Frequently Asked Questions

Sun Transformer (operating as STC, Inc.) is a ISO 9001:2015-certified custom transformer manufacturing company. For over 35 years, we have designed and built custom transformers for high-reliability applications. The main industries we serve include aerospace, defense, medical, marine, broadcast, and industrial applications.

STC is based in Illinois, and ships out manufactured products to the United States and Canada.

We work with companies across aerospace and avionics, defense and military, medical device manufacturing, marine electronics, broadcast and communications, renewable energy, environmental monitoring, and commercial and industrial applications.

Our client list includes companies like Honeywell, Garmin, and Gates Air. At STC, our team is committed to delivering high-reliability transformers, and we have been recognized for upholding exceptional manufacturing standards.

Yes. Our manufacturing facility is located in Illinois.

STC manufactures a wide range of electronic transformers. We specialize in custom builds. We also produce inductors, chokes, and coils.

Transformers we frequently build and ship include:

• Power transformers
• Isolation and high-isolation transformers
• Toroidal transformers
• PC-mount transformers
• High-voltage transformers
• Three-phase transformers
• Control transformers
• Switching transformers
• Instrument transformers
• High-frequency transformers
• Encapsulated transformers
• Autotransformers
• Ferroresonant transformers

For custom requests or to discuss solutions for your project, please contact us for a quote.

Our manufacturing is optimized for small to mid-size magnetics. STC builds custom electronic transformers up to approximately 5 KVA. If your project requires a larger transformer, we will identify that during the quote process and recommend an alternative manufacturer.

All. We can build transformers for virtually any input voltage and frequency combination. In North America, standard outlet power runs at 110 to 120 volts at 60 Hz, but we understand that the circuitry feeding into a given application may operate differently. For international applications, please reference worldwide voltage and frequency standards. Transformers designed for 60 Hz will need to be redesigned for 50 Hz use (such as European markets), which typically increases the transformers’ physical size by roughly 20%.

Yes. Through our sister company STC Electronics, we offer full electronics manufacturing services, including both surface-mount and through-hole assembly. If you need a transformer as part of a larger PCB assembly, we can handle the whole thing. Visit STCElectronics.com for more on those capabilities.

We build to custom specifications. The majority of transformers we ship are built to customer-specific requirements. If you have electrical specs, dimensional constraints, environmental requirements, or regulatory compliance needs, send them to our engineering team for review. We will design a solution that fits your needs.

Yes. It is common for our customers not to have the technical specs for a transformer. Contact us to arrange shipment of the non-functional transformer to our facility in Illinois. Our team will inspect and disassemble it to determine the exact specifications including turns ratios, wire gauges, core material, and more. If you have the original schematic, that is also helpful. However, we still recommend sending us the physical unit to ensure accuracy.

Yes. Dimensional constraints are a common part of the custom design process, especially in applications where space is limited, like avionics enclosures, implantable or portable medical devices, and compact industrial controllers. Provide your electrical requirements alongside your dimensional limits and we’ll give you an accurate assessment of what’s achievable.

In most situations, yes. First, our engineering team must assess the obsolete transformer. Contact us to coordinate the shipment of the obsolete transformer to our facility. Our engineering team will deconstruct it and give an honest assessment. Depending on the availability of components, materials, and other factors, we may not be able to exactly replicate the original transformer. We are honest about our capabilities and will inform you of alternative options if necessary. As a custom manufacturer, STC can build a transformer to suit your specs.

We are ISO 9001:2015 certified, ITAR registered (in full compliance with the Arms Export Control Act and International Traffic in Arms Regulations), and certified to IPC-A-610 and J-STD-001 manufacturing standards. This allows us to access unclassified but sensitive military technical data required for government projects under DoD/DND security protocols.

Our certifications inform our daily manufacturing and operations. We work at the highest standards in the industry, bringing extensive knowledge and experience to every project.

Yes. Our standard LPC-style PC-mount transformers carry UL approval. For transformers built to custom specifications, UL approval is available for an additional fee. Reach out to discuss what that process looks like for your project.

Sun Transformer maintains UL recognized insulation systems to meet strict compliance standards for performance, safety, and fire resistance.

Yes. We can manufacture transformers in full compliance with the RoHS Directive. This must be specified at the time of order. Please make sure your team includes that requirement when you submit your quote request.

ITAR stands for International Traffic in Arms Regulations, a set of US government regulations that control the export and import of defense-related articles and services. Being ITAR registered means Sun Transformer is registered with the U.S. Department of State to manufacture transformers for military and defense applications, and that we operate under strict compliance protocols governing how that work is handled, documented, and controlled. For defense and aerospace customers, working with an ITAR-registered supplier is a requirement.

We take quality control seriously. Every transformer we build is fully tested. The specific testing protocol depends on the transformer type and your specifications, but our testing capabilities include continuity, exciting current (magnetic current), winding inductance, leakage inductance, winding resistance, open circuit voltage, loaded circuit voltage, turns ratio, dielectric testing (HiPot / high potential difference), quality factor, interwinding capacitance, and insulation resistance. If your application requires specific test documentation or test reports, include that in your quote request and we will do our best to accommodate.

We primarily ship via FedEx and UPS for smaller shipments, and use numerous LTL freight companies for larger shipments. If your organization has a preferred carrier or specific shipping requirements, we’re flexible; just let us know at the time of order.

Submit a quote request through our website at suntransformer.com/quote-request, or call us directly at 618-643-2555. You can also email sales@suntransformer.com. The more detail you can provide about your electrical requirements, application environment, compliance needs, and timeline, the faster we can turn around an accurate quote.

Include your electrical specifications—input voltage, output voltage, frequency, power rating—and any turns ratio requirements. If you have dimensional constraints, operating temperature range, required certifications, or specific testing requirements, include those as well. If you’re replacing an existing transformer, sending the unit or its documentation significantly speeds up the process. Please contact us to coordinate shipments to our facility.