ISE, Inc. .

Variable Transformer General Information

Click Here For Single Ganged Variable Transformer Standard Product List and Specifications.

Our product line includes variable transformers, the most versatile and reliable voltage controls available. Variable transformers have many industrial and laboratory applications as basic components to control voltage, current, power, heat, speed, light, and electromechanical force.

A basic STACO Variable Transformer consists of a single layer, magnet wire winding on a toroidal core of laminated silicon steel. A carbon brush, connected to an output lead, is rotated over a precision ground, plated commutator track to tap off voltage at any turn from zero to the maximum output voltage of the winding.

STACO research has developed design features and proprietary processes providing longer lasting, more reliable products. Particularly important is the high-temperature foundation material bonding the coil securely to the core assembly. This material (which has a high thermal transfer characteristic) dissipates heat from the brush contact area, increases the heat-distribution of the core itself and provides the transformer with greater tolerance to transients and short-term overloads.


Basic single STACO Variable Transformers are rated either 120 volts or 240 volts. Higher voltage requirements are met by combining or ganging 120-volt or 240-volt units. A 480-volt single-phase application can be met with two 240-volt variable transformers ganged in a series connection. In three-phase applications, three 120-volt units are ganged in a wye connection to result in a 240-volt line-to-line three-phase assembly. Similarly, three 240-volt units are ganged in a wye connection to result in a 380-volt or a 480-volt line-to-line three-phase assembly. In each of these instances, the individual transformers, or coils, are identified with the basic voltage rating, either 120 volts or 240 volts. When variable transformers are connected in open delta for three-phase applications, two 120-volt units are ganged for 120-volt line-to-line usage. For 380-volt and 480-volt open delta applications, two 240-volt units are used in series in each of the two legs of the open delta assembly. In any of the above voltage applications, higher current requirements are met by paralleling two or more units in the ganged assembly.


In contrast to inefficient, wattage-burning resistive-type controllers such as rheostats, STACO Variable Transformers have an extremely low power loss and efficiencies as high as 98%.

STACO Variable Transformers deliver any desired voltage (within the transformer rating) with negligible variation in output voltage from no-load to full-load current. Individual regulation curves for all types are shown in the product section of this catalog.


STACO Variable Transformers produce an accurate transfer of input wave to output circuit, providing distortionless voltage control (a requisite of many sophisticated electronic applications).


The commutator surface of each coil is specially plated with precious metal, giving STACO commutators longer life, increased resistance to corrosion and the capacity to withstand greater overloads (while maintaining a constant contact voltage drop).


Mounting and hook-up of STACO units is convenient and easy. Most Series units are designed with an adjustable shaft to accommodate either bench or panel mount (adjustable to accommodate varying panel thickness). Terminals are easily accessible; screw, lug, quickconnect or solder design. Connections deliver increasing output voltage with either clockwise or counter-clockwise knob rotation. Manually operated units have standard dials graduated 0-100 (percentage of output voltage).


Precise design assembly of the brush (at a constant pressure to a smoothly finished and securely bonded commutator surface) provides excellent mechanical performance, long life, and low-driving torque. Brush replacement is seldom needed, but it is easily performed. High safety margins of voltage, current-carrying capacity and dielectric strength are why you can expect longer life from STACO Variable Transformers.


STACO Variable Transformers are designed with a fraction of a volt per turn. Close adjustment of output voltage is easy because the brush always contacts one or more turns. Coil turns are evenly spaced and output voltage is proportional to angular rotation. Full angular travel is approximately 320 degrees on all Series.


Most 240 volt models have an additional input voltage tap permitting normal overvoltage output, with half normal input voltage. The output current must be reduced when the output voltage exceeds 125% of the input voltage as shown in Fig. A.


The low loss of STACO Variable Transformers allows operation at full current rating @ ambient temperatures up to 50 degrees C (122 degrees Fl. In locations above this temperature, the output current must be reduced according to Fig. B. On single-transient loads and on-off cycled loads, output currents up to 10 times normal may be carried for brief intervals (as shown in Fig. C).


All STACO Variable Transformer models are available on special order to meet certain military specifications. Typical of the requirements which can be met are: Altitude, Connecting wire, Corrosion, Humidity, Shock, Vibration.


STACO Variable Transformers are precision built to exacting mechanical tolerances using the finest materials available. Quality assurance inspections are performed to insure that the high designed-in quality is maintained throughout the manufacturing cycle. A STACO Variable Transformer provides accurate, reliable and lasting voltage control for a broad variety of applications.


Click Here For Standard  Variable Transformer Standard Product list and Specifications.

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