Encapsulated transformers – also called potted or cast-resin transformers – protect the windings with a sealed resin housing, which gives them outstanding moisture resistance, vibration immunity, and heat dissipation. They are the preferred choice for demanding industrial, outdoor, and safety-critical applications. This guide explains how encapsulated transformers work, their key specifications, and how to select one for your OEM or ODM design.
What Is an Encapsulated Transformer?
An encapsulated transformer is a transformer whose core and windings are fully embedded in a resin – typically epoxy, polyurethane, or silicone – inside a molded or metal housing. The encapsulation provides mechanical protection, electrical insulation, and environmental sealing, so the transformer can operate in humid, dusty, vibrating, or chemically aggressive environments where open-frame transformers would fail. Encapsulated transformers are available in low-frequency power versions and high-frequency switch-mode versions, with PCB-mount, chassis-mount, and bushing-terminal styles.
How Encapsulated Transformers Work
Electrically, an encapsulated transformer works exactly like any transformer: an alternating current in the primary winding creates a changing flux in the core, inducing voltage in the secondary winding. The difference is mechanical and thermal. The resin filling eliminates air pockets around the windings, so heat conducts directly to the housing and away from the core – this often allows the same electrical design to run at higher power than an open version. The resin also fixes the windings in place, preventing vibration-induced wire fatigue, and provides creepage and clearance protection between terminals.
Key Specifications of Encapsulated Transformers
Power rating: The continuous VA/W the transformer can deliver at its rated temperature rise, often derated by the encapsulation’s thermal resistance.
Input and output voltages: Primary and secondary ratings, plus regulation for low-frequency designs.
Insulation class: Class B (130 C), Class F (155 C), or Class H (180 C) winding insulation, and the resin’s own thermal class.
Isolation / hipot voltage: Primary-to-secondary and winding-to-ground isolation, typically 1.5 kV to 6 kV for reinforced isolation applications.
Environmental protection: IP rating or resin type that defines moisture, dust, and chemical resistance; operating temperature range.
Mounting: PCB pins, screw terminals, flying leads, or busbars; core clamping and housing material.
Standards compliance: UL, IEC, EN, or VDE approvals relevant to medical, industrial, or appliance applications.
How to Choose an Encapsulated Transformer
Start from the electrical requirements – power, input/output voltage, frequency, and isolation – then decide the environmental grade: indoor PCB use can often use a simple epoxy-coated version, while outdoor or washdown environments need a full molded housing with higher IP rating. Check the thermal path: confirm the resin and housing can dissipate the losses at your duty cycle and ambient temperature. For safety-certified products, specify the insulation class and hipot rating up front so the design can be approved. Finally, match the mounting style to your assembly process. Shaanxi SiRui Technology Co., Ltd manufactures encapsulated transformers – PCB, chassis, and terminal styles with custom voltage and isolation ratings – under ISO 9001:2015 quality management with RoHS and REACH compliant materials.
Applications of Encapsulated Transformers
Industrial control panels and PLCs, motor drives and VFDs, UPS and power supplies, LED lighting drivers, medical devices, HVAC and building automation, renewable energy inverters, EV chargers and onboard chargers, railway and marine electronics, and outdoor telecom equipment.
FAQ
What is the difference between potted and encapsulated transformers?
The terms are often used interchangeably. Encapsulation usually implies a molded housing with the resin filling the cavity, while potting can also mean resin fill without an outer housing – both provide the same protection principle.
Are encapsulated transformers more expensive?
Typically yes, because of the resin and molding process, but they last much longer in harsh environments and often allow higher power density, which can lower total system cost.
Can encapsulated transformers be repaired?
Generally no – the resin makes rewinding impractical. This is why correct specification and derating matter at the design stage.
Do you supply custom encapsulated transformers?
Yes. Shaanxi SiRui Technology Co., Ltd designs and manufactures custom encapsulated transformers with your power, voltage, isolation, housing, and mounting requirements, from samples to volume production with full quality documentation.
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