your rating?Our ranges are a starting point, not a limit. Send us your requirement and we’ll design to it.
Send us your specIn service
You’ll never see our capacitors. They’re sealed inside aircraft-carrier propulsion drives, traction converters, signalling cabinets and particle accelerators, charging and discharging thousands of times a second. Nobody thinks about them. That’s exactly the point.
Naval propulsion
Our capacitors are an essential part of the main propulsion systems on the UK’s two aircraft carriers. They’re also fitted across the fleet, from destroyers to the submarines of the deterrent.
Our research into partial discharge has refined our processes to all but eliminate PD from the capacitors we build for marine propulsion.
Metro · Life extension
Replacement filter capacitors for the entire 92TS fleet, part of a life-extension and traction overhaul to keep the trains running for another 15–20 years.
Rail · Obsolescence
We replaced a bank of Siemens electrolytic capacitors in the auxiliary converter with an all-thin-film design. It powers the lighting, heating and ventilation for passengers.
Rail · Re-engineering
We recreated obsolete 1980s capacitor designs for two new battery-electric locomotives, keeping them fully compatible with MTR’s existing rolling stock.
Research · Motorsport
Energy-storage capacitors for CERN and plasma-physics research, and capacitors chosen by leading Formula 1 powertrain manufacturers.
Obsolete parts
Power capacitors often need replacing before the equipment around them. That usually happens at a mid-life refurbishment, 20–30 years in, when the original maker no longer produces the part. We design and build equivalents, and in most cases they drop straight in.
Equivalents engineered for parts from
Tell us what you’re replacing. An engineer will review it and come back to you about an API equivalent.
An engineer will review the part and get back to you. If it’s urgent, call +44 (0)1493 652752 and select option 1.
Inside an API capacitor
Our capacitors fail significantly less often than the industry standard. That comes down to materials, process control and four decades of learning what makes a power capacitor last.
High-isotactic metallised polypropylene with an extended working temperature range.
If the dielectric is ever punctured, the metallisation around the fault clears and isolates it. The capacitor carries on working.
Elements are wound on precision edge-controlled automatic winding machines.
High-conductivity copper gives low-resistance internal connections. Low-resistance foil electrodes carry high currents in our snubbers.
Vacuum impregnated with an environmentally safe oil, or sealed in a dry, leak-free resin.
Powder-coated, corrosion-free metal or insulated cases. UV-resistant, halogen-free, low-smoke and flame-retardant.
Industries
Since the 1980s our capacitors have gone into locomotives, warships, drives, grids and research machines for customers across Europe, North America, Africa, the Middle East and Asia.
Traction converters, line filters, auxiliary supplies and track-circuit signalling, on new builds and mid-life overhauls.
Eurostar · Central line · MTR
PWM propulsion drives for merchant and naval vessels: snubber, AC harmonic filter, DC-link and DC tuned filter capacitors.
QE-class carriers · Type 45
DC bus, EMI filter and snubber capacitors for VFDs, plus elevators, escalators, conveyors and cable cars.
VFDs · Lifts · Conveyors
FACTS, STATCOM, SVC and HVDC, detuned filters and power-factor correction, including renewable energy.
FACTS · STATCOM · HVDC
Particle accelerators, lasers, lightning simulation and high-voltage capacitor banks.
CERN · LHC · ISIS
Radar, range finders, railguns, missile systems and EMP, plus capacitors for avionics.
Radar · Railguns · Avionics
Formula 1 powertrains, kinetic energy recovery (KERS) and electric and hybrid vehicles.
Formula 1 · KERS
Medical equipment, subsea survey sparkers and boomers, induction heating, magnetisers and UV sterilisation.
Medical · Oceanography · Food
Don’t see your sector? If it switches, smooths or stores power, talk to us.
Talk to an engineerCustom design
Work with us at concept stage, or late in a project when a time-critical design is needed. You’ll see exactly what we propose, and what it costs, before anything is built.
Send your requirement, scope and any specifications.
