Johnson Electric Coil Company
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Single Phase and Three Phase Autotransformers

We supply single and three phase autotransformers to a number of different industries, delivering the high-quality, durable components they need, for a wide range of applications. Our engineers are adept at working to different specifications. In addition to the “off the-shelf” selection of single and three phase autotransformer options other companies offer, we can customize transformers to meet your specific requirements. Our team is experienced at working on specialist projects, providing innovative, cost-effective transformers that exactly meet your needs.

Being a specialty autotransformer manufacturer, we can move your design requirements forward by creating a prototype, testing that it works, and assuring production of electrical single or three phase autotransformers that are exactly what you need—to your schedule, on time, in shipments that work for you. To find out more about our single phase autotransformers, three phase autotransformers, or other products, call us at (800) 826-9741.

Transformers are vital components of electrical usage that transfer electrical energy from one electrical circuit to another. They change current to make it capable for an application. The typical transformer has two windings, with one being the primary winding which draws in energy, and the other being the secondary winding for transmitting this energy. Autotransformers have a different configuration with one winding serving as both the primary and secondary winding. This configuration is just as effective, but less expensive.

Johnson Electric Coil Company is one of the primary companies for the production of transformers and produces single and three-phase autotransformers made of highly durable components to fit a wide range of applications. Their devotion to excellence and high-quality products includes both their in-stock autotransformers as well as ones they custom design to meet their customers’ unique requirements.

What is an Autotransformer?

Autotransformers have a single coil winding design. They are used to interconnect systems with single windings that perform as both the primary and secondary sides. In a two-winding transformer, there are two separate windings that are connected by a magnetic field, which provides an electrical isolation of the windings.

An autotransformer has a single winding wrapped around a laminated core, which is used for the primary and secondary circuits. They have three terminals, one of the terminals is common to both input and the load. AC energy is supplied to the common and one of the other fixed terminals with the load connected to the common and the other fixed terminal.

Aside from the AC connection between the windings, energy flows through induction because of the variations of the windings. The variation generates magnetic flux which, in turn, induces an EMF or self-induction. The two fixed points of the winding act as the primary while the winding between the tap point and one fixed point acts as the secondary.

How Autotransformers Protect People

One of the problems associated with long power lines is voltage drop, especially with applications that draw a great deal of current. Autotransformers are used to compensate for the drop in voltage in order to keep equipment operating at peak efficiency.

Another, very common, use for autotransformers is in the starting of large AC motors to keep the potential voltage difference reduced at startup. Autotransformers hold the motor at the start-up level until the motor reaches 75% of its rated speed where the motor is then switched over to its full potential.

Benefits of Autotransformers

There are an endless number of benefits to the use of autotransformers. Some of those benefits include:

  • Save on Copper: Autotransformers use just one copper winding and, as a result, far less copper wire than traditional transformers of the same rating. This reduces the cost of manufacturing.
  • Single Winding: The single winding of autotransformers reduces their size & weight, which gives them greater flexibility for use in a wide variety of applications.
  • VA Rating: The smaller size and weight of autotransformers enables them to have a higher VA rating.
  • Voltage Regulation: Since autotransformers have a single wind, they do not suffer a voltage loss due to the second winding.
  • Efficiency: The second winding of a two winding transformer creates losses due to electrical conduction, magnetic induction, and reduction. Since an autotransformer does not have the second winding and subsequent losses, it operates more efficiently.

Features of Our Autotransformers

Autotransformers from Johnson Electric Coil have proven to be a major factor in providing our customers with a safe means of controlling electrical current. Our precision crafted autotransformers meet safety agency requirements for both domestic and international agency specifications.

Range of Applications

The convenience and adaptability of autotransformers makes them ideal for a wide variety of applications. They are more efficient at boosting the potential difference across a distribution line by a small fraction to compensate for power drop. This aspect of their operation is at a fraction of the cost for a two-winding transformer.

Cost Effective and Highly Efficient

Autotransformers cost less to produce but provide exceptional service. Johnson Electric Coil’s staff of highly trained specialists custom design autotransformers that are highly efficient made from the highest quality materials. Essentially, at a lower price, an autotransformer provides the same efficiency in a smaller, more compact package.

Compact Design

Since there are fewer wires and a more streamline design, autotransformers are smaller and capable of being used in a wider assortment of equipment and applications. This flexibility makes them an ideal method for voltage output control.

In certain applications, voltage control is a necessity to avoid harm to engines and components. Sending a full load into an application can be detrimental and requires precision control, which is engineered into every Johnson Electrical Coil autotransformer.

Autotransformers Applications

There are an endless number of uses for autotransformers from controlling the startup of large AC motors to controlling the potential voltage drop in distribution transformers to helping to set the perfect temperature for your morning coffee.

Autotransformers are normally used in conditions where primary and secondary isolation is not necessary. Due to their size and compactness, they are used as household AC regulators and three phase motor auto decompression starter boxes.

A common application for autotransformers is boosting the potential difference drop for distribution lines by a small fraction to compensate for the voltage drop in the line. Long power lines over long distances have a power drop due to the distance. Autotransformers step up the voltage to help maintain constant power.

How to Choose an Autotransformer

There are several factors to consider when choosing an autotransformer. The critical factors include:

  • KVA – The size of an autotransformer is determined by the KVA of the load, which is dependent on the number of pieces of equipment being serviced. The anagram KVA stands for kilovolt ampere or thousand-volt ampere and should be equal to or greater than the KVA of the load.
  • Supply Voltage – The supply voltage is the line voltage from the local power source.
  • Required Voltage – It is important to determine the voltage required by the load, which is the output voltage of the autotransformer and is the voltage required to operate the load.
  • Supply Source Frequency – The frequency of the supply source and the load have to be the same.

Custom Autotransformers at Johnson Electric Coil

After making a complete assessment of your needs, you may find that you require a custom-designed autotransformer. Johnson Electric Coil Company’s engineers and designers are ready to provide you with the necessary guidance and to develop an autotransformer that will precisely meet your needs. Maybe, you’re still not quite sure what an autotransformer is exactly and how it can benefit your company’s bottom line. Johnson’s staff has the know-how, skill, and ability to meet your every need.

Our products are all made in Antigo, WI

Johnson Electric Coil Company provides complete design, engineering, and manufacturing services to supply our customers with the finest, most efficient and cost-effective single phase and three phase autotransformers. Our autotransformer design and manufacturing capabilities are some of the broadest in the industry. We can fully support our customer’s safety agency requirements with expertise in both domestic and foreign agency requirements. In addition to our specialty engineering and manufacturing services, we work with our customers to customize scheduling, packaging, shipping, billing, and communication practices to meet their unique inventory management, product handling, delivery, and customer service needs. Our goal is to provide a level of quality and service that enables our customers to be leaders in their markets. While we mainly sell in the US, our single phase and three phase autotransformers are found all over the world as components in OEM equipment. We pride ourselves on being the only transformer company our customers need.

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