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Compact soft-starter meets demands of greener heat-pumps

02 March 2009

Carlo Gavazzi has introduced a new digital soft-starter providing all the features required for optimal control of single-phase compressors, such as those used in geothermal and similar heat pump installations. Rated up to 25A maximum continuous current for 230Vac, 50Hz motors, the RSBS Compact starter incorporates special control algorithms to limit starting current and on-board diagnostics to ensure reliability for this increasingly popular form of environmentally-friendly heating.

Starting current is measured by the device’s integral current transformer and limited to 40A RMS, thus ensuring that installations meet the limits established by energy companies and allowing users to avoid the high cost of peak electricity rates. A matching on-board capacitor is also available to boost starting torque.

The RSBS is capable of 12 starts per hour and operates from -20ºC to +65ºC, guaranteeing operation in demanding environments. The system helps avoid damage to other equipment within the residential area caused by voltage dips, and it also prevents nuisance light flicker. In addition, the unit continuously monitors line voltage, automatically disengaging when it drops more than 15%.

Ramp-up time is preset to 0.6s; well within the limits prescribed for scroll-type compressors used in typical residential central heat pump applications. Feedback techniques ensure an improved torque control and integrated bypass relays bridge the circuit across the semiconductors at the top of the ramp. These relays are rated at 60A RMS to ensure robustness and reliability.

Further features are included to enhance longevity. For example, over-current monitoring notifies users by LED indication when a blocked rotor occurs. Locked rotor protection during starting improves lifetime of both the compressor and soft starter, and the RSBS Compact will try to restart for a second time before eventually switching output thyristors off until the problem has been rectified.

Product reliability is enhanced still further by means of integrated transient overvoltage protection, using varistors across the output and control terminals.

The RSBS can be DIN rail or panel mounted, offering a footprint of 76 x 135mm and a low 60mm profile. Such compact dimensions allow the device to fit in panels with limited component space, making it especially useful where there is no cellar to house the heat exchanging unit. Locating heating systems in the living area necessitates using smaller heat pumps and panels.

Protection against dust and moisture ingress is to IP20 standards, and the RSBS Compact meets major requirements for electromagnetic compatibility including EMC Directive 2004/108/EEC, IEC/EN 60947-4-2, EN61000-6-2, and EN61000-6-3. The device also carries UR certification and the CE mark.

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