# UPS required to power 850W system??



## razor2890 (Aug 3, 2012)

Hi...
I need to kno the basic req for a ups to support my 850W psu??
I have a UPS with O/P as 600VA
Many forums tell me that 600VA can only support 400W PSU...

But I/P of PSU is always 230V mains...& O/P is Watts??
So how does issue of wattage arise with UPS??


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## m4gicfour (Aug 3, 2012)

Ohms law.

VA is apparent power, it is sort of an "Ideal" number of Watts, without accounting for Power Factor and other efficiencies.

Basically, VA is how much power the device could supply if there was no resistance in the circuit (impossible), no capacitance issues, etc etc etc

In the electrical world, "Power" is a word meaning the amount of electrical work being done. 230V is a voltage (electrical pressure) not a measure of how much work it can do.

If you have a 600VA UPS, ohm's law tells us that it can supply about 2.61 Amperes (electrical flow) at 230V of electrical pressure. In order to find out Watts, you multiply the Voltage by the Amperage (V x A = W). I just did the reverse (600VA / 230V = 2.608....A)

Power supply wattage is measured at their output. So your 850W PSU running at, lets say an efficiency of 90% at full load would draw 930W from the wall if my math is correct.

Now, since 600VA is a fancy way of saying "a certain amount less than 600 watts", you can clearly see that your PSU will draw much more that what the UPS can provide if you ever get the PSU running at full load. 930W is a much bigger number than 600VA, and remember VA is simply the theoretical amount of Watts possible under ideal conditions.

If you aren't using your PSU at full load (if you aren't using all 850W of power) then it will be drawing less than its maximum, and the UPS *may* be able to provide enough power. This is still bad, because if you ever upgrade your computer and it *does* draw close to that 850W on the output (remember that means around 930W on the input of your PSU), then you would be overloading the UPS by 330W or to put it another way, you're running the UPS at more than 150% of its maximum. Hopefully the worst that would happen is that the UPS would have a circuit breaker or fuse inside that would turn off or burn out(respectively), and the UPS would turn off all power but nothing would be damaged; *hopefully*.


*Long story short, find a UPS rated for better than 900W if you want to ever be able to use your PSU at max capacity.*

For example: THIS would be more than enough to support your computer's power supply running at full load. How long the battery in the UPS would last before running out is a completely different matter. (there are probably better options; this is just an example)


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## LGV (Aug 3, 2012)

Short: if your system pull less then 400 watt from the WALL, then ok. if more then thet , not ok.
Personally I would leave some headroom tho. 10-20% min.
 not matter your PSU regarding this question.

Fill up your system specs
Get A watt mater for wall plugs to be accurate. 
Or simply upgrade your UPS what support 850 watt output .

m4gicfour beat me to it.
Anyway, like to add: 

your 400 watt UPS run 20 min if load 100watt (PC)
But just 2 min at full load.
So bigger better


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## m4gicfour (Aug 3, 2012)

LGV said:


> Short: if your system pull less then 400 watt from the WALL, then ok. if more then thet , not ok.
> Personally I would leave some headroom tho. 10-20% min.
> not matter your PSU regarding this question.
> 
> ...



NO.

The UPS needs to support MORE than 850W. 850W is how much DC power the power supply can provide, not how much AC power it needs from the input. (otherwise, you are correct)


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## LGV (Aug 3, 2012)

m4gicfour said:


> NO.




I want it to see a system what take 850 watt  

( I know may some of you have like 4 GPU system with 10 hdd, but come on.... )


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## FordGT90Concept (Aug 3, 2012)

1350VA: CyberPower CP1350PFCLCD UPS  1350VA / 810W  PFC co...
1500VA: CyberPower CP1500PFCLCD UPS  1500VA / 900W  PFC co...

Would not recommend less than 1350VA.


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## m4gicfour (Aug 3, 2012)

LGV said:


> I want it to see a system what take 850 watt
> 
> ( I know may some of you have like 4 GPU system with 10 hdd, but come on.... )



Irrellevant. 850W is the PSU's output power not its input draw. He asked for a UPS that can support his power supply's 850W output. That requires more than 850 from the UPS.

Telling to upgrade to an 850W  UPS is misleading and would offer a false sense of security. You could have just said to get a bigger UPS and not quoted the number, which would be less confusing to a layman. If he buys an 850W UPS knowing that it's not going to support the max output possible from his PSU, that's fine; even if 850W of UPS is an incredibly arbitrary number and has nothing to do with the requirements of the power supply. 

On the other hand, if he buys an 850W power supply thinking that it *will* support the max output possible from his PSU, and ever overloads it, he's going to be upset and rightly so. *Here's my main problem: By reccommending a UPS with the exact output of the PSU's output, you're not accounting for efficiency and the layman won't know to account for it unless he's told.*

I can easily draw near 500W from my UPS with just my PC attached, with dual cards, an SSD and one HDD. Add a monitor, a RAID array, and another two GPUs into that (or more powerful GPUs) and you get pretty close. If he plugs other things into it as well...


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## Kreij (Aug 3, 2012)

I think that several of the answers in this thread are correct even if they seem conflicting.

There are several questions that need to be considered when deciding on the level of power a UPS can deliver.
- How often (if ever) is the system drawing 100% of the UPSs rated power?
- How many devices is the UPS going to try to keep running? Computer, router, switches, modem, etc.
- How critical is it to keep the unit(s) running in the event of a power failure and for how long?

If you want the system and the devices connected to the UPS running for 5 to 10 minutes after a power fail, you probably want the UPS to deliver about twice the power consumed by the devices (50% load) at the time of failure. This time will vary with the quality of the UPS.

If you only need a minute of less (as in the case of a sudden, short drop of power) then you want a UPS that will provide the needed amount of power plus about 10%.

If you are trying to keep multiple devices up and running, it may be more prudent and cost effective to use 2 smaller UPSs than one large one.

If you plug non-essential devices (printer, speakers, etc.) into the UPS on outlets that use the battery along with your system you are asking for trouble.

Just some thoughts based on what I've experienced over the years.


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## m4gicfour (Aug 3, 2012)

I have a hard time getting to the point sometimes. Thanks Kreij. 

EDIT - although you seem to have made a couple typos involving UPS and PSU which would be confusing to OP.


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## Kreij (Aug 3, 2012)

Thanks m4gic, I think I corrected them. It's past my bedtime.


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## m4gicfour (Aug 3, 2012)

Typos are why 90% of my posts have "Last edited by m4gicfour at..." after them. I've conditioned myself to look for them since I make so many myself


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