Determining DC Power Requirements for Your MX2020 Router

MX 2020 DC Power Subsystem Components

The MX2020 DC power system is comprised of two subsystems. Each subsystem provides power to:

• 10 line-card slots

• Nine DC Power Supply Modules (PSMs)

• Two DC Power Distribution Modules (PDMs)

• 20 Modular Port Concentrators (MPCs) (10 MPCs per zone)

• Two fan trays

• Eight Switch Fabric Boards (SFBs)

• Two Control Board and Routing Engines (CB-REs)

Understanding Power Zones in the MX2020 DC Power Subsystem

The MX2020 DC power subsystem has two power zones: zone 0 and zone 1. Some FRUs draw power only from zone 0, some FRUs draw power only from zone 1, and some FRUs draw power from both zone 0 and zone 1. When calculating power requirements, ensure there is adequate power for each zone. Each zone needs to provide 70% of the total power required by shared FRUs. This means 140% of the power required by the FRUs is available in the two power zones combined.

There are two types of DC power subsystems available for the MX2020: a “base” DC power subsystem (MX2020-BASE-DC) and an “optimized” or premium DC power subsystem (MX2020-PREMIUM2-DC). The fan trays in an optimized DC power subsystem draw power from the power zones differently than the fan trays in a base DC power subsystem. In a base DC power subsystem, two of the four fan trays draw power from both zones. In the optimized DC power subsystem, two of the fan trays draw power from only one zone. Because of this, the optimized power subsystem requires less power. Since the two fantrays share power in a zone, they only require 100% of the power they are rated at (not 140%). This is a net savings of 40% * 1700W/fantray * 2 for the system and half that amount per power zone.

As illustrated in Figure 1 and described in Table 1, the power zones in the MX2020 DC base power subsystem distribute power to FRUs as follows:

• Zone 0 powers only line card slots 0-9, and fan tray 1

• Zone 1 powers only line card slots 10-19, and fan tray 3

• Zone 0 + Zone 1 (both zones provide power) to CB-RE slot 0 and CB-RE slot 1, fabric card slots 0-7, and fan tray 0 and 2

Figure 1: Power Distribution in a DC Base Power Subsystem

As illustrated in Figure 2 and described in Table 2, the power zones in MX2020 DC optimized power subsystems distribute power to FRUs as follows:

• Zone 0 powers only line card slots 1-7, and fan trays 0 and 1

• Zone 1 powers only line card slots 10-16, and fan trays 2 and 3

• Zone 0 and Zone 1 (both zones provide power) to CB-RE slot 0 and CB-RE slot 1, and fabric card slots 0-7

Figure 2: Power Distribution in an Optimized DC Power Subsystem

Calculating the DC Power Requirements for Your MX2020 Router

Follow these steps to calculate the DC power requirements for your MX2020 Router configuration.

1. Calculate the total output power required for your MX2020 FRUs.Table 3 shows the typical power usage for the MX2020 DC power subsystem FRUs.

   Table 3: Typical DC Power Usage for MX2020 Router

   Component	Model Number	Power Requirement (Watts) with 91% Efficiency
   Base chassis	CHAS-BP-MX2020
   Fan trays (upper and lower)	MX2000-FANTRAY	1700 W * 4 = 6800 W
   MPC	MPC-3D-16XGE-SFPP	440 W * 20 = 8800 W
   ADC	ADC	150 W * 20 = 3000 W
   CB-RE	RE-MX2000-1800X4	250 W * 2 = 500 W
   SFB—slots 0 through 7	MX2000-SFB	220 W * 8 = 1760 W
   MX2020 DC power subsystem (upper and lower half of chassis, 60 A feeds to each PDM input) MX2020 DC power subsystem (upper and lower half of chassis, 80 A feeds to each PDM input)		2100 W * 8 PSMs=16,800 W (+ 1 PSM@2100 W redundant capacity) 2500 W * 8 PSMs=20,000 W (+ 1 PSM@2500 W redundant capacity)
   MX2020 DC power subsystem (upper and lower half of chassis, 240-V feeds to each PDM input)		2500 W * 8 PSMs=20,000 W (+ 1 PSM@2500 W redundant capacity)

   Note:

   The power reservation for the critical FRUs is 7360 W. With power droop-sharing between the two zones, the power reservation for critical FRUs is reduced to 5662 W. This number assumes a 70/30% load on the power zones when droop sharing is enabled.

2. Evaluate the power budget, including the budget for each configuration if applicable, and check the required power against the maximum output power of available PSM options. Table 4 lists the MX2020 PSMs, their maximum output power, and unused power (or power deficit).

   Table 4: MX2020 PSM DC Output Power Budget

   Power Supply Module	Maximum Output Power of Power Supply Module (Watt)	Maximum Output Power for System (Watt)—including redundant capacity
   MX2020 DC PSM 60 A (feed to each input)	2100	37,800
   MX2020 DC PSM 80 A or DC PSM (240 V China) (feed to each input)	2500	45,000

3. Calculate input power. Divide the total output requirement by the efficiency of the PSM. Refer to Table 5.

   Table 5: Calculating DC Input Power

   Power Supply Module	Power Supply Module Efficiency	Output Power Requirement (Watt)—per PSM	Input Power Requirement (Watt)—per PSM
   MX2020 DC PSM 60 A	91%	2100	2307
   MX2020 DC PSM 80 A or DC PSM (240 V China)	91%	2500	2747

4. Calculate thermal output (BTUs) for cooling requirements. Multiply the input power requirement (in watts) by 3.41. Refer to Table 6.

   Table 6: Calculating DC Thermal Output (BTUs)

   Loaded Chassis Heat Load	Thermal Output (BTUs per hour)
   Loaded chassis configuration	34.5 KW divided by 0.91 * 3.41 = 129,280 BTU/hr (Zone 0 output. The calculation method for Zone 1 is the same as for Zone 0). 34.5 KW of output power consumed by the chassis. This is the maximum output the chassis can consume in a redundant configuration. The input power is 34.5 divided by 0.91 = 37.9 KW.