Industrial control transformer has multiple taps on either the primary winding or the secondary winding. ATO designs and manufactures single phase control transformer from 500 VA to 10 kVA power rating, AC primary supply from 110 to 480 volt, multiple secondary voltages applicable to AC 50Hz or 60Hz circuits. If you are looking for high efficiency custom control transformers in China, we can provide you with the solution.


Product Model ATO-T-BK
Phase Single phase
Winding Material Enameled copper wire or enameled aluminum wire
Capacity 500 VA to 10 kVA (customized)
Primary Voltage (VAC) 0 to 690V (customized)
Secondary Voltage (VAC) 0 to 690V (customized)
Frequency 50 / 60Hz
Insulation Level F / H
Cooling Method Natural or air cooling
Impedance Voltage about 6%
Total Losses 0.1

Control Transformer Customization

Provide us with the specifications you need in detail, we can manufacture the suitable control transformer for you. Here are some considerations before customization:
  1. Determine the basic type, required specifications, capacity and quantity of the control transformer.
  2. Primary and secondary voltages of control transformer.
  3. Provide capacity allocation for each output voltage. (Estimate the total capacity of the good appliance, and leave a margin, so as not to burn the transformer at the instantaneous start)
  4. Provide the shape of the control transformer and the required mounting dimensions.

Material Design

Control transformer design element Being one of the leading step up and down transformer manufacturers in China, we offer performance-driven industrial control transformers. ATO consistently invest in advanced manufacturing techniques and high-quality tooling and winding equipment. This helps us improve our capabilities and assure high returns on investment to our clients. We provide customized control transformers with the following elements:

  1. Pure copper core wire. We adopt all copper coil, so that the control transformer conductivity is excellent, low resistivity. At the same time, low temperature rise can also greatly improve the reliability of product performance. Also, aluminum can be provided.
  2. Metal bracket. The metal bracket can connect the terminal and skeleton together to improve the protection level of the control transformer and prevent accidental contact with the circuit.
  3. Silicon steel sheet. The silicon steel sheet is used as the iron core of the transformer, because the silicon steel itself is a magnetic material with strong magnetic conductivity. In the energizing coil, it can produce a large magnetic induction intensity, so that the volume of the transformer can be reduced.
  4. Cold-pressed terminal. Cold-pressed terminal can be connected into wires without welding or screws. The wiring mode can improve the density of the line.

Control Transformer Applications

Industrial Robot

An essential component in industrial robots, providing the necessary power and voltage levels to control and operate the robot's electrical systems.

Molding Machine

Provides appropriate voltage for control circuits in a molding machine, ensuring safe and efficient operation of the machine.

HVAC Controllers

Provides the necessary voltage transformation and isolation to power and control various components in the HVAC system.

Power Distribution

Used in power distribution systems to step down voltage levels for controlling and operating various electrical equipment.

Rail Traffic

Used in rail traffic systems to step down voltage and provide power for control circuits, ensuring safe and efficient operation.

Welding Machine

Used in a welding machine to provide the necessary power and voltage regulation for controlling various aspects of the welding process.


Provides low voltage power to control circuits in a compressor, ensuring proper functioning and safety of the equipment.

New Energy Resources

Step down voltage and provide safe and reliable control signals for monitoring the power generation and distribution systems.

R & D Center

ATO has a mature R & D center in China and has become a professional customized service provider in the control transformer industry.
Our company continuously strengthens the optimization of power transformer raw materials and the improvement of transformer manufacturing process, and has more than 1,000 independent research and development projects.

Technology Leading

ATO has a technology-leading intelligent production system that can efficiently respond to customer needs. We have created a total quality management TQM system, which has set an industry benchmark in the manufacture of control power transformers.


Should a control transformer be grounded?

