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In Variacs

Manual Variacs

In the world of electric circuits and electrical engineering projects, transformers are defined as passive electrical devices capable of transferring energy from one circuit to another circuit (or even to multiple other circuits). They typically have two or more wire coils and two circuits—a primary one and a secondary one.

What are Variable Voltage Transformers?

Variable Voltage Transformers (also known as Adjustable Voltage Transformers) are transformers that can produce different levels of output voltage from just one input voltage. These provide users with an efficient, trouble-free way to change the voltage in a short amount of time.



ompensation is one of the main reasons why people would want to change the secondary voltage so quickly. When the incoming line voltage changes, it’s best that the secondary voltage that serves the load remains regulated. This lessens the risk of intense fluctuation or continual voltage hunting conditions. This is why a voltage tolerance limit—from half a volt to a handful of volts—is maintained.

Variable voltage transformers are honestly the best choice for professionals and hobbyists who desire a more versatile option for changing the ratio between primary and secondary coils. They’re widely accessible, easy to operate, and (depending on the model and brand) can be highly intuitive. You can even program variable voltage transformers to automatically adjust to maintain constant or regular voltage output.

What are Variacs?

An “autotransformer” is a transformer that consists of only one coil shared by both the primary and secondary side of the circuit. The term “variable” in a variable autotransformer basically refers to the ratio of the primary windings to the secondary windings—i.e., the ratio of the secondary voltage to the primary voltage.

“Variac” is the generic name for variable autotransformers.

Variacs are arguably the most popular type of variable voltage transformers. They are AC power supplies that are cheaper, smaller, and a lot more portable than dual-winding transformers. They also have a number of useful casual and industrial applications that make them highly sought after.

Variac Structure

Although different types of Variacs will have variations in design, all models follow roughly the same basic structure.

Parts of a Variac/Variable Autotransformer:

  • Winding
  • Tappings on the winding
  • Laminated magnetic core
  • Carbon brush (for secondary voltage, rotates)
  • Carbon brush (variable tap, moves up and down)

How a Variac Works:

Variable autotransformers have a single partially exposed winding the primary winding wrapped around a laminated magnetic core. There is a carbon brush (also known as the movable wiper) that is positioned in such a way that it can create an electrical connection with the winding. The transformer’s primary connection is made to both ends of the primary winding.

It is secondary connection called the common connection is made to just one end of the winding and is tapped through a movable carbon brush. This carbon brush can rotate or slide along the exposed section of the primary winding. The transformer’s ratio changes as the wiper moves.

Variable voltage transformers are typically designed with several primary windings enough to produce a secondary adjustable voltage that can be tuned from a few volts to fractions of a volt per turn. As long as the carbon brush is always in contact with the primary windings, the secondary voltage can be adjusted.

Common Applications for Variacs

There are a lot of common uses and practical applications for Variacs. As we mentioned earlier, they’re more portable and more cost-effective than regular AC power supplies, which pretty much makes them a top pick for short-term projects and casual hobbies. Variacs can be used to gradually revive previously dormant electronic equipment. They can also be used to regulate servo motors and control the temperature of ovens and heaters.

Voltage adjustment, when used with thermostatic control, provides more uniform heating.

You can also use Variacs to simulate various voltage and line conditions for experiments, or power electrical equipment designed for voltage that isn’t the typical 220V or 440V supplied domestically.

Here are some other applications:

  1. Regulating voltage
  2. Controlling specified input voltage to rectifier elements to generate variable DC voltages from an AC source
  3. Operating electrical equipment—typically motors—at the correct or optimal voltage even with subnormal or higher-than-normal supply
  4. Varying step-transformer output voltage by control of input voltage
  5. Starting synchronous or induction motors in order to provide 50%-60% of the total voltage to the motor stator during start-up.
  6. Correcting voltage in subnormal or over-voltage supplies on 1-phase, 2-phase, or 3-phase circuits
  7. Compensating for voltage drops by giving small boosts to the distribution of a cable
  8. Controlling AC motors and DC motors operation rectified AC circuits
  9. Powering fans and other motors with low starting torque
  10. Controlling the brightness/dimness of incandescent lamp circuits
  11. Extending lamp life by operating it below rated voltage
  12. Calibrating electrical equipment and controls
  13. Compensating for appreciable voltage drops at the end of lines where distances run too long (like in rural distribution systems).

Advantages of Variacs/Variable Voltage Transformers

Affordable. As mentioned earlier, Variacs are affordable AC power supplies that are capable of fulfilling voltage needs and operating at the same level of transformers or power sources that go for four times its price.

Efficient. A Variac or autotransformer is much more efficient for voltage conversion compared to a two-winding transformer. This has to do with less ohmic loss and core loss thanks to the reduction of transformer material.

Effective. Variable voltage transformers or variable autotransformers are better at regulating voltage than an ordinary two-winding transformer of the same rating. This is due to their significantly lower drop in resistance and reactance.

Portability. Variable autotransformers are about half the size of a standard two-winding transformer. This makes them easier to handle. It also is partly why they’re much cheaper.

Product Features

  • Winding is done using double coated H Class super enamelled copper wire.
  • Mounting Base are made of heavy Aluminium to add strength to Overall construction and provide stability along with keeping overall weight to the minimum. 
  • Easy-to-read label with complete technical and connection details.
  • Constructed with high quality silicon steel laminations to minimize core losses and increase performance and efficiency. 
  • High Quality Carbon Brush for the longevity and trouble-free operation. Up to 10 Amps Capacity a round carbon provides extremely smooth operation and long life. A Spare carbon is also provided with each Variac coil for future replacement.
  • A knob and voltage indicating Dial is provided with Manual Variacs
  • For Motorized Variac a suitable AC Synchronous motor along with gear arrangement is provided for reduction in speed. A Typical speed of the AC Synchronous motor is 60 RPM.
  • The Motorized Variacs are completed with micro switch arrangement for starting and ending voltage cut-off.
  • Voltage can be boosted from the supply voltage as per requirement.
  • Voltmeter and Ammeter can also be provided on Variacs with enclosure.

Product Classifications

  • Current Capacity: From 1 Amps to 40 Amps
  • Construction Type Input Supply wise:
    • Single Phase Variacs
    • Two Phase Variacs
    • Three Phase Variacs
  • Construction Type by operation:
    • Manual Variacs
      • Single Phase Manual Variacs
      • Two Phase Manual Variacs
      • Three Phase Manual Variacs
    • Motorized Variacs
      • Single Phase Motorized Variacs
      • Two Phase Motorized Variacs
      • Three Phase Motorized Variacs
  • Input Voltage:
    • 230 Volts
    • 415 / 440 Volts
    • 110 Volts 
  • Conductor Type: 
    • Copper
  • Conductor Covering Type: 
    • Enamelled ‘H’ Class
  • Core Type: Cold Rolled Grain Oriented (CRGO) Laminated Silicon Steel Toroidal Core
  • Varnishing Type: Epoxy Coated
  • Terminal Type: Wago, Brass Bolts

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