Uninterruptible Power Supplies

Standby vs Line Interactive vs Online

• Standby / Offline
  • Normally operates off utility power
  • Switches to battery power when a power disruption is detected
  • Cheap
  • Waveform: Typically produces a stepped approximation to a sine wave (also known as a modified sine wave or quasi-sine wave)
• Line Interactive
  • Actively regulates voltage by boosting or decreasing utility power without switching to battery
  • Uses battery power during significant power disruptions
  • More expensive but still relatively affordable
  • Waveform: The waveform is smoother and more consistent, closely mimicking the standard utility power sine wave
• Online / Double Conversion
  • Continuously converts incoming AC power to DC and then back to AC
  • Ensures a seamless and uninterrupted power supply with no transfer time during an outage
  • Expensive, outside of the budget of most consumers
  • Waveform: Pure sine wave, which is smooth and continuous, resembling the standard utility power sine wave

Waveforms

• Square Wave
  • A waveform that switches directly between high and low levels, without any intermediate steps
  • Sharp transitions between high and low voltage levels
  • High total harmonic distortion
  • Generally not suitable for most modern electronic devices
• Stepped Approximation to a Sine Wave (Modified Sine Wave)
  • A waveform that approximates a sine wave but with a series of steps rather than smooth transitions
  • Consists of flat, stair-step-like segments.
  • Higher total harmonic distortion compared to pure sine wave
  • Can cause more electrical noise and potential compatibility issues with sensitive devices
• Sine Wave / Pure Sine Wave
  • A smooth and continuous wave that oscillates sinusoidally, similar to the standard utility power waveform
  • Smooth, rounded peaks and troughs.
  • Low total harmonic distortion (THD), typically less than 3%.
  • Stable frequency and voltage
  • There may be a difference between Sine Wave vs Pure Sine Wave UPSs but either are better than Stepped or Square Wave

Pure Sine Wave (Recommended)

I use an APC Back-UPS Pro 1350 S, which is a Line Interactive, Pure(?) Sine Wave UPS, in an old house that lacks up-to-date wiring, including lacking consistent, proper grounding.

Prior to this, I was using standby UPSs and would experience random drops in power resulting in my computer rebooting. These problems were resolved with the Line Interactive Sine Wave UPS.

It might actually have something more to do with the Line Interactive part and the APC AVR (Automatic Voltage Regulation) feature, I'm not actually sure.

I even have two Standby UPSs powering another computer which remains on 24/7 and I don't experience random power drops there so it might have to do with the outlet or a wiring problem, I just don't know.

All I know is that when I had the random drops problem, a better Line Interactive Sine Wave UPS solved my problems.