How to size a generator for an Irish food + coffee trailer
Most Irish festival pitches do not include power — you bring your own generator. Picking the wrong one is the most expensive mistake new operators make: undersized = the generator overloads, trips out, ruins service; oversized = burns excess fuel, costs more upfront, blocks pitch space. This guide shows how to calculate the actual load your trailer draws, how to add the right safety margin, and which brands the Irish trade trusts.
1. List every appliance + its rated wattage
Walk the trailer with a clipboard. Espresso machine 2-group: 3,500-6,000 W startup, 2,800-4,500 W running. Espresso machine 1-group: 2,200-3,500 W startup, 1,800-2,800 W running. Coffee grinder: 200-450 W. Lights (LED): 60-180 W total. Fryer twin-tank gas: 0 W (LPG, not generator); + 50 W for thermostat + ignition. Fridge under-counter: 200-400 W startup spike, 50-150 W running. Chest freezer: 250-500 W startup, 80-200 W running. Card terminal: 5-15 W. Phone charger / WiFi router: 30-80 W. Note rated wattage from the appliance plate, NOT the marketing brochure.
2. Calculate startup vs running load
Equipment with motors (compressors in fridges, pumps in espresso machines) draws a startup spike of 2-4× the running load for ~1-2 seconds. The generator must handle ALL devices starting up simultaneously without tripping. Add the running loads of everything that runs continuously, then add the LARGEST startup spike of any single device. That total is your peak demand — the generator must comfortably exceed it.
3. Add a 25-40% safety margin
Generators run most efficiently at 70-80% load — pushing one at 95% all day burns extra fuel + shortens engine life. Take your peak-demand calculation and divide by 0.75 to get the recommended generator capacity. Example: 3,000 W peak demand ÷ 0.75 = 4,000 W = 4 kVA recommended capacity.
4. Pick silent diesel vs inverter petrol
Silent diesel (Hyundai DHY, Pramac, FG Wilson, SDMO, Stephill) is the festival workhorse — sub-70 dB at 7m, 12-24 hours per fuel tank, 5,000+ engine hour life. Higher capital cost (€1,800-€9,000 depending on size) but lower running cost + festival-rule compliant. Inverter petrol (Honda EU22i, Yamaha EF2200is, Hyundai HY2000Si) is for small mobile coffee carts running 1-2 kVA — quiet, lighter, clean sine-wave output for sensitive electronics. €600-€1,500 typical price. Petrol generators are NOT permitted indoors or under canopies + sometimes excluded from festival pitches due to fuel storage rules.
5. Plan fuel storage + festival logistics
A 5 kVA silent diesel running at 75% load burns 1.0-1.5 litres/hour. A 3-day festival running 12 hours/day = 36-54 litres of diesel. Bring 1.5x what you calculated. Diesel storage on the trailer is regulated — keep it in approved metal jerry cans, max 30 litres without a separate fuel licence. Most festivals provide a fuel-bowser refilling service onsite at premium prices; cheaper to bring your own. Festival organisers check fuel storage compliance at gate-in.
6. Test under realistic load before the festival
Two weeks before your first festival, run the trailer on the generator with EVERY appliance running simultaneously for at least 2 hours. Watch for: voltage drop (should stay 220-240V), generator over-heating (silent diesels with poor airflow can throttle in summer), ground-fault trips on RCD-protected hookups (common with damp festival pitches). If anything trips or browns out, you found the issue with time to fix it.
7. Maintenance + service contract
Silent diesels need an oil + filter change every 100-250 engine hours. Plan for one full service mid-summer if you're running festivals every weekend. Most Irish generator dealers offer service contracts (€150-€400/year) including 2 onsite calls + a winter de-commission. Off-season: drain the diesel down or add stabiliser, run for 15 minutes monthly to keep injectors clean.
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