Magnetic toroidal powder cores are coated with a special epoxy finish that provides a tough, wax tight, moisture and chemical resistant barrier having excellent dielectric properties.
The finish is tested for voltage breakdown by inserting the core between two weighted mesh pads. Force is adjusted to produce a uniform pressure of 10 psi, simulating winding pressure. The test condition for each core in the random sample set, to guarantee minimum voltage breakdown voltage in each production batch, is 60 Hz voltage at 1.25 the guaranteed limit. A2 and A7 samples are tested at 1250 Volts min. AY samples are tested to 750 V min.
Magnetics' customers use various techniques for testing voltage breakdown. In most cases, the technique used is different from the procedure described above. As a result, the measurements can differ from the guarantees listed in the Magnetics Powder Core catalog. In such cases, correlating the customer test results to Magnetics test results can help incoming QC inspectors detect poorly coated cores as opposed to reporting a testing error.