A conventional generator holds its engine at one fixed speed, because the engine speed sets the output frequency. Fifty hertz means 3,000 rpm; sixty hertz means 3,600. The engine keeps that speed whether it carries full load or almost none.
An inverter set removes that link. The alternator output is rectified and then rebuilt electronically, so the engine can slow down when the load is light and speed up when it is heavy. Everything below follows from that one change.
The difference, from our own datasheets
| 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 |
Look at the fuel row again. It shows the opposite of what most buyers expect.
At full load, the inverter uses more fuel
At rated output, our inverter models publish ≤320 g/kW·h, against 280 for the conventional air-cooled sets. Rectifying the current and rebuilding the waveform costs energy. At full load the engine runs close to its top speed anyway, so you pay the conversion loss and gain nothing in return.
The saving comes at part load, and it can be large. A conventional set at 25% load still runs at full speed, burning fuel to hold a frequency that the load does not need. An inverter set slows toward its minimum speed and burns less fuel. The lighter and more variable your load, the more the inverter saves; the closer you run to rated output, the more it costs.
That gives a simple rule:
- The load varies widely, or stays low most of the time: the inverter pays for itself.
- The load is steady and close to rated output: a conventional set costs less to buy and less to run.
Here it matters even more than usual to size by your real average load rather than the nameplate. The method is in how to size a diesel generator, and the fuel calculation is in fuel consumption per hour.
What the extra electronics give you
Cleaner output. With a permanent-magnet alternator feeding a digital inverter, the electronics shape the waveform, not the rotation of the machine. This matters for any equipment with a switching power supply: laptops, controllers, instruments, medical and laboratory equipment, and modern LED lighting. Ask any supplier for the total harmonic distortion (THD) figure and the load at which it was measured. A set intended for sensitive electronics should have one.
Quieter at part load, for the same reason that it uses less fuel: an engine running slower makes less noise. A generator’s quoted noise figure is measured at a stated load and distance, so compare figures measured the same way; see how quiet is a silent diesel generator.
One machine for both frequencies. Because the output frequency no longer depends on engine speed, the same unit covers 50 Hz and 60 Hz. The rated voltages differ between the two, so check the pair for your destination instead of assuming the 50 Hz figure applies.
Smaller and lighter for the same output, because a permanent-magnet alternator needs less iron.
What it costs beyond the price
- More that can fail. An IGBT inverter and its control board are electronics working in a hot, dusty place with vibration. A copper-wound alternator with an AVR is much simpler to repair in the field.
- Electric start only, so a charged battery is essential. Electric start is also what makes automatic operation possible; see what an ATS is.
- Narrower power range. Inverter technology is mostly found in smaller sets. Above a certain output, the conventional design 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 figure. On an inverter set, a single figure hides the whole advantage.
- THD, and the load at which it was measured.
- Rated voltage at both 50 Hz and 60 Hz for your destination.
- Which parts can be replaced in the field if the inverter board fails, and the lead time for those parts.
Where HTX fits
Our inverter range covers 3.0 to 9.0 kVA single-phase (up to 11.2 kVA three-phase). Every model has a permanent-magnet alternator, an IGBT digital inverter, variable engine speed and electric start. Every model also publishes its speed range, its ratings at both frequencies and its fuel figure, so you can check the comparison above against the datasheet. See the inverter generator range, or the full diesel generator range if a conventional set suits you better.
Not sure which design 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. Our engineers will reply with a recommendation, and will tell you clearly if a conventional set would serve you better.