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that makes sure that the internal voltage regulators operate with low
mains voltage too, is much too high. This results in a high voltage across
the voltage regulator, therefore in a high power that causes higher heat
dissipation.
If the line voltage is very low, the regulation reserve is not sufficient to
assure proper operation of the voltage regulators. The heat dissipation
is very low, however, as soon as the mains voltage drops below the
regulator's drop out point, a 100Hz or 120 Hz interference appears on
the DC output voltage. This AC component will cause a hum noise of
approximately – 50 dB in all master outputs of the console; the solution
is to use a different setting for the primary voltage. It is best to test the
mains voltage every couple of hours for several days before making any
changes. Make a note of the values, and after a few days check for the
highest and the lowest value. Then change the setting -
AFTER YOU HAVE DISCONNECTED THE MAINS – FOLLOW THE
SAFETY RULES LISTED ABOVE!
to a setting, that is the next lower value to the lowest value on your list.
If your lowest value is 223 V, you are supposed to use transformer tap
220 V, for example. Now, check the highest value on your list. If it is
lower than the lowest value + 10 V, you are done. If not, it is necessary
to check the temperature of the power supply unit every once in a while
for a couple of days. If the temperature exceeds 60°C for several hours,
you should improve the ventilation of the power supply (outside the rack,
some free rack spaces above and below the power supply, switching on
the fans, or a change of location).
1.3 Fail-safe Power Supply
The C1000 and C1750 crossover units are optionally available if
failsafe operation is required . These unit can be used with all the
power supply units. The failsafe device is a passive diode cross
over with an additional, active, failure response system. The C1000
and C1750 cross over units are equipped with Shottky diodes
with very low drop out voltage to keep voltage drop and power
dissipation of the failsafe system as low as possible. A connector
for a remote display that can be installed in the console's meter
bridge is available.
Capacity
The passive diode cross over section of the C1000 and C1750 failsafe units
can handle forward currents of up to 10 or 20 ampere per output voltage
for the C1000 or C1750 version, therefore the operation with any of the
standard power supply units for the SRC51 consoles is possible.
Mounting and Dimensions
The cross over unit is a 3U high rack mountable device. The total width
of the front panel 483 mm. The actual width behind the top plate is 440
mm. Without attached connectors the C1000 and C1750 are approx. 320
mm deep. The only differences between the C1000 and C1750 version are
the current of the diodes and the type of connectors that are used. While
the C1000 uses diodes for a current load of 10 amps, the C1750 uses
diodes for currents of 20 amps. Both units have the SRC51 standard 26-
pin connector. The pinning is same as as the pinning that is used with the
power supply units.
Ventilation
Due to the low drop Shottky type power diodes, the power and heat
dissipation of the C1000 cross over unit is pretty low, even under full load
Abb. 4 - Failsafe Power Supply - Crossover-Unit C1000
SRC
5 1
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