Custom Transformers
Custom transformers wound on toroidal and bobbin cores for current measurement, power conversion, and galvanic isolation. 1J85 permalloy for high-permeability sensing. Silicon-iron and ferrite for power applications. Every unit tested for DCR, inductance, and dielectric withstand.
Transformer Types
Each transformer type has distinct core material requirements, winding configurations, and performance characteristics. We manufacture all three to your exact drawings.
High-permeability 1J85 and silicon-iron toroidal cores for accurate current measurement. 750 to 1,500 turns of fine-gauge wire. The foundation of industrial power monitoring systems.
Silicon-iron and ferrite cores for efficient power conversion. Toroidal geometry for low EMI and high efficiency. Designed for AC/DC converters, DC/DC converters, and power conditioning circuits.
Galvanic isolation between primary and secondary windings. Hi-pot tested per IEC 60950. Used in medical equipment, industrial controls, and any application requiring safety-rated voltage separation.
Current Sensing Transformers
A current sensing transformer (CT) works by measuring the magnetic field created when current flows through a conductor passing through the center of the toroid. The secondary winding on the toroidal core produces an output proportional to the measured current.
Accuracy depends on core material permeability, winding uniformity, and turn count precision. We wind CTs on 1J85 permalloy cores with permeability exceeding 100,000, delivering the sensitivity required for industrial power monitoring, energy metering, and fault detection systems.
Every CT is wound with even distribution across the full 360 degrees, maintaining consistent coupling to the core and linear output across the measurement range.
| Parameter | Current Sensing Specification |
|---|---|
| Core Material | 1J85 Permalloy (Ni-Fe alloy), Grain-Oriented 3% Silicon-Iron |
| Core Permeability | 100,000+ (1J85), 2,000 to 10,000 (Silicon-Iron) |
| Core OD | 0.800" to 1.550" (20.32 mm to 39.37 mm) |
| Core ID | 0.551" to 1.100" (14.00 mm to 27.94 mm) |
| Core Height | 0.256" (6.50 mm) |
| Core Coating | Epoxy, 0.015" (0.381 mm) thickness |
| Wire Gauge | 34 AWG copper, 34 AWG nickel |
| Turn Count | 750 to 1,500 |
| DCR Range | 19.85 to 39.15 ohms |
| DCR Tolerance | ±5% to ±15% |
| Lead Length | 1.25" to 1.60" (31.75 mm to 40.64 mm) |
| Tape | Yellow Mylar, 3M Type 74 |
| Compliance | RoHS, Lead-Free (SN100 solder) |
Power Transformers
Power transformers transfer energy between circuits through electromagnetic coupling. Core material selection determines the operating frequency range and efficiency characteristics. Silicon-iron cores handle power-frequency (50/60 Hz) applications with high saturation flux density. Ferrite cores operate efficiently at switching frequencies above 20 kHz.
Toroidal construction provides inherent advantages for power transformers: lower leakage inductance, reduced audible noise, and a smaller footprint compared to EI-core laminations at equivalent power ratings. The closed magnetic path keeps stray flux to a minimum.
| Parameter | Power Transformer Specification |
|---|---|
| Core Materials | Grain-Oriented 3% Silicon-Iron, Ferrite |
| Silicon-Iron Bsat | 1.6 to 2.0 Tesla |
| Tape Thickness (Si-Fe) | 0.007" (0.1778 mm), 9 mil strip |
| Core OD | 1.424" to 2.250" (36.17 mm to 57.15 mm) |
| Core ID | 0.878" to 1.750" (22.30 mm to 44.45 mm) |
| Core Height | 0.415" to 0.500" (10.54 mm to 12.70 mm) |
| Core Coating | Powder Coat, Epoxy |
| Wire Gauges | 18, 26, 34 AWG copper |
| Winding Types | Toroidal (even distribution), Bobbin-wound |
| Insulation | Yellow Mylar tape (3M Type 74), layer insulation |
| Compliance | RoHS, Lead-Free (SN100 solder) |
Isolation Transformers
Isolation transformers provide galvanic separation between primary and secondary circuits, preventing direct conduction of current between the input and output sides. This is a safety requirement in medical devices, test equipment, and any application where personnel or sensitive circuits must be protected from hazardous voltages.
We build isolation transformers with reinforced insulation between primary and secondary windings, tested per IEC 60950 dielectric withstand requirements. Core material and winding configuration are selected based on your isolation voltage rating, power level, and operating frequency.
Selection Guide
The core material determines the transformer's operating frequency, efficiency, and sensitivity. This guide maps our three core materials to the transformer types they serve.
| Property | 1J85 Permalloy | Silicon-Iron | Ferrite |
|---|---|---|---|
| Primary Use | Current Sensing | Power (50/60 Hz) | Power (High Freq.) |
| Permeability | 100,000+ | 2,000 to 10,000 | 750 to 15,000 |
| Saturation (Bsat) | 0.7 to 0.8 T | 1.6 to 2.0 T | 0.3 to 0.5 T |
| Frequency Range | DC to 10 kHz | 50/60 Hz to 1 kHz | 20 kHz to 1 MHz+ |
| Core Loss | Very Low | Low at 50/60 Hz | Low at high frequency |
| Core Coating | Epoxy | Epoxy, Powder Coat | Uncoated |
| Typical Turn Count | 750 to 1,500 | 200 to 1,000 | 200 to 750 |
| Best Transformer Type | Current Sensing CT | Power, Isolation | Switch-Mode Power |
Construction
Transformer winding requires careful attention to insulation, coupling, and leakage inductance. Here is how we approach each configuration.
One primary winding and one secondary winding, separated by Mylar tape insulation. The most common configuration for current sensing transformers and simple power transformers. Turn ratio determines voltage transformation.
One primary driving two or more secondary windings. Each secondary can have a different turn count for different output voltages. Used in power supplies with multiple output rails and multi-channel measurement systems.
Wire wound evenly across the full 360 degrees of a toroidal core. Provides maximum coupling, minimum leakage inductance, and lowest radiated EMI. Standard for current sensing transformers and high-performance power transformers.
Primary and secondary wound in organized layers on a bobbin form. Provides controlled spacing between windings for consistent insulation. Core inserted after winding. Efficient for lower turn counts and applications requiring pin termination.
Gallery
Currently in Production: NK Technologies, San Jose
We manufacture current sensing transformer assemblies for NK Technologies' industrial power monitoring products. Six active product lines. Over 150,000 cores delivered since April 2025. Toroidal CTs on 1J85 and silicon-iron cores with 750 to 1,500 turns. 34 AWG copper and nickel wire. Zero rejected lots.
Send us your drawings, schematic, or a description of the application. We review every specification and respond within 24 hours.