MIL-PRF-19978K
6.3 Definitions.
6.3.1 Liquid-impregnanted capacitor. A liquid-impregnanted capacitor is a capacitor in which a liquid impregnant
is dominantly contained within the capacitor element, but does not occupy substantially all of the case volume not
required by the capacitor element and its connection.
6.3.2 Liquid-filled capacitor. A liquid-filled capacitor is a capacitor in which a liquid impregnant occupies
substantially all of the case volume not required by the capacitor element and its connections. Space may be
allowed for the expansion of the liquid with temperature variations.
6.3.3 Nonmagnetic case capacitor. A nonmagnetic case capacitor is a capacitor in which no part of the case or
retainer is made of magnetizable material; however, the end seal may be made of a material having a ferrous metal
content in order to affect a glass-to-metal seal.
6.3.4 Hermetic seal. For the purpose of this specification, a hermetically sealed capacitor is one in which the
capacitive element is contained within a sealed enclosure of ceramic, glass or metal, or combinations thereof, where
sealing is accomplished by material fusion, welding, brazing, or soldering. The capacitor shall be capable of passing
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the seal test specified in 4.7.5 or of meeting a leak-rate requirement of not more than 1.76 by 10 cubic centimeters
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(cm ) per second, when determined by any other method having sensitivity equal to or better than the stated limit.
When capacitors are tested as specified in 4.7.5, there shall be no continuous visible stream of bubbles.
6.4 Qualification. With respect to products requiring qualification, awards will be made only for products which
are, at the time of award of contract, qualified for inclusion in the Qualified Products List (QPL) whether or not such
products have actually been so listed by that date. The attention of the contractors is called to these requirements,
and manufacturers are urged to arrange to have the products that they propose to offer to the Federal Government
tested for qualification in order that they may be eligible to be awarded contracts or orders for the products covered
by this specification. Information pertaining to qualification of products may be obtained from Defense Supply
Center, Columbus, Attn: DSCC-VQP, PO Box 3990, Columbus, Ohio 43218-3990, or by email to vqp.chief@dla.mil.
An online listing of products qualified to this specification may be found in the Qualified Products Database (QPD) at
6.5 Application information.
6.5.1 Mounting. Capacitors covered by this specification shall be mounted by a retainer or clasp or should be
potted when vibration or shock are likely to be encountered in service.
6.5.2 Voltage derating with temperature (for characteristic M). Characteristic M tubular capacitors may be used in
applications up to +125C with voltage derating as indicated in figure 2. However, insulation resistance
requirements at +125C cannot be expected to exceed 100 megohm-microfarads; greater capacitance change may
be encountered, and life expectancy of the unit will be reduced.
6.5.3 Energy content (in watt-seconds). The energy content of a fully charged dc capacitor is determined by the
following formula:
Where:
W = energy content in watt-seconds.
2
CE
C = nominal capacitance in farads.
W =
E = dc voltage rating in volts.
2
6.5.4 AC component. The rating given is the steady-state dc voltage, or the sum of the dc voltage and the peak
ac voltage, provided that the peak ac voltage does not exceed 20 percent of the rating at 60 Hz, 15 percent at 120
Hz, or 1 percent at 10,000 Hz. Where heavy transient or pulse currents are encountered, the requirements of this
specification are not sufficient to guarantee satisfactory performance, and due allowance must therefore be made in
the selection of a capacitor.
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