Case Study: Ignition Coils Put out 65,000 Volts and Survive – with Rynite® PET
Rynite® PET thermoplastic polyester resin proves its performance in high-voltage electrical parts.
Application Description
After rigorous open-circuit bench testing of ignition coils at up to 65,000 volts and extensive field trials on racing cars, MSD Ignition, part of Autotronic Controls, is developing coils with bobbins and housings molded from Rynite® PET. The first MSD® Pro Mag coil is engineered for maximum output in competitive drag racing, tractor pulls and boat racing. This coil is wired to produce output of up to 50,000 volts. Prototypes of other coils engineered for use in stock car racers, or highly modified street cars, are undergoing field trials. Additional coil designs are under consideration
Materials Selected and Why
The coil bobbins are molded from a flame-retardant, 46% glass-reinforced modified grade of Rynite® PET. In addition to providing high temperature dielectric performance, it has an excellent balance of stiffness, strength, and toughness. At 150°C, a 1.59 mm thick sample disk molded from this resin maintains almost 90% of its room temperature dielectric strength in the standard 500 V/s short-time test (ASTM D149).
The housings are molded from another flame-retardant grade of Rynite® PET, which also provides an excellent balance of mechanical and electrical properties.
Benefits Gained
- Hot dielectric performance. The coil bobbins have proven in tests to provide effective insulation up to 65,000 V.
- Savings on production costs. Autotronic formerly used a machined plastic part for the complex bobbin for secondary windings. It cost $35, versus about $3 for the part molded from Rynite® PET.
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