Technical Documentation
M320 DC Power Supplies Description
In the DC power configuration, the router contains either two or four DC power supplies, located at the lower rear of the chassis in slots PEM0 through PEM3 (top to bottom).
If only two DC power supplies are installed, the power supplies in either slots PEM0 and PEM1 or slots PEM2 and PEM3 can provide full power to the router. You can upgrade your DC power supply from two to four power supplies for full redundancy.
 | Note: Except during upgrade, all DC power supplies installed in the chassis must be the same model number, either all isolated or all nonisolated DC power supplies. Using both isolated and nonisolated DC power supplies during normal operations prevents load sharing. |
Nonisolated DC Power Supply
Each nonisolated power supply consists of a single DC input (-48 VDC and return), a circuit breaker, a fan (each power supply is cooled by its own internal cooling system), and LEDs to monitor the status of the power supply. Each nonisolated power supply weighs approximately 10 lb (4.5 kg).
Isolated DC Power Supply
Each isolated power supply consists of a single DC input (-48 VDC and return), a circuit breaker, a fan (each power supply is cooled by its own internal cooling system), and LEDs to monitor the status of the power supply. Each isolated power supply weighs approximately 10 lb (4.5 kg).
| Note: The Isolated DC power supply is designed to be more resilient to power irregularity such as noise or surge in power environment. |
Components Powered by Each Power Supply Slot
The DC power supplies in the slots indicated provide power to the components listed in Table 1.
Table 1: Components Powered by Each DC Power Supply Slot
| Slot | Provide Power to These Components |
|---|---|
PEM0 and PEM2 | FPCs in slots FPC3 through FPC7 |
PEM1 and PEM3 | FPCs in slots FPC0 through FPC2, SIBs, CBs, and Routing Engines, and fan trays. |
DC Power Supply Load Sharing and Fault Tolerance
When the router is fully configured with four DC power supplies:
- The DC power supplies provide full redundancy
- The DC power supply in PEM2 serves as the backup to the DC power supply in slot PEM0.
- DC power supply in PEM3 serves as the backup to the DC power supply in slot PEM1
- Load sharing occurs between the DC power supplies installed in slots PEM0 and PEM2
- Load sharing occurs between the DC power supplies in slots PEM1 and PEM3
| Note: Isolated DC power supplies share current over the full input operating voltage range. The current sharing between nonisolated power supplies relies on equal voltages at the power supply input terminals. |
