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PSU question

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December 30, 2010 12:51:04 PM

I ordered parts and it seems that my build will be very close to exceeding the wattage on my PSU (older psu that hasnt been used much). I want to know what happens if the computer demands more watts than the psu can supply. can it damage parts in the computer from the lack of power? or does it turn off/cause a error and fail like if you pressed the power button.

im going to order a new psu when i can but i want to know if i can try to see if i can use my graphics card while i wait to get money instead of using onboard video

CPU: AMD Phenom II X4 965 Black Edition (normal 3.4ghz clock)
RAM: G.SKILL Ripjaws Series 4GB (2 x 2GB) DDR3 SDRAM 1333 (PC3 10666)
MB: GIGABYTE GA-890GPA-UD3H AM3 AMD 890GX
GPU:MSI nVidia n260GTX (needs 136 watts at max
PSU:Vantec VAN-420A 420w (+ 3.3v 26A, +5v 42A, +12v 18a)
HD: 250gb 7200rpm mediamax

possibly a dvd-rom drive

Mouse: Razor Deathadder
Keyboard: normal



More about : psu question

a b B Homebuilt system
December 30, 2010 1:16:45 PM

It will be really close on your current PSU. Both your CPU and your GPU get all their power from the 12V rail, your PSU only has 215W available on its 12V rail, ~100W for your CPU, ~120W for the GPU and you are out of power there without the fans, or other motherboard components counted yet, i wouldnt try it.

If you try to draw more from a PSU than it can supply you have a couple options. One, the OCP or OPP kicks in and shuts down the PSU and the system, two, it does its best and keeps plugging away but may die a silent death, or three, it tries to do it, but over heats and suffers a failure, the result of the failure varies greatly, sometimes it just dies silently, sometimes it makes a pop and lets out some magic smoke, but sometimes it will make a pop and let out the magic smoke on some other component in your system.
a c 84 B Homebuilt system
December 30, 2010 1:26:32 PM

Here's the thing about the power a computer needs: it's not static. The wattage requirements fluctuate based on what you're running. The maximum numbers you're seeing is if you're running the card at full blast all the time. GPUs (and CPUs) rarely run at 100% load, and they certainly won't stay there. If you look at the "Peak 2D" numbers, that's more typical of what you'd be running normally. If you're not doing anything, all the parts will be Idle, using a lot less power. This is close to the normal state of the PC when you're just entering Windows, or doing very light tasks like browsing the web.

Now for the second part of the equation: the maximum wattage a PSU can provide. Generally, the wattage stated (in your case, 420W) is not what the PSU can actually do. Higher quality PSUs (like Corsairs, Antecs, Silverstones, SeaSonics, and XFXs) are able to provide a lot more power than what's stated. Lower quality PSUs (like yours) often provide less. What this means most of the time is that the higher quality PSUs run at better efficiencies than what's stated when they're under heavy load. It also means that lower quality PSUs have a lower ceiling than what is indicated.

Now here's where things get really hairy for you. That PSU is an absolute POS. It's rated efficiency is under 70%. That means it's more likely to be providing a lot less than the 420W. Even more problematic is that it doesn't have Active PFC.

To answer your original question about what happens when your PC wants more power than what your PSU can give it, nothing really. The active process that's stressing the parts will tell the hardware that it needs more power, the hardware will try to draw that from the PSU, and it won't get it. So the hardware won't speed up, and the process will either crash or run really slow. The biggest issue is that the PSU will be running at 100% load. Your efficiency will tank (the power bill goes up), and the PSU gets put under enormous prolonged stress. It will fail sooner rather than later, which is where you have a major problem. Due to the fact that the PSU is an absolute POS, when it fails, it will likely take other parts with it. The most likely candidates are the GPU, motherboard and CPU, which happen to be the most expensive parts of a build.

