A conventional generator locks its engine at one speed because the engine speed is the output frequency. Fifty hertz means 3,000 rpm; sixty means 3,600. The engine holds that speed whether it is carrying full load or almost nothing.
An inverter set breaks that link. The alternator output is rectified and rebuilt electronically, so the engine is free to slow down when the load is light and speed up when it is not. Everything below follows from that one change.
The difference, from our own specification sheets
| Conventional set | Inverter set | |
|---|---|---|
| Engine speed | 3,000 / 3,600 rpm, fixed | 2,200–3,400 rpm, variable |
| Alternator | Copper-wound with AVR voltage stabiliser | Outer-rotor multi-pole permanent-magnet, IGBT digital inverter |
| Fuel at rated output | 280 g/kW·h | ≤320 g/kW·h |
| Start | Recoil or electric, by model | Electric only |
Read the fuel row again, because it is the opposite of what most buyers expect.
The inverter is worse at full load
At rated output our inverter models publish ≤320 g/kW·h against 280 for the conventional air-cooled sets. Rectifying and re-synthesising the waveform costs energy, and at full load the engine is running near its top speed anyway — so you pay the conversion penalty and get nothing back for it.
The saving is at part load, and it can be large. A conventional set at 25% load still spins at full speed, burning fuel to hold a frequency nobody is drawing on. An inverter set drops toward its lower speed limit and burns proportionally less. The lighter and more variable your load, the more the inverter wins; the closer you sit to rated output, the more it loses.
That gives a clean decision rule:
- Load swings widely, or sits low most of the time → the inverter earns its price.
- Load is steady and near rated → a conventional set is cheaper to buy and cheaper to run.
Sizing against your real average load rather than the nameplate matters even more here than usual. The method is in how to size a diesel generator, and the fuel arithmetic in fuel consumption per hour.
What you get for the extra electronics
Cleaner output. A permanent-magnet alternator feeding a digital inverter produces a waveform built by the electronics rather than by the mechanics of the machine. That matters for anything with a switching power supply — laptops, controllers, instrumentation, medical and lab equipment, modern LED lighting. Ask any supplier for the total harmonic distortion (THD) figure and the load it was measured at; a set intended for sensitive electronics should be able to give you one.
Quieter at part load, for the same reason it burns less: a slower engine is a quieter engine. The quoted noise figure on any genset is measured at a stated load and distance, so compare like with like — see how quiet is a silent diesel generator.
One machine for either frequency. Because output frequency no longer comes from engine speed, the same unit covers 50 Hz and 60 Hz. Note the rated voltages differ between the two — check the pair for your destination rather than assuming the 50 Hz figure applies.
Smaller and lighter for a given output, since a permanent-magnet alternator does more with less iron.
What it costs you beyond the price
- More to go wrong. An IGBT inverter and its control board are electronics in a hot, vibrating, dusty place. A copper-wound alternator with an AVR is a far simpler thing to repair in the field.
- Electric start only, so a charged battery is not optional. That is also what makes automatic operation possible — see what an ATS is.
- Narrower power range. Inverter technology is concentrated in smaller sets; above a certain output the conventional architecture still dominates.
What to ask before you order
- Speed range — the actual minimum and maximum rpm, not just “variable speed”.
- Fuel consumption at 25%, 50% and 100% load, not a single number. On an inverter set the single number hides the entire advantage.
- THD, and the load it was measured at.
- Rated voltage at both 50 Hz and 60 Hz for your destination.
- What is field-replaceable if the inverter board fails, and what the lead time on that part is.
Where HTX fits
Our inverter range runs 3.0 to 9.0 kVA single-phase (up to 11.2 kVA three-phase), all with permanent-magnet alternators, IGBT digital inverters, variable engine speed and electric start. Every model publishes its speed range, both frequency ratings and its fuel figure, so the comparison above can be checked against the specification rather than taken on trust — see the inverter generator range, or the full diesel generator range if a conventional set is the better fit.
Not sure which architecture suits your duty cycle? Tell us your average load, how much it varies, and the frequency and voltage at your destination — or message us on WhatsApp — and our engineers will come back with a recommendation, and say plainly if a conventional set would serve you better.