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# Simple UPS question

Posted on 2004-10-19
Medium Priority
206 Views
Hi All,

I'm doing an experiment with an UPS and lightbulb ...

I have a 1000VA UPS and a 15watt energy saver light bulb. I would like to know how long 'theoretically' I can get it to run for.

Also if I connect 2 x 15W bulbs .. will it be exactly half the time ?

Txs

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Question by:Pete2003
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LVL 6

Expert Comment

ID: 12351038
If your UPS is 1000 va

1000/ 15 = 66.6 hours

likely  33.3 hour

2  15 watt bubs =  .5 x 33.3
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LVL 8

Expert Comment

ID: 12351095
Pete2003,

Remember, the rating of a UPS typically is using a fairly new set of batteries. If you are planning for operational requirements, be VERY conservative (at least a factor of 2, possibly more) in terms of your safety factor. Old batteries have lower performance than a fresh set of batteries.

I hope that the above is helpful.

- Bob (aka RLGSC)
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LVL 69

Expert Comment

ID: 12351102
You need the conversion factor of 0.7 to translate 1000VA into 700watts.  The run time can be calculated by looking at MikProg's answer (the accepted answer) here: http://www.experts-exchange.com/Hardware/Q_21045370.html
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Author Comment

ID: 12366813
33 hours seems a bit much gjohnson99
RLGSC, the UPS is fairly new
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LVL 69

Accepted Solution

Callandor earned 1200 total points
ID: 12368887
I just tried it and it worked.  Here's the gist.

MikProg said:

"Power consumption calculation is simple. Take a sum of numbers signed on  every power supplay in your servers. And calculate VA as reverse Callandor (thanks) formula. I.e.
(400+500+450+...)/0.7
It will garantee that maximum computer consumption does not affect your UPS. UPS will not crush, not burn out if power consumption larger than maximum allowed. Simply power quality will lower. It is really bad for your servers too.

Why VA is used for UPS instead of W for power supplay. UPS must hold power until servers becomes down. It is easyer to calulate time using VA. Example: UPS 2200 VA with 2 AH (amper-hour) capacity. 220 V out.

2200 VA / 220 V = 10 A

60 minutes * 2 AH / 10 A = 12 minutes  UPS will hold 10A power at 220 V

If power consumptions is less then 10 A for example 5 A time will be not 24 minutes but slightly more about 26-27 min.
Taking total servers power and down time as target you can calculate parameters of new UPS. Usually manufacturers are publish power in VA and offline work time. The parameters you really need is UPS VA and battary AH. Serious manufacturers are always publish them. The only thing you need is check if UPS maximum allowed current is less then possible consumption it is
UPSmac A > (400+500+450+...)/0.7/220 A"
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Author Comment

ID: 12369007
I'm not sure where you got the 60 minutes from ?

also where do you get the amp rating for the UPS ...

Here is the UPS link http://www.cellpower.com.tw/main3.html (the 1000VA UPS)

and the bulb is still a 220V (15Watt) energy saver light bulb
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LVL 69

Expert Comment

ID: 12372948
The 60 minutes is to convert from ampere-hours to ampere-minutes, and finally minutes.  You need to know the current capacity of your UPS (the example above is 2AH, but yours may be different); as MikProg said, the better models have this specification on the label.

Your calculation would be 1000VA / 220V = 4.545 amps, so whatever the current capacity is divided by 4.545 would give you the run time in hours at full power.  Multiply by 60 to get it in minutes; if using less current, your run time will be longer.
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