MIL-DTL-52876D
3.5.3 Primary power supply. The primary power supply shall operate as
specified herein from 110 to 125 volts, 48 to 62 Hz ac power. The power
supply shall provide a 20 ±1 Vdc regulated output voltage, a 22.5 ±3.5 volts
ac (Vac) output voltage, and an unregulated dc voltage as specified herein to
maintain a standby battery supply on trickle charge. The power supply shall
also provide, at the battery terminals TB2-2 to TB2-1, a fast charge voltage
which shall function as specified herein. The trickle charge voltage shall
vary as a function of the applied loads and ambient temperature in accordance
with table I and the Appendix A test procedures. The fast charge voltage
output shall be capable of supplying up to the maximum current specified in
table II. The fast charge mode shall be initiated when the voltage at the
battery terminals falls to 24.0 ±0.3 Vdc (fast charge threshold voltage) for
the 1 and 5 zone and 26.0 ±0.3 Vdc for the 25 zone power supply at a room
ambient temperature of 77 ±5 °F. For temperatures outside this temperature
range, the fast charge threshold voltage tolerance shall be ±1 Vdc. The
trickle charge mode shall be restored when the battery terminal voltage rises
2 ±0.5 volts above the fast charge threshold voltage and shall exist whenever
the battery terminal voltage is above the fast charge threshold voltage,
provided fast charge operation has not been initiated. The power supply shall
also conform to the current output, line regulation, load regulation and
ripple voltage requirements specified in table II. A power off/on switch
shall be provided which in the "OFF" position shall disconnect ac power and
the standby battery power from the power supply circuitry. With the power
switch in the "ON" position, a loss of input ac power shall cause the power
supply to automatically operate from the standby battery supply without false
alarm, incorrect status indication or other impairments of function. With a
battery (batteries) or equivalent standby supply capable of providing the
required current at 24 Vdc, the power supply shall continue to provide the
regulated 20 Vdc output specified. The twenty-five zone power supply shall
have a thermal overload switch (thermostat) in the battery fast charge circuit
which shall open when the switch temperature rises to 150 ±5 °F and close when
the temperature falls to 130 ±6 °F.
3.6 Burn-in. Each monitor cabinet (power supply component only) and power
supply when furnished separately shall be subjected to an eight-hour burn-in
to reduce the number of infant mortality failures (see 4.4.2.4).
TABLE I.
Charging voltage as function of loads and temperatures.
Power
Supply
Applied Loads
Voltage:
TB2-2 to TB2-1 (Vdc)
Type
77 ±5 °F
-20 °F
+150 °F
TB3-1 to
TB3-2 to
TB2-2 to
TB3-7
TB3-7
TB2-1
±.3
±.7
±.7
1 Zone
no load
no load
no load
27.9
30.2
25.6
±.5
±.8
±.8
1 Zone
20K ohms
80 ohms
270 ohms
27.0
29.8
25.2
±.3
±.7
±.7
5 Zone
no load
no load
no load
28.2
30.8
26.6
±.8
±1.0
±1.0
5 Zone
20K ohms
16 ohms
150 ohms
26.4
29.0
24.8
±.8
±1.0
±1.0
25 Zone
no load
no load
no load
29.4
32.8
27.0
±.3
±.8
±.8
25 Zone
20K ohms
3.2 ohms
no load
27.7
31.0
25.4
5
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