Now you know what Kill-a-Watt does. Tried Amprobe? If your measurement is accurate, that means the PSU draws ~1 Ampere of AC current. If you care to calculate the Total Wattage of major componenta of your PC draw and compare it to the Kill-a-Watt reading keeping in mind efficiency of the PSU. How does it look?
When it comes to non-linear loads (ie - switching power supplies) - those kill-a-watt meters are crap at measuring the load correctly.
If this is a new build, then you probably aren't running the older Pentium Extreme edition 90 or 135 watt CPU's from circa 7 years ago, so I'd be surprised if your new build is using more than 200 watts.
9 sata drives?
What - are they all 250 gb?
If this is a server, then no need for a gaming video card.
The unique thing here is that you have 9 drives. Are they all active when you're doing your measurements? They probably draw 20watts or so each.
That kind of PC would ship with a 350 to 500w power supply, without all those drives. With it, I think you're sized about right. But, what's the difference? As long as it's big enough, which it obviously is, you're OK. The PC is only going to use whatever power it needs. Yeah, there is some small additional power penalty if you have an oversized supply, but it's not that much.
These new SATA drives are not that big a power hog. I would figure on less than 10w each. I had 5 on a compaq small FF desk top (2 mounted externally with the power cord coming out the back)
On Sunday 17 March 2013 21:36 Hench wrote in alt.home.repair:
That's not implausible *once everything's running**at idle conditions*.
Stick an ammeter inline with the mains feed if you want a double check the kill-a-watt. The power factor of modern computers is near as matters 1.0 so a straight forward amps RMS times supply volts RMS will give you the power.
However what you should probably do is to put some artifical load on the PC
- the easiest way is to run some benchmarking type software that thrashes the disks and runs the CPU cores flat out and measure during that.
Then you'll want to oversize anyway for startup (do all the disks spin up at once or do they have staged start?).
Ballpark 500W PSU is a fairly safe bet for your sort of rig. If you are a hardcore gamer and have a mental video card, that could add a bit. No harm in going to a slightly bigger PSU apart from cost but I'd feel failry happy with your sizing :)
It is a nice set-up and with 60 MBps from the ISP to boot. With all these fans running it sure feels like a wind tunnel under the desk.
I always thought the power supplies were the most inefficient (percentage of wasted power) at low power so I'm using a 750 watt supply to a PC that wants 130?
I get that 130 watt draw from Kill-a-watt, but have no way to tell how accurate that reading is at all. Personally I don't think it jives.
The video card spec sheet alone says it uses 100 watts and it has two fans on it by itself...
The theory is I could go for a lower watt rating power supply and get more efficiency during the idle times.
Fileserver and a gaming pc at the same time. I game, but three teevees and other assorted devices will pull multimedia/music from the pc.
I'm gonna try encoding some video files tonight to test the kill-a-watt. Then I'll try a couple of video games with the most intensive graphics options set to test the same meter and see what happens.
The power supply has to handle the peak loading that might occur and a Kill-A-Watt is just a cheap device that certainly is not intended for measuring non-linear waveforms such as those produced by switching power supplies. Almost every manufacturer of pc power supplies offers an online calculator.
Run your test while performing a GPU-intensive benchmarking application, one of the more recent ones. Do the same with prime95 (whatever version runs multicores).
On Monday 18 March 2013 01:58 Metspitzer wrote in alt.home.repair:
Fairly sure - at least for the EU.
I had a small computer room at a previous job - 200-odd servers talking around 70kW total. This particular room had an industrial meter wired into the main incoming 3 phase circuit. Meter showed PF, amps and volts. PF was
0.95
The CE approval (for the EU) requires a PF >= 0.95 for >=300W (lower soon, if it hasn't already). Given that most far eastern PC PSUs these days are wide input 100-240V so designed to ship anywhere, I'd be very surprised if there was much available in the US that did not conform - unless there are domestic PSU manufacturers and local regulation is not as strong?
I agree. There is a significant difference between peak power usage and idle. And I doubt the difference in power consumption having a somewhat oversize power supply is worth worrying about. There is some penalty, but I bet it's small. The fact that he's only measuring
I wouldn't be so sure about the Kill-a-Watt meter being incapable of measuring the power draw of a switching power supply. Measuring voltage and amps, multiplying the two, and doing it at a fast enough rate to get an accurate reading isn't a difficult thing. That function can be done in a fairly simple and cheap chip, it's nothing exotic. It's less complicated that what's done in other cheap, consumer electronics.
The original Kill-A-Watt is rated 0.2% basic accuracy, and one person who tested it against an old Simpson analog wattmeter said the two units gave identical readings. I believe the Simpson is rated 2% accuracy, but I don't know if that's 2% of the reading or 2% of full scale. Another person who built an adapter for reading watts from the wall outlet (Electronics Design magazine, maybe a Bob Pease column) said the same. Also I tried plugging a P-4400 Kill-A-Watt into another P-4400 Kill-A-Watt (different internal designs, despite same model number) and got readings that matched within 1-2 counts. However a person who writes reviews of PC power supplies said he doesn't give efficiency numbers because he doesn't think the Kill-A-Watt is quite accurate enough, but that may simply mean its accuracy is in the range of
1% to 2% while the rest of his other instruments are way better.
Apparently Kill-A-Watt type devices are really good at measuring nonlinear type waveforms because I got about the same watt numbers from a cheap backup power supply, whether it was plugged into the AC outlet and putting out real sine waves or running off battery and putting out stepped square waves.
The 90W - 130W readings you get are probably accurate, while power supply estimation worksheets can be way off. XbitLabs.com and SilentPCreview.com measured power consumption and found that few systems with only one video card ever consumed over 500W:
formatting link
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Even old 7200 RPM hard disks didn't consume more than 9W while spinning, maybe 15-20W while seeking. Here's what some contemporary drives consume:
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