Which Devices Care About Waveform

Plenty of gear runs fine on a modified sine wave, and some doesn't. The honest answer for any single device is in that device's manual. This page shows what usually matters and how to look it up.

What tends to cope

Wikipedia says "numerous items of electric equipment will operate quite well" on modified sine wave inverters¹. Two kinds get named.

• Resistive loads, such as traditional incandescent light bulbs. A resistive load simply turns power into heat or light.
• Items with a switched-mode power supply. They "operate almost entirely without problems"¹. Many phone and laptop chargers are built this way, but check the one you own.

"Almost entirely" isn't "always". If a charger's label or manual mentions waveform, follow that.

What may struggle

Some equipment gets less comfortable.

• Anything with a mains transformer. The source says it "can overheat depending on how marginally it is rated"¹.
• Audio gear and loads that hum. The harmonics can cause "a humming noise during operation"¹.
• AC motors, found in many fans, pumps and tools. Wikipedia says most will run, but with an efficiency reduction of about 20% owing to harmonic content, and they may be quite noisy¹.

The word "may" matters. None of these is certain to fail. They're just the cases where it pays to check first.

Medical and sensitive gear

If a device keeps someone healthy or safe, don't experiment. This includes breathing equipment and similar items. Read the device's manual and ask its maker, or the supplier, what power it needs. Where the maker names pure sine wave, treat that as a requirement.

Why ratings get confusing

An inverter's rating may be in watts or VA, and a device's label may use either. For a purely resistive load they're identical². Motors and transformers aren't purely resistive, so the numbers can differ. Transformers are often rated in VA². The power factor page has the full picture.

How to check a device

1. Find the manual, or the label on the device itself.
2. Look for the words "pure sine wave", "modified sine wave" or "inverter" in the power section.
3. Write down the device's power draw, and the starting surge if it's given.
4. Compare it with the inverter's continuous rating, as covered in reading an inverter label.
5. If the manual is silent, ask the maker in writing and keep the reply.

If you can't find an answer, a pure sine wave output is the cautious choice for anything you can't afford to damage. The waveform page explains the difference between the two.

A note on safety

Follow your product's manual for ventilation and placement. Anything that plugs into a household circuit through a permanent connection is for a licensed electrician to install. Never feed power back into a home through an outlet.