How many watts do you really need?

Here is a thread for you...some electrical engineers can't figure it out, because they don't know the circuitry of the Kill-A-watt link

I don't think it really matters why the kill-a-watt can be inaccurate sometimes, it only matters that it is inaccurate sometimes. For Joe consumer, who doesn't have an expensive load test, which tells exactly what load it is putting on the PSU, or a very expensive ammeter to know how much current is actually flowing, they are not going to know whether or not the kill-a-watt is being accurate. Also, different power supplies will effect the Kill-a-watt in different ways...not to mention how clean your mains power is. Jonny found the kill-a-watt to be utterly useless for the Seventeam ST-1200-EF and OK Wolf found it to be utterly useless when testing the Enermax Galaxy Evo.
 
blivit4 said:
Danny - Your point would have been better served if your reference was to that entire thread which not only provides a context, but also some other useful posts.

Within that thread Paul makes no assertion that the inaccuracy of the Kill-a-Watt is due to APFC. In fact, his example refers to a PS with 62% efficincy that almost certainly didn't have APFC. If if a Kill-a-Watt isn't all that accurate, JonnyGuru still thinks it can be useful for sizing power supplies (post #14 in that thread).

Back on point: this current thread makes mention of efficiency and effects of APFC. A Kill-a-Watt makes no efficiency measurement. There is nothing in that other thread that connects APFC to inaccurate power measurements. Unless someone here can reference some valid data linking APFC and Kill-a-Watt inaccuracies, I'll just be of the opinion that the Kill-a-Watt isn't real precise, but useful anyway.
Click to expand...

No a Kill-A-Watt is useless without knowing your DC load. Repeatedly we (myself, Jon, and Oklohoma_wolf) have had problems with them and have stopped using them because it got to the point where a Kill-A-Watt would not read the AC power draw on units with APFC correctly 9/10 times.
 
M4573R said:
If I got a whole new system here's what I planned out:

i7 920
3x2gigs ddr3 1600
3 WD 640GB caviar blacks
gtx285 ssc
1 dvd drive & 1 dvd burner
My left over x-fi extreme gamer
case with 6 120mm fans
Click to expand...

I have built about 9 computers very similar to this and Used the PC Power and Cooling Silencer 750 in them. all without an issue. Specs for the ones i built below.

i7 940
2gbx6 ddr3
640gb wd caviar black
GTX285
LG DVD burner
A couple of them have x-fi's in them

I have always been a fan of the PC Power and Cooling Silencer 750 so went with that. but for the setup, 750 watts is plenty for your rig.
 
I have a PC Power and Cooling 1KW SR that shuts down every now and then when SLI gaming under Crysis. I have to RMA it eventually but I don't play that game much anyhow. So I don't think name brands mean much. Though I just order their 1200 Watt ESA version this morning as I don't think you can ever have enough amps...
 
NichoTL said:
Hmm it only proves the Kill-A-Watts problem. How can I tell if my power meter (different maker, different country, different everything) works the same?
Click to expand...

TBH, not too sure. But AFAIK, most power meters under $150 or so are not that accurate.

NichoTL said:
I'm not trying to be funny or anything, but check this on Tom's
http://www.tomshardware.com/reviews/geforce-gtx-285,2139-9.html
And that's with an overclocked 920. That's pretty consistent with my results, don't you think?
Click to expand...

Unfortunately that review doesn't tell us what device they used to measure the power draw. It could be a Kill-A-Watt for all we know.
 
when i was building... i was constantly pushed towards the corsair modular 620..... glad they did... see sig for gaming rig...
runs great.... and the other day I had 4 sata drives and 3 ide drives in it.. consolidating files..... and cleaning up drives...never had a power issue....
 
NichoTL said:
I don't need accurate. I just need meaningful. A 5% margin of error doesn't make a difference.
Click to expand...

Unfortunately, AFAIK, that's no device under $150 that's even meaningful within a 5% or even 15% margin of error.
 
