Inverter Generators

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An inverter generator differs from a conventional one in what it does with the current before it reaches the socket. A standard alternator sends voltage straight from its windings, so the quality of that voltage depends on engine speed. An inverter generator rectifies the current first and then rebuilds the waveform electronically, which means frequency and shape stay constant whether the engine runs flat out or idles.

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The measure of that quality is total harmonic distortion. Our units hold THD ≤ 2% — a waveform close to mains supply. That is the threshold below which controllers, chargers, laptops and switch-mode power supplies work safely, the same equipment that can reset or fail on current from a plain alternator.

The second consequence is engine speed that follows demand. The engine no longer has to hold a fixed 3 000 rpm to produce 50 Hz, so it drops back when little power is drawn: less fuel, less noise. Hence run times of 5 to 10 hours at half load and sound levels of 94–97 dB, with every unit built into a sound-attenuating enclosure.

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Weight matters as much as output when a machine moves between jobs: the single-phase units weigh 21 to 30 kg and stay genuinely portable, while the three-phase model is a 110 kg stationary set for a site compound.

The range runs from 3,5 kW to 11 kW, single and three phase, with recoil or electric start, and windings rated to class F insulation. These machines power site compounds without a supply, houses during an outage and equipment that needs clean voltage. The tools most often run from them in our own range are concrete grinders, core drills and electric air heaters.

Where an inverter generator earns its keep

Generated power costs more than mains power, so it gets bought where there is no supply or where losing it stops the work. The inverter adds one thing on top: it lets you run equipment a plain alternator would damage.

Home backup during an outage

A power cut stops the circulation pump, the boiler controller and the ventilation — in winter that is a matter of hours before the building cools down. A gas boiler with its pump typically draws 100–200 W, so keeping the heating alive sits far inside the smallest 3,5 kW unit. The headroom goes on the rest: fridge, lighting, router, chargers. Waveform quality matters here, because a boiler controller is electronics that can throw a fault and lock out on distorted supply.

Sites with no connection

On a plot before the supply is connected, the generator carries the whole job. What decides the size is not the rated power of the tool but its starting current — induction motors draw a multiple of rated power at the moment they start. A 2,2 kW concrete grinder can ask for twice that in the first second, which is why a single tool of that size calls for the 4,5 kW unit rather than the 3,5 kW one. Where several machines run together, or anything three-phase appears, the 11 kW unit with its 400 V outlet is the right answer.

Survey equipment and electronics

Laser levels, inspection cameras, battery chargers, laptops and switch-mode power supplies respond not to the voltage figure but to the shape of the waveform. Distortion above a few percent shows up as overheating supplies, spontaneous restarts and shortened capacitor life. Holding THD ≤ 2% puts these units below the threshold where those problems start — comparable to what comes out of a wall socket.

Work where noise is restricted

Residential streets, parks, outdoor events, servicing outside working hours — in all of these the sound level decides whether work is permitted at all. Because engine speed follows load, a unit running light drops to 94 dB and burns proportionally less fuel. A conventional alternator has to hold full engine speed the whole time, regardless of how much current is actually drawn. Every unit here sits in a sound-attenuating enclosure, marked S in the model designation.

Toolsa GK inverter generator specifications

Model Rated power Phases Starting Tank Run time Noise Weight
GK3500iS Pro 3,5 kW 1 × 230 V recoil 5,5 l 5 h 95 dB 21 kg
GK3500iSE Pro 3,5 kW 1 × 230 V electric 5,5 l 5 h 95 dB 22 kg
GK4500iS Pro 4,5 kW 1 × 230 V recoil 7 l 6,5 h 94 dB 28,5 kg
GK4500iSE Pro 4,5 kW 1 × 230 V electric 7 l 6,5 h 94 dB 30 kg
GK12000iS 11 kW 1 × 230 V and 3 × 400 V electric 32 l 10 h 97 dB 110 kg

Run time is quoted at 50% load, the reference point manufacturers use for comparison, because fuel goes considerably faster at full load. Every unit has automatic voltage regulation, class F winding insulation and holds THD ≤ 2%.

