ERS II and ERS/FT II
Appendix B - Power Supply

Power Supply

Each Series II Subsystem 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 subsystem. In the ERS/FT II, each of the two supplies will normally carry approximately one-half of the total load.

Each supply is fan cooled. The fans and other subsystem electronics require 24 watts, leaving 356 watts available for controller boards, disk drives, CD ROM drive, tape drive, etc. When the power supply load is properly limited, and the inlet air temperature is maintained between 0 and 40 degrees C, 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 subsystems are 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.

Load Considerations

The power supply has four available voltage sources: +5vdc, +12vdc, -12vdc, and -5vdc. The subsystem provides the following power for each of these four voltage sources.

                        Table B-1
               375 Watt Power Supply Ratings

Steady State Total Power Available   = 356 watts maximum
Peak Total Power Available           = 422 watts maximum

* 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 356 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 356 watts.

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 and Table B - 3 to calculate the total power.

Table B-2
Cubix Product Power Requirements (Watts)

Note: When referring to Table B-2 an asterisk to the right of the device name indicates that a math coprocessor is installed. If no math coprocessor is installed, subtract 1.0 watt on the +5vdc requirement

Table B-3
Peripheral DevicesPower Requirements (Watts)

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

1. Add the total internal processor bay wattage.

2. Add to +24 watts consumed by the subsystem 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 - 4.

                           Table B-4
                    BTU Calculation Example


                 Typical Power Requirements (Watts)

BTU Calculation    ( (81.6+24) * 1.43) * 3.4 = approx. 513 BTU/hour 

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