Calculating Dc Input Current - Cisco 4500 Series Installation Manual

Chapter 2 Preparing for Installation

Calculating DC Input Current

Step 1
Step 2
Step 3
Step 4
Step 5
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Complete power usage tables are in the Catalyst 4500 Series Module Installation
Guide. To calculate the DC input current needed for data and inline power
applications, use the following steps (the example shows the DC input current
requirement in a Catalyst 4503 with a Supervisor Engine II and two
WS-X4306-GB modules, and assumes a DC input voltage of -48 VDC):
Add the power requirement for each component in your system.
Catalyst 4503 uses 54 W
•
• Supervisor Engine II uses 147 W
WS-X4306-GB uses 2 X 47 = 94 W
•
Total DC input power = 295 W
•
After the entries for all components have been added together, divide that number
by the DC input voltage to determine the DC input current.
Input current = 295 W/48 VDC = 6.14 A for data only.
•
Step 3 to Step 5 are for applications requiring inline power. If your configuration
does not include inline power devices, the DC input current is the result of Step 2.
If you want to add an inline-capable module (WS-X4148-RJ45V) with 10 inline
devices (such as IP Phones) to your system, calculate the DC output power sent
to inline devices.
10 X 6.3 W = 63 W for inline devices.
•
6.3 Watts is correct for a Cisco IP phone. Wattage consumption will depend on
the inline device used.
Find the DC input power using the DC output power.
63/.96 (efficiency) = 65 W of DC input power.
•
Divide the DC input power by the DC voltage input of –48 V to find the DC input
current used by inline devices.
65/48 = 1.4 Amps for inline devices.
•
Power Connection Guidelines for DC-Powered Systems
Catalyst 4500 Series Switches Installation Guide
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