Active Power CleanSource HD flywheel UPS, 675 kW

Active Power's battery-free flywheel UPS at 675 kW, still built in Austin under Piller ownership since 2016

Active Power CleanSource HD flywheel UPS, 675 kW is one of 22 UPS systems tracked in the SecondWatt catalogue, each with specifications, lead times and indicative secondary-market pricing.

Active Power CleanSource HD dossier: 675 kW battery-free flywheel UPS, 7,700 rpm and 10.2 MJ, 15 s ride-through, bearing service intervals, and inspection tips.

CleanSource HD is a battery-free flywheel UPS rated 675 kW and 750 kVA at 480 V on the UL datasheet, or 625 kW at 380, 400 and 415 V on the CE version. An integrated steel flywheel spinning at 7,700 rpm stores 10.2 MJ and delivers 15 seconds at full load, 20 at 75%, 29 at 50% and 56 at 25%. Efficiency runs 96.5% at half load and up to 98% at full, output regulation holds within 1%, and up to seven systems parallel for 4,725 kW. The whole package occupies 35 square feet across two cabinets and weighs 10,971 lb. The ownership record needs correcting wherever it is stated. Active Power was established in 1996 and listed on NASDAQ in 2000, but in November 2016 the business and assets were acquired by Piller Power Systems and merged into the Piller division, with Langley Holdings plc as ultimate parent. Active Power Inc. survives as an operating entity and brand, manufactures in a 135,000 square foot ISO 9001:2015 plant in Austin with capacity above 300 MW of flywheel UPS a year, and runs its own 24/7 US service organisation. Piller and Active Power should be treated as one supplier group. The line is not a legacy holdout. In June 2025 more than 200 CleanSource battery-free UPS units built in Austin shipped for a 75 MW data center expansion in Mantsala, Finland, described as one of Europe's largest, and the parent's 2025 annual report records a much larger follow-on US order for delivery in the current year.

Why it matters

The economic case is the absence of a consumable. Active Power markets 20 or more years with no battery changes against VRLA replacement every three to five years and lithium or nickel-zinc every ten, and quotes battery UPS efficiency at 96% or lower against its own 98%. Against a battery plant that has to be bought three or four times over a twenty-year life, the flywheel's higher first cost is the whole argument.

Who buys it

Data center and industrial operators who want backup energy with no battery replacement cycle, no battery room cooling load and no lithium fire code exposure, and who already run fast-start generators. The design is only valid where the genset is proven, because ride-through is 15 seconds at full load rather than minutes.

Role in the data center

Battery-free ride-through between a utility failure and a fast-start generator, sized in 675 kW increments and paralleled to 4,725 kW.

Key specifications

Technical summary

Rating (60 Hz, UL): 675 kW maximum, 750 kVA maximum, 480 V Rating (50 Hz, CE): 625 kW at 380, 400 or 415 V Input: 480 VAC three-phase, three-wire plus ground; 60 Hz; range +10% to -15% Output: 480 VAC three-phase; voltage regulation within 1%; mains-synchronized Efficiency: 96.5% at 50% load, up to 98% at 100%; above 96% at 40% load Flywheel: integrated steel rotor at 7,700 rpm storing 10.2 MJ Ride-through: 15 s at 100%, 20 s at 75%, 29 s at 50%, 56 s at 25% load Bearings: precision ceramic ball bearings in a field-replaceable cartridge Physical: 80 x 132.0 x 39 in (2,032 x 3,353 x 991 mm); 10,971 lb; 35 sq ft over two cabinets Standards and life: UL 1778 listed, cUL CAN/CSA 22.2 No. 107.1, FCC Class A; 20-year design life

Pricing and availability

Trend: up Warranty, used: 1-year typical from refurbishment dealers.

Lifecycle and maintenance

Flywheel and rotary systems are built around a 20-year design life with no stored-energy replacement, which is the whole economic case against batteries: Active Power markets CleanSource as 20+ years with no battery changes and VYCON rates the VDC above 20 years with runtime that does not degrade. The consumables move to bearings, vacuum and capacitors instead, at a ceramic bearing cartridge every third year on CleanSource HD, annual vacuum-pump oil with an 8-10 year pump on the VDC, and DC capacitors at 7-8 years. Piller extends rotary service intervals to 5 years with condition monitoring. Service history, not calendar age, sets the value of a used rotary asset.

Common failure points

• Bearings — Ceramic ball bearings wear on a fixed interval and a missed change ends the machine
• Vacuum integrity — Lost vacuum raises windage losses and the published runtime no longer holds
• DC capacitors — Aged DC capacitors degrade the converter and the energy it can deliver
• Bearing controller electronics — Active magnetic bearing controllers are proprietary and not field-substitutable
• Generator dependency — Ride-through is 15-60 seconds, so a slow or unproven genset leaves the load exposed
• Lubrication systems — Auto-greased bearing sets run dry when a decommissioned unit sits unserviced

Inspection checklist

Bearing type — establish it first; CleanSource HD runs ceramic ball bearings, the VYCON VDC uses 5-axis levitation Bearing service log — Active Power specifies a cartridge change every 3rd year on HD and every 4th on PLUS MMS Vacuum system — VYCON runs a medical-grade vacuum pump on annual oil service with an 8-10 year pump life DC capacitors — VYCON publishes a 7-8 year replacement point for the VDC's DC capacitors Rotor drop log — the VDC spins 18,500-36,000 rpm and recovers from backup-bearing drops a limited number of times Grease reservoir — Piller POWERBRIDGE auto-greases from a reservoir; an unserviced one voids the 20-year life case Runtime verification — CleanSource HD holds 15 s at 100% load, 29 s at 50% and 56 s at 25% per the UL datasheet Flywheel data — HD spins a steel rotor at 7,700 rpm storing 10.2 MJ; the 6.2 MJ web figure is a page error Efficiency — check against the datasheet: HD is 96.5% at 50% load and up to 98% at full load Generator interface — a flywheel is a bet on the genset; verify start-to-load against a 10-second class requirement Ambient limits — CleanSource HD is rated 32-104 degrees F (0-40 degrees C); verify how the unit was stored Controls and parts — magnetic bearing controllers are proprietary; VYCON ownership has been undisclosed since 2022 Parallel rating — HD parallels up to 7 systems for 4,725 kW; confirm frame count matches the nameplate claim Standards — confirm UL 1778 and cUL CAN/CSA 22.2 No. 107.1; the VDC's UL scope covers 400-600 VDC only Service entitlement — get a written parts letter; Active Power runs a 135,000 sq ft Austin plant with 24/7 service

Procurement channels

New units and service direct from Active Power in Austin, with international coverage through the Piller network across 50 or more countries. Active Power Rentals offers standalone POWERHOUSE and containerized systems from one month upward with turnkey installation and commissioning, and an OEM rental fleet is the most likely origin of any future ex-fleet secondary units.

Regional notes

UL 675 kW builds for North America and CE 625 kW builds for 50 Hz markets. US customers are served from Austin, Texas and international customers through Piller subsidiaries and service centres.