AC capacitors
Power-factor correction, harmonic filtering and smoothing for demanding alternating-current circuits.
- Traction & drives
- FACTS, STATCOM, SVC
- Line filters
- Induction heating
Power film capacitors · Designed & made in Norfolk, UK
API Capacitors: custom power capacitors. Made to measure. Made to last.
We design high-performance power capacitors around your application, matching voltage, current, footprint and terminations. And when another maker discontinues a part, we build its drop-in replacement. Every capacitor is wound, impregnated and tested in our Great Yarmouth factory.
Talk directly to the engineers who design your part, from prototype to production.
- ISO 9001:2015 UKAS-accredited
- 40 years in Great Yarmouth
- 70%+ exported worldwide
| Item | Made to measure |
|---|---|
| 1 | Terminations: busbar, stud or bespoke |
| 2 | Fill: dry resin or environmentally safe oil |
| 3 | Case: metal or insulated, around self-healing polypropylene film |
| 4 | Mounting: to your drawing |
| 5 | Rating: your capacitance, voltage and current |
- Drg no.
- YOUR-SPEC-001
- Rev
- A
- Scale
- NTS
- Made in
- Great Yarmouth, UK
API Capacitors LtdIn service where failure isn’t an option.
For four decades, engineers have specified our capacitors for systems that simply have to keep running, with failure rates significantly lower than the industry standard.
- Royal Navy HMS Queen Elizabeth & HMS Prince of Wales Main propulsion systems on the UK’s aircraft carriers
- Royal Navy Type 45 destroyers & the Trident fleet Plus HMS Bulwark and RFA Wave Ruler
- High-speed rail Eurostar Class 373 All-film replacement for an electrolytic capacitor bank
- Metro London Underground Central line Filter capacitors for the 1992 Tube Stock life extension
- Research CERN & ISIS Pulse capacitors for particle accelerators
- Motorsport Formula 1 Used by leading powertrain manufacturers
- Years making power capacitors in Great Yarmouth
- 40
- Share of turnover from export markets
- 70%+
- Dedicated manufacturing facility
- 2,000 m²
- Certified quality management, UKAS-accredited
- ISO 9001
C1Start here
What do you need?
Tell us where you’re starting from. We’ll take it from there.
01
A capacitor designed for my application
New build or new specification? We engineer capacitance, voltage, current, footprint and terminations around your system.
Start a custom design 02A replacement for an obsolete part
Original maker stopped producing it? We design fully interchangeable drop-in equivalents, often from just a part number, datasheet or photo.
Find a replacement 03A proven part from your range
AC, DC-link, snubber, energy storage, track circuit and IGBT filter capacitors, with datasheets ready to download.
Browse the rangeC2The range
Six families. Endless configurations.
Our range is a starting point, not a limit. Current, voltage, size, mass and terminations are matched to each application, so you get the part your system needs rather than the nearest one in a catalogue.
DC & DC-link capacitors
Energy storage and voltage stabilisation for DC-link, filter and converter circuits, including electrolytic replacement.
- Inverters & converters
- Propulsion & traction
- HVDC
- Lasers & scanners
Snubber capacitors
Protect GTO, IGCT, IGBT and thyristor devices from voltage spikes as they switch, with high-current foil electrodes.
- Traction converters
- Welding & furnaces
- Hybrid & EV (KERS)
- Power transmission
Energy storage capacitors
Rapid charge and discharge for pulsed power, from high-voltage capacitor banks to research and defence systems.
- Particle accelerators
- Lightning simulation
- Radar & defence
- Subsea survey
Track circuit capacitors
Adjustable AC feed and relay-end capacitors, plus high-frequency DC fixed capacitors for jointless track circuits.
- Railway signalling
- IP67 insulated cases
- <1% tolerance (HF DC)
- Hermetically sealed
IGBT filter capacitors
Smooth inverter output and absorb ripple current in IGBT-based drives. Compact, efficient and built for continuous duty.
- Variable-speed drives
- Servo systems
- Industrial inverters
- High temperature
Every family, built the same way
- Ultra-low-defect, high-isotactic metallised polypropylene film
- Controlled self-healing for long life
- Precision edge-controlled automatic winding
- High-conductivity copper internal connections
- Dry leak-free resin or environmentally safe oil
- UV-resistant, halogen-free, low-smoke, flame-retardant materials
Fully interchangeable. No redesign of your equipment.
