Power cuts keep happening: is it a UPS you need, or a generator?
The question is framed wrongly, because these two are not competitors. They answer different questions.
A UPS answers what to do about electricity that disappears for one second, or for ten minutes.
A generator answers what to do about electricity that disappears for six hours, or for two days.
So the question to ask first is how long the power actually goes off at your house, and why.
Answer that and the equipment answers itself. In plenty of cases the answer turns out to be that you need neither.
Three kinds of outage, each wanting something different
Before choosing equipment, work out which one you get.
The first kind, the flicker. Power vanishes for a fraction of a second and returns on its own, because a protective device opened when something touched a line, a branch or an animal, and then reclosed.
What you notice at home is the computer restarting, the router rebooting, the microwave clock blinking again.
A UPS solves this completely. A generator solves none of it, because the power is back before the engine has started.
The second kind, one to three hours. A fault in the local network, or planned maintenance the authority announced in advance.
This middle band is the hardest to decide about.
A large UPS carries some things through it. A generator earns its keep if this happens often.
The third kind, half a day or longer. A storm, a tree across the lines, a pole down, or flooding severe enough that the whole area is cut off for safety.
Only a generator helps here. Every domestic UPS on the market runs its battery flat first.
Now think back over the last three months and count honestly which kind you actually had, and how often.
A lot of people buy a generator because they remember the big flood, when what they meet every month is a flicker.
What a UPS actually does, and why the three types cost different money
A UPS is a battery and a converter sitting between the socket and your equipment.
It has two real jobs: carrying the load when the supply fails, and delivering something steadier than what came in.
There are three types on the market, and the difference is not battery size.
Standby, also called offline, is the cheapest. It passes mains straight through and switches to battery when the supply fails.
The switch takes a short moment during which power really is absent, measured in milliseconds, which ordinary computers and routers never notice.
Line interactive adds a voltage regulating circuit, so a modest sag or surge is pulled back into a usable range without calling on the battery at all.
The advantage people rarely mention is battery life, because the battery is not woken up every time the voltage dips a little.
In a house at the end of a feeder where the voltage sags every evening, this type is clearly worth the difference.
Online double conversion converts to DC and back to AC continuously, so the equipment downstream never sees the incoming supply directly.
There is no transfer time because there is no transfer. It also costs a great deal more and consumes power the whole time it is on.
For an ordinary house there is almost no reason to buy the third type.
The waveform a UPS produces is a question to ask before buying
Many budget units output a stepped waveform rather than a true sine wave.
Equipment with a switching power supply, computers and routers among them, mostly copes.
Things with motors and transformers, water pumps, refrigerators and fans, run hotter than normal and buzz audibly on that waveform.
If the plan is to feed anything with a motor in it, buy a unit that states pure sine wave output.
And if the question is whether a UPS can run the refrigerator, the short answer is that technically it can, for about a minute, which helps nobody.
Work out the runtime yourself before spending
The VA figure on the box is not watts, and it is not runtime.
Step one, convert VA to watts. A unit marked 1000VA typically delivers around 600 watts in a budget model and around 900 in one that states a high power factor.
The real watt figure is on the label or in the manual. Use that, not the large number on the box.
Step two, total the load you will actually plug in. A router plus the fibre terminal is usually somewhere between ten and twenty watts together. A desktop computer with a monitor runs into the hundreds.
How to measure rather than guess is covered in which appliance uses the most electricity.
Step three, do not load it to the rating. A UPS run near its maximum all day runs hot, and heat is what kills the battery.
Plan for around half the rating and the service life differs by years.
Step four, accept the truth about runtime. A domestic UPS on a very light load, feeding only the router, lasts hours.
The same unit with a desktop computer plugged in lasts minutes.
So if the goal is that the internet does not drop when the power does, buy a small UPS for the router alone rather than a large one for everything.
That is the smartest money in this whole category.
Size a generator on starting watts, not running watts
This is where people most often buy the wrong size.
Anything with a motor draws several times more current getting going than it does while running. Refrigerators, water pumps and air conditioners are all in that group.