We agree ratings, envelope, environment and deliverables.
We assess technical and production feasibility, then confirm the way forward.
You receive an initial design proposal to review.
A detailed costing follows for your approval.
Amendments are made and the final design is signed off.
Production begins to the approved design and specification.
Capacitors designed and built for a specific application, to precise specifications.
We analyse how an existing capacitor is built and performs, then develop a better alternative.
Prompt preliminary designs and prototypes, with favourable lead times subject to technical data.
Specialist in-house equipment for high-voltage test and measurement.
Designs created with exclusivity in mind, with unique, dedicated part numbers.
Designed and built for onward sale, with your branding integrated.
About API Capacitors
Design, production, sales and after-sales support work side by side on one site in Great Yarmouth. The engineer who designs your capacitor is a short walk from the people who wind, impregnate and test it.
Our story
Western Electric is founded in London. It becomes STC, Standard Telephones and Cables.
STC establishes capacitor manufacturing in Great Yarmouth as part of its electrical and telecoms business.
The capacitor business becomes Norfolk Capacitors Ltd, building an international name in traction, drives, defence, medical and plasma systems.
API Capacitors Ltd acquires the business and assets, keeping its people, IP, customers and the Great Yarmouth works.
Backed by a four-company engineering group, with more than 70% of turnover exported.
The Group
API Holdings brings together four specialist engineering businesses. Each is expert in its own field, backed by the stability and collaborative approach of the wider Group and an international network of representatives and partners.
Meet us · Stand J195
Bring a drawing, a part number or a problem you’re trying to solve, and talk it through with our team. Book ahead and we’ll keep time free for you.
Book a meeting at the showInsights
Rail 1 min read
Snubber, AC harmonic filter and DC-link capacitors for GTO- and IGBT-based traction, built for the heat and humidity of rail service.
Read articleDrives 1 min read
The three capacitor roles inside every variable-frequency drive (DC bus, EMI filter and snubber) and how we design for each.
Read articleMarine 1 min read
From QE-class carriers to Trident submarines: our partial-discharge research and the capacitors inside PWM propulsion drives.
Read articleProjects, events and new roles, as they happen.
Follow on LinkedInFAQs
Can’t see yours? Call us on +44 (0)1493 652752 (option 1) and you’ll speak to someone who knows capacitors.
Ask the engineering teamWe’re a high-mix, low-volume manufacturer, so prototypes, one-offs and small batches are everyday work for us. When you need to scale, our Group’s Norwich facility gives us the option of volume production.
Almost always. We design and supply equivalents to current and discontinued power capacitors that use metallised-film and film/foil technology, and in most cases they’re drop-in replacements. Send us the manufacturer, the part number and, ideally, a datasheet or photos.
As much as you have: capacitance, rated voltage (AC or DC), RMS and peak current, frequency, operating temperature, size and mass limits, terminations, applicable standards, quantities and timescales. A drawing or an existing datasheet helps.
If you only have part of the picture, that’s fine; we’ll work through the rest with you.
We turn around preliminary designs and prototype capacitors promptly, with favourable lead times. How quickly depends mainly on how much technical data is available at the start.
We operate a UKAS-accredited ISO 9001:2015 quality management system. Our designs reference the relevant product standards, for example BS EN 61071 for power-electronics capacitors and BS EN 61881 for railway applications, and our rail capacitors are designed to meet European and applicable rail standards.
Yes. More than 70% of our turnover comes from export, with customers across mainland Europe, North America, Africa, the Middle East and Asia, supported by our network of overseas partners.
Yes. We design and manufacture capacitors for white-label and onward sale, can integrate your branding, and can assign exclusive, dedicated part numbers.
Start an enquiry
Share as much or as little as you have. A drawing, a part number or a rough set of ratings is enough to get going.
Fields marked * are required. Everything else helps us come back with better answers, faster.
We’ll review your requirement and get back to you to talk through the detail. If it’s urgent, call +44 (0)1493 652752 and select option 1.