What all of this means is that I wouldn't trust that PSU to run a lightbulb, much less a PC. Get a new one ASAP. Make sure it's a quality one. I know Antec's PSUs are really cheap right now (their 650W Earthwatt unit is $50 after promo and rebate).
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December 30, 2010 1:45:11 PM

is there a way to reduce the ammount of power my cpu and take? like run at 60% or something? very detailed answer above, tyz

also ill probably upgrade to a 460 gtx or something better or something with crossfire, what psu do you suggest? tyz
December 30, 2010 2:24:44 PM

I'm also having a similar issue dealing with the PSU. Currently I've put together an HTPC for the family room with Windows 7 professional and don't have the right amount of connectors coming from the PSU to the motherboard. I'm using the GIGABYTE GA-MA785GM-US2H Motherboard and the SeaSonic SS-300TFX 300W PSU together. Everything fits nicely except when I connect the power pins to the motherboard. The PSU offers both a 24 pin and 4 pin connector to power the CPU (AMD Athlon II X2 255 Regor 3.1GHz) and rest of the PC. However, the issue I'm having is that instead of a 4 pin connector I need 8 pins.

My question is will I be able to run just 4 pins in the 8 pin connector without any issues? I'd like to know because the case I have is very small and adding more cables to the inside is going to be very difficult. I've already ran the system for 24 hours and have seen no instability (while installing the OS and other software). As far as I know both connectors are on two separate rails so they can supply enough power and the other 4 unused pins are just a "ground".

With all the research I've done on this issue I'd really like to get a few opinions here because I'm getting half of the people saying don't do it because it will burn out the pins, melt them, whatever, and the other half saying that I shouldn't have any issues.

Finally, you should know that I can't get another PSU, case or anything. I want to know if the voltage supplied from the PSU to the 8 pins (through 4 pins) will continue to work all the time without issues. Below are full system specs.

--System Specs--

GIGABYTE GA-MA785GM-US2H (using on-board graphics and sound)
AMD Athlon II X2 255 Regor 3.1GHz
SeaSonic SS-300TFX 300W PSU
Hauppauge 2250
Rosewill RNX-G300LX IEEE 802.11b/g PCI Wireless Card
Lite-On 4x Blu-ray Drive
Western Digital 500GB Green Drive
G.Skill 2GB (2, 1GB Sticks)
hec Black 0.7mm Thickness SECC Steel 7K09BBA30FNRX Micro ATX Media Center 300W Power Supply / HTPC Case
Windows 7 Professional x86
a c 84 B Homebuilt system
December 30, 2010 2:54:26 PM

@bubba: Make you're own thread. Don't hijack.

@Goko: You can underclock the CPU and GPU. That would make them use less power, but also slow them down considerably. I don't know a whole lot about the process, simply because it's not very common. I'm sure you can find some guides if you Google it. I would advise just waiting until you get a new PSU.

If you do get a GTX 460, the same PSUs would be recommended. A 450W from Antec, Corsair, Silverstone or SeaSonic if you don't want to be able to SLI, a 650W from the same companies plus XFX (the smallest they make is 650W, I think) if you do. A 650W would be enough to handle dual 460s, dual HD 5850s, dual 6850s, and really any single card except the GTX 480.
December 30, 2010 6:54:00 PM

so if i wanted a gtx 480 i'd have to get 700-800 watt? i saw a cool single rail 650watt but i'd probably need more? i might just order a decent one for around 50-70$ for my gtx 260/maybe 460

i know how to under and overclock but and is there a program you can use to read how much watts your processor is taking under full load same for gpu? i dont mind if it turns out to be a 2.8ghz quad core if it's stable for now (965be amd 3.4ghz) - also will i need to manually adjust the voltage for different speeds like ram? this is my first actual build so any info is good

Best solution

a c 84 B Homebuilt system
December 30, 2010 6:59:16 PM
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The 480 is a massive power sucker. It's advisable to avoid it altogether. I'd rather have the HD 6950.

