# My rig's power related queries - need new PC UPS?



## abhi_10_20 (Dec 16, 2012)

People, I had been using my system till now with no probs. But am smelling something fishy here.
Feel free to bash me anywhere!

PSU is FSP Saga II - 500 W
My sys has GTX 660 - which has a minimum power req of 450 W

I had been using APC Back-UPS ES 500 which outputs 300 Watts / 500 VA ( !!!!! )
as my sys's power source and was all good. 

Q1: No much electrical background, but how it possible for my PC to run good always under 300 W? 
I guess all components running live might'nt all be summing up to 300?

Now the UPS is gone kaput, mostly because its too old and needs a battery replacement.
(Or maybe I was overloading it too often?)
I pulled out the connection to my cabby and tried switching on, well the same thing.

Q2: Postponing to last.

My home has a UPS provided by Genus Sine wave converter, which's 600 VA.
Now I try to connect my sys direct to a plug point, but the home UPS always trips down 'coz of overload.

Q3: Now how the hell din't my home inverter complain when I was using my APC UPS?
Well, here's another: It did use to complain some times.
But most times, there was no problem.

Q2: Should I be getting a new UPS for my sys (say 600 VA), or go for a home UPS giving out 700-800VA?

Q4: What is the general power factor we get? Does it hover around 0 to 1? Am trying to find out what's W = VA * PF for all the above case studies


----------



## hitman4 (Dec 17, 2012)

apc 1100va


----------



## vkl (Dec 18, 2012)

@abhi_10_20
Please mention your full system specifications.Would be easier to calculate things.

Anyway,the power consumed by all your components can't be directly compared with the maximum power that UPS can supply.
The 300Watts you are talking about is the total maximum AC power that can be provided by the UPS to the PC without an interruption.
The PSU inside takes the AC power from the outlet/mains supply and supplies power according to PC's requirement depending upon the load.
The outlet in your case is the UPS.
Now lets take an example.Suppose your PC requires 250W at maximum load and let at that particular load and time the PSU efficiencyis 80%.
PSU efficiency=(DC Power consumed by the PC)*/*(AC power drawn)
Then the input AC power that your PSU would require is (250/0.8)=312.5W i.e. in order to provide 250W to the PC the AC power required from the UPS would be 312.5W.
312.5W>300W(max power UPS can supply) 
In such conditions the UPS won't be able to provide back-up.
Most of the consumer level UPSs have power factor in the range of 0.6-0.67.Some UPSs have power factor above 0.8 and some UPSs used for large loads like data-centers have power factors above 0.9.

Just mention your system specs and budget so suggestion for a suitable UPS can be made.


----------



## abhi_10_20 (Dec 18, 2012)

^^ thanks a lot for the description.

Please suggest whether you are referring to changing my home UPS or the UPS for my rig? Am guessing that you mentioned about my rig's UPS.

While I am inclined to say that if I already have a home UPS, having another one for my system is redundant and not necessarily needed --- am again not sure about this.

Here goes the full specs:

proc - intel core i5 2500
mobo - intel dh67CL
RAM - corsair vengeance 2*4 GB
HDD - WD HDD - 640 GB (Guess)
PSU - FSP Saga II - 500 W
Gfx card - MSI nVidia N660 (non Ti)
Cabby fans = having only 1

Monitor(22''), speakers(2.1) till now weren't using my system's UPS outlets. They were just connected to mains supply(rather to my home UPS)

@hitman4, if I go get an APC 1100 va  - and connect it to mains - which means - is connected to my home UPS - then I reckon it's going to trip down all the time.. as my home UPS is just 600 VA


----------



## vkl (Dec 20, 2012)

^^I was referring to the UPS for your rig.
APC Back-UPS ES 500/300W on its own can provide back-up to your system in situations but at high load with monitor and other peripherals attached to it,it won't be able to do that.

I will refer the points to which the home-UPS is suppose to provide back-up in case of power failure as "load-points of/for the home-UPS".These are the points where your appliances or other loads would have been directlt connected in order to have back-up during power-failure.

You have a home-UPS which has VA rating of 600VA.It's exact rating in Watts is unknown,maybe around 360Watts or so,need to know its actual specifications for rated maximum wattage.
When you are connecting monitor,speaker and other peripherals along with your PC to the load points of home-UPS,in case of power failure there are chances that it might get overloaded if your PC has high load at that point of time as the total load might exceed the maximum load the home-UPS can take.
Your config would consume around 280Watts(rough estimate excluding monitor and other peripherals) at full load i.e.DC power.
AC power requirement would be more,depending upon the efficiency of the PSU at that load.Lower the efficiency,higher the AC power required for a certain level of DC output.
At idle or low loads the consumption would be very less.In such cases your home-UPS would be able to power up your PC provided there are not some power hungry equipments connected to 
the other load-points of home-UPS to make the total power required higher than what the home-UPS can supply.
Suppose you had a higher capacity home-UPS say 1kVA with wattage around 660Watts,then there won't have been any need of extra UPS for the PC even in case of full load.You could have connected the PC and other equipments/appliances that you need to power up to load-points of the home-UPS(obviously within the maximum power limit).

In most cases plugging an UPS to another UPS is not considered good.The reason is that the UPS needs a pure sine wave input.The supply from the mains/wall outlet provides that.
The output AC by the UPS might be stepped approximated sine wave,pure sine-wave depending upon the UPS.
Now if your home-UPS is not providing a pure sine-wave or it provides a wave which deviates much from a pure sine-wave then the UPS for the rig would consider the output provided by the home-UPS faulty/distorted and reject it,which would mean that the UPS(for the rig) would go into the battery mode.Most of the good sine-wave home-UPS/inverters would have proper sine-wave production though.

You can buy a good UPS like APC 1.1kVA/660W,connect the PC to it and connect the UPS to wall socket/plug-point which is not a load-point for the home-UPS.
Alternatively you can get APC 700VA/420W UPS,connect the PC to it,connect the UPS to wall socket/plug-point which is not a load-point for the home-UPS and connect the monitor,speaker and other peripherals to an outlet(maybe to load-points of home-UPS) other than this UPS.Though APC 700VA should be able to take the load of your PC with some other peripherals but it might fail at full load i.e. it won't be able to provide back-up.
Else you can go for a more Wattage home-UPS.You would have to make calculations keeping in mind your PC,peripherals and what appliances you want to run with it.


----------



## anirbandd (Dec 20, 2012)

firstly, it is not recommended to run a ups on another ups, dunno why you were doing that. ups should run directly from mains. you could sell of both ups and go for a higher capacity home ups and run everything on that. 
secondly, its recommendable that a home ups be atleast 1.1kva, to support appliances runnning parallel in emergency cases, buts its okay to have a 600va ups.
thirdly, ups should support only the critical parts, ie, cpu and monitor. no need to connect modem, printer, speakers, but you may. only its back up time will fall.


----------



## topgear (Dec 21, 2012)

never connect a laser printer into a 600VA ! if the UPS is good it won't start and will give a overload warning !!


----------



## hitman4 (Dec 21, 2012)

reply to my pm abhi


----------

