Votage or wattage meter

[jose]

Hello everyone,

I'm looking for a device to measure wattage or draw from a server.

I need to calculate the power requirements to size a ups.

Radio shack use to have a line voltage meter, but they don't sell that anymore. (so I'm told by the sales person)

Anyway, I'd like some that you could plug into a wall socket then plug the server into the meter and see how much wattage is being drawn..

FYI Here's my spec's if it matters:
2 -248's, 4 gigs memory,
10 - 15k 36g scsi drives plus tape & cdrom plus fans..

Thanks for the help.

Regards,
Jose

 

[imported_rod]

voltage would be whatever the wall outlet gives. either ~120V or ~240V, depending what country you are in.

If you cant find a device specifically to measure the power usage, you could try an AC clamp meter, but one of these will set you back $50-$100.

An easier way could just be to buy a UPS that can supply the maximum draw from your power-supply unit.

RoD

 

[jose]

I'll be using the 700w 45A Zippy psu.

I've called local electronics & electrical supply houses and they don't have any idea. I'll call them again to see how much an ac clamp meter would cost.

So I'm thinking a 1000VA Network APC ups would be sufficient, but we will also have an old Dell poweredge server plugged in also..

Thanks for the help

Regards,
Jose

 

[imported_Kensai]

APC Smart-UPS XL Modular 3000VA 120V Rackmount/Tower + (4)SUM48RMXLBP2U Battery Unit
You might be able to survive with less depending on the number of drives but you'll be limited by expansion.

APC Smart-UPS XL 2200VA 120V + (1)UXBP48 Battery Unit
Cheaper cost, but don't expect to plug anything but those two servers in as it won't have enough juice to power it.

Seasonic has a PowerAngel which displays how much power whatever is plugged into it is drawing.
http://www.seasonicusa.com/products.php?lineId=8

 

[jose]

Thanks everyone,

I just found a kilowatt meter for $40, it will measure the wattage/amp draw at the outlet.

http://www.safehomeproducts.com/shp2/sm/electricity_monitor.asp

I'll get this asap and see how much the servers draw..

thanks again

Regards,
Jose

 

[Mark R]

I'll just mention one thing to be careful of when you measure the servers' power draw, especially if you only want to leave a relatively small capacity margin.

UPSs generally have 2 ratings - one for VA (volt-amps) and one for W (Watts). The kill-a-watt meter will give you the W measurement, but you'll have to calculate the VA by multiplying A x V (it'll measure both for you).

You'll need to make sure that both the VA and W measurements are within the specs of the UPS.

Generally the manufacturer's spec their UPSs in VA - but the W rating can be quite a lot lower (as much as 40% lower). This is because historically computer equipment had a much higher VA demand than W. This is not necessarily the case with modern servers.

 

[volrath]

I don't get it. V*A=W.

 

[Zepper]

. V*A=W but only in DC. In AC that is Volt-Amps. In AC, Watts=(volt amps*Power Factor). In AC, Volt-Amps=Watts when driving a resistive load (PF=1). The Kill A Watt can display all three values (volt-amps, watts, Power Factor) and more. Here is a Review.
. You can get the same thing under the Seasonic name - it's called the Power Angel. Only the packaging is changed to protect the innocent...
. The Kill A Watt is cheapest on eBay and almost always cheaper than the Power Angel.

.bh.

 

[jose]

Update: So this is what I got to power:

2 - 248 opterons stock heatsinks
K8W w/ 4 - 1gig pc3200 sticks
LSI 320-2X raid contoller
Adaptec 29160
extra parallel card
Nvidia 5200 agp card
floppy
Nec 3520 dvd-rw
2 - dds4 scsi tape drives
8 - Fuj Mau 15K 36g hd's raid5
3 - 80mm fans
2 - 120mm fans (Stealth & Panaflow M1)
2 - SuperMicro Hotswap bays w/ fans

Just got my Kill A Watt meter and here's what I got:

Peak at startup: 459VA

Normal: 326VA, 322watts, 2.53amps, .98PF, 59.9Hz

So my system is only pulling 322 watts, that's not too much, I'd thought it would have be more w/ 8 scsi hd's..

