Question 1

What is the difference between kW and kVA on a generator?

Accepted Answer

kW is the real power — the actual work the generator does. kVA is the apparent power, including reactive load from motors. Most generators are rated in kVA. To convert, multiply by the power factor (typically 0.8). A 10 kVA generator produces approximately 8 kW of usable power.

Question 2

What are surge watts and why do they matter?

Accepted Answer

Electric motors — compressors, pumps, grinders — draw 2 to 3 times their running wattage for a fraction of a second when starting. If your generator cannot supply this surge, it will fail to start the motor or trip its overload protection. Always size on the highest surge load, not just the running load.

Question 3

Should I buy a diesel or petrol generator?

Accepted Answer

For occasional use (under 100 hours/year), petrol is cheaper to buy. For regular use, diesel is significantly more economical to run (roughly 30% less fuel per kWh), more durable, and easier to source fuel for alongside a diesel fleet.

Question 4

Can I run a welder from a generator?

Accepted Answer

Yes, but check both the generator output and the welder's input requirement. A MIG welder at 140 amps typically needs around 4 kW of input power at 240V — a generator of at least 5–6 kVA to run it reliably, accounting for power factor and headroom.

Question 5

How much fuel will my generator use?

Accepted Answer

At 75% load, a typical diesel generator uses approximately 0.21 litres per kVA per hour. A 10 kVA diesel generator running at 75% load uses around 2.1 litres per hour. Petrol generators of the same size use around 3 litres per hour.

Question 6

How much headroom should I allow when sizing a generator?

Accepted Answer

Always allow at least 20% headroom above your calculated peak load. Running a generator near its maximum rating continuously shortens its life and reduces voltage stability. The calculator applies a 20% headroom factor automatically.

Equipment	Running Watts	Surge Factor	Peak Surge
Air compressor (2.2 kW)	2200 W	×3	6600 W
Water pump (1.5 kW)	1500 W	×3	4500 W
MIG welder (140A)	4000 W	×1.2	4800 W
Angle grinder (large)	2300 W	×2	4600 W
Vehicle lift motor (2.2 kW)	2200 W	×2.5	5500 W
Refrigerated unit	3000 W	×2.5	7500 W
Conveyor / auger (1.5 kW)	1500 W	×2.5	3750 W
Pressure washer (2.5 kW)	2500 W	×2	5000 W
LED floodlight (200W)	200 W	×1	200 W
Electric fan heater (3kW)	3000 W	×1.5	4500 W

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