What the model designation means

The number states peak output in watts; the letters describe the build. i means inverter, S a sound-attenuating enclosure and E electric start. That is why GK3500iS Pro and GK3500iSE Pro share identical electrical specifications and differ only in how they are started and by 1 kg of weight, which is the battery.

Inverter or AVR — what actually separates them

This comparison comes up at every purchase and is regularly misread, because both stabilise voltage — but at completely different levels.

AVR is automatic voltage regulation: a circuit that keeps output near 230 V by controlling alternator excitation. It responds to the voltage figure, but has no influence on frequency or on waveform shape. Frequency comes straight from engine speed — a two-pole alternator has to turn at exactly 3 000 rpm to deliver 50 Hz. When load steps up, speed dips momentarily and frequency falls with it.

Inverter works differently: current from the alternator is rectified to DC first, and electronics then build the AC waveform from it. Frequency is set by the control circuit rather than by mechanics, so 50 Hz stays 50 Hz whatever the engine and the momentary load are doing. That is exactly why the engine is free to slow down at light load — and where the fuel saving and the lower noise come from.

The practical conclusion: AVR alone is enough for resistive loads and simple tools — heaters, lighting, mixers, pumps. For anything with control electronics inside, the inverter is the right choice. The two are not alternatives: our units run automatic voltage regulation and an inverter stage.

Sizing a generator

First: add up what runs at the same time

Total the loads that will be switched on together, not everything you own. Keeping a boiler alive is usually 100–200 W, a fridge draws 100–200 W in normal running, and LED lighting across a whole house rarely passes 300 W. A domestic backup set therefore sits inside 1 kW until heating loads join in: a kettle, immersion heater or electric radiator is 2 kW each, and those are what decide generator size.

Second: allow for starting current

Induction motors — in pumps, compressors, grinders and saws — draw several times their rated power at the instant they start. Assume the largest motor in the set needs two to three times its rating in that first second. A 3,5 kW unit will run a 1,5 kW tool with margin to spare; at 2,2 kW of tool, the 4,5 kW model becomes the correct choice. Heating loads and lighting need no such allowance — they start at rated power.

Third: keep a reserve and check the phases

A generator working permanently at its limit burns more fuel per kilowatt-hour and wears faster. A sensible reserve is 20–30% above the calculated total. If a single three-phase machine is in the set, the decision makes itself: you need a 400 V outlet, which means GK12000iS. Its 32 l tank gives 10 hours at half load, so a full shift passes without refuelling.

Fourth: recoil or electric start

On units up to 4,5 kW a recoil start is entirely practical and saves 1–1,5 kg of weight along with the need to look after a battery. Electric start earns its place where the machine is started many times a day, sits somewhere awkward to pull, or works in cold weather — a cold engine resists the cord noticeably harder. On the 110 kg unit it is not an option but standard equipment.

Frequently asked questions

What is the difference between a generator and an inverter generator?

A conventional generator sends current straight from the alternator windings to the socket, so voltage frequency depends directly on engine speed — a two-pole machine must hold 3 000 rpm to produce 50 Hz. An inverter generator rectifies that current and rebuilds the waveform electronically, so frequency is set by the control circuit instead. Three practical differences follow: a clean waveform at THD ≤ 2%, lower fuel consumption at part load because the engine can slow down, and less noise — 94–97 dB across this range.

What are the disadvantages of an inverter generator?

Three, and they are worth knowing before buying. The purchase price is higher than a conventional generator of the same output, because the inverter stage is additional electronics. Those electronics are also a failure point that a plain alternator does not have — though with no moving parts and clear cooling vents they are effectively maintenance-free. Third, the advantage narrows at constant full load: the fuel saving comes from the engine dropping speed at part load, so a machine working permanently near its 3,5 kW or 4,5 kW rating behaves much like any other generator.

Which is better: inverter or AVR?

The comparison misleads, because these are not competing solutions — AVR stabilises the voltage figure, the inverter governs frequency and waveform. AVR alone will hold roughly 230 V, but cannot prevent frequency dropping when engine speed dips under load. The inverter keeps 50 Hz regardless of what the engine is doing, and only that produces a waveform close to mains. In practice an inverter generator carries both circuits, and that is the case here: automatic voltage regulation works alongside the inverter stage.

