Inverters

An inverter converts DC battery power into 230V AC mains power, so you can run ordinary household and office appliances where there is no mains outlet. It earns its keep wherever mains power is not available.

There are three waveforms. Square wave came from the first generation of inverters and is rare now, because the power it produces is neither reliable nor consistent. After that came modified sine wave, and pure sine wave.

For the detail on modified sine against pure sine, our eBook on the 10 mistakes people make when buying a power inverter goes through it.

An inverter takes DC power from a battery or other stored source and converts it to the AC our everyday devices run on. You use one when you need AC power on the road or at home, for anything you would normally plug into a wall socket: a fan, a lamp, a microwave.

They come in a range of shapes and capacities. Small units up to a couple of hundred watts are a rectangular box with a lead and a plug for the cigarette lighter socket. Larger ones connect straight to the battery terminals.

Typical uses are a road trip where you want the laptop, a fishing trip where you want the DVD player, or a power cut at home. Areas with no electricity at all, the bush and the far flung parts of New Zealand, benefit most: lighting and simple appliances where there is nothing else. Camping, beaches and parks are the same story.

Two things decide which one you need: the wattage you have to run, and how you will connect the unit to your power source. Inverters come in different power ratings, and the rating sets the type and number of devices you can run. Work out the devices you will connect and the wattage they draw, then get an inverter that covers it and produces the right waveform.

Our eBook on the 10 mistakes people make when buying a power inverter works through case studies on calculating the rating you need.

The longer you run it the more energy comes out of the battery, and every extra device plugged in drains it faster. Start with a fully charged battery, and carry a spare if you plan to run the inverter for a long stretch. If the inverter is on a car that is not running, start the engine every 10 to 15 minutes so you do not flatten the battery. Read the owner's manual before working on batteries: a bad connection can injure you, and an inverter carries a risk of electrocution.

Size it to your largest simultaneous load plus surge headroom. A kettle, microwave or toaster pulls far more than people expect, so a load that might look physically small on paper can still overload the inverter. Surging behaviour in your load will cause the power on startup to be many multiple times a loads nominal amount. This gets into a complex area we will need to consult with you on. I can give you one extreme example, water pumps, we usually factor in a surge rating of 7 times its nominal value, so for an example a 500w water pump will surge up to 3500w momentarily and the inverter needs to handle that without over loading.

Pure sine for anything with a motor, compressor, digital clock or sensitive electronics - fridges, microwaves, power tools, CPAP. Modified sine only suits simple resistive loads, and honestly, we steer everyone to pure sine wave, modified sine was a temporary trend 20 years ago when electronics was very expensive to produce, so still seen occasional around still.

Yes, on pure sine. One that comes up regularly on chat is a CPAP user wanting overnight runtime - confirm it's a 230V unit first, and note the humidifier roughly doubles the draw. Send us the exact model and we should be able to look up its exact energy requirements.

Yes, with a pure sine unit sized sufficient for the surge - a "900W" microwave can draw up to 1,600 -2100W of input. Never run one on modified sinewave inverter; it may under power it and also stress the magnetron.

It can, but a kettle is a big resistive hit - one customer's inverter kept cutting out and we traced it straight to the kettle. Budget it to be 2,100W+ and expect it to be your limiting load.

For the PassPower inverter-charger range, 3000W is the smallest. For standalone pure sine, the NOMAD NPS 700W is a popular small unit for CPAP and light AC loads.

It's an inverter with a built-in mains battery charger and automatic changeover from grid or generator, ideal for a caravan that runs off battery, then tops up and passes mains through when you plug in at a park.

No - that's a misconception we correct weekly. An inverter-charger charges from mains; you still need a MPPT solar charger for solar as well. If you combine all these functions into an all-in-one unit, you could call that a solar inverter.

Yes, with our stackable units - you can parallel onto the same phase, up to six units, so 2 or 3 is common for bigger builds. Check your exact model has this ability.

Solar goes through a solar charge controller which is either a separate unit or integrated into the solar inverter and then to the battery.

Usually either overloading or DC under voltage. Low battery voltage is from an undersized bank or undersized/too-thin DC cable causing voltage drop on surge. Contact us to get advice on how to determine which issue you are having.

It's the increased amount of power the inverter can tolerate for a second or two, it useful to start motors and compressors and other surging loads

Yes, small car inverters for light loads, but a cigarette-socket unit is limited by the socket fuse and the cabling and connection. A cigarette socket was never designed for transferring a high amount of current and is fundamentally limited despite how convenient and common it is. For anything above very light loads, proper cabling and connection is required through to the battery.

Inverters use power just being on. On a small battery, leaving a big inverter idling overnight quietly flattens the bank. Switch it off when not in use.

Only if generation and storage are sized for it. We design the complete system; the inverter is just the final conversion stage.

Yes. Keep the cord as short as you can, because length costs you power and degrades the signal.

Keep it out of direct sunlight, between 10 and 30 degrees C, with enough ventilation that it cannot overheat.

That is a modified sine wave inverter. Some audio gear picks up the electronic hum from the waveform, and modified sine inverters are known for it. A pure sine wave inverter filters out the common-mode noise, so even lower quality audio devices run quietly on one.

An inkjet. It draws far less than a laser printer, so it runs more happily on an inverter. For home or office use on inverter power, an inkjet is the sensible choice.

It is a feature built into the inverter that sounds when your DC voltage drops too low, for example below 11V on a 12V system. It means the battery is nearly flat.

If the voltage keeps falling the inverter shuts down completely. That protects the battery from being drained flat, and stops the inverter putting non-standard power out on its AC side when it cannot get enough energy in on the DC side. Do not ignore it: once the battery is fully drained the inverter will not restart until it has some charge back.

Mistake #8 in our eBook, not getting an inverter with the essential features, covers what else to look for.