The voltage is what determines the wattage. I'm sure there are programs that monitor the power usage, but I don't know of any off the top of my head. As for it being stable, I don't think undervolting would cause any instability. It's not like you're trying to push the CPU to do something it isn't supposed to, you're just limiting it's functionality.
December 30, 2010 7:05:31 PM

MadAdmiral said:
The 480 is a massive power sucker. It's advisable to avoid it altogether. I'd rather have the HD 6950.

The voltage is what determines the wattage. I'm sure there are programs that monitor the power usage, but I don't know of any off the top of my head. As for it being stable, I don't think undervolting would cause any instability. It's not like you're trying to push the CPU to do something it isn't supposed to, you're just limiting it's functionality.


ya my dads laptop - what im using now - has a "power saving" battery option or hp recommended or high performance and one of the differances is it lets the cpu use 5%-100% power, so ill have to get something like that to manually set my cpu to 50% power it's about 12.45w and cant go above right now and the max is about 24.5%, if anyone knows of something that can do this for the desktop or point me in a direction of doing this in bios or software specifically for the cpu
a b B Homebuilt system
December 30, 2010 7:08:36 PM

You can download motherboard monitor http://majorgeeks.com/Motherboard_Monitor_d311.html which can be downloaded there will show you all kinds of info on your parts and is a great heads up way to check and make sure stuff isn't going to blow on your build. Also http://www.msi.com/index.php?func=power check out the calculator here and plus in what you have hooked up. It'll give you a good idea of the power you are going to need. I'd try to leave yourself about 25 to 30 percent in spare power above and beyond what it suggests too. That way you don't get any surprises. If you PSU dies under strain it can wipe out several of the other components. Blue/ green smoke upon death can be a sign it cooked your motherboard in the process.
a b B Homebuilt system
December 30, 2010 7:19:45 PM

Goko said:
so if i wanted a gtx 480 i'd have to get 700-800 watt? i saw a cool single rail 650watt but i'd probably need more? i might just order a decent one for around 50-70$ for my gtx 260/maybe 460

i know how to under and overclock but and is there a program you can use to read how much watts your processor is taking under full load same for gpu? i dont mind if it turns out to be a 2.8ghz quad core if it's stable for now (965be amd 3.4ghz) - also will i need to manually adjust the voltage for different speeds like ram? this is my first actual build so any info is good


For a single GPU, any decent 650 watter will suffice....for twin GFX, an 850 watter should handle all but the most demanding cards. You can measure power used with the Kill-o-watt

http://www.degreedays.net/kill-a-watt-meter

I'd recommend the 570 over the 6970 and a decent 650 watter. The cost savings isn't great to go smaller and remember that PSU's are most efficient at 50% load.

http://benchmarkreviews.com/index.php?option=com_conten...

Quote:
Overall, the graphics frame rate performance has the AMD Radeon HD 6970 matched nicely to the GeForce GTX 570. Measured at stock (reference) speeds in ten different tests, the Radeon HD 6970 was either slightly ahead in half of them or deeply trailed in the other half. We've excluded HAWX 2 from this review, until AMD drivers can compensate for the performance skew. The DirectX 10 tests seemed to really score the GeForce GTX 570 way ahead, while many of the DirectX 11 tests pulled the Radeon HD 6970 ahead by a few FPS:


The 470 has now dropped below $200 with specials on newegg which makes it a great buy also.

Here's an OC'd 570 for $350
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

And a 470 FOR $209
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

And $50 FOR AN Antec EA-650
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
a c 84 B Homebuilt system
December 30, 2010 7:24:24 PM

^Except that a 470 uses power like crazy. I wouldn't trust a 650W to run it comfortably.

Besides, the OP wasn't asking about what GPU to buy, just if the GPU already owned would work with the PSU owned.
December 30, 2010 7:33:21 PM

ya ill run it on the crappy psu with onboard video, then ill either wait till the psu or if i find something to limit my cpu to a % of power, and i know how to underclock my 260 gtx.. thanx for the links and the motherboard app and looking into graphics cards except that's in the future :p . ty all i found the answer
December 30, 2010 7:34:46 PM

Best answer selected by Goko.
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