A standby UPS (uninterruptible power supply) sits between your mains socket and your equipment, constantly monitoring the incoming electrical supply. When it detects a power outage or significant voltage drop, it automatically switches your devices to run on its internal battery instead.
The switch happens quickly, usually within 5-10 milliseconds, which is fast enough for most computers and networking equipment to continue working without losing data or shutting down. However, this switching delay can cause brief interruptions in sensitive equipment like medical devices or industrial machinery.
How it differs from other UPS types:
- Unlike an online UPS, the standby model does not continuously regulate power or filter it while mains power is present. It only acts when problems are detected.
- Standby units cost significantly less than online alternatives, making them popular for home offices and small businesses.
- They offer no protection against brownouts (low voltage), voltage spikes, or electrical noise travelling through the mains.
Common limitations:
Standby UPS systems don't stabilise your electricity supply, so your equipment still experiences power quality issues. They also need battery replacement every 3-5 years, and the batteries degrade faster if kept in warm environments. During a power cut, battery runtime is typically 5-30 minutes depending on your load.
When to use one:
Standby UPS works well for protecting computers, routers, and server equipment from unexpected outages. If you need consistent voltage regulation or live in an area with frequent brownouts, an online UPS or line-interactive UPS is better. Always check the wattage rating matches your total device power consumption, and test the battery monthly by triggering a manual switch.