Constant Voltage Transformers

Shop constant voltage transformers designed to maintain a more stable AC output as incoming line voltage varies within the operating range of the equipment. Depending on the design, these transformers may also provide electrical isolation, noise attenuation and protection from selected power-line disturbances.

Compare constant voltage transformers by input and output voltage, VA capacity, regulation range, frequency, load requirements and installation configuration. Proper sizing is important because output regulation and performance can depend on the connected load.

How to Select a Constant Voltage Transformer

A constant voltage transformer is designed to maintain a relatively stable output voltage while the incoming line voltage changes within its specified operating range. Many traditional constant-voltage designs use ferroresonant transformer technology to provide voltage regulation without electronic switching or moving components.

Constant voltage transformers can be useful for sensitive electronic and control equipment exposed to recurring voltage variation. Depending on the specific design, additional benefits may include electrical isolation and attenuation of selected electrical noise and transient disturbances.

Important Selection Factors

• Nominal input voltage: Match the transformer to the available electrical source.
• Input operating range: Verify the expected minimum and maximum line voltage.
• Output voltage: Confirm the regulated voltage required by the connected equipment.
• VA capacity: Size the transformer for the actual connected load.
• Minimum loading: Review any manufacturer requirements for maintaining rated regulation performance.
• Inrush demand: Account for loads that temporarily draw additional current during startup.
• Frequency: Confirm compatibility with the available source.
• Isolation requirements: Verify whether the selected transformer provides the isolation required by the application.
• Heat and ventilation: Provide suitable clearance and airflow for the installation.

Constant Voltage Transformer vs. Standard Transformer

A conventional transformer primarily changes voltage and may provide isolation, but its output generally follows changes in the incoming source according to the transformer ratio. A constant voltage transformer is specifically designed to regulate its output over a defined input-voltage range.

Replacement Checklist

• Manufacturer and complete model number
• Nominal and measured input voltage
• Required output voltage
• VA rating and actual connected load
• Frequency
• Required voltage-regulation range
• Hardwired or portable installation
• Photographs of the nameplate and wiring connections