In general, control transformers do not require a separate ground connection. Control transformers are typically used to step down voltage levels for control circuits and are isolated from the power distribution system. They have primary and secondary windings that are electrically isolated from each other and from the ground.
However, it's important to note that local electrical codes and regulations may vary. It's always recommended to consult the relevant electrical codes, standards, and the manufacturer's instructions for the specific control transformer being used. These sources will provide the most accurate and up-to-date information regarding grounding requirements for control transformers in your specific location and application.
If you are unsure about the grounding requirements for a control transformer, it's best to consult with a qualified electrician or an electrical engineer who can assess the specific installation and provide appropriate guidance.

What is the reason for control transformer failure?

Control transformer failure can occur due to various reasons. Here are some common causes:
  • Overloading: Control transformers are designed to handle specific loads. If the connected devices draw more current than the transformer's rated capacity, it can lead to overheating and eventual failure.
  • Voltage spikes or surges: Power fluctuations, voltage spikes, or electrical surges can put excessive stress on the transformer windings, leading to insulation breakdown and failure.
  • Poor maintenance: Lack of regular maintenance, such as cleaning, inspection, and tightening of connections, can result in degradation of the transformer's components over time, increasing the likelihood of failure.
  • Short circuits or electrical faults: A short circuit or electrical fault in the control circuit can cause a sudden surge of current, overwhelming the transformer and potentially damaging its internal components.
  • Aging or wear and tear: Control transformers, like any electrical equipment, have a finite lifespan. Over time, the insulation may deteriorate, windings can become loose, or the core may degrade, all of which can contribute to transformer failure.
  • Environmental factors: Harsh operating environments, such as extreme temperatures, excessive moisture, dust, or corrosive substances, can accelerate the degradation of the transformer's components and increase the risk of failure.
  • Manufacturing defects: In rare cases, control transformers may have manufacturing defects, such as poor winding insulation or faulty connections, which can lead to premature failure.

It's worth noting that control transformers are generally more robust than power transformers, and their failure rates are relatively low compared to other electrical components. However, these factors mentioned above can still contribute to their failure. Regular maintenance, proper load sizing, and protection mechanisms such as fuses or circuit breakers can help mitigate the risk of control transformer failure.

What is the voltage regulation of a control transformer?

The voltage regulation of a control transformer refers to its ability to maintain a constant output voltage under varying input voltage conditions. It is typically expressed as a percentage and indicates the maximum deviation in output voltage when the input voltage varies within a specified range.
Control transformers are designed to provide a stable and reliable voltage source for control circuits and equipment. They typically have a high turns ratio, which means that the primary winding has significantly more turns than the secondary winding. This configuration allows them to step down the input voltage to a lower level suitable for control applications.
The voltage regulation of a control transformer is influenced by factors such as the design, construction, and quality of the transformer. Different transformers may have varying voltage regulation characteristics. Generally, control transformers are designed to have a low voltage regulation to ensure that the output voltage remains relatively constant even if the input voltage fluctuates.
Commonly, control transformers have a voltage regulation between 1% to 5%. This means that the output voltage of the transformer will deviate by a maximum of 1% to 5% from the rated output voltage when the input voltage varies within its specified range. However, it's important to note that the actual voltage regulation can vary depending on the specific transformer model and manufacturer.

Why are control transformers made with two primary windings?

Control transformers are often made with two primary windings to accommodate different voltage requirements and to provide flexibility in electrical systems. Here are a few reasons why control transformers may have two primary windings:
  • Voltage compatibility: The primary purpose of a control transformer is to step down or step up voltage levels to match the specific requirements of control circuits. By providing two primary windings, the transformer can be connected to different input voltage sources. For example, if a control system is designed to operate with either 120V or 240V input, a control transformer with two primary windings can be configured to work with either voltage level.
  • Voltage selection: In some cases, a control transformer may have selectable primary voltage. Each primary winding might be wound to match a specific input voltage. By switching the connection between the windings, the user can select the desired input voltage for the transformer. This feature allows the transformer to be used in different regions or with various electrical standards.
  • Power supply redundancy: In certain applications where power supply redundancy is crucial, control transformers with dual primary windings can be employed. By connecting the primary windings to two separate power sources, if one power source fails, the transformer can automatically switch to the other primary winding, ensuring uninterrupted power supply to the control circuit.
  • Multiple system compatibility: Control transformers are commonly used in industrial and commercial settings where multiple control systems with different voltage requirements may coexist. Having two primary windings enables the transformer to be adaptable to various systems, simplifying installation and maintenance.

