Variable Transformers

What are variable transformers?

transformerVariable transformers are transformers that can put out differing amounts of voltage from the same input voltage. There are trademarked versions of these transformers and there are versions that are simply sold as variable transformers, some of which are built to custom specifications. These are used in a wide variety of different applications and are among the most common electrical components found in the home and in industrial settings.

Variable transformers are a type of autotransformer, which is a transformer that does not have the dual-coil core design. Variable transformers are oftentimes controlled with a dial, which allows them to be utilized as lighting dimmers and in other applications where precise control over the amount of voltage that a load receives is desired.

Variable transformers, even though they operate on similar principles, do vary substantially from standard transformers. The autotransformer design means that they only have a single coil. Because they only do have a single coil, there is actually no physical separation between the source voltage and the load. This means that they are not as suitable for certain applications, particularly when keeping a device or an operator safe by isolating them from a high-voltage is a consideration.

Variacs, in particular, are used in low-voltage applications and the design itself is typically not suitable for use in high-voltage applications. They do, however, make it possible to conduct sophisticated tests and to exert a great deal of control over the amount of voltage put out by a power source to a given load.

What are variable transformers used for?

Variable transformers have an immense number of different applications. Essentially, in any application where the amount of voltage that a load is receiving needs to be varied on the fly, a variable transformer is likely employed.

These types of transformers can be used to speed up and slow down electric motors, make lights brighter or dimmer or to simulate specific conditions so that various testing procedures can be carried out.

Variable transformers, due to their control knobs, have the quality of allowing for a very smooth and continuous variation on voltage. This makes them markedly different from digitally controlled devices, which go up or down in terms of output based on a specific interval.

In testing, the fact that variable transformers can be utilized to change the voltage on a circuit to such fine degrees is particularly useful. This allows people conducting tests to lower voltages to extremely low levels or to easily increase that voltage to above the levels at which a component being tested was designed to operate.

Variable transformers are not used as isolating devices. They are, however, found in numerous different devices where separation from a source voltage is not as much a concern as providing control over the amount of voltage that is provided to a load. These devices, under the trademarked name Variac, have been common sense the early 20th century and remain among the most common electrical components today.

Where does the name Variac come from?

The name Variac is a trademark that is currently owned by Instrument Service Equipment. It was formerly owned by General Radio and the original design was utilized to provide a way to take a steady AC input voltage and allow it to be varied as needed.

Variac is simply a trademarked term for a variable transformer, though these devices can be manufactured and sold as simple variable transformers, without the trademarked term. The term does refer specifically to variable low-voltage AC transformers.

What are the physical principles applied within a variable transformer?

A variable transformer is a type of autotransformer that works on the same principles as those devices, with more flexibility due to the design. In an autotransformer, there is only one coil with multiple taps located along the coil. The load for the transformer is hooked up to the load and the source of voltage on one end. The load is connected to one of the other taps located along the secondary side of the transformer, allowing the amount of voltage received by that load to be varied.

The number of windings in a transformer determines how much voltage the load receives. By having taps located at different points along the coil, a different number of windings are utilized, allowing the voltage to be varied.

There is a significant difference between double coil transformers and auto transformers. In a double coil transformer, the load is separated from the input voltage physically. In an auto transformer, it is possible, in the event that the device fails, for the entire voltage being input to the transformer to be output to the load. This obviously has dangerous implications for equipment.

What are the various parts in a variable transformer?

The parts within any variable transformer are remarkably similar. The most important parts in the transformer consist of the winding coils and a sliding brush. The knob on the device provides a way of insulating the user from the voltage going through the device, allowing them to adjust the surface area of the brush that is actually touching the coil.

A variable transformer will also contain parts that are designed simply for safety's sake. For example, insulating materials will be utilized to protect the user from the electrical current, connections will be provided to offer a safe path from electricity to flow from the transformer itself to the output terminal and so forth. The most important parts, however, are the coil and the brush, the latter of which essentially takes the place of the secondary coil in a standard two coil transformer.

How does a variable transformer function?

As the user rotates the dial knob, the amount of surface area on the brush actually touching the coil changes. As more of the brush touches the coil, higher voltage is output to the load.

The standout function of variable transformers is the fact that the voltage can be altered so smoothly from zero to, in most cases, higher than the input voltage. This makes them useful on testing equipment and for many other types of equipment where altering the voltage output needs to be done in a smooth and efficient manner.

