You're in the middle of editing a document on your computer but haven't saved it yet, the server suddenly crashes and loses data, or the router loses power and cuts off the internet connection, causing you to miss an important meeting... These frustrating situations are most likely related to "unstable power." And a UPS (Uninterruptible Power Supply) acts as an "umbrella" for your devices. But do you know that UPSs come in two types: "online" and "standby"? Choosing the wrong one could mean wasting your money.
First, understand: What is the core function of a UPS?
In simple terms, a UPS is a "power buffer station." When the mains power is normal, it quietly "stores energy." When the mains power is interrupted (due to a power outage, or a sudden increase or decrease in voltage), it immediately "steps in" to supply power, giving your devices time to save data or shut down normally.
However, the way online and standby UPSs "step in" is vastly different.
Online UPS: 24-hour "on-duty," with zero power interruption
Working principle:
An online UPS is like a "full-time bodyguard." Regardless of whether the mains power is normal, it always uses "its own power" to supply the devices.
When the mains power is normal: It first converts the alternating current (AC) into direct current (DC) (rectification), then converts the DC back into stable AC (inversion) to supply the devices. At the same time, it charges the built-in battery.
When the mains power is interrupted: The battery immediately takes over and continues to supply power through the inverter. There is no "switching" process during this time, resulting in zero power interruption.
Core advantages:
- Zero switching time: At the moment of power outage, there is a seamless transition, and the devices are completely unaware of any "power fluctuations." The voltage stability is akin to that of a "constant-temperature air conditioner."
- Comprehensive protection: It not only guards against power outages but also filters out noise and voltage instability in the mains power, delivering a "pure" version of the electricity.
Suitable scenarios:
Devices that require "zero tolerance" for power stability, such as hospital monitors, enterprise servers, and industrial automation equipment. Even a slight "jitter" in voltage can cause irreparable damage. In such cases, an online UPS is the "anchor of stability."
Standby UPS: "Part-time on call," a cost-effective choice
Working principle:
A standby UPS is more like a "part-time bodyguard." It usually allows the mains power to directly supply the devices while quietly charging the battery in "standby" mode.
When the mains power is normal: The mains power directly reaches the devices, while the charger replenishes the battery's energy.
When the mains power is interrupted: It quickly "switches" to the battery mode, converting the battery's DC into AC through the inverter to supply power.
Core advantages:
- Cost-effective: With a simple structure and low cost, it is suitable for scenarios with a slightly higher "tolerance" for power supply.
- Low energy consumption: Since it allows the mains power to directly supply the devices most of the time, its own power consumption is low.
Minor drawback:
There is a "delay" (usually a few tens of milliseconds) during the switching process. For ordinary computers and routers, this delay may not be noticeable. However, for precision equipment (such as servers), even millisecond-level fluctuations can lead to data loss.