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Publication Title | Unifin-2 Interposing Relay Requirements

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Capstone Turbine Corporation • 21211 Nordhoff Street • Chatsworth • CA 91311 • USA Telephone: (818) 734-5300 • Facsimile: (818) 734-5320 • Website:

Service Bulletin SB0045

Date: From: Subject:

July 2003

Capstone Technical Support

Unifin-2 Interposing Relay Requirements

Systems Affected

All existing Unifin Corporation® second generation (Unifin-2) heat exchanger units connected to Capstone MicroTurbines.

Safety Precautions

Only Capstone Authorized Service Providers (ASP’s) should open the MicroTurbine and other equipment connected to the MicroTurbine. The systems can include multiple sources of power. Observe and adhere to Safety Instructions contained within MicroTurbine manuals.

Description of Problem

Unifin-2 heat exchangers may not signal the MicroTurbine if a fault condition or power-off condition occurs. This heat exchanger is equipped with a fault out contact configured using a DIP-switch with Normally Open (N/O) and Normally Closed (N/C) settings. Up to this point, Capstone has recommended that this switch be configured in the Normally Closed (N/C) position such that when the Unifin is operating correctly the contacts are open to the MicroTurbine indicating ok to run. The contacts will close indicating a fault when a problem with the Unifin occurs. However, if the Unifin-2 has a power failure where the control circuitry does not operate, a fault could occur and the Unifin-2 would be incapable of providing a fault signal to the MicroTurbine.

Failure to report a fault condition to the MicroTurbine can result in overheating the water and potential damage to the heat exchanger. Water will no longer be pumped through the heat exchanger core when the Unifin fails. Without a fault signal, the MicroTurbine will continue exhausting hot air into the Unifin-2 heat exchanger. This continued operation could heat the stagnant water beyond control temperatures, turn the water into steam, and result in the pressure relief valve releasing hot water or steam. The heat exchanger core material itself can be damaged with the elevated temperatures that can result.

A fault signal must be provided to the MicroTurbine when the Unifin heat exchanger no longer has control power. This can be accomplished by setting the DIP switch on the Unifin-2 heat exchanger to the Normally Open (N/O) position such that the Power Off and Fault condition have the same output logic. An interposing relay must be inserted between the Unifin-2 and MicroTurbine to compensate for differences in logic. The interposing relay inverts the Unifin fault signal and activates the MicroTurbine fault logic when the heat exchanger is powered down or disabled due to faults.

Note that there are several versions of Unifin controllers and the correct version must be identified for troubleshooting purposes. This service bulletin covers ONLY Unifin-2 controller configuration issues. For earlier versions than Unifin-2, contact Capstone Technical Support for assistance.

450010-001 Rev A (July 2003) Page 1 of 4 SB0045

This information is proprietary to Capstone Turbine Corporation. Neither this document nor the information contained herein shall be copied, disclosed to others, or used for any purposes other than the specific purpose for which this document was delivered. Capstone reserves the right to change or modify without notice, the design, the product specifications, and/or the contents of this document without incurring any obligation either with respect to equipment previously sold or in the process of construction.

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