Introduction

Many line‑interactive UPS advertise “simulated” or “stepped” sine wave on battery, while others promise “pure sine.” Which one do you need? The answer depends on your power supplies, noise tolerance, and how critical graceful shutdown is.

Quick definitions

• Pure sine output (on battery): The inverter approximates utility‑grade AC with low total harmonic distortion; best for sensitive electronics and active‑PFC PSUs.

• Simulated/stepped sine: The inverter produces a stepped approximation. It’s usable for many basic loads but can cause noise or stress in some electronics.

Why active‑PFC PSUs care

Modern PC and server PSUs use active PFC to improve efficiency. On poor waveforms, they can draw current in pulses, leading to coil whine, excess heat, or, in edge cases, resets. NAS devices and some audio/video gear may also exhibit noise.

When simulated sine is fine

• Simple routers, switches, ONTs

• Basic DVR/NVR, low‑power CCTV kits

• Phone chargers, LED desk lamps, fans with simple supplies If the device runs cool, quiet, and stable during short outages, simulated sine may be acceptable.

When to insist on pure sine

• Desktops or workstations with active‑PFC PSUs

• NAS/storage with write caches (Synology/QNAP‑class)

• Audio interfaces, studio gear, medical/lab electronics

• Any load where brief waveform issues can corrupt data or recordings

A simple compatibility test (no lab gear needed)

1. Plug the device into the UPS.

2. Force the UPS to battery (pull input or use the test button).

3. Listen for coil whine and observe stability for 10–15 minutes under typical use.

4. Monitor temperature by touch (carefully) or software where available.

5. If noise/heat or instability appears, step up to a pure sine model or to an online (VFI) UPS.

Buying checklist for line‑interactive UPS

• Publish watt (kW) rating alongside kVA and pure sine on battery if needed.

• Transfer time clearly stated; faster is better.

• Replaceable batteries and charger capacity sized for any external packs.

• USB/SNMP support for graceful shutdown of PCs/NAS.

• Service & warranty with real coverage in your city.

FAQs

Is simulated sine dangerous for PCs? Not inherently, but it can cause noise, heat, or rare stability issues with active‑PFC PSUs. Prefer pure sine for PCs and NAS.

If I choose pure sine, do I still need online UPS? If you need zero‑transfer‑feel and better isolation from sags/noise, online UPS (VFI) is the safer option.

Will simulated sine harm CCTV gear? Most DVR/NVRs and simple cameras are fine; test to be sure and size runtime appropriately.