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FT
Subsystems
Appendix B - Power Supply
Specification and Load Considerations
Load Considerations
Each Cubix Fault Tolerant Subsystem normally contains two power supplies. Each power supply must be capable of delivering the current needed to power all controller boards, fans, and disk drives (i.e., the total load) mounted in the Fault Tolerant Subsystem. With two supplies installed, each will normally carry approximately one-half of the total load.
Each supply is fan cooled. When the power supply load is limited to 380 watts average, and the inlet air temperature is maintained between 00C and 400C, the power supply will provide a long life of trouble-free service. Cubix RETMA cabinets are designed to provide an ample supply of air to the intake vents of the Fault Tolerant Subsystem.
F If the FT Subsystems are installed in a non-Cubix supplied RETMA enclosure, it is the responsibility of the end-user to ensure the FT Subsystem inlet air does not exceed 40 degrees C. This is a critical requirement.
The Fault Tolerant Power Supply has four available voltage sources: +5 vdc, +12 vdc, -12 vdc, and -5 vdc. The subsystem provides the following power for each of these four voltage sources. Table B-1
F Peak power is defined as the power required during the IDE hard disk drive ramp-up time. This time is normally 10 seconds or less.
The user must ensure that no single voltage source power rating exceeds the maximum listed in Table B-1. In addition, these maximums are limited by the fact that no more than 380 watts total power may be drawn from all voltage sources combined. It is the responsibility of the user to verify that the sum of the power drain from the four sources does not exceed 380 watts.
The most straight forward method to determine if the power supply is capable of furnishing sufficient power is to add the power required for each load using the power requirements in Table B-2 and calculate the total power.
For example, Table B-3 illustrates the power requirements for a typical Fault Tolerant Expansion Subsystem.
Since the power consumption for each voltage and the total power consumption is less than the allowed maximum power consumption, the configuration in Table B-3 can be properly powered with the 380 watt Fault Tolerant power supply.
CAUTION: DO NOT EXCEED THE MAXIMUM LOAD FOR ANY INDIVIDUAL VOLTAGE OR THE TOTAL LOAD. IF THAT CONDITION SHOULD OCCUR, THE POWER SUPPLY WILL SAFELY SHUT DOWN AND THE FAULT LIGHT WILL BE TURNED ON.
BTU Calculations
After the internal processor bay wattage has been calculated (see Table B-3), heat generation of the FT subsystem may be calculated.
1. Multiply the calculated total watts load by 1.43 to account for power supply losses.
2. Multiply the new total watts by 3.4129 BTU/hr-watts to obtain the number of BTUs per hour.
This document, and all Web contents, Copyright © 1997
by Cubix Corp., Carson City, NV, USA.
