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Calculating High-Voltage Second-Generation Universal Power Requirements for MX2008 Routers


The MX2008, MX2010, and MX2020 routers support the same power modules AC, DC, 240 V China, and universal PSMs and PDMs.

The information in this topic helps you determine which PSMs are suitable for various configurations, as well as which PSMs are not suitable because output power is exceeded. You determine suitability by subtracting the total power draw from the maximum output of the PSMs. Afterward, you calculate the required input current. Finally, you calculate the thermal output. A sample configuration is provided in Table 1.

We recommend that you provision power according to the maximum input current listed in the power system electrical specifications (see MX2000 Router High-Voltage Universal (HVAC/HVDC) Power Subsystem Electrical Specifications and High-Voltage Universal (HVAC/HVDC) Power Circuit Breaker Requirements for the MX2000 Router).

Use the following procedures to calculate the power requirement:

  1. Calculate the power requirement.
  2. Evaluate the power budget.
  3. Calculate input power.
  4. Calculate thermal output (BTUs) for cooling requirements. High-Voltage Universal (HVAC/HVDC) Power Circuit Breaker Requirements for the MX2000 Router.

The MX2008 DC power system provides power to the FRUs in the chassis (seeTable 1 for information about power). Each power system is made up of two DC PDMs, nine PSMs, ten MPCs, two fan trays, eight SFBs, and two RCBs.

When calculating power requirements, be sure that there is adequate power for the system.

Table 1: MX2008 Power System Sample Configuration

Chassis Power Configuration

Power Distribution Modules (PDMs)

Power Supply Modules (PSMs)


2 PSMs, 2 RCBs, 8 SFBs, and 2 fan trays (no line cards installed)

PDM 0 and 1

2 PSMs

The power consumed by RCBs and SFBs is 100 W each.

The power consumed by 2 RCBs and 8 SFBs is 1 KW.

The power consumed by fan trays 0 and 1 is 1.5 KW each.

The total Kilowatts of power consumed is 4.0 KW.

10 Line cards

PDM 0 and 1

5 PSMs

Each line card consumes up to 1 KW. One PSM is needed for every set of 2 line cards.

N+1 redundant system with N+N redundancy for SFBs, RCBs, and 1 out of 2 fan trays.

PDM 0 and 1

9 PSMs

This provides N+N redundnacy for critical FRUs (RCBs, SFBs, and fan trays) and N+1 redundancy for line cards.

  1. Calculate the power requirements (usage) using the values in MX2008 High-Voltage Second-Generation Universal Power Requirements as shown in Table 2.

    Table 2: Typical HVAC/HVDC Power Requirements for MX2008 Router


    Model Number

    Power Requirement (Watts) with 91% Efficiency

    Base chassis


    Fan trays


    1500 * 2 W = 3000 W



    440 W * 10 = 4400 W



    150 W * 10 = 1500 W



    100 W * 2 = 200 W

    SFB—slots 0 through 7


    100 W * 8 = 800 W

    MX2010 HVAC/HVDC power system (upper and lower half of chassis, 19 A feeds to each PDM input)

    3000 W * 8 PSMs=24,000 W (+ 1 PSM@3000 W redundant capacity)

  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 PDM options.

    Table 3 lists the PSMs, their maximum output power, and unused power (or a power deficit).

    Table 3: Calculating HVAC/HVDC Power Budget

    Power Supply Module

    Maximum Output Power of Power Supply Module (Watt)

    Maximum Output Power for System (Watt)—Including Redundant Capacity

    MX2008 Universal (HVAC/HVDC) PSM

    3000 W for single feed

    3400 W for dual feed

    3000 * 8 PSM = 24,000 W (single feed)

    3400 * 8 PSM = 27,200 W (dual feed)

  3. Calculate input power. Divide the total output requirement by the efficiency of the PSM as shown in Table 4.

    Table 4: Calculating HVAC/HVDC Input Power

    Power Supply Module

    Power Supply Module Efficiency

    Input Power Requirement (Watt)—per PSM

    MX2008 Universal (HVAC/HVDC) PSM


    3300 W for single feed, 3800 W for dual feed

  4. Calculate thermal output (BTUs). Multiply the input power requirement (in watts) by 3.41 as shown in Table 5.

    Table 5: Calculating HVAC/HVDC Input Power

    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.

    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 16.5 divided by 0.91 = 37.9 KW.