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Appendix B
Power Supply
Power Supply
Load Considerations
BTU Calculations
Each SafeStor\FT power supply must be capable of delivering the current needed to power all fans and disk drives (i.e., the total load) mounted in the subsystem. Each of the two supplies will normally carry approximately one-half of the total load.
Each supply is fan cooled. The SafeStor\FT is equipped with two 170 watt power supplies. The fans and other electronics require 17 watts, leaving 153 watts available for disk drives. When the power supply load is properly limited, 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 subsystem.
CRITICAL REQUIREMENT!
If the SafeStor\FT is installed in a non-Cubix supplied RETMA enclosure, it is the responsibility of the end-user to ensure the subsystem inlet air does not exceed 40 degrees C. This is a critical requirement.
The power supply has two available voltage sources: +5vdc and +12vdc. The system provides the following power for each of these four voltage sources.
Table B-1
Power Supply Ratings
+5V @ 9A = 45 watts maximum (steady state)
+12V @ 9A = 108 watts maximum (steady state)
+5V @ 9A = 45 watts maximum (peak)
+12V @ 29A = 348 watts maximum (peak)
Steady State Total Power Available = 153 watts maximum
Peak Total Power Available = 383 watts maximum
Duration of Peak Power must not exceed 10 Seconds!
Peak power is defined as the power required during the disk drive spin-up time. This time period must not exceed 10 seconds.
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 153 watts total steady power or 383 watts of peak power may be drawn from all voltage sources combined.
The most straightforward 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 to calculate the total power.
Table B-2
SCSI Disk Drive Power Requirements
Disk Drive OP Mode +12VDC +5VDC
Power
Conner CFP 1080 spin-up 1.5a 500ma
20.5W
read/write
4.5W
seek
6.5W
idle 200ma 275ma
3.8W
Conner CFP 2105 spin-up 1.7a 700ma
23.9W
read/write
7.0W
seek
7.0W
idle 300ma 420ma
5.7W
Conner CFP 4207 spin-up 3.5a 880ma
46.4W
read/write
13.2W
seek
14.3W
idle 780ma 685ma
12.8W
Seagate ST31230N spin-up 1.5a 500ma
18.0W
idle 500ma 200ma
7.0W
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.
1. Add the total disk drive wattage.
2. Add 17 watts consumed by the system fans and electronics.
3. Multiply the calculated total watts load by 1.43 to account for power supply losses.
4. Multiply the new total watts by 3.4 to obtain the number of BTUs per hour.
An example is shown in Table B - 3.
Table B-3
BTU Calculation Example
Device Type Qty Idle Spin-up Total
Seagate ST31230N 2 14.0 36.0 50.0
Conner CFP 1080 4 15.2 82.0 97.2
Disk Drive Watts 29.2 118.0 147.2
BTU Calculation ((147.2+17)*1.43)*3.4 = 798 BTU/Hour
This document, and all Web contents, Copyright © 1997
by Cubix Corp., Carson City, NV, USA.