A 140 kW energy storage flywheel has been developed to provide 15 seconds of ride-through power for industrial UPS applications. The flywheel, which operates in a vacuum, is supported by Active Magnetic Bearings (AMB) to minimize bearing losses, and has a high power motor/generator coupled to an efficient power conversion module. The backup bearing system was tested extensively due to the potential for very long spin down times in the event of a failure in or loss of power to the magnetic bearing system. Key issues encountered during testing are discussed and solutions identified. High fidelity orbit and time-history data from a full speed drop and spin down are presented and discussed in detail. The final backup bearing system is capable of three 2.75 hour spin downs from 36,000 RP:M.