What is the "PF" mean ? It shows (PF=W/Vrms Arms)

So anyone have an idea what size UPS to use ? Or how to size up the ups ?

I'd probably only need 15min runtime because I'll have the server monitor the ups and do a shutdown if the power goes off.

Thanks for the help.

Regards,
Jose


BTW Having 8 scsi hd's are real loud...... 65dbs @ 1ft from the front of the case...

 

[imported_Phil]

Is that figure with both processors maxed out and the same with the hard disks? Otherwise, that's just your idle load, which is not of much use if you're going to power servers that are actually doing something

BTW, why a DDS-4 and not an AIT drive?

 

[Navid]

Originally posted by: jose
What is the "PF" mean ? It shows (PF=W/Vrms Arms)

PF stands for Power Factor.
For Direct Current (DC), power (in Watts) is Voltage (in Volts) multiplied by current (in Amps).

For Alternating Current (AC), both current and voltage are sinusoids. A sinusoid has a phase. The voltage and current are in general not in phase.
The real power delivered to a load with an AC source is calculated as RMS Voltage multiplied by RMS current multiplied by the power factor, which is the Cosine of the phase difference between the current and the voltage.

In case of a resistive load, the current and the voltage are in phase. Then, the power factor is 1. Then, power is equal to RMS voltage multiplied by RMS current (since PF=1, you don't have to multiply VA by 1).

The larger the angle between the current and the voltage, the lower the power will be for the same voltage and current. Until you reach 90 degrees. This is a very large angle for the phase between current and voltage. Cosine of 90 degrees is 0. So, at 90 degrees, no matter how much current you draw, the real power delivered is 0!

This is why both VA and W (real power) are important figures to keep in mind when you buy a UPS.

 

[JackMDS]

Measuring the actual draw might be a mistake since it might widely vary while in real action.

The computer would not draw more than the Power supply rating. So consider the computer rated as the Power supply indicates.

Monitor, LCD, or any device would indicate the Wattage on the back sticker.

If it is not rated in Watt you would have to compute.

W= I x V I.e. if a unit is 110V (Volt) and it rated 5A (Ampere) the wattage is 550W

Some times you would see 550VA (Volt Ampere) which is the same as Watt.

So tally up the Wattage that the units are rated to draw and get an UPs unit.

:sun:

 

[Zepper]

In the case of a PSU with active PFC (power factor correction) like the Zippy, Watts are almost equal to Volt-Amps. My old, no PFC, PSU had a PF of about 0.6. A UPS of around 700VA should do you fine as you want a bit of headroom for the monitor and anything else you may want to have on battery backup - get more only if you need a longer hold up time. I usually plug my cordless phone system and answering machine into battery backup as well, so I can use them if the power goes out. You may have some other low power devices that would be useful to have backed up too.

.bh.

 

[Navid]

Originally posted by: JackMDS
W= I x V I.e. if a unit is 110V (Volt) and it rated 5A (Ampere) the wattage is 550W

Not true. You are missing the power factor!

 

[jose]

That's the idle load. I'll have to see what the load is when I finish installing & configuring the Linux box.
I figure a 1000VA APC unit will be fine. I'll monitor what the draw is when I do a recompile & reconfigure of the database.

The only problem I still have is those MAU drives are real loud and have a high pitch.

As far as the dds tape drives , we still need compatablity from our development machines and backup servers.. But most likely we'll get an AIT2 or AIT3 drive later.
We have one 5.25 bay left open on the stacker case..

As far as apps go, once completed we'll have a firewall, proxy, samba and a very large database running on this RH 4.0 Linux system.

Thanks everyone,

Regards,
Jose

 

[Zepper]

re. drive noise. Try isolating the hot swap cages from the case metal. Places like McMaster-Carr have special elastomer vibe damping bushings that can be modded into most cases. And there are a multitude of other ways. If you do isolate the cages, you may want to consider creating a solid ground from the cages to the chassis to be sure static energy is drained adequately. Probably not necessary but I like to dot all the i's and cross all the t's...

.bh.