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# Server Power usage - Watts to Amps

Posted on 2013-11-08
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I have a rack of servers which I am trying to consolidate. I have an APC meter which is not configured, but it does give us a amp reading.

Anyhow, I was looking at the Hp specs and it seems like my most powerful server (DL380 G4) uses 575 WATTS. I tried to convert this to amps using several calculators i found via search engines..but i don't trust the output of the calculators - or maybe my math is not correct.

How can I calculate how much amperage my servers are using based on Hp specs sheets?

although I have an apc meter, at the moment I cannot configure this in order to read exact readings due to the fact that I am far away from my data center.

Specification
Power Supply

575 Watt, CE Mark Compliant
Rated Input Voltage

100-132 VAC, 200-240 VAC
Rated Input Current

7.5A (100VAC), 3.8A (200VAC)
Rated Input Frequency

50 to 60 Hz
Rated Input Power

735 W

575W
Maximum Peak Power

575W
Operational Input Voltage Range (Vrms)

90 - 264
Frequency Range (Nominal) (Hz)

47 - 63 (50/60)
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thx
t
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Question by:tobe1424

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Expert Comment

ID: 39634068
Ampere times Volts will give you the Watts. Normally though Watts are only used for DC type current. For AC type current you use VA (Volt Ampere), but also here it's the same equation.
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Author Comment

ID: 39634108
Based on the specs in my first post, would i be able to figure out the ampere?

thx
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LVL 32

Accepted Solution

_ earned 1000 total points
ID: 39634167
Not really.
You can get the Maximum by dividing the Watts by the Voltage (which looks like the AC amps is already posted).

The only way to really get the Actual draw, is with a meter.

Specification

Power Supply
575 Watt, CE Mark Compliant

Rated Input Voltage
100-132 VAC, 200-240 VAC

Rated Input Current
7.5A (100VAC), 3.8A (200VAC)

Rated Input Frequency
50 to 60 Hz

Rated Input Power
735 W

575W

Maximum Peak Power
575W

Operational Input Voltage Range (Vrms)
90 - 264

Frequency Range (Nominal) (Hz)
47 - 63 (50/60)
0

Author Comment

ID: 39634208
ahhh...so the  7.5A rating is theoretically the MAX ampere the server could possibly draw?

I see how the meter would help with specifics. My APC meter states we are consuming about 23 amps. I have about 10 servers + network equipment on my 42U rack.

I assume when the servers power up, more amp is drawn..

thx
0

LVL 84

Assisted Solution

Dave Baldwin earned 1000 total points
ID: 39634209
According to the specs you have posted, that computer uses 735W to produce 575W internally.  Your electrical load is the 735W.  The difference is because power supplies are not 100% efficient.  The Rated Input Current that coral highlighted is what you need to be able to provide.
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LVL 57

Expert Comment

ID: 39634662
You cannot use the PSUs ratings to determine the power that the server will use since it's rated far higher than is needed in most configurations. What you have to do instead is use HP's (or APCs) power calculator. HP's calculators seem to have been highjacked by the G8 marketing team but APCs UPS selector ought to work still.
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Author Comment

ID: 39634810
thanks much for the help.

I have all my servers on apc pdu's (ap7801) . they have a visual amp reading. i guess i can remote into these and see the power rating on each exact port?
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LVL 32

Expert Comment

ID: 39634946
I'm not familiar with the 7801's, but I'm going with a tentative yes.

Just remember, you are dealing with 2 sets of current.
The AC coming in from the wall (through the UPS and into the computers power supply). This will usually have "high" volts and "low" amps.

Then there's the DC the computers uses internally, coming out of the power supply. This is usually "low" volts, and "high" amps.

Be careful not to get the numbers mixed up.   ; )

>> I assume when the servers power up, more amp is drawn...

Correct, but usually for less than a minute. Once all the HDDs, ram, video, etc, get 'up to speed', it should drop back down.
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Expert Comment

ID: 39661317
Thank you much.     : )
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