UPS power rating

Thread Starter

MCH170

Joined May 13, 2021
16
Hello, I am looking to buy a line-interactive ups. As far as I understand the ups power rating only comes into play when the power goes out and the inverter starts working. When mains power is available, the computer (in this case) can draw the full power the wall socket can provide. Is that correct?

Also, is it ok to buy a ups that can't support my computer's peak power draw? I understand that if I am doing something very power-intensive when the power goes out the ups won't be of any help but considering how rare that is I think its worth taking my chances.

Thanks for your advice.
 

crutschow

Joined Mar 14, 2008
34,280
When mains power is available, the computer (in this case) can draw the full power the wall socket can provide. Is that correct?
Depends upon the type of UPS.
Some operate continuously from the inverter so there is absolutely no glitch when the power goes out.
is it ok to buy a ups that can't support my computer's peak power draw?
I would not do that, but can you measure the computer's power to see what you really need.
It might be less than the peak rating.
 

dl324

Joined Mar 30, 2015
16,839
When mains power is available, the computer (in this case) can draw the full power the wall socket can provide. Is that correct?
It depends on the UPS and the socket the computer plugged into. On my UPS's, half of the outlets are only surge protected.
Also, is it ok to buy a ups that can't support my computer's peak power draw?
Peak power is a misnomer. By definition, it's averaged over time. What is the "peak" wattage of your computer and the VA rating of the UPS you're considering? How much runtime to you want?
 

Thread Starter

MCH170

Joined May 13, 2021
16
How much runtime to you want?
That is not an issue. I built a diy online ups but it is way too noisy to have operating 24/7 so I thought it would be a good idea to buy a line-interactive and, when the power goes out I will use those few minutes I have to connect the ups' input to my diy one and turn it on.

What is the "peak" wattage of your computer
According to PCPartPicker (and considering psu efficiency and some overclocking) I can see my (future) PC drawing about 600-650W at the maximum. The UPS I am considering is 900VA 540W.
 

dl324

Joined Mar 30, 2015
16,839
I can see my (future) PC drawing about 600-650W at the maximum. The UPS I am considering is 900VA 540W.
Shouldn't have a problem with your future configuration.

I have half a dozen computers and various other devices on a 1200VA UPS. Only a few of them are likely to be on, and probably in standby. When I lose power, I turn them off if I don't need to do anything critical.
 

bassbindevil

Joined Jan 23, 2014
824
I'd want to measure the actual power consumption with something like a Kill-A-Watt power meter. Then pick a UPS with a comfortable amount of headroom in wattage capacity, and a big battery. More battery capacity pays off in both runtime and service life.
 
Last edited:

Ian0

Joined Aug 7, 2020
9,667
Also, is it ok to buy a ups that can't support my computer's peak power draw?
No, but a UPS will have a peak power output rating. It should be more than the computer's peak power input.
Of course, the normal running output power of the UPS need to be greater than the normal running load of the computer,
However, I very much doubt that the UPS would ever have to supply the startup inrush of the computer - how often would you be powering up your computer when the mains has failed?
 
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