In 1997, this field of ten AC-powered Martin-Marietta two-axis positioners, located at the Arizona Public Service's Solar Testing and Research (STAR) Center in Tempe, Arizona, just in front of the Occatllo Power Sub-station, became the first opportunity to install multiple controllers side-by-side. These units had been controlled by sun-sensor electronics dating back to the 1970's and were beginning to fail due to age. Very simple modifications to the motors, adding quadrature-based digital feedback, allowed a straight-forward retrofit of AC-powered SolarTrak® Controllers.
The motors on these drives were of the '3-wire' category and used the original SCR solid-state relay power control design. The power for the controller board itself was provided by a simple 'Wall Wart' transformer which converted the 115 AC input power to 14 volts of DC.
Each tracking pedestal is equipped with its own controller providing distributed tracking control without the need for a central control computer that generally requires a broad-band network rife with electronic noise and prone to failure.
Each axis of the two-axis system uses a pair of solid-state SCR relays. The wiring of low