150-231-165-01, Revision 01
Appendix C - Functional Operation
HLU-231 List 6E
September 22, 1998
49
P
OWER
C
ONSUMPTION
The three most important power parameters of an HLU are its maximum power consumption, its maximum power
dissipation, and its maximum current drain.
The Maximum Power Consumption is the total power that the HLU-231 consumes or draws from its -48 V shelf
power source. This parameter is needed when the HLU-231 is remotely located to its serving CO. It determines
the battery capacity required to maintain an eight-hour standby battery reserve for emergency situations; thus
limiting the maximum number of plugs per line unit’s remote enclosure.
The Maximum Power Dissipation measures the power that is converted into heat buildup within the unit. It
contributes to the total heat generated in the space around the unit. It is used to determine the maximum number
of fully loaded shelves per bay that does not exceed the maximum allowable power dissipation density in
Watts/sq. ft. In COs, the maximum power dissipation for open-faced, natural convection cooled mountings is
limited to 134.7 Watts/sq. ft. per Section 4.2.3 of the NEBS GR-63-CORE. The footprint of a standard 28-slot
23-inch HLU-231 shelf is 7.024 sq. ft. Thus, the maximum bay dissipation is limited to 946 Watts. At 8 Watts per
slot, this limits the number of occupied slots to 118 per bay. The thermal loading limitations, imposed when using
the HLU-231 in a Controlled Environmental Vault (CEV) or other enclosures, are determined by applying the
HLU-231 power parameters to the manufacturer's requirements for each specific housing.
The Maximum Current Drain is the maximum current drawn from the shelf power supply when it is at its
minimum voltage (-42.5 V). It determines the shelf fusing requirements. All HLU-231 shelves are partitioned into
two equal halves, each fused at 10 amps for a total of 20 amps per shelf. A fully loaded shelf draws 10.5 amps (no
doublers) or 17 amps (with doublers) worst case. This is within the 20 amp fuse limit.
Heat baffles should be placed between every other shelf, in racks containing more than two shelves. This
technique deflects the rack’s heat outward and reduces thermal stress on the plugs.
Power Consumption: Without Doublers
Maximum Power Dissipation:
•
Per Slot = 8 Watts
•
Per Shelf = 104 Watts
Maximum Power Consumption:
•
Per Slot = 18 Watts
•
Per Shelf = 234 Watts
Maximum Current Drain:
•
Per Slot = 0.423 Amps
•
Per Shelf = 5.5 Amps
The worst case conditions, under which these parameters were measured, include a 9,000 ft.,
AWG 26 loop, 60 mA of Customer Provided Equipment (CPE) current, a fully loaded 13-slot
shelf, and a -42.5 V shelf battery voltage with the HLU-231 4-character display “OFF.”