950-734-100-01, Revision 01
Product Overview
PLL-734 List 1
December 18, 1998
3
P
OWER
C
ONSUMPTION
AND
H
EAT
D
ISSIPATION
The three most important power demands of a COLU on the COTS power supply are its maximum power
consumption, heat dissipation, and current drain.
Table 1
lists the power consumption and heat dissipation for the
COLU, on a per slot and per COTS basis
.
Maximum Heat Dissipation
The maximum heat dissipation measures the power converted into heat that is built up within the COLU. It
contributes to the total heat generated in the space around the COLU. This conversion factor is used to determine
the maximum number of fully loaded COTS per bay that will not exceed the maximum allowable power
dissipation density in Watts per square foot.
In CO locations, the maximum heat dissipation for open-faced, natural convection-cooled mountings is limited to
134.7 W per square foot per Section 4.1.4 of the NEBS standard GR-63-CORE. The footprint of a standard
16-slot, 23-inch COTS is 7.042 square foot. The maximum bay dissipation is therefore limited to 948.6 W. At
113.6 W per COTS, this limits the number of fully loaded COTS to eight per bay with a heat baffle above each
COTS.
Thermal Loading Limitations
The thermal loading limitations imposed when using the COLU in a CEV or other enclosures are determined by
applying the COLU power parameters to the manufacturer's requirements for each specific housing.
The worst case conditions under which these parameters are measured include a 18,000 ft.,
26 AWG loop, a fully loaded COTS, and a -42.5 Vdc COTS battery voltage. The remote is
assumed to be ringing one line with a load of 5 REN, with the second line off hook on both RTs.
Loop current sink at the COTS is assumed to be 23 mA. Loop current feed higher than 23 mA
restricts the number of COTS in a bay due to heating.
Table 1.
Power Consumption and Heat Dissipation
Power
COLU Slot
COTS
19-inch
23-inch
Maximum Heat Dissipation
HDSL Line Power Off
3.0 W
36 W
48 W
HDSL Line Power On
7.1 W
85.2 W
113.6 W
Maximum Power Consumption
HDSL Line Power Off
3.0 W
36 W
48 W
HDSL Line Power On
30.1 W
361.2 W
481.6 W
Maximum Current Drain
HDSL Line Power Off
71 mA
0.852 A
1.14 A
HDSL Line Power On
709 mA
8.50 A
11.35 A
This is a worst case situation in that it assumes the entire CO is subjected to the maximum
power density. Conditions other than worst case would permit increasing the number of COTS
per bay without jeopardizing the CO thermal integrity. Due to the chimney effect, PairGain
recommends you install one heat-dissipating baffle between every COTS. This action would
prevent exceeding the rated operating temperature of the COLU units.