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Superior Electric Bristol- main plant 1970

70 Years Superior Electric

The Company

This section of gives an historical overview of the company Superior Electric and its products, like Slo-Syn stepper motors and motion controls. I was always interested in technical history, and, since I worked a very long time for Superior Electric, I do have an interesting collection of old Slo-Syn stuff.

Superior Electric

Superior Electric is located in Bristol Ct. The company was founded in 1938 by Mr. Alfred B. Nelson and Thor L. Hannon.

The first product was the POWERSTAT variable transformer. This product was expanded into a complete line of voltage control equipment which provided the first step in the company's growth. POWERSTAT variable transformers are widely used to control voltage in industrial, military, laboratory and communications areas.

Another voltage control product, the STABILINE automatic voltage regulator, was developed to maintain constant voltage required for television broadcasting, main frame computer operation and other applications.

The LUXTROL line of lighting controls was designed and introduced for use in public and industrial buildings, school, theatres, broadcasting facilities and private homes.

Superior Electric's SLO-SYN synchronous and stepping motors were developed in early 1958 for use with the company's voltage control equipment. SLO-SYN synchronous motors run "in step" with the electrical current. The SLO-SYN motor is, as its name implies, is designed for slow speed synchronous rotation.

With conventional 60 cycle current, SLO-SYN motors rotate at exactly seventy-two revolutions per minute, connected to 50 cycle power, they rotate with 60 revolutions per minute. This is all done without any gearing.

As a stepping motor, it advances a precise angle of 1.8 degrees (1/200 of a revolution) without error accumulation for each pulse of power that is supplied. This rotational motion combined with a five-pitch lead screw on a machine tool produces a table movement of exactly one thousandth of an inch for each pulse of power.

126U Powerstat


Most recognized trademark in the technology, POWERSTAT® Variable Transformers offer 31 series in either single or three phase 120, 240 or 480 V types in ratings from 0.13 to 365 kVA. Manual and motor driven, open and enclosed, portable with and without meters. Epoxy-coated POWERKOTE® Coils give 20% average higher current ratings, greater overload capacity.

Connection diagram of single phase Slo-Syn AC motor

Synchronous Motors

To turn these Powerstats they started to make synchronous motors. These motors are driven by single phase 115 or 230 vac. They need a phase shift network consisting of a capacitor and a resistor. In principle these motors runs on two phases, with a 90-degree phase shift. The brand name of these motors is Slo-Syn

STM1800CV, very popular drive in the past (1973)

Motion Controls

After the synchronous motors it was found that just with other windings these synchronous motors could be converted to "Stepper Motors". Also these stepper motors runs on two phases, with a 90-degree phase shift. The brand name of these motors and drives is also Slo-Syn

The first drive was the STM250, later followed by the long time very popular STM1800 series. The STM1800CV was equipped with an oscillator made with a Unijunction transistor, 2N1671B from General Electric. The power section was made with four of the also very famous Delco Germanium transistors, Superior Electrics part number: BM144640a

Links: Slo-Syn and Superior Electric

PID: 10000 CLT: 0.001 LMD: 2013-Aug-17

Updated 2007 Oct. 09