Most decent inverter generators will run a drill, a circular saw or a nail gun without complaint. The trouble starts with the machines that pull hard the moment you switch them on. Motors surge, welders draw in heavy bursts, and air compressors kick against pressure every time they cycle. A generator that looks big enough on the box can still stall, trip, or shut itself down under those loads if you have read the wrong number.
This guide explains which number matters, how to size a generator for tools rather than a caravan fridge, and when a petrol generator stops being the right answer. The figures and operating notes here come straight from the Gentrax inverter generator manuals sold through Outbax, so you can see what these units are rated to do before you spend a dollar.
Why Generators Struggle with Some Power Tools
The problem is almost always the start-up surge, not the running load. An induction motor, a bench saw, or a compressor draws far more current in the first fraction of a second than it does once it is spinning. A tool that runs happily at 1500 watts can demand two or three times that for a heartbeat as it gets going.
The Gentrax manuals describe this behaviour plainly. When an electric motor starts, both the red overload light and the green output light come on together for about four seconds, then the overload light goes out once the tool is up to speed. That flash is normal. If the overload light stays on, the generator has run out of headroom and has cut power to protect itself and whatever is plugged into it.
This is why two tools with the same running wattage can behave very differently. A resistive load such as a work light or a heat gun draws a steady, predictable current. A motor or a compressor spikes. Size a generator for the steady figure alone, and the first hard start-up can shut it down.
Gentrax GS2-7500IE 7kW Portable Inverter Generator
Rated Output Is the Number That Matters
Every generator carries two output figures, and buyers routinely read the wrong one. Maximum output is a short burst the unit can supply for a few seconds. Rated output, sometimes called continuous output, is what it can deliver hour after hour without strain. Rated is the number to size your tools against.
The gap is real. An Outbax Gentrax GT3500 lists 3.5kW maximum but 3.0kW rated. The Gentrax GTX6600 lists 6.6kW maximum and 6.0kW rated. Plan your load around the rated figure and treat the maximum as a brief allowance for that startup surge, nothing more.
Here’s what one of our customers said about the Gentrax GT3500 Inverter Generator:
“Great product. Works exactly as it should. Runs my whole house during power outages.”
The manuals reinforce the point in their own words: exceeding the rated load will damage the unit, shorten its life and void the guarantee. There is also a break in the rule that is easy to miss. For the first 25 hours of use, Gentrax advises keeping the load under 75 per cent of rated capacity, so a brand new unit has even less to give than the sticker suggests.
How to Size a Generator for Your Tools
Sizing is simple arithmetic once you know what to look for. Add up the running watts of everything you will use at the same time, then add the single largest start-up surge on top, because tools rarely start together. Give yourself some headroom above that total rather than buying right on the limit.
A few practical habits make more difference than the maths:
Start one motor at a time where you can. Kicking off a compressor and a grinder together stacks two surges into a single moment.
Turn economy mode off for compressors and pumps. The Gentrax manuals are specific: turn off the economy control switch when using devices that need a large starting current, such as a compressor or a submersible pump, because that mode keeps engine speed low and slows response to a surge.
Mind the cable. A long or thin extension lead drops voltage and makes a tool draw more current, which can push a marginal generator over the edge.
As a rough guide, a large 9-inch angle grinder or a single-stage air compressor can pull well past 2000 watts on startup, a small inverter welder wants serious continuous output, and a cordless tool charger barely registers. Always check the plate on your own tool rather than trusting a category average.
» More: Browse the full Outbax portable generator range to compare rated outputs.
Gentrax GT2000 Inverter Generator
Power Quality and Why Pure Sine Wave Matters
Wattage is only half the story. The other half is the power’s shape. Cheap conventional generators can produce a rough waveform with high total harmonic distortion, the electrical equivalent of a bumpy road. Battery chargers, brushless tools, engine control boards, and inverter welders don’t like it, and over time dirty power can shorten the life of sensitive electronics or trip their internal protection.
Inverter generators solve this by producing pure sine wave output, clean enough to sit alongside mains power. The Gentrax units in the Outbax range are digital inverter models, and the larger ones quote a power factor of 1.0, meaning connected electronics can use close to all the power on offer. For an inverter welder, an on-site laptop, or a tool with a smart charger, clean output matters as much as raw wattage.
