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I am trying to find out the UPS capacity in amp-hours for my HP UPS system. I've already done some calculations based on the UPS information from the HP Power Manager software.

HP UPS Parametars

Bellow are my calculations but somehow I doubt them and I think I am making a mistake somewhere:

Output Power: 1160W
Output Voltage: 235V
Run time remaining: 12min - Converted to hours that is 0.2h

First I am converting the W to A:
1160W / 235V = 4.936A

Now to find the amp-hours for 12min that are specified in the run time remaining:

4.936A * 0.2h = 0.987Ah

Can someone more experienced in batteries, current and UPS Systems tell me if my calculations are correct?

I am not sure that I have taken the correct values into consideration since my calculations are based upon the output values from the UPS.
Also as a side note I must tell you that I am not very fond of current and all that stuff and I have only basic knowledge about amps, volts and watts from college.

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closed as too localized by Qmechanic, David Z Oct 21 '12 at 9:47

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1 Answer 1

up vote 2 down vote accepted

You have a typo that the Amperes output is 4.936, but that is corrected later on. You also slipped a decimal when you did 4.936 * 0.2, which should give 0.9872. The battery is at 130V, so the current out of the battery is $\frac {235}{130}\cdot 4.936=8.922$ and it is really a little higher for the losses in the conversion. Let's say it is 9A out of the battery. Then you would have 1.8 A-hr in the battery to run for 12 minutes. I don't see where it says you can in fact run for an hour, so it looks to me like about 1.8 A-hr. If you can run for an hour, it would be 9 A-hr.

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Thanks Ross. I've corrected my calculations above. So I guess based on your calculations, I must first find the current out of the battery and then find the Amp-hours out of that current. This really helped me a lot :) –  Spirit Oct 21 '12 at 9:24

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