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# How to calculate KVA ?

Posted on 2011-05-12
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Hi all,

I am looking into co-locating my servers into a data center.
The data centers are putting a cap on my power usage to about 3.0 to 5.0 KVA.

So now i need to calculate my stack's power usage and convert it to KVA units.

I am currently planning to move:

4 X Dell Power-edge 1950 (Rated at 670Watts each)
2 X Dell Power-edge 2950 (Rated at 750Watts each)
2 X Barracuda Firewall 460 (Rated at 336 Watts each)
2 X Cisco ASA 5510 Security Plus (Rated at 170 Watts Each)

Any idea how do i calculate the KVA for the above scenario?

I am currently offered 3.0 KVA for the rack is it enough?

This is my first time dealing with data center providers so please be patient if i am misunderstanding anything.

Thanks!,

Jack
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Question by:jaglin84
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ID: 35745446
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ID: 35745471
i think 3 KVA will not be sufficient, i don't no what UPS offered to you but i think you should have more then 5KVA UPS + Extra battery.

UPS should provide you backup of minimum 50-60 minutes on full load, you can try here as well.
once you have estimated load take mouse to graph and check load & time,

http://www.apc.com/resource/include/techspec_index.cfm?base_sku=SURT6000XLI&ISOCountryCode=bh

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Author Comment

ID: 35745535
Hi Syed,

Thanks for the reply. I tried the link you sent so what i converted was 5.19 KW to 6.4875 KVA. Is my calculation correct?

what i basically did was just add the watts all together divide by 1000 and which came up to 5.19 KW.

Punched those numbers into the converter and it came up with 6.4875 KVA

Thanks!
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Syed_M_Usman earned 252 total points
ID: 35745573
i also calculated the watts its coming almost near 3000.

the difference is 2x750 watts mean, 1 active one passive. you will see power and power supply will be redundant but passive stat.
so where you have 2 supply you try calculating one.

apart from above Dell server will consume more power + require more cooling in case of Ac/Split absent sue to power shortage.
if all above devices are in a same DATA Center and racked in a single rack and you have budget i suggest you order minimum 10KVA UPS, with SMS notification system capabilities (i am using APC).

10KVA will give you 6 Heavy duty outputs + you can add more batteries in future. SMS device allows you alerts in case of any power trip.

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andyalder earned 500 total points
ID: 35745705
You really can't just add up the PSUs ratings and say that that is what they draw, a PSU rated at 500W may only be taking 250W.

Go to http://www.apc.com/tools/ups_selector/index.cfm and select configure by device - you'll see your PoowerEdge 2950 is probably only taking 450W rathe than 750. You don't have to buy a UPS from APC of course but the calculation's still right.

You also don't add the power taken by redundant PSUs together since they're not both supplying the full power required, normally they're providing half the power each.
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ID: 35748999
i agree with andyale, thats why i told its almost 3000, nearly 2.5KVA and thays why some one offered you 3KVA.

i fordwared apc link as i was using, you can select any brand you like.

why i reomended you 10KVA, or minimum 5KVA because this will give you more backup time and feature upgrades.

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Expert Comment

ID: 35749097
The cap is for power draw.  A 5KVA rating is the max current, not the reserve time of batteries.

You can have 5KVA power with no backup...or with 5 days of diesel generator backup.

If you ask for 5KVA, this should spec the wiring, circuit, and help them do capacity planning.

For instance, if they already have 100 customers with 5KVA requirements, and their SLA includes X minutes on battery and Y hours on generator...then they'll need to buy more equipment if customers start upgrading to 10KVA each.

Current is measured in Amps.  Battery capacity is measured in Amp-hours.

Maybe I'm misunderstanding.  But asking for (and paying for) a 10KVA supply when you're only using 2.5KVA isn't going to let your servers run longer.  It will increase you monthly spend.
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andyalder earned 500 total points
ID: 35749212
I don't think they're actually buying a UPS, it says it's in a co-lo centre so the UPS is probably a humongous datacenter one. It is important to minimise what you tell the provider as you say they would have to pay more if they say it takes more power than it actually does.
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Assisted Solution

aleghart earned 248 total points
ID: 35749301
^ that's my point.  I installed a 60-amp 240V 3-ph panel for equipment, HVAC, and miscellaneous circuits.  Everything but the supplemental HVAC is covered in a Watt/sq.ft. formula in the existing contract.

So, we agreed to put a meter on the circuit for the HVAC _only_ to monitor usage.  If we had just asked for 60A of 3ph power, we would be paying a ton of extra money every month.  Instead, we have a meter to show only the additional.

No sense throwing away money.
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Author Closing Comment

ID: 35751497
Hi all thanks for the input!

That really cleared alot of things up for me!

Those links you gave were really helpful now i have a better idea on how to get the right power plans from the co location providers

Thanks!
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