A short, useless intro to the question, feel free to skip it:

I had a power outage in my home yesterday. Power outages aren't what they used to be - Back in the day, it rendered me completely unable to do anything, but nowadays I have my laptop, which is still connected to the internet via my phone, which is connected to a strong mobile recharger I have (10 Ah) - and I can hardly care less about the rest of the power.

Except for the part about my fan. It gets really hot where I live. And I currently simply have no solution for this. Small USB fans don't do the trick. And I just can't figure out how nobody I know has a solution for such a simple, supposedly common problem. Is mankind simply not advanced enough to take on such problems? Will we be able to operate fans during blackouts? What level on the Kardashev scale must we advance to before we can solve this?


Is it possible to operate a normal, standing fan during a power outage? How?

Is connecting it to a UPS a good idea? I've read elsewhere that the waveform generated by UPS devices doesn't behave well with these sort of devices.

And how long is a fan expected to last on a standard UPS?


A UPS as I understand it is an battery attached to an inverter. I have used portable fans on an inverter with no issues. Assuming they are designed for the same frequency. If you have a AC motor designed for 60 Hz and a inverter operating at 50 Hz it would just alter the speed of rotation.

One thing I don't recommend is plugging an electric digital clock into an inverter because a minute will pass every 30 seconds or so. If your laptop is OK with it then your fan will tolerate it OK.

  • \$\begingroup\$ Great. I'm not sure I get the part about 50 vs 60 hz, but the UPS I wanted to get says "50/60Hz", so hopefully that will do. How can I calculate how long it should operate? Say the UPS is 850VA/480W, and the fan is 60W, 50Hz; - Would that means 8 hours? \$\endgroup\$ – user976850 Oct 17 '18 at 7:36
  • \$\begingroup\$ You you would have consider the efficiency of the inverter in your calculations. My inverter was 87%. Your 60W fan would consume about 70 watts. The battery voltage would have a role to play as well. How long could you run the inverter until it cuts out due to low battery voltage. \$\endgroup\$ – Old_Fossil Oct 18 '18 at 7:47

A battery UPS will work, but a UPS has a high loss even with no load. It's meant for temporary solutions. Either to safely shutdown, or bridge the gap for the diesel to start running.

Fans for comfort are a luxury, sometimes this luxury is unavailable to those who cannot improvise.

Get some 12V PC box fans and fangrill that you can run from a cheap lead acid battery.
Either silent breeze, or tornado amounts of moving air on request.

Or go to the scrapyard and take the radiator fans from an old car. These are also 12V.

Or you can go the old fashioned way, for fans and lighting.

  • \$\begingroup\$ I'm not sure, but if the OP's climate is the same as mine, then PC fans don't really cut it unfortunately, unless you are up fairly close to them. I've tried it, and yes it is a brief respite, but not that much better than USB fans, TBH, and not that much use when trying to work at a desk. We are probably talking 14", 16' or 18" fans for (small-ish) room sized brusque movement of air, probably with a rotating/oscillatiing fan head, at a distance of 2-3, maybe 4, meters. I have the same issues and it is unbearable. The chainsaw solution... now we are talking (+1) :-) \$\endgroup\$ – Greenonline Oct 17 '18 at 8:17
  • 1
    \$\begingroup\$ @Greenonline You can get very decent high CFM pc fans. And you can use a laminar flow grid to direct the flow more precise. \$\endgroup\$ – Jeroen3 Oct 17 '18 at 14:37

It depends upon the power of the fan. In Thailand a Hatari 18" fan consumes between 78 W and 114 W (depending upon model) , so at 240 V, that is a maximum of 0.3 A - 0.5 A (let's say 1 A for simplicity).

The capacities of UPS appear to be measured in kVA rather than Ah, even though it really is just a battery with an inverter.

Going by this kVA calculator, for (single phase) 230 V and 1 A:

  • the Power is 0.16 kW and;
  • the kVA required is 0.23 kVA.

There are plenty of small 10-20 kVA UPS out there.

With respect to how long it will last:

Lets say you get a 20 kVA UPS, and for simplicity's sake, the fan is 100 W. So the fan consumes 100 W every hour.

The kW of the UPS is 20 kVA x 0.7 = 16 kW

Therefore the UPS will last 160 hours.

That seems like an awfully long time - I may have made a mistake


Apparent Power (VA) = Load (W) / Power Factor

where Power Factor = 0.7

UPS Backup [in hours] = Battery Ah * Volts * Power Factor/Load

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