A water pump marked two hundred watts may pull several times that figure briefly as the motor breaks away.
A generator chosen on running figures alone will stall every time the pump cuts in.
The workable method is to write out what you genuinely need during an outage, add the running watts of all of it, then add headroom for the starting surge of the single largest motor.
One motor of headroom is enough, because two motors starting at precisely the same instant is unlikely, and if it worries you, switch them on one at a time.
What most households really need turns out to be a much shorter list than expected.
- The refrigerator, so food does not spoil.
- Two or three fans.
- Lighting in a few places.
- The router and phone chargers.
- The water pump, if the house draws from a tank.
Notice that air conditioning is not on the list, because it moves the machine up a whole size class, and the price with it.
A household willing to sleep under a fan during an outage can buy a far smaller machine and save a great deal.
Conventional against inverter generators
A conventional generator runs its engine at a fixed speed whatever the load.
Which means feeding only a refrigerator and a fan burns nearly as much fuel as feeding everything, and makes the same noise doing it.
An inverter machine varies engine speed with load, so a light load means low revs.
The result is much quieter, more economical on light loads, and produces cleaner power, which suits electronics.
The drawback is price at the same output.
In an estate with neighbours close by, noise is not a secondary matter, because a machine loud enough that the neighbours cannot bear it is a machine that ends up never being switched on.
Three prohibitions that people actually die from
This section is not politeness. These are causes of death that recur every storm season around the world.
Never run the engine in an enclosed space. It produces carbon monoxide, which has no colour and no smell, and which causes unconsciousness before anybody notices anything is wrong.
A garage with the door open is not safe. Under the house is not safe. A balcony walled on three sides is not safe.
Safe means outdoors, away from windows, doors and vents.
Never feed a generator backwards into a household socket. The trick some people use is a lead with a plug on both ends, run from the machine into a wall socket.
What happens is that the generator's output travels back up to the transformer and is stepped up to high voltage on lines that utility crews are working on in the belief that they are dead.
And when the grid returns while the machine is running, the generator is destroyed instantly because the phases do not match.
There is no shortcut around this one.
Never site the machine in the rain or on wet ground, and never refuel while it is hot, because petrol vapour ignites off a hot exhaust.
Shut it down and let it cool before refuelling, every time, however inconvenient that feels.
There are exactly two correct ways to connect it
The first, extension leads straight to the appliance. Run a lead from the machine and plug the refrigerator and the fans into it directly, touching the house wiring not at all.
This is the safest and the cheapest. The drawback is leads across the floor and walking round to plug things in one by one.
If you take this route, use lead heavy enough for the distance and the load, because undersized cable runs hot, which is the same subject as choosing the wrong cable size.
The second, install a transfer switch. Its single job is to make sure the house is connected either to the utility or to the generator, never to both.
They come in manual and automatic forms, the automatic being dearer and switching itself when the supply fails.
This work belongs to a competent electrician, and it is worth asking the local electricity authority beforehand what has to be notified or complied with, since it connects into the main supply of the house.
Which household should buy which
Decide on the outages you actually get, not on the ones you fear.
Frequent flickers, nothing over ten minutes: a small UPS for the router and the computer. Done. Do not think about generators.
Working from home with video calls: a line interactive UPS carrying router, computer and monitor long enough to finish the call, or at minimum to save the work and shut down properly.
Somebody at home on mains powered medical equipment: this is not a shopping decision but a safety one. Ask the doctor and the equipment maker how much backup is required and in what form.
Outages over three hours, several times a year: a generator big enough for the refrigerator, fans, lights and router already pays.
A house in a repeatedly flooded area, or at the end of a line that is slow to repair: a generator with a transfer switch, and a safe plan for storing fuel.
A house that already has solar: find out first whether the installed system is grid tied without batteries, because a system without storage stops producing when the grid fails, by design, to protect crews working on the lines.
That last point surprises a lot of owners who assumed panels meant never being without power.
What to own before either of them
The first money belongs here, because it buys more per baht.