This differs from an autotransformer, in which fixed taps provide specific voltages. The variable transformer makes it possible to provide an essentially limitless variation on the amount of voltage being put out by the device, making it useful in specific applications.

A variable transformer can be manufactured to work with any range of different voltages, all the way up to higher voltages when testing in industrial applications is being undertaken.

What are Variac brushes and what are they used for?

variac brushesThe brushes inside a variable transformer, specifically a Variac, are typically high resistance components that are in contact with the windings on the transformer. A Variac brush can be brought into greater or lesser levels of contact with the transformer's coils by rotating the knob.

This particular design is most common in low-voltage designs and is part of the trademarked Variac product design. Without the brushes, a Variac would not be able to provide its core functionality.

The brushes within a Variac transformer can easily be removed and examined from an older device. In fact, the basic design of a variable transformer is not particularly hard to manufacture, given that the brush, coil and the container which houses it all constitute the main components and the operation of the device, while mathematically complex, is practically very simple.

What are Variac connectors?

Variac connectors allow these particular types of variable Transformers to be connected to specific types of equipment. They are generally designed to be used for testing purposes, though there are other designs available. They are available separately from the Variac itself, allowing the device to be used for a very long time and likely through the lifecycle of several different connectors. Variac connectors are sometimes simply called variable autotransformer connectors.

There are also input connectors on Variac Transformers. These input connectors typically match the common connectors used to get mains voltage into any electrical appliance in the nation where the Variac was sold. They may, however, include different types of inputs under specialized circumstances.

Some of these devices are designed to be wired directly into specific circuits, so they will have connectors that are designed for that capacity. For example, light dimmer switches that utilize variable transformers will have the same types of electrical connectors that any other device connected to house wiring will have.

As is the case with any electrical component, there are always specialized cases where the connectors will be designed to accommodate a specific piece of equipment, a specific input source or another variable that defines the capacity in which the transformer is to be used.

What are Variac dial knobs?

The dial knob on a Variac provides the means of manually altering the output voltage. These dials are made of insulating materials that provide a safety barrier between the user and the voltage going through the transformer.

Dial knobs come in many different designs. Some of them are very large, allowing for very slight and incremental adjustments in voltage. Others are designed to be more compact, particularly in cases when the Variac needs to be part of a small, fixed system, such as a light dimmer switch.

Some Variac dial knobs contain graduations so that it is easier to keep track of the amount of voltage being output. This can also be measured with a voltmeter.

There are designs of Variac that are motorized, allowing them to be controlled remotely with a switch. There are also designs available that are controlled by microprocessors, allowing a certain series of voltage variations to be applied to a given load, typically for testing purposes but sometimes for automation purposes, as well. Because of the widespread applications of these devices, there are many variations on the control features.

What are the following variables of Variacs?

Variacs are labeled with the following information denoting their operating characteristics.

What is the primary voltage rating?

This is the voltage that is input into the Variac to enable it to provide the desired output voltages. This is typically a fixed number. Most often, the primary voltage rating will appear first, and oftentimes be described as the input rating. Common input ratings on Variacs coincide with common wiring voltages, including 120 VAC, 240 VAC and 480 VAC.

What is the secondary voltage rating?

The secondary voltage on a Variac is variable. In some cases, a Variac will be able to output much higher voltages than the input, with some models being able to go more than two times as high as the input voltage, providing tremendous flexability in terms of conducting tests and for other tasks. This is usually expressed as a range.

What is the power rating?

The power rating describes the highest amount of power that can be utilized with a Variac without endangering the device or the user themselves. In most cases, the power rating will be set so that there is a bit of a safety buffer between the power rating and the actual amount of power that the device can handle without catastrophically breaking down and causing a hazard.

What does the knob rotation define?

The knob rotation on a Variac either increases or decreases the output voltage. In most cases, a clockwise rotation will increase the output voltage coming from the Variac, while a counterclockwise rotation will decrease the output voltage. This is not always, but is most commonly, the case.

What does the number of phases define?

phasesPhase is a feature of alternating current that has to be taken into consideration in the design of a transformer. The phase of the transformer will match the phase of the electricity with which it is designed to be used. For example, standard AC power delivered to house mains is three-phase power.

Variacs are commonly available in single phase and three-phase designs.

How many outputs can a Variac have?

Variacs are typically supplied with a single output. In addition to being able to get custom variable transformers manufactured at higher or lower voltage ratings, it is possible to order different types of outputs from companies that manufacture these devices on a custom basis. For some applications, customized devices are the best options.