MIL-PRF-15305F
4.6.6.1 For cylindrical insulated coils. The coils under test shall be connected to a test fixture conforming to
figure 11 with each wire lead wrapped one turn around the test fixture terminal and shall be soldered to the terminal or
only soldered to Federal #1268 (U" Notch) terminals or equivalent, for uniform low contact resistance. The test fixture,
with the attached coil, shall then be placed in a test chamber which allows forced air circulation to be shut off during
testing. The test chamber shall be free of test area drafts and direct thermal radiation. A temperature indicating device
with an accuracy of ±0.5°C shall be located in the area surrounding the coil under test, but not where it will be
influenced by the temperature rise of the coil. The test chamber temperature shall then be stabilized at the specified
ambient temperature (see 3.1). The dc resistance (r) shall be measured with one-tenth rated dc applied at the specified
ambient temperature (t). When the resistance of the coil is stabilized, the resistance value shall be recorded. The
ammeter-voltmeter method may be used for determining this resistance, provided that the accuracy of these meters is
0.5 percent or better and the resistance of the voltmeter is at leas 1,000Ω per volt. The rated dc (see 3.1) shall then be
applied to the coil under test, when rated current is applied. When the resistance of the coil under test is stabilized with
rated current applied, the resistance (r) and the test chamber temperature (T) shall be recorded. The temperature rise
(ΔT) shall be calculated by the following formula:
R-r
(t + 234.5) - (T - t )
ĆT
=
r
ΔT = Temperature rise in °C above the specified ambient temperature of the coil under test.
Where:
R = Resistance of coil in ohms with rated dc applied at temperature (T+ ΔT).
r = Resistance of coil in ohms at temperature (t), the specified ambient temperature.
t = Stabilized specified ambient temperature in °C of the coil under test without dc applied.
T = Ambient temperature in °C (at time forced air circulation is shut off) with rated dc applied.
T shall not differ from t by more than 5°C.
4.6.7 Overload (see 3.10). DC equivalent to 1-1/2 times the specified rated current (see 3.1) shall be applied to
the windings for 5 minutes. After the test, coils shall be examined for evidence of cracked cases, distorted or softened
insulation, or loosened windings or terminals.
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