Interactive lesson

Generators and backup, step by step

Interactive lesson: what must keep running, which generator and how big, outdoors only, a changeover switch instead of a socket, fuel, batteries and a plan.

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The whole lesson as text

1. When the power goes off

In the countryside the power goes off when you need it most: in a snowstorm or a summer thunderstorm.

How long the power goes off — Up to 1–2 hours, a UPS or portable power bank will do. For 1–3 days you need a 2–6 kW generator with a changeover switch and fuel for 3 days.
Boiler pump first — A wood-fired boiler without its circulation pump can boil over. If it has no safety heat exchanger or gravity circuit, the 30–90 W pump is essential load number one.
Pressure pump, biggest motor — A well pump or pressure pump draws 750–1,100 W, and 3–5 times more at start-up. A fridge runs on 80–150 W and starts at 600–1,000 W.
Keep the freezer shut — A full freezer holds for 36–48 hours, a half-full one about 24 hours. A closed fridge keeps food safe for 4 hours.

Why: Backup doesn't have to cover the whole house. How often and how long the power goes off decides whether you need a battery, a small generator or a bigger one with a changeover switch. Life and health come first in sizing, then food and animals.

The best approach is a combination: what works without electricity, a small battery for short cuts and a generator only for long ones.
A water heater, cooker or fan heater of 2,000 W and more doesn't go on a small generator.

2. Generator type and size

You choose a generator by what it has to run.

Inverter for electronics — A 1–3.5 kW petrol inverter generator is quiet, light and gives clean voltage. For the boiler, fridge, lights and computer, and for shorter cuts.
Open-frame and diesel — A 2–8 kW open-frame generator is cheap and strong for pumps and tools, but for electronics it needs voltage regulation (AVR). A 5–15 kW diesel is for long cuts and livestock.
Add up and add 25 % — Add up the W of everything running at once and multiply by 1.25. The rated (continuous) power on the generator's plate must be higher than that total.
Starting the biggest motor — A 900 W pressure pump draws roughly 3,600 W at start-up, plus whatever else is running. Switch loads on one at a time, from the biggest motor to the smallest.

Why: A generator that's too small can't start the pump, and one that's too big runs nearly unloaded all day and wastes fuel. A boiler with electronics, an inverter and chargers need a stable voltage.

On many homesteads a pair works best: a small 2 kW inverter generator for everyday cuts and a bigger one only when the pump or tools are needed.
Check in the boiler manual which generators it may run on. In the US and Canada, a 240 V well pump needs a 120/240 V generator.