Gentrax Inverter Generator Specifications
The table below pulls the key figures from the Gentrax manuals so you can match rated output to the job. Every model produces 240-volt pure sine wave power and is RCM-approved for use in Australia.
| Model | Rated output | Max output | Engine | Fuel tank | Weight | Starting |
|---|---|---|---|---|---|---|
| Gentrax GT800 | 700 W | 800 W | 40 cc | 2.1 L | 8.5 kg | Recoil |
| Gentrax GT2000 | 1.7 kW | 2.0 kW | 100 cc | 4.1 L | 18.5 kg | Recoil |
| Gentrax GT3500 | 3.0 kW | 3.5 kW | 149 cc | 5.7 L | 28 kg | Recoil |
| Gentrax GTX3500 | 3.2 kW | 3.5 kW | 149.5 cc | 7.5 L | 37.5 kg | Recoil, electric and remote |
| Gentrax GTX6600 | 6.0 kW | 6.6 kW | 389 cc | 18.5 L | 89 kg | Electric and remote |
Figures are drawn from the Gentrax GT800, GT2000, GT3500, GTX3500, and GTX6600 user manuals. Runtime varies with load; the GTX6600 runs around four and a half hours at full load on a single tank.
Here’s what one of our customers said about the Gentrax GT2000 Inverter Generator:
“Bought 1 year ago and has been the best asset when away for days or weeks at a time, fuel efficient and smooth running. Have a powered up heater, a/c and microwave. I love the luxuries in the Aussie outback.”
VoltX VX6600 2-Wire Inverter Generator
Where Generators Fall Short: Welders and Air Compressors
Welders and air compressors are where honest advice matters, because a generator can disappoint even when the wattage looks fine on paper.
An inverter welder is kinder to a generator than an old transformer welder, but welding is still a demanding, bursty load. Light stick or MIG work at low amps can run off a strong portable unit, yet push the amperage up and even a 6.0kW rated generator can run short, especially at a high duty cycle. For regular heavy welding, a purpose-built diesel welder generator or an engine-driven welder is the machine built for the job, not a general-purpose genset.
Air compressors bring their own trap. The motor surge on start-up is punishing, and a large single-stage compressor can draw more at that instant than a mid-sized generator can supply. This is exactly why the manuals tell you to switch economy mode off before you plug one in. Match the generator to the compressor motor, not to its running figure.
There is also a quieter failure that has nothing to do with size. Running a small charger or a couple of lights off a big petrol generator wastes fuel, makes noise, and produces exhaust fumes that must never be released in an enclosed space, as every Gentrax manual warns. For low-draw jobs, a portable power station or lithium battery setup provides clean, silent power without petrol. A generator earns its keep on sustained high loads, not trickle-charging a phone.
» More: When a portable power station beats a generator for quiet, clean power.
Matching an Outbax Generator to the Job
The right choice comes down to rated output and how you want to start it.
For light power tools, camping and caravan use, the Gentrax GT800 and GT2000 are compact and easy to carry. The GT800 at 8.5kg suits a single tool or campsite basics, while the GT2000 gives a bit more room to work.
For a tradesperson running mid-sized tools, the GT3500 offers 3.0kW rated in a recoil start unit, while the GTX3500 adds electric and remote start for broadly the same output, handy when the generator lives in a ute tray.
For heavy loads, larger compressors and serious welding, the GTX6600 steps up to 6.0kW rated with a 30-amp Australian industrial socket, electric and remote start, and an 18.5 litre tank for long runs. Pair any of them with a portable power station from the Outbax range when you only need quiet power for low-draw electronics, and keep the generator for the work that genuinely needs an engine.
Kuller 4200 Inverter Generator
The Bottom Line
Choosing a generator for tools comes down to two decisions. Size the unit against its rated output with enough headroom for the biggest startup surge, and choose pure sine wave power if you run anything with sensitive electronics. Get those right, and a generator will handle most tools on a worksite or a campsite without drama. Push a welder or a big compressor beyond what the rated figure allows, and the honest answer is a larger unit or a machine built for that load. The Outbax range spans compact 700-watt units up to a 6.0kW workhorse, so you can match the generator to the job rather than hoping the job fits the generator.
