Three types of UPS and their output waveforms ( Part 1)

Standby UPS : Inexpensive, but avoid connecting unauthorized electrical appliances.

Standby UPS is the most common “economical” model on the market. If you go to a computer mall to buy a UPS, the shopkeeper will most likely recommend this type. Its working principle is very simple: when the power is good, it allows the power to pass directly through while charging its own battery. Once a power outage occurs, its internal inverter starts working, converting the battery’s DC power into AC power for supply.

This process involves a switching time of approximately a few milliseconds. The capacitors in your computer’s power supply can handle this brief interval, so the computer won’t restart.

The key is its output waveform. Most standby UPS outputs a square wave, and better ones will give a “corrected sine wave”—the name sounds nice, but it is actually still a stepped square wave.

What’s wrong with square waves? If you’re only connecting to a regular computer, monitor, or router, it’s perfectly fine. The first thing the power supply of these devices does is convert the AC power back to DC, so whether it’s a square wave or a sine wave makes little difference.

However, if you try to save money by connecting your home fan, water pump, or aquarium circulation pump to this type of UPS, you’ll end up with a buzzing motor, overheating, unstable speed, and eventually, it will burn out. I’ve personally witnessed someone connect a floor fan to a backup UPS for emergency use, and the motor started smoking ten minutes later.

So, who is a standby UPS suitable for? Personal office computers, broadband modems, routers, and cash registers. Remember this: Don’t plug anything with an electric motor into a standby UPS.

Online interactive UPS : A compromise solution with added voltage stabilization function

Online interactive voltage regulators can be understood as an “enhanced” version of backup voltage regulators. They have an additional automatic voltage regulation function compared to backup voltage regulators. For example, if your office voltage is unstable, ranging from 210V during the day to 240V at night, a backup voltage regulator cannot handle this, but an online interactive voltage regulator can actively pull the voltage back to around 220V before outputting.

In terms of waveform, the online interactive output is an analog sine wave . When viewed on an oscilloscope, it looks like a series of steps going up and down, which is smoother than the backup square wave, but still quite different from a true sine wave.

This waveform can barely drive some small inductive loads, such as a small cooling fan in a server rack or a regular inkjet printer. But it won’t work for larger motors.