Product Design and Engineering Data

General Information

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Staco Energy Products Co. is a leading manufacturer of 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, gold plated commutator track to tap off voltage at any turn from zero to the maximum output voltage of the winding.

Staco Energy research has developed design features and proprietary processes that provide 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.

Voltage Ratings

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  a240-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 240-volt open delta applications, two 240-volt units are ganged with 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.

Efficiency and Regulation

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.  Voltage drop tables and a sample regulation curve are provided in our full catalog, "Variable Transformer Voltage Control."

Distortionless Voltage Control

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

Plated Commutator Surface

The commutator surface of each coil is specially plated with gold, giving Staco variable transformers longer life, increased resistance to corrosion, and the capacity to withstand greater overloads while maintaining a constant contact voltage drop.

Simple Installation and Connection

Mounting and hook-up of Staco Variable Transformer units is convenient and easy.  Most series unit are designed with an adjustable shaft to accommodate either bench or pan3l mount (adjustable to accommodate varying panel thicknesses).  Terminals are easily accessible, with screw, lug, quick-connect, or solder design.  Connections deliver increasing output voltage with either clockwise or counter-clockwise knob rotation.  Manually operated units have standard dials graduated from 0 - 100 (percentage of output voltage).

Longer Life with Negligible Maintenance

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 is easily accomplished.  High safety margins of voltage, current-carrying capacity and dielectric strength are why you can expect longer life from Staco Variable Transformers.

Smooth and Linear Voltage Control

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.

Voltage Doubler (Dual Input)

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 with the output voltage exceeds 125% of the rated input voltage.

Temperature and Rating

The low loss of Staco Variable Transformers allows operation at full current rating at ambient temperatures up to 122 degrees F (50 degrees C).  In locations above this temperature, the out put current must be reduced according to Figure A shown below.  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 Figure B below.

120 Volt Series Unit Ratings

 

240 Volt Series Unit Ratings