What causes high voltage from control transformer?

A control transformer is typically used to provide lower voltage levels for control circuits in electrical systems. However, if you are experiencing high voltage from a control transformer, it could be due to several potential causes:
  • Faulty winding: A control transformer consists of primary and secondary windings. If there is a fault in the winding insulation or a short circuit in the windings, it can cause a high voltage condition.
  • Overloading: If the control transformer is overloaded, it may not be able to handle the required load, resulting in increased voltage output. Overloading can be caused by excessive current demand from the control circuit or by connecting too many devices to the transformer.
  • Incorrect tapping: Control transformers often have multiple taps on the primary side to provide different voltage levels. If the wrong tap is selected or if there is a wiring error, it can lead to higher-than-expected voltage output.
  • Voltage fluctuations: Fluctuations in the input voltage can also affect the output voltage of the control transformer. If the input voltage is higher than the rated value, it will result in a corresponding increase in the output voltage.
  • Regulation issues: Control transformers are designed to provide a specific level of voltage regulation. If the transformer's regulation capability is compromised due to aging, loose connections, or other factors, it can lead to high voltage output.

If you are experiencing high voltage from a control transformer, it is crucial to address the issue promptly to prevent damage to connected equipment or risk of electrical hazards. It is recommended to consult a qualified electrician or technician to diagnose and resolve the problem safely.

How do you protect a control transformer?

To protect a control transformer, you can employ several measures to ensure its safe operation and prevent damage. Here are some common methods for protecting a control transformer:
  • Overcurrent Protection: Install an appropriately sized fuse or circuit breaker in series with the transformer's primary winding. This protection device should be rated to handle the maximum expected current in the transformer.
  • Thermal Protection: Use a thermal overload relay or a temperature sensing device to monitor the transformer's temperature. If the temperature exceeds safe limits due to excessive loading or other factors, the protection device will trip and disconnect power to the transformer.
  • Voltage Protection: Incorporate surge protection devices (SPDs) or voltage regulating devices to safeguard the transformer against voltage spikes, surges, or transients. These devices can help prevent damage to the transformer from voltage irregularities.
  • Ground Fault Protection: Implement ground fault protection to detect any fault currents flowing to ground and quickly interrupt the circuit. Ground fault protection devices, such as ground fault circuit interrupters (GFCIs) or ground fault relays, can prevent damage caused by ground faults and ensure personnel safety.
  • Proper Sizing: Ensure the control transformer is appropriately sized for the load it is intended to handle. Oversizing the transformer provides a margin of safety and helps prevent overheating and premature failure.
  • Proper Ventilation: Allow for adequate ventilation around the control transformer to dissipate heat effectively. Avoid placing the transformer in enclosed spaces or near heat sources that could impede heat dissipation.
  • Regular Maintenance: Perform routine inspections and maintenance checks to identify any signs of wear, damage, or abnormal conditions. Regularly clean the transformer and its surroundings to prevent dust accumulation, which can affect performance.
  • Monitoring Systems: Consider implementing a monitoring system that continuously monitors the transformer's operating parameters such as temperature, voltage, and current. These systems can provide real-time alerts or notifications in case of any abnormal conditions.

  • It's crucial to consult the transformer manufacturer's guidelines, local electrical codes, and industry standards when selecting and implementing protective measures for a control transformer. Additionally, involving a qualified electrician or engineer in the design and installation process can help ensure the transformer's proper protection.

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