Can an inverter generator power a house?

For essential circuits, comfortably. Heating and lighting together rarely exceed 1 kW, which even the smallest 3,5 kW unit covers with a wide margin. Running an entire house including electric heating and hot water is a different matter — each such appliance is around 2 kW and they quickly consume the available output. Note also that connecting a generator to a building's fixed wiring requires a proper changeover arrangement so that generated power cannot back-feed the network; that work belongs to a qualified electrician and the rules differ between jurisdictions.

How quiet is an inverter generator really?

These units are rated at 94–97 dB, and two things bring the working figure below that. The enclosure absorbs part of the sound, which is what the S in the designation refers to. More significantly, engine speed follows load: at light draw the engine drops back instead of holding 3 000 rpm, so a generator idling on a small load is audibly quieter than the same machine at full output. A conventional alternator cannot do this — it runs at full speed whether it is supplying 200 W or its full rating.

What is the difference between rated and peak power?

Rated power is what the generator will hold continuously. Peak power is higher and available only for a few seconds, to cover the starting current of motors. Manufacturers generally put the second figure in the model name, which is why the unit designated GK12000iS has 11 kW of rated output. Only the rated figure counts when sizing: it tells you how much equipment will run together for a full shift. Treat peak output as start-up headroom, never as a working parameter.

Will it run sensitive electronics?

What decides this is not output but waveform quality, expressed as total harmonic distortion. Switch-mode power supplies, chargers and controllers operate safely while distortion stays within a few percent; above that they overheat and capacitor life shortens. These units hold THD ≤ 2%, comparable to mains supply. Output is rarely the constraint for such equipment — a laptop draws 50–100 W, so even the smallest 3,5 kW unit has headroom of several dozen times over.

How long does it run on one tank?

Run times are quoted at 50% load, because only a common reference point allows models to be compared. The 3,5 kW units with a 5,5 l tank manage about 5 hours on that basis, the 4,5 kW models with 7 l reach roughly 6,5 hours, and GK12000iS with its 32 l tank runs 10 hours — a full working shift. Expect noticeably less at full load and rather more at light draw, since the inverter lets the engine slow down.

When do I need a three-phase generator?

A 400 V three-phase outlet becomes necessary as soon as one piece of equipment has a three-phase motor — typically larger floor saws, rig-mounted core drills and workshop machinery. There is no way around it with adaptors or by combining single phases. In this range the three-phase outlet belongs to GK12000iS, which also provides 230 V sockets and therefore serves both kinds of load. If all your equipment is single-phase, a three-phase generator offers no advantage — only more weight and higher running cost.

Why will a generator not start after months in storage?

The usual cause is not wear but fuel left in the tank. Petrol degrades and gums up the carburettor, so a generator bought for emergencies fails at precisely the moment it is needed. Before a long stand, drain the tank or add a fuel stabiliser and run the engine for a few minutes so the treatment reaches the whole fuel system. On electric-start versions there is a second cause: a flat battery. Seasonal use means charging between periods of storage — otherwise the starter fails at the same moment the mains does.

What wears out first?

Oil comes first: an initial change after the running-in period, then every few dozen hours of operation — on a unit running 10 hours per tank that is a matter of a few full shifts. Second is the air filter, which clogs with concrete dust on site far faster than in domestic use; restricted airflow shows up as lost power and higher fuel consumption before the engine starts running roughly. Third is the spark plug, usually replaced once per season of heavy use. The inverter electronics have no moving parts and run maintenance-free, provided the enclosure vents stay clear — the enclosure doubles as the cooling duct.

What you will be powering

A generator is bought for specific loads, so it is worth matching it against the tools it has to run. The electrical equipment in our own range most often powered on sites without a supply is concrete grinders, core drills, floor saws and industrial vacuum cleaners, which run alongside the machine during grinding and drilling. In winter electric air heaters join them — these are resistive loads, so they need no starting headroom, but they draw their rated power continuously.