How many watts does a UPS draw when powering from a generator

I am in South Africa 220V power, with constant power outages I have purchased a small generator 2500 Watts just to run computers.  I have a 650VA UPS & a 1000VA UPS the manual says they use 390W and 600W respectively.  I just want to confirm that they will infact draw 390W and 600W when powered by a generator as this will influence what equipment I run off my generator.
Who is Participating?
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

the easies t way is to measure it, use a wattmeter, or Amps meter and calculate the power used

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
Gary CaseRetiredCommented:
I believe your UPS units probably saw they can PROVIDE 390W and 600W respectively.   They will actually draw an apparent load of 650VA and 1000VA, respectively, but have a power factor of about 60%.   The power factor determines the actual relationship between the "apparent power" (VA) and "real power" (W).   If the power factor was 1, then Ohm's law of W = VA would apply (but it does not in this case).

This means your source (the generator) needs to be able to supply the full apparent power of 1650VA.   Most generators are rated for both KVA and KW output --> be sure you know which you are dealing with.   The "safe" assumption is that you need 1650W of the generator's 2500W output.

Note that this is only drawn under maximum load ... it would only be drawn if you're loading the UPS at 100% of its stated capacity (not likely and certainly not a good idea).   If you know you never draw full load from the UPS's, you can reasonably assume a somewhat lower load when computing what you can power from the generator.
schwegumsAuthor Commented:
Thank you for your help.  I bought an amp meter and it did the trick.
then please close the question
Gary CaseRetiredCommented:
Measuring the actual draw is always the best way :-)  => Don't forget to close the question.
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today

From novice to tech pro — start learning today.