Inverter Generator NZ Buying Guide: Sizing, Noise, Fuel & Safety

For most NZ buyers an inverter generator is the right choice: it gives clean, stable power for laptops, TVs and chargers, and it runs quieter and uses less fuel at light loads. A conventional open-frame generator makes more sense when you need lots of watts for the money, a big fuel tank for long run times, or rugged site power for heavy tools. Either way, size it by adding up your running watts and then allowing for the start-up surge of the biggest motor you will plug in.

Inverter vs conventional (open-frame) generators

Inverter generators

An inverter generator converts the alternator's raw output to DC and then electronically back to AC. Because the electronics, not the engine speed, set the output frequency, the engine can slow down when demand is low. Makers call this smart throttle or engine smart control. The result is usually less noise and less fuel used at part load, and a steady sine wave that sensitive electronics are happy with.

Conventional (open-frame) generators

A conventional generator runs its engine at a constant speed to hold 50 Hz, in a tubular steel frame. They are generally louder, but they give you plenty of output and large fuel tanks for the price. Better models use an AVR (automatic voltage regulator) to keep voltage steady, and construction-style units add RCD protection, IP66 outlets and wheel kits for site work.

Rated vs peak (starting) watts

Every listing shows two numbers. Rated (running or continuous) watts is what the generator can supply all day. Maximum (peak or starting) watts is a short burst above that, which covers the moment a motor starts. For example, the W&C WC-P6000Si is listed at 5,500 W rated and 6,000 W max. Always plan your normal running load against the rated figure, not the max.

How to size a generator

1. List what must run at the same time, using the wattage on each appliance's plate or manual.
2. Add up the running watts. That total needs to sit comfortably under the generator's rated output.
3. Allow for motor start-up surge. Anything with an electric motor (fridges, freezers, compressors, water pumps, saws) can draw a multiple of its running watts for a moment as it starts. Add the extra surge of the largest motor, and start motors one at a time.
4. Leave headroom. A generator working flat out at its rated limit for hours runs hotter, louder and thirstier than one with spare capacity.

A note on surge: Welling & Crossley's own listings for its Smart Silent inverters say they give their best performance with appliances that need steady loads with little surge or in-rush current. If you mainly run a large compressor or pump, check the motor's starting requirement carefully, or look at a larger unit.

Clean power for electronics

Cheap or unregulated generators can deliver a rough waveform with voltage that wanders as the load changes. Look for pure sine wave output and a quoted THD (total harmonic distortion) figure: lower is cleaner. The W&C Smart Silent inverters quote THD under 3%. Some conventional units also regulate well; ITM lists its AVR construction generators at THD under 5%. If you plan to run computers, TVs, battery chargers or anything with a control board, an inverter or a well-regulated AVR model is the safer pick.

Fuel type and run time

Most portable generators run on 91 unleaded petrol. Diesel open-frame models suit heavy, regular use but are heavier and louder: the ITM 6,500 W diesel is listed at 107 kg and 85 dB at 7 m at full load. When comparing run times, check the load each maker quotes it at. Our listings variously quote run time at 25%, 50% or 75% load, and a figure at 25% load will always look better than one at 75%. Bigger tanks mean longer runs but more weight.

Noise

Decibels are logarithmic, so a few dB makes an audible difference. Check how each figure was measured (distance and load). Inverters are usually the quiet option, which matters at campsites and markets.

Electric start and remote start

Electric start saves pulling a recoil cord, which is worth having on bigger engines. Models such as the W&C WC-P6000Si and WC-P13750RCD also list wireless remote and 2-wire start, which lets an external switch (for example a transfer switch or float switch) start the generator. Keep the starter battery charged.

Parallel capability

Some inverter generators can be linked to a second compatible unit to combine their output. ITM says any two of its inverter generators can be joined in parallel for the full combined rated power, and its 1,800 W model includes the parallel cable. Two small units can be easier to carry than one big one.

Generators in stock: comparison

Figures are as quoted on each product listing. Makers test run time and noise at different loads, so compare like with like.

How to choose by job

• Camping, caravans and tramping huts: a light, quiet inverter such as the ITM 1800W (21 kg) or the W&C WC-P3200Si (23 kg). Two ITM units in parallel give more output when you need it.
• Home backup during outages: a mid-size inverter in the 3,000-5,500 W rated range, such as the Tooline PG5000i, ITM 4500W E-Start or W&C WC-P6000Si. Work out which essentials (fridge, freezer, lights, chargers) must run together.
• Trades and building sites: an open-frame AVR unit with RCD and IP66 outlets, such as the ITM 7.5kVA with its Honda GX390 engine and 25 L tank.
• Farms, events and big loads: the W&C WC-P13750RCD, with a 32 A outlet, a 45 L tank and remote start options, or the ITM diesel for regular heavy use.

Safety and use tips

• Never run a generator indoors, or in a garage, shed, tent, caravan or under a closed awning. Exhaust contains carbon monoxide, which you cannot see or smell and which can kill. Keep it well away from doors, windows and vents.
• Connecting a generator to a building's wiring must be done by a licensed electrician.
• Plug appliances directly into the generator's outlets, using leads rated for the load. Welling & Crossley notes that RCDs cannot be used with power boards or equipment that has built-in RCD protection.
• Check the oil before every start. A low-oil cut-out, where fitted, is a backstop, not a substitute.

FAQ

What size inverter generator do I need in NZ?

Add up the running watts of everything you will use at once, add the extra start-up surge of the largest motor, and choose a generator whose rated (not max) output covers the total with some room to spare. Charging devices and running lights at a campsite needs far less than running a fridge, freezer and lights through an outage.

Is an inverter generator worth it?

If you run electronics, need quiet operation or mostly run light loads, yes. If you need maximum watts and long run times for heavy tools at the lowest cost, an open-frame AVR generator can be better value.

Can an inverter generator run a fridge or compressor?

Often, as long as the rated output covers the running load and the max output covers the start-up surge. Check the appliance's nameplate, start motors one at a time and size up if in doubt.

Can I plug a generator into my house?

Not yourself. Connecting a generator to a building's wiring must be done by a licensed electrician.

Browse the full range of generators, or see the Welling & Crossley range.