Calculating Power Requirements for MX104 Routers

The information in this topic helps you determine which power supplies are suitable for various configurations, as well as which power supplies are not suitable because output power is exceeded. You determine suitability by subtracting the total power draw from the maximum output of the power supplies. Afterward, the required input power is calculated. 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 supply electrical specifications (see MX104 AC Power Specifications and MX104 DC Power Specifications).

1. Calculate the power requirement.
2. Evaluate the power budget.
3. Calculate input power.
4. Calculate thermal output (BTUs) for cooling requirements.

• Two (redundant) power supplies
• Two (redundant) Routing Engines
• Two 20-port Gigabit Ethernet MICs with SFP
• Cooling system (standard fan tray and air filter)

1. Calculate the power requirements (usage) using the values in Power Requirements for MX104 Components as shown in Table 1.

   Table 1: Sample Power Requirements for an MX104 Router

   Chassis Component	Part Number	Power Requirement
   Base system	MX104-AC	350 W
   MIC 0	MIC-3D-20GE-SFP	37 W
   MIC 1	MIC-3D-20GE-SFP	37 W
   Total output power		424 W

   Note: The power consumed by an MX104 router as shown in Table 1, may differ slightly, due the power conversion losses in the power supply.

2. Evaluate the power budget. In this step, we check the total output power against the maximum output power of available power supply options.
3. Calculate input power. In this step, the input power requirements for the example configuration are calculated. To do this, calculate the total input power including the MICs as shown in Table 2.

   Table 2: Calculating Input Power Example

   Item	Value
   Total input power requirement (maximum)	625 W
   AC/DC power supply efficiency	91 %
   Sum of MIC power requirements	37 W + 37 W = 74 W
   Additional power supply conversion losses, due to added MICs (Sum of MIC power requirements) * (efficiency) - (Sum of MIC power requirements)	(74 W) * 91 % – (74 W) = 7.3 W
   Input power to base system (includes power conversion losses in power supplies)	350 W
   Total calculated input power requirement with MICs (Sum of MIC power requirements) + (Additional power supply conversion losses) + (Input power to base system)	74 W + 7.3 W + 350 W= 431.3 W

4. Calculate thermal output (BTUs). To calculate this, multiply the input power requirement (in watts) by 3.41.

   Table 3: Calculating Thermal Output

   Power Supply	Thermal Output (BTUs per hour)
   MX104 power supply (as shown in the example)	431.3 W * 3.41 = 1471 BTU/hr
   MX104 power supply (maximum)	625 * 3.41 = 2131 BTU/hr