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Underated psu, Can I make it work?

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November 19, 2010 8:39:37 PM

I'm having a little trouble understanding how amps work and trying to run a gtx 275 off a underrated psu so this is a question for the electrical junkies with more skills than dollar bills.. Is the amps and wattage on a power supply the max amps it can put out or just at average expected load? can I lower power to other things and increase the amps or watts available to another to make it run safely?

I have a 500w antec basiq psu, I think the max of both rails is 27 amp and I have a gtx 275 i got dirt cheap I'd like to install. the gtx draws 177-251w based off test on toms and nvidia recommends 40a but I think 36 would do fine, I would like to overvolt and clock this card If I have any watts to spare. my last card 8600GTS I covered in wires, heatsinks and resistors and moved it up 44 ranks on pcmark lol (which is for sale btw)

Here are the only things that will be running on the basiqm all fans from gpu to cpu and case will run off a alternate psu. I'm scared to run anything sharing circuits like drives, mobo, cpu or vga off multiple psu's because they are all connected for data transfer and while it may run (i've done it on crap rigs for fun) I don't know if it will risk damage.

Pentium D 950 3.4ghz. I think its rated between 95-105w depending on the exact sub model.

seagate sata 2.0 7200rpm barracuda 250gb (not sure, i've heard 10w but have had trouble confirming this)

Gtx 275 177-251w

2.5gb 667 ram (2 sticks)

intel 845 or 915 board.. pretty basic onboard ethernet is used on it and 3 usb devices, I can make a self powered hub for these If I have to I think. (illuminated led keyboard, wireless mouse, ps2 dual shock adapter) I don't think they use much though.
a b ) Power supply
November 19, 2010 9:31:04 PM

Hi tetsusaiga, Welcome to THW.

First, the rated amps and volts are the max the PSU is rated for and are not to be exceeded. You cannot lower power to parts unless maybe you underclock your CPU of GPU and I doubt you want to do that, the parts draw what they need and no more or less, the only way to reduce power is to remove parts. Is this the PSU you have: Antec Basiq BP500U 500W ? If so this is the power output of that PSU:

Output +3.3V@30A, +5V@30A, +12V1@18A, +12V2@18A, -12V@0.8A, +5VSB@2.5A

If you have not already you can put your system into a PSU Calc and see what it recommends for your PC and that number will give you an idea of where you are at. On the other hand this Calc: http://www.raptoxx.com/calculator.php, is much more thorough and will recoomend how many amps you want to have available

If you were to ask me of the top of my head, I would say that your current PSU will be just fine. You have 18amps on 2 rails thats 432w of power (watts = amps x volts) that will give you about ~200w for the rest of your PC which is plenty. And really there should be no harm in trying it out as the features of the basic500w are:

Built-in Industrial-grade protection circuitry prevents damage resulting from short circuits,
power overloads, and over voltage

The number that Nvidia recommends is made to give you headroom in the first place to avoid any chance of trouble and take into account that cheap/no name brand PSU's rarely if ever provide the power listed in thier specs.
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a c 144 ) Power supply
November 19, 2010 9:33:43 PM

tetsusaiga said:
Is the amps and wattage on a power supply the max amps it can put out or just at average expected load?

It depends. Some PSU's are very conservatively rated and can produce as much as 20% more power than their rating. Corsair comes to mind. Others will destroy themselves trying to produce their rated power.

tetsusaiga said:
can I lower power to other things and increase the amps or watts available to another to make it run safely?