Variac Variable Transformers


Important VARIAC Technical Notes:

CURRENT RATING TERMINOLOGY: To permit maximum utilization of STACO Variable Transformers, output ratings are given for both constant current and constant impedance loads. All current ratings are based on continuous use at ambient temperatures to 122 F (50 C).  Use derating curve for higher ambients.  Short duration overloads to 10 times transformer rating are possible.  See graph for acceptable limits.

CONSTANT CURRENT RATING: Output current that can be carried regardless of output voltage setting. (Reduce, for output above 125% of input voltage, on voltage doubler connection. See Graph

CONSTANT IMPEDANCE RATING*: Output current that can be carried with loads such as incandescent lamps or resistance heaters in which the current drawn is approximately proportional to the applied voltage, increasing to maximum current at line voltage. This rating applies only to applications where maximum output voltage is limited to line voltage.

THREE PHASE CONNECTED TRANSFORMERS: If ganged units are used in a system that ordinarily has a common neutral or ground between source and load, the neutral or ground must be connected to the common terminals of the variable transformer assembly. If the system has no neutral, the load must be balanced or the transformers will be damaged.

OPERATION AT HIGHER FREQUENCIES: All Staco variable transformers are designed for operation at 60 or 50/60 Hz.  Most models can also properly operate with input frequencies to 2000 Hz.  Some models output ratings must be derated at higher frequencies. See derating table for details.

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