NichoTL said:
I'm not trying to be funny or anything, but check this on Tom's
http://www.tomshardware.com/reviews/geforce-gtx-285,2139-9.html
And that's with an overclocked 920. That's pretty consistent with my results, don't you think?
Click to expand...
No testing methodology is listed for how they measure their power draw, and I would bet that they use something like a Kill-A-Watt as well. Just as a bit of general advice, I would recommend that you take anything from Tom's Hardware with a big grain of salt.

I won't deny that it's possible your power draw numbers are accurate. I'm just saying that it isn't really possible to tell one way or the other.
 
You will need around a 650 to be safe,as 500 would most likely do,but consider the load and heat drop stick with atleast a 650 or 700 watts.900 or better if by chance you think of adding extra harddrives and another videocard down the line.
 
I just ran prime95 on my quad Opteron workstation and was surprised by the results. 389w AC load was as high as it went. That's with a 1kw PC P&C, 4 x 8347 Opterons, and a single hard drive. No video card or anything else (apart from some fans). Mind you, this was tested via a UPS, however, it is a rather high end on-line UPS (link), so I imagine it would be more accurate than most. Once you consider AC to DC conversion, it isn't so bad considering that the system has four quad core processors.
 
Blue Fox said:
Mind you, this was tested via a UPS, however, it is a rather high end on-line UPS (link), so I imagine it would be more accurate than most.
Click to expand...

According to the PSU editor here:
Paul_Johnson said:
1) APFC can fool Kill-A-Watts into giving you abnormally low readings (some times giving better than 100% efficiency)

The power meters in UPS software are just as bad. You have to spend some change before you get anywhere near an accurate power meter when your PSU has APFC.
Click to expand...
 
Yeah, I know that much. I just imagine that an on-line UPS would be more accurate than a standby one due to the design differences. I don't have anything better to test with, so that's about as good of a measurement as I'm going to get. I'm also not using any software to test that. The UPS has an ethernet port and runs its own web server (or telnet/console connection if you prefer), though I'm not sure if that makes it any better either. It does report apparent and real power however, so does that help?
 
I was looking at the linked post from Paul_Johnson and I couldn't figure out what was bothering me:
Maybe on the instruments he was using one could read the phase between voltage and current at the source, because without it you can't do a proper power calculation. Current measured * 120V does not equal power if the V and I are not in phase.
The formula is: I*V*Cos(phase)=Power because we are talking averages over the length of a cycle.
Sorry but maybe this has been talked about before.
 
NichoTL said:
I was looking at the linked post from Paul_Johnson and I couldn't figure out what was bothering me:
Maybe on the instruments he was using one could read the phase between voltage and current at the source, because without it you can't do a proper power calculation. Current measured * 120V does not equal power if the V and I are not in phase.
The formula is: I*V*Cos(phase)=Power because we are talking averages over the length of a cycle.
Sorry but maybe this has been talked about before.
Click to expand...

And what exactly do you think the Extech and Brand do in order to get their numbers? As has been discussed before the only reason in that picture you see current instead of power is because the load tester, and brand both cycle their information output and that was the only timed photo I could snag with all three and relevant information.

Kill-A-Watt's are $20 for a reason.
 
Paul_Johnson said:
And what exactly do you think the Extech and Brand do in order to get their numbers? As has been discussed before the only reason in that picture you see current instead of power is because the load tester, and brand both cycle their information output and that was the only timed photo I could snag with all three and relevant information.

Kill-A-Watt's are $20 for a reason.
Click to expand...

I never presumed that the information was wrong. I'm just saying that you subtitled it by saying 2.94*120=xxxW which is wrong if the phase is not 0. 2.94A is right. 120V is right. But 352W COULD be wrong (I don't have the phase, but I'd be surprised if it was 0). Obviously when the Brand cycles its display it will show the right number for wattage.
 
You must log in or register to reply here.
Back
Top