Electrical Safety Precautions
- Always disconnect from any power source before working inside a computer to avoid
electrocution or damage to components.
- Capacitors inside a computer can store power even after disconnection; ensure they
are discharged before handling.
- Avoid connecting yourself to a building’s electrical system, including the
ground wire, as it may become energized unexpectedly.
- Exercise caution when working with electrical equipment to prevent accidents or
equipment damage.
Power Supply Basics
- A power supply unit (PSU) converts AC (alternating current) from
wall outlets into DC (direct current) for computer components.
- Wall outlets provide AC power, while motherboards and components require DC
power to operate.
- PSUs convert 120V AC (US/Canada) or 230V AC (Europe) into
3.3V, 5V, and 12V DC for system use.
- The PSU is a critical component, as all internal hardware relies on its power output.
Key Electrical Terms
- Ampere (Amp or A): Measures the flow of electrons (current) past a point per
second; analogous to water flow in a hose.
- Voltage (Volt or V): Represents electrical "pressure"; similar to water pressure in
a hose.
- Wattage (Watt or W): Measures real power use, calculated as Volts × Amps =
Watts (e.g., 120V × 0.5A = 60W).
AC vs. DC Power
- AC (Alternating Current): Constantly reverses direction; represented as a wave.
Used for power transmission (e.g., 120V AC at 60Hz in the US, 230V AC at 50Hz in Europe).
- DC (Direct Current): Flows in one direction with constant voltage; used by computer
components (e.g., 3.3V, 5V, 12V).
- PSUs automatically adjust or require manual switching for different AC inputs (e.g., 120V vs. 230V).
- Using the wrong voltage setting (e.g., 120V PSU on 230V) can cause catastrophic
failure.
Power Supply Outputs
- PSUs provide multiple DC voltages for different components:
- +12V: Powers PCIe adapters, hard drives, and high-demand devices.
- +5V: Used by motherboard components (older systems) and standby power (5V
SB).
- +3.3V: Powers RAM, M.2 slots, and modern motherboard components.
- -12V: Supports legacy LAN connections and older PCI cards.
- -5V: Rarely used; found in older systems for legacy adapter cards.
- Check the PSU manual or label for voltage and ampere ratings per output.
Motherboard Power Connectors
- The 24-pin ATX connector is the primary power connection to the motherboard,
providing 3.3V, 5V, and 12V DC.
- Older systems may use a 20-pin connector; modern 24-pin connectors are
backward-compatible (extra 4 pins unused).
- The connector is keyed to prevent incorrect insertion.
Redundant and Modular Power Supplies
- Redundant PSUs: Used in servers for high availability; each PSU
can handle 100% of the load. If one fails, the other takes over.
- Hot-swappable: Allows PSU replacement without shutting down the system.
- Modular PSUs: Allow customization of cables, reducing clutter and improving
airflow.
- Fully modular: All cables are detachable.
- Semi-modular: Some cables are fixed; others are detachable.
Power Supply Wattage and Efficiency
- Wattage: Determines the PSU’s capacity; higher wattage supports more components
(e.g., high-end GPUs).
- Calculate total system wattage by summing component requirements (CPU, GPU, storage, etc.).
- Aim for a PSU that supports 50% more than your system’s peak load for efficiency
and future upgrades.
- Efficiency: Measures how well the PSU converts AC to DC (higher efficiency = less
heat and power loss).
- Certifications: 80 PLUS (Bronze, Silver, Gold, Platinum, Titanium).
- Higher efficiency reduces heat and operating costs.