Certified to UL, Canadian, EN and IEC safety standards Please call us at 800-836-5920 to discuss your application.
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Safety Standard Agency Approvals Our standard and custom designed transformers are certified to the following standards: General Purpose Transformers
Medical Application Transformers
Primary Windings Choose from the inputs listed in the Standard Line Section, or specify your custom input – by line frequency and voltage.
Operating Frequency Standard transformers are designed to operate at 50 or 60 Hz line frequency. Grain-oriented steel cores can be used at frequencies up to 1KHz. If the transformer will only be operating at 400Hz. We can use a core that is about 1/3 smaller than for normal line frequency. A 50Hz core is 20% larger than a 60Hz core. For higher frequencies, we substitute such materials as ferrite, powdered metal and other composites.
Power We can quote on power requirements from 7VA to 20KVA (Single Phase) or 60KVA (Three-Phase)
Insulation The standard insulation is Class A (105 C) or Class B (130ºC). Other insulation classes may be specified as required, such as class F (155ºC).
Secondary Windings You can specify the output loading in either of two ways: You can specify the output loading in either of two ways: 1. AC (RMS) voltage and current or power (VA) and duty cycle for each secondary output. 2. DC load parameters. This data should include: DC voltage, current, rectifier type (full wave, full wave bridge, etc.) and specification, capacitor type and value, regulator type and specifications, any special load characteristics, including duty cycle. Please supply a schematic, if possible. With this information, we will determine the optimum secondary DC specifications for each output.
 MountingWe supply the standard hardware, potted center or vertical bracket listed in the Standard Design Section. We can also supply the transformers with threaded inserts or studs imbedded in an epoxy potted center. We also offer special molded bases, complete molded enclosures, or custom sheet metal brackets and weather proof steel enclosures.
Connections and Leads Our factory standard is to provide our toroidal transformers with multi-stranded leads. Self leads are optional. Connector assembly is an available option.
Thermal Protection Thermal protection by auto-resettable switch or fuse is optional. Unless otherwise requested we will use fuse that opens at 110ºC. All lighting transformers have 110ºC thermal auto-resettable cut-offs.
Static Shielding The toroidal transformer may need static shielding to minimize capacitive coupling between primary and secondary windings when operating in an extremely noisy environment.
Ultra-Low Magnetic Stray Field Emission Our standard design greatly reduces stray fields compared to a laminated transformer. For sensitive electronic applications, our optional Ultra-Low Stray Field Design, achieved through a proprietary process, further reduces the emissions. In applications such as audio equipment, high-resolution CRT displays, a magnetic shield around the circumference of the transformer achieves even lower stray field levels.
Aspects of Size Reduction Increasing the working flux density of our toroidal transformers permits fewer turns and/or a smaller cross sectional core area. Experience has shown that working flux densities of 12 to 14 kilogauss are the practical limits for the conventional laminated cores with air gaps. Since toroidals can be designed with flux density of 16 kilogauss, the toroidal core geometry may directly reduce the core size and the number of turns. The former lowers the size and weight of the transformer and the latter reduces the copper losses. You can significantly reduce transformer size and weight where the transformer is loaded intermittently. In such cases, the load is energized for a small time duration, which is much shorter than the overall thermal time constant of the transformer.
Physical Dimensions Typical sizes and weights listed in the chart below serve as a basic guideline to determine size and weight based on power (VA) rating. Height and diameter can be varied, as long as the core cross section holds constant. Specify diameter and height or as maximum physical envelope available.
Rectifier Circuits When using a toroidal power transformer, some rectifier circuit designs are more efficient than others. Four typical circuits are illustrated here with recommendations. Consult Bridgeport Magnetics for further information and assistance.
Dual Center Tap Rectifier
Full Wave Bridge
Full Wave Center Tap
Half Wave Rectifier Voltage Regulation Output voltage regulation varies with the size of the toroidal electrical transformer. Regulation can be improved by selecting a transformer with a higher VA rating than actually required. 
Shorted Turn Condition A completed path by any conductor passing through the center hole of the toroid constitutes a shorted turn. A through-the-center screw making contact to the chassis at both ends can inadvertently establish a shorted turn. As with any short circuit, this condition will result in high circulating currents and high local heat. Such mounting must be avoided. Our standard mounting options include a single screw, two rubber washers and a steel washer (disk mount) with no outside metal structure to complete a shorted turn.
Inrush Current Precautions Because toroidal electrical transformers have excellent magnetic properties and no air gaps, the inrush current when power is turned on is sometimes higher than with stacked transformers. Inrush current can be as high as 15 times the peak steady state rated current. However, the inrush transient rarely lasts over a half cycle. Choose a delayed action fuse or circuit breaker protection to avoid nuisance power loss.
Aspects of Size Reduction Increasing the working flux density permits fewer turns and/or a smaller cross sectional core area. Experience has shown that working flux densities of 12 to 14 kilogauss are the practical limits for the conventional laminated cores with air gaps. Since toroidals can be designed with flux density of 16 kilogauss, the toroidal core geometry may directly reduce the core size and the number of turns. The former lowers the size and weight of the transformer and the latter reduces the copper losses. You can significantly reduce transformer size and weight where the transformer is loaded intermittently. In such cases, the load is energized for a small time duration, which is much shorter than the overall thermal time constant of the toroidal electrical transformer.
Efficiency The graph illustrates the effect of increasing load on the toroid's efficiency for various nominal ratings.
Temperature Rise May be specified as required, or tell us the operating ambient temperature. Our basic design guideline is not to exceed 50ºC to comply with ClassB(130C) requirements for room temperature applications with a comfortable safety margin. . Actual increase will depend on how and where the transformer is mounted and how well it is cooled. When higher temperature ratings are needed, we offer transformers built to Class F (155C). Temperature rise varies with the actual output power (P-out) in relation to nominal power (P-nom) for a given core size.
Using a larger core size will reduce the temperature rise. The toroidal's small core losses will cause the temperature rise to drop drastically when reducing the output power. At half the load, the temperature rise will only be about 25% of the rise at full load. Total losses for the transformer, including winding loss and core loss per pound of silicon steel at a given flux level, may be calculated from design data and data furnished by steel suppliers. The graph illustrates the rise in transformer temperature as the actual power approaches the toroidal transformer's nominal power rating.
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