Overview
This lecture covers best practices for handling computer power, the basics of AC and DC electricity, how power supplies work, and considerations for choosing and connecting power supplies in computer systems.
Safety Practices
- Always disconnect the computer from all power sources before working inside to prevent electric shock.
- Components can retain power in capacitors after unplugging; follow manufacturer's instructions to dissipate stored electricity.
- Never connect your body to any part of the electrical system, including electrical ground.
Types of Power and Conversion
- Computers use Direct Current (DC), but receive Alternating Current (AC) from power outlets.
- Power supplies convert AC to DC, commonly providing 3.3V, 5V, and 12V outputs.
- AC (Alternating Current) can be transmitted long distances and alternates direction; DC (Direct Current) flows in one direction.
Electrical Measurements
- Ampere (A): Measures electron flow rate, similar to water flowing through a hose.
- Volt (V): Measures electrical force pushing electrons, like water pressure.
- Watt (W): Measures real power (Watts = Volts × Amps).
AC vs. DC Power in Different Regions
- U.S./Canada: 110–120V AC at 60 Hz; Europe: 220–240V AC at 50 Hz.
- Power supplies may have switches or auto-switching for different input voltages; match supply to local voltage to avoid damage.
Power Supply Outputs and Motherboard Connections
- Power supplies provide multiple voltages, including positive and negative values, to support various components.
- Main motherboard power is supplied via a 24-pin (or legacy 20-pin) connector, keyed for proper installation.
- Standby voltage (+5VSB) keeps checking for power-on events during hibernate.
Modular vs. Fixed Power Supplies
- Fixed power supplies have permanently attached cables, which can limit flexibility.
- Modular power supplies allow customization of connected cables, improving airflow and ease of installation.
Sizing and Installation of Power Supplies
- Power supplies are rated by maximum wattage; choose one based on total component requirements.
- Use calculators or add up component wattages manually for sizing.
- Doubling the calculated wattage is recommended for efficiency and future upgrades.
- ATX physical sizes are standardized, but proprietary or old systems may differ.
Data Center Redundancy
- Servers often use multiple (redundant) hot-swappable power supplies to ensure continuous operation.
Key Terms & Definitions
- Direct Current (DC): Electrical flow in one direction, used by computer components.
- Alternating Current (AC): Electrical flow that switches direction, supplied by wall outlets.
- Ampere (A): Electron flow rate.
- Volt (V): Electrical potential force.
- Watt (W): Real power usage (Volts × Amps).
- Hot Swappable: Component can be replaced without shutting down the system.
- Modular Power Supply: Allows customization of power cables attached.
Action Items / Next Steps
- Always disconnect power and follow safety protocols when working inside computers.
- Use a multimeter to verify outlet voltage if unsure.
- Calculate required wattage for your system before purchasing a power supply.
- Review power supply documentation and manufacturer instructions for your hardware.