Reading the Label on an Inverter

An inverter label packs a lot into a small space. Read it in the right order and it answers most of what you need. You're hunting for four things: volts, hertz, watts and VA.

Volts

Volts describe electrical pressure. A label usually has two voltage figures, and they belong to opposite ends.

• DC input voltage. This is the battery side. It has to match the battery the inverter is paired with, according to the maker's manual.
• AC output voltage. This is what comes out for your appliances. It should match the supply your equipment expects.

Output voltage varies worldwide. Premises in most of the world receive a supply of between 220 and 240 volts, and North America is the biggest exception¹. Your appliance label tells you which one it wants. If the numbers differ, don't plug it in.

Hertz

Hertz (Hz) counts how many times the current flips direction each second. It's the "nominal frequency of the oscillations of alternating current"².

An inverter's output frequency is usually the same as the local power line frequency, either 50 or 60 hertz³. Both frequencies are in use today in different places². A label that says 60 on a unit you plan to use somewhere that runs on 50 is a warning. Check the manual to see whether the setting can change, and don't assume it can.

Watts

Watts measure the real work being done: the power that runs a heater element or a motor. An inverter label typically gives a continuous rating, which is what it can supply for long periods. Some also list a surge or peak rating for a short burst, such as when a motor starts.

Don't mix up the two. A device that needs a big start-up kick may exceed the continuous number for a moment. Read the manual to see how long the surge is allowed and how the maker defines it.

VA

VA stands for volt-amperes. It's a second way of rating the same output. The link between real power in watts and apparent power in VA "is described by the power factor"⁴. That's a bigger topic, so it has its own page: the power factor page.

For now, remember that a VA figure and a watt figure on one label aren't the same number. Check which unit each rating uses before you compare products.

Other things to look for

• Output waveform type, which the waveform comparison covers.
• Whether the label lists any standards or approvals, and what they cover. Ask the maker what a mark means if it isn't explained.
• Operating temperature or ventilation notes, which the manual spells out.
• A model or serial number, so you can find the exact manual.

Putting it together

Start with the load. Add up the watts of the equipment you'd run together, using each item's own label. Then check three things against the inverter: voltage matches, frequency matches, and the continuous rating is high enough. Leave some room above that total.

Any connection to your house wiring is for a licensed electrician. A label tells you what a unit is rated for. It doesn't tell you how to install it, and the installation instructions come from the maker's manual.