C3Obsolete & replacement parts
Discontinued isn’t the end of the line.
Rail and marine fleets usually reach mid-life refurbishment after 20–30 years, and often find the original capacitors are no longer made. We design replacements for current and discontinued metallised film and film/foil capacitors, and in most cases they’re a straight drop-in fit.
Replacements for most brands, including
- EPCOS
- TDK
- Vishay
- Electronicon
- ICAR
- NWL
Brand names are trademarks of their owners and are used only to identify the parts we replace.
Recent replacement programmes
Eurostar Class 373
We designed and built an all thin-film capacitor to replace a bank of Siemens electrolytic capacitors in the auxiliary converter that powers lighting, heating and ventilation for passengers.
London Underground Central line
Replacement filter capacitors for the whole 1992 Tube Stock fleet, part of the traction overhaul that keeps these trains running for another 15–20 years.
Brush Traction for MTR, Hong Kong
Obsolete 1980s capacitor designs recreated for two new battery-electric locomotives, keeping them fully compatible with existing rolling stock.
C4Custom design
Engineered around your system, not squeezed from a catalogue.
Our engineers use 3D CAD, finite element analysis and mathematical modelling of electrical, thermal and mechanical behaviour to design each capacitor for its exact duty. You’re involved at every stage, so lead times and costs stay under control.
Custom engineering
Capacitors designed and built for a specific application, to precise specifications.
Reverse engineering
We analyse an existing capacitor’s construction and performance, then build a better equivalent.
Rapid prototyping
Prompt preliminary designs and prototypes on favourable lead times, given the technical data.
High-voltage testing
Specialist in-house test and measurement equipment to prove every design.
Exclusive part numbers
Unique, dedicated part numbers, so your design stays yours.
White-label manufacture
Capacitors designed and made for onward sale, carrying your branding.
From enquiry to production in seven steps
Start with step one- 01
Enquiry
Share your requirement, scope and any specifications.
- 02
Requirements
We confirm the key specs, expectations and deliverables with you.
- 03
Feasibility
We assess technical feasibility and production before agreeing the way forward.
- 04
Design proposal
You review an initial design built around your requirements.
- 05
Costing
A detailed costing for your review and approval.
- 06
Approval
Any amendments made, the final design is formally signed off.
- 07
Manufacture
Production starts in Great Yarmouth, to the approved design.
C5Applications
Wherever power is switched, filtered or stored.
Our capacitors work in transportation, marine, automotive, aerospace, defence, medical, research, renewable energy and power distribution. These are the places they work hardest.
Rail & metro
Traction converters for GTO and IGBT designs, auxiliary supplies for lighting, heating and ventilation, line filters and trackside signalling. Rail designs are oil-free, UV-resistant, halogen-free, low-smoke and flame-retardant.
In serviceEurostar · London Underground · MTR Hong Kong
Marine & naval
Snubber, AC harmonic filter, DC-link and DC tuned filter capacitors for PWM propulsion inverters. Our partial discharge research has all but eliminated PD in these designs.
In serviceHMS Queen Elizabeth · HMS Prince of Wales · Type 45 · Trident fleet
Drives & power electronics
DC bus, EMI filter and snubber capacitors for variable frequency drives, plus welding, furnaces, induction heating, elevators, escalators and conveyors.
ProductsDC-link · IGBT filter · Snubber · AC
Power transmission & renewables
Power conditioning, detuned filters, FACTS, STATCOM, SVC, power-factor correction and HVDC.
ProductsAC · DC · Snubber
Research & pulsed power
Particle accelerators, lasers, lightning simulation and high-voltage capacitor banks, plus magnetisers and pulse-forming networks.
In serviceCERN · ISIS
Defence, aerospace & motorsport
Radar, range finders, railguns, missile systems and EMP, plus kinetic energy recovery (KERS) in hybrid powertrains.
In serviceFormula 1 powertrain manufacturers
Medical, subsea & specialist
Scanners and detectors, subsea survey sparkers and boomers, and UV sterilisation in food processing.
ProductsEnergy storage · DC · AC
C6Inside the factory
Wound, impregnated and tested in Great Yarmouth.