- A rechargeable torch that lives in the same place every time. A torch you cannot find in the dark is a torch you do not have.
- A power bank kept charged. The phone is the torch, the radio and the way to report the fault all at once.
- Drinking water in reserve, because a house on a pump has no water the moment the power goes.
- Knowing where the breakers are and how to work them. Power returning in a surge damages equipment, and dropping the heavy loads first then restoring them one at a time genuinely helps.
- The local fault reporting number, saved in the phone in advance.
All five together cost less than one UPS and are useful in every outage, of any kind.
The costs people forget to count
The ticket price is not the real price of either machine.
UPS batteries have a life. The sealed lead acid batteries in domestic units last a few years rather than a decade, and heat shortens that further.
A UPS in a closed cabinet or an unventilated corner needs new batteries sooner than it should.
A UPS with a dead battery is worse than no UPS, because people still believe they have backup while it actually drops out the instant the power does. Test it by pulling the plug for real, once a year.
Petrol goes stale. Fuel left in the tank and the carburettor for months leaves a sticky residue, which is the leading reason a generator will not start on the day it is needed.
Prevention is a short monthly run under real load, then closing the fuel tap and letting the engine run itself dry.
Storing spare fuel means containers designed for it, kept ventilated, away from the house and from heat, and no more than can be rotated through.
The cost of installing a transfer switch, which sometimes exceeds the price of a small machine, and belongs in the budget from the start.
Test it like the real thing, at least once a year
Backup equipment that has never been tested is equipment nobody yet knows works.
The UPS: pull the plug for real with the normal load connected, and time how long it lasts.
If it once gave forty minutes and now gives five, that is the battery telling you.
The generator: start it and run it under real load, not started and shut down again.
The faults that appear under load are a different set from the ones that appear without.
Leads and transfer switch: rehearse in daylight, not for the first time at two in the morning in the rain.
Somebody who has rehearsed takes ten minutes. Somebody who has not takes an hour and usually gets the order wrong.
Frequently asked questions
UPS or generator first?
It depends on how long your power stays off. Seconds to minutes means a UPS. Hours, several times a year, is where a generator starts to pay.
Can a UPS run the refrigerator?
Technically yes with a pure sine wave unit of sufficient rating, but only for a few minutes, which does not preserve anything in a longer outage. Simply not opening the door does more.
What does the VA figure mean?
It is apparent power, not watts. A 1000VA unit typically delivers around 600 watts in a budget model. Work from the watt figure on the label.
How do I size a generator?
Add the running watts of everything you will use, then allow headroom for the starting surge of the largest motor, because refrigerators, pumps and air conditioners draw several times their running current on start up.
Can I plug a generator into a household socket?
Never. The output travels back up the line and is stepped up to high voltage where utility crews may be working. The correct methods are leads straight to appliances, or a properly installed transfer switch.
Is a garage with the door open safe?
No. Carbon monoxide accumulates to dangerous levels in semi enclosed spaces even with the door open. The machine belongs outdoors, away from windows, doors and vents.
I have solar panels, will the power still go off?
Yes, if the system is grid tied without batteries. Such systems are designed to stop producing during an outage so that nothing is fed back onto lines where people may be working.
How do I look after a generator that mostly sits idle?
Run it under real load once a month and close the fuel tap so it runs itself dry, which keeps petrol from leaving sticky residue in the carburettor, the leading reason a machine will not start on the day it is wanted.
In short
- A UPS and a generator are not rivals. One covers seconds, the other covers days.
- Count what you actually had over the last three months before choosing anything.
- A small UPS on the router alone beats a large one that carries everything for a few minutes.
- VA is not watts. Work from the label and plan around half the rating.
- Size a generator on motor starting surge, not on running watts.
- Never run it enclosed, never backfeed a socket, never refuel it hot.
- Connect it either straight to appliances or through a properly installed transfer switch.
- Solar without batteries stops during an outage, deliberately, for the safety of line crews.
- Test both once a year, because untested backup is backup nobody knows works.