Generator Trips in the Field Workshop
A field workshop is powered by one generator rated 2.0 kW continuous and 2.4 kW for up to ten minutes. Connected loads: a radio set at 350 W; six floodlights at 40 W each; a laptop and printer at 160 W; a water pump with a 550 W motor drawing 3.2 times running current for about two seconds on start; and a refrigerator rated 300 W whose compressor draws 2.5 times running current for about a second each time it cycles. The generator sits three metres outside the tent, and the distribution board is inside. The pump and the refrigerator share the same circuit. Everything is plugged in and switched on together, and the generator trips within seconds of the refrigerator cycling. Fuel consumption is 1.3 litres per hour at full load, roughly proportional below that, from a 15-litre tank.
1. Show the load arithmetic and explain exactly what is causing the trip.
Read the worked answer
Running load, everything steady: 350 (radio) + 6 x 40 = 240 (lights) + 160 (laptop and printer) + 550 (pump) + 300 (fridge) = 1600 W That is 80 per cent of the 2.0 kW continuous rating - fine, with headroom for a warm day.
Now add starts:
- Pump start: 550 x 3.2 = 1760 W
- Fridge start: 300 x 2.5 = 750 W
Fridge starts while everything else, including the pump, is running: 750 + 350 + 240 + 160 + 550 = 2050 W. Above continuous, below the 2.4 kW short-term rating - survivable.
Pump starts while everything else is running: 1760 + 350 + 240 + 160 + 300 = 2810 W - above the 2.4 kW short-term rating.
Both starting coincidentally: 1760 + 750 + 350 + 240 + 160 = 3260 W - more than a third above the short-term rating.
Conclusion: the steady load is not the problem; the sum of two motor inrushes is. The trip happens when the fridge cycles because that is often the moment the pump is already running or starting. The generator is behaving correctly - it is protecting its alternator.
2. What do you actually change, and why is fitting a larger fuse or breaker not the answer?
Read the worked answer
Changes, in order of cost:
- Sequence the starts. Pump on with the fridge switched off; once the pump is running, bring the fridge back in. Two seconds of discipline removes the 3260 W coincidence entirely.
- Shed non-essential load before starting the pump. Drop the printer (160 W) and three floodlights (120 W) for the start; peak falls to roughly 2530 W even with the fridge running - still tight, so keep the sequencing as the primary control.
- Fit a start-delay or interlock so the fridge cannot restart for 30 seconds after the pump starts. This makes the control structural rather than dependent on who is on shift.
- Split the circuits so the pump is not sharing with the fridge, which also makes future faults easier to find.
Why not a bigger fuse? The breaker is sized to protect the alternator and the cable, not to accommodate the load. Upsizing it would let a genuine overload - a stalled pump, a short, a seized compressor - run until the windings burn, and would not make more power. The generator can supply 16 kW-seconds; it cannot supply 3.2 kW. The fault is coordination of loads, not protection.
3. The workshop must run 12 hours a day for three days at the 1600 W load. How much fuel do you plan for, and how many spare 20-litre cans does that mean?
Read the worked answer
Load fraction: 1600 / 2000 = 80 per cent. Consumption: 1.3 x 0.8 = 1.04 L/h (proportional, as stated). Running hours: 12 x 3 = 36 h. Fuel needed: 36 x 1.04 = 37.4 L. Tank: 15 L, so 22.4 L must be carried - that is 2 cans of 20 L, giving 55 L total and a margin of 17.6 L.
Why the margin is not generous:
- Cold-start enrichment and short cycling push consumption above the proportional figure; a fridge cycling hard on a hot day is worse than a steady load.
- The generator should not be run dry - sediment and air in the line cost more time than the fuel saved.
- If the load grows, or the fridge is left on overnight, the 17.6 L disappears quickly.
Recommendation: plan for two cans but request three. Refuel with the generator off and cool, outdoors, never inside the tent, and record hours run against fuel drawn each day so the estimate can be corrected on day two rather than discovered on day three.