How to Size a Generator for a Kenyan Home or Shop

Start with a load list, not a guess

Sizing starts with a written list of everything the generator must carry at the same moment. Every appliance has a nameplate giving its watts. If it gives amps, multiply by the supply voltage, so on Kenya's 240 V single-phase supply a 3 A appliance draws about 720 W.

Leave off anything you can simply switch off during an outage, such as a kettle or an iron. Here is a worked list for a small shop or family house. Write yours the same way before you look at any machine.

• Eight LED lamps at 10 W each: 80 W running
• Television and decoder: 130 W running
• Router, chargers and a small radio: 60 W running
• Chest freezer: 250 W running, plus about 500 W extra when the compressor starts
• Half horsepower water pump: 370 W running, plus about 740 W extra on start
• Total running watts: 890 W

Add the biggest starting surge

Running watts are only half the sum. Anything with a motor, meaning fridges, freezers, pumps, compressors and grinders, pulls two to three times its running figure for the first fraction of a second. A set matched only to the running total will sag, trip or stall when the pump kicks in.

You do not add every surge together, because motors rarely start at the same instant. Add the single largest surge to the full running total. Above, that is 890 W plus 740 W for the pump, so peak demand is 1,630 W. Lamps, kettles and irons are resistive, so they count once.

How to size a generator in kVA: kVA to watts and the 0.8 power factor

Generators are sold in kVA, and kVA is not watts. kVA is apparent power, the total current the alternator must push. kW is real power, the part that does work. The ratio between them is the power factor, taken as roughly 0.8 for a mixed load.

So multiply kVA by 1,000 and then by 0.8 for usable watts, or divide peak watts by 0.8 for the kVA you need. Our 1,630 W divided by 0.8 is about 2,040 VA. Add roughly 20 percent so the engine is not flogged at its limit and you land on a 2.5 kVA class set such as the GENERATOR 2.5 KVA (KEY START).

Run the same sum on your own list. Lights, a TV and chargers rarely need more than a GENERATOR 1.0 KVA. A house with a fridge and a pump lands near the GENERATOR 3.0KVA (KEY START), and a shop with a freezer and a workshop tool is often a GENERATOR 4.0 KVA (KEYSTART) job.

• Watts to kVA: divide peak watts by 800
• kVA to watts: multiply the kVA figure by 800
• 1.0 kVA is roughly 800 W of usable load
• 2.5 kVA is roughly 2,000 W, 3.0 kVA roughly 2,400 W, 4.0 kVA roughly 3,200 W

What goes wrong when the size is off

Too small and the symptoms show fast. Voltage sags when the pump starts, lights flicker, the breaker trips, or the engine bogs down and stalls. A motor fed low voltage draws more current to do the same work, runs hot and eventually cooks its windings.

Far too big costs you differently. Fuel burn follows engine size and speed, so a large set on a light load wastes fuel every hour. Diesels suffer worse: lightly loaded they never reach proper combustion temperature, so unburnt fuel collects in the exhaust and glazes the bores. That is wet stacking. Work a set between about half and three quarters of its rating.

Petrol or diesel, key start, run time and noise

The petrol versus diesel generator choice comes down to hours. Petrol sets are lighter, quieter, easier to start cold and simpler to service, which suits a few hours of backup a week. Diesel uses less fuel once properly loaded and lasts more hours, so the DIESEL GENERATOR3KW,5.7HP.TP430001 and its class suit daily running.

Recoil start means pulling a rope, fine on a small set but tiring on a bigger engine at night or in the rain. Key start models turn over from a battery, which matters when the machine lives outside. Keep that battery charged and the recoil handle working as a backup.

Run time depends on tank size and on how hard the engine works, so the same tank empties far faster carrying a freezer and a pump. Never refuel a hot or running engine, because petrol on a hot exhaust ignites easily. Site the set on level ground away from bedroom windows, under an open shelter that sheds rain without blocking airflow.

Running a generator safely

Never run a generator indoors. That includes a closed garage, a store, a verandah or anywhere under a window, even with a door propped open. Exhaust contains carbon monoxide, a gas with no smell and no colour that kills people who simply feel sleepy and lie down.

Never back-feed the house by plugging the generator into a wall socket with a double-ended lead. It makes your sockets live, can push voltage back onto the supply line where a lineman is working, and bypasses your protection. Use a changeover switch fitted by a licensed electrician, who should also confirm the earthing and any earth rod required.

Store fuel in proper metal or approved plastic containers, kept shut, out of the sun and away from any flame, never inside the house. Petrol goes stale within a couple of months and gums up the carburettor, so add a fuel stabiliser when you fill the can, or run the carburettor dry before storing the machine.

Generator maintenance that decides how long it lasts

More small generators in Kenya die from neglected oil than anything else. These are small air-cooled engines with a modest oil capacity, working hot and in dust. Check the level before every start. Change the oil early after break-in, since the first hours leave metal in the sump, then keep to the manual's hour interval.

Air filters clog fast on a dusty compound, and a choked filter makes the engine run rich and lose power. Petrol sets need the spark plug checked; diesel sets need the fuel filter and water separator drained, since watered fuel ruins an injection pump. Start the set monthly under a real load, because a machine that sits develops a flat battery and stale fuel.

• Check the oil level before every start
• Change oil early after break-in, then on the manual's hour interval
• Clean or replace the air filter more often in dust
• Spark plug on petrol, fuel filter and water separator on diesel
• Run the set under load for twenty to thirty minutes monthly