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How long could a 600va UPS run a light bulb?


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#1 Violater

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Posted 18 January 2011 - 06:44 AM

Out of interest, I thinking of connecting a cheap UPS like this one to my light circuit, so that when the power goes off, I can at least carry on with one or two lights on in the house.
But the question is, realistically, how long would I be able to run, say, a 15w CCFL light off of it?
I'm sure the manufacturers website's estimation of running a PC for "25 to 35 minutes" for a PC is a bit optimistic.
Anyone with a more realistic estimation for a light?
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#2 Pyro

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Posted 18 January 2011 - 08:56 AM

The VA rating only tells half the tale :p

It basically give you the maximum amount of power the UPS can supply.

Mathematically Watt=VA, but the UPS isn't 100% efficient so you'd probably get ~75% of that. So Max 450W.

And at maximum load a battery is much less efficient :p

15W on its own should be able to run for a looooooong time on its own, but without the W.h rating of the battery, you can't really say.

I've never actually had a brand spanking new UPS to play with, so don't have any numbers :( My oooold 1200VA at home was a used unit, and the battery isn't very useful anymore. It's good for maybe 5 minutes for my PC now, but I'm pretty sure it's saved me from a few replacements by handling line noise and spikes.

A 600VA that can handle 300W for about 30 minutes, should theoretically be able to carry 15W on its own for 10 hours.

Edited by Pyro, 18 January 2011 - 09:02 AM.

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#3 Deezil

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Posted 18 January 2011 - 09:46 AM

Ja difficult question ... to me VA only indicates the number of devices you can safely connect to an UPS (i.e total wattage), maH capacity of the actual battery will tell you how long it will last at any particular load. Since bigger UPS's usually have bigger batteries a fallacy exists that the the bigger the VA rating the longer it will be capable to provide power. For a UPS to run for a couple of hours (assuming normal PC use) you actually need to add a more batteries to it and not necessarily buy something with a huge VA rating.

Looking at this article and using a power factor of .6 to get the actual VA rating of the CFL light bulb (15W / .6 = 25VA) it is reasonable to assume that 2 CFL light bulbs should last approximately 2 hours on a 600VA UPS. Single light bulb maybe 4-5 hours? I sure hope you actually do this experiment one day :p

Here's another interesting discussion that actually goes way over my head.
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#4 Violater

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Posted 28 January 2011 - 04:57 PM

Small update
I ended up getting a second hand 600va ups for cheap - I realised that the battery wouldn't be very good - basically just wanted it for everything else.
As a test, I connected it up and switched on some of my lights - about 120watts in total, It only lasted about 2 minutes before shutting itself down. <_<

I managed to get a 95ah deep cycle battery which I've wired to the UPS.
Now I realise the UPS is not designed to charge such a bit behemoth, so I manually fully charged it. Depending on the length of the outages, I might have to do that every now and again.

I didn't want this ugly contraption lying around in the house, so I've connected up everything in the roof.
I should ad that lugging the 20kg battery up into the roof was not fun, especially not the second time (It didn't work the initially, brought it back down to test, figured out I have to manually turn the UPS on after connecting the battery...:rolleyes:)

Theoretically, even the most pessimistic estimations should give me ample hours next time the power goes out.
Will report back next time this happens.
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