We break down exactly what each size of portable inverter generator will power, why starting watts matter more than the headline number, and how to pick the right one for camping, caravanning, or home backup.
Ask anyone who has spent a summer towing a caravan around Australia, and they will tell you the same thing: the generator question is never really about the generator. It is about the fridge that has to stay cold, the air conditioner that has to cope with 40-degree afternoons, and the phone that has to hold enough charge to call home. The machine is just the means to an end.
Yet, that is exactly where buyers come unstuck. Almost every generator on the market quotes two power figures, and the gap between them is where the money is either well spent or wasted. Pick the wrong size, and you either lug around a unit far bigger than you need, or you plug in a caravan air conditioner on a hot day and watch the whole thing cut out.
So, we have done the legwork. Drawing on the real specifications of the four most common sizes we stock, the 1.2 kW, 2.0 kW, 3.5 kW, and 4.2 kW Gentrax Inverter Generators, this guide sets out plainly what each one will run, where it makes sense, and where it does not. No marketing gloss, just the numbers and what they mean for your trip.
First, the Only Spec That Really Matters
Before you look at price or weight, understand the two output numbers every generator carries. The rated output is the power it can supply continuously, hour after hour. The maximum output is a brief surge it can deliver for a few seconds. You size the rated figure to the load you want to run all day. You size the maximum figure to the single biggest jolt of power your gear demands at the instant it switches on.
That switch-on jolt is the part most people miss. Anything with a motor or a compressor, like a fridge, an air conditioner, a power drill, or a water pump, draws two to three times its running wattage for a split second as it starts. A fridge that hums along on 200 watts can demand 600 watts or more to kick over. Feed it from a generator with no surge headroom, and the overload protection trips every time.
Gentrax GT1200 Inverter Generator
Across the four Gentrax sizes, the two numbers line up like this:
- 1.2 kW class (GT1200): 1.2 kW maximum, around 1 kW continuous. Built for charging and light electronics, not for motors.
- 2.0 kW class (GT2000): 2.0 kW maximum, 1.7 kW rated. Enough steady power for a portable fridge plus lights and devices.
- 3.5 kW class (GT3500): 3.5 kW maximum, 3.0 kW rated. Real headroom to start a caravan air conditioner.
- 4.2 kW class (GTX4200 Pro): 4.2 kW maximum, 3.5 kW rated, and able to run in parallel with a second unit if you ever need more.
Keep those pairs in mind and the rest of the decision falls into place.
It helps to see the method in action. Take a family caravan heading away for a long weekend in summer. The air conditioner draws about 2,000 watts running and roughly 3,000 on start-up. The fridge adds 200 watts steady but 600 on startup, lights and a fan another 150, and phone and laptop charging perhaps 150 more. That is about 2,500 watts of continuous load, peaking near 3,400 watts the instant the air conditioner kicks in. A generator rated at exactly 3.0 kW would be cutting that surge fine, which is precisely why the GT3500, with its 3.5 kW maximum, is the unit that copes. Drop the air conditioner from the list, and a GT2000 handles the rest with room to spare.
What a 1.2 kW or 2.0 kW Generator Runs
The smallest two sizes are about precision, not brute force. The Gentrax GT1200, at 1.2 kW peak and roughly 1 kW continuous, is happiest charging phones and laptops, running LED camp lights, a small television, a fan, or a CPAP machine through the night. What it will not do is start a fridge and an air conditioner together, and it is honest about that. Running at 58 decibels and light enough to carry in one hand, it is the quiet minimalist's choice, and at $469, it is the cheapest way into clean, pure sine wave power.
Here’s what one of our customers said:
"I bought one of these for the cloudy days whilst off grid camping and solar not so good, it works great, we use it to charge 2 camper trailers with 200AMP/HR batteries each, plus the starlink system for our NRL games whilst in the bush. Just did its first oil change after the run in period, or slightly longer to be fair, using a good quality Penrite small engine oil to give it the best shot at longevity, oil was a bit darker than straw colored but nothing alarming. Be careful taking off the side covers and you wont have a problem here, they are screws designed to hold the covers on, not required to be tightened like they are holding the wing on an Aircraft!! Highly recommend this little unit, goes easily for 6 hours running above setup on ECO setting, starts first, or second pull if you forget to turn the switch on first time :) very happy campers here."
Gentrax GT2000 Inverter Generator
Step up to the Gentrax GT2000 and the picture broadens. With 2.0 kW maximum and 1.7 kW rated from a 100cc four-stroke engine, plus a 4.1-litre tank good for up to 6.1 hours, it adds a portable fridge, a microwave used briefly on its own, and lighter power tools to the list. It weighs 18.5 kilograms, carries two AC outlets, and at $649, suits the weekend camper running a handful of appliances rather than a fully kitted rig. The rule of thumb we give customers is simple: if you are not running an air conditioner, the GT2000 is usually plenty.