We’re a high-mix, low-volume specialist, run by professional engineers. Design, production, sales and after-sales support work side by side, so the people who design your capacitor are never far from the line that builds it.
- 2,000 m² manufacturing facility, close to major ports and airports
- Clean-room winding on precision automatic machines
- Vacuum impregnation and an in-house CNC machine shop
- 3D CAD, FEA and electrical, thermal and mechanical modelling
- Specialist high-voltage test and measurement equipment
- Volume production capacity across the API group
ISO 9001:2015 certified by Alcumus ISOQAR (UKAS-accredited) for the design and manufacture of capacitor products for rail, industrial, research, marine and aerospace applications.
View certificate 17087-QMS-001C7Our story
Four decades of capacitors from one Norfolk site.
Our roots run back through STC, one of Britain’s great electrical engineering names. The people, know-how and Great Yarmouth factory have carried on through every chapter since.
Follow us on LinkedIn- Before 1986
STC era. Standard Telephones and Cables, a business with roots going back to 1883, makes capacitors in Great Yarmouth.
- 1986
Norfolk Capacitors. A management buyout from STC creates Norfolk Capacitors Ltd, keeping the workforce, expertise and product range.
- 1986–2012
An international reputation in rail traction, industrial drives, defence, medical equipment, plasma systems and power electronics.
- Oct 2012
API Capacitors. API Capacitors Ltd acquires the business, preserving the factory, team, IP and customer relationships. Production continues without a break.
- 2013
Norwich head office. The API group moves into its new Norwich head office, home to our design team.
- 2024
A wider range for rail, industrial, energy, defence, aerospace and medical applications.
- Today
Designing and building in Norfolk for customers across Europe, North America, Africa, the Middle East and Asia.
C8Part of API Holdings
A specialist, backed by a group.
API Capacitors is one of four specialist engineering businesses in API Holdings. You get the focus and responsiveness of a specialist, with the stability, manufacturing capacity and international reach of a wider group.
- API Capacitors
- API Engineering
- PPI Engineering
- API Stone
Representatives and partners in numerous countries support customers locally.
See us live · Stand J195
Meet us at Advanced Engineering 2026.
Bring a drawing, a datasheet or a discontinued part. Our engineers will be on stand J195 at the NEC Birmingham (Halls 3 & 3a) on Wednesday 4 November, 9:00–17:00, and Thursday 5 November, 9:00–16:00.
C9Questions
Straight answers.
Can’t see your question? Call +44 (0)1493 652752 (option 1) or email sales@api-capacitors.com.
Can you replace a capacitor that’s no longer made?
In most cases, yes. Send us the part number, datasheet, drawing or a photo of the nameplate. We’ll design a fully interchangeable equivalent, usually a straight drop-in fit, for current and discontinued metallised film and film/foil capacitors.
What information do you need to quote?
Ideally capacitance, rated voltage (AC or DC), rms or ripple current, frequency, operating temperature, size limits, terminations, mounting, quantity and timescale. If you don’t have all of it, send what you have and we’ll fill the gaps together.
Do you have minimum order quantities?
We specialise in high-mix, low-volume manufacture, so prototypes, small batches and production runs are all routine. For higher volumes we can draw on manufacturing capacity across the API group. Tell us your quantities and we’ll advise.
How long does a custom capacitor take?
It depends on the design. Once we have the technical data, we provide preliminary designs and prototypes on favourable lead times, and we’ll confirm a clear timeline with your quotation.
Which quality standards do you work to?
We’re ISO 9001:2015 certified by Alcumus ISOQAR (UKAS-accredited). Our rail capacitors are designed to meet European and applicable rail standards, using UV-resistant, halogen-free, low-smoke and flame-retardant materials. Tell us which standards your project must meet.
Do you supply customers outside the UK?
Yes. More than 70% of our turnover comes from export markets, with customers across mainland Europe, North America, Africa, the Middle East and Asia, supported by a network of overseas partners.
Can you make capacitors under our brand?
Yes. We design and manufacture white-label capacitors for onward sale, and can give your designs exclusive part numbers.
C10Send us your spec
Tell us what you need to power.
A new design, a replacement or a part from our range: an engineer will review your requirement and come back with questions, a feasibility view or a quotation.
- 1An engineer reviews your requirement
- 2We confirm feasibility and any questions
- 3You receive a design proposal and costing