Here’s what one of our customers said:
"Great product. I bought this to power our caravan aircon while we are off grid. 2kva is just enough to power our Dometic harrier unit which has a soft start up and is roughly about 1800kwh, unsure how many hours it’ll run for on a full tank of fuel yet. Really happy with the purchase so far."
What a 3.5 kW Generator Runs
This is the size most Australian buyers end up with, and for good reason. The Gentrax GT3500 delivers 3.5 kW maximum and 3.0 kW rated, which is the first point in the range where you can confidently start a caravan air conditioner of up to 2.5 horsepower, about 2,000 watts, while keeping a 400 to 600-litre household fridge or freezer running alongside it.
On a 5.7-litre tank, it runs for about 4.1 hours at half load, and switching on eco mode stretches that further by letting the engine throttle back to the load. It will also drive power tools up to 2,500 watts on a work site, charge devices, and keep the lights on through a blackout. At 28 kilograms, it is still genuinely portable, and at $899, it is the unit we point most caravanners and home backup buyers towards first. Backed by stellar reviews across different platforms, it has earned that reputation in the field, not on paper.
Here’s what one of our customers said:
“Connected to the caravan and ran the aircon with ease, also started the microwave with the aircon running. Great product so far.”
Gentrax GT3500 Inverter Generator
What a 4.2 kW Generator Runs
When the rig is fully loaded, the Gentrax GTX4200 Pro is the answer. At 4.2 kW maximum and 3.5 kW rated, it can hold an air conditioner, a fridge, and a microwave at the same time, plus a washing machine or a water pump on top. Owners running food vans tell us it powers a fridge and twin bain-maries all day without missing a beat, which is a fair indication of its working capacity.
It is the most feature-rich unit in the range, with key, remote, and pull start, an LCD that shows run time at a glance, and an 8.8-litre tank that gives roughly 6.8 hours of continuous runtime at 50% load. Crucially, it is parallel-capable, so if your needs grow, you can link a second unit rather than replace it. At 41.5 kilograms, it is the heaviest of the four, and at $1,449, the most expensive, but for a permanent caravan setup or light commercial use, it earns its keep. It also carries a 36-month warranty, double that of the rest of the range.
Beyond Wattage: Noise, Standards, and What Happens After You Buy
Output gets a generator onto your shortlist. Three other things decide whether it is right for Australian conditions. The first is noise. Most national parks allow generators under 65 decibels, the accepted threshold for a quiet unit. The GT1200 and GTX4200 Pro run at 58 decibels at 7 metres, the GT2000 at 60 and the GT3500 at 62, all comfortably under the line and about as loud as a television on low volume. Always check with the park authority, still, but these ranges sit on the right side of the rules.
The second is certification. Every Gentrax unit is EURO 5 emissions-certified, RCM-approved to Australian standards, and US EPA-tested. Every unit also produces a pure sine wave power that is safe for laptops, televisions, and other sensitive electronics. The third is weight and value, and this is where the budget brands look very different from the premium ones:
| Spec | Gentrax GT3500 | Premium Brand A | Premium Brand B |
|---|---|---|---|
| Max / rated output | 3.5 / 3.0 kW | 3.0 / 2.8 kW | 3.0 / 2.8 kW |
| Weight | 28 kg | 59 to 61 kg | ~67 kg |
| Price (AUD) | $899 | $4,070 to $4,599 | $4,360 |
Comparison figures as published on the Outbax GT3500 product page.
One last piece of advice, and it runs against the usual sales instinct: do not buy bigger than you need. A generator pinned near its limit works harder, burns more fuel, and wears faster, but so does an oversized unit that idles half empty for years. The right size is the one that matches your real load with a sensible buffer, nothing more. Buying the GT3500 when a GT2000 would do is money spent on capacity you will never use.
After-sales support closes the loop. These generators ship fast from a Sydney warehouse with free delivery to most metro areas, carry a full Australian warranty under Consumer Law, and come with a 60-day money-back guarantee. Common spare parts, fuel filters, carburettors and ignition modules are stocked online, so a unit bought today is still serviceable years from now. More than 60,000 have sold across Australia since 2010, and the range has been voted best generator every year since 2018.
Gentrax GTX4200 Pro Inverter Generator
How to Land on the Right Size
It comes down to three steps. Total the running watts of everything you will have on at once. Identify the appliance with the biggest startup surge. Then, choose the class whose rated output covers the total and whose maximum output covers that surge, with a 20 to 30 per cent buffer on top for efficiency and for the gear you will inevitably add later. For most people, that points to the GT3500; lighter setups suit the GT1200 or GT2000, and fully loaded rigs want the GTX4200 Pro.
You can compare all four side by side, with full specifications and verified reviews on every listing, in the Outbax inverter generator range. Still unsure which size fits your gear? Reach out to the Outbax team, and we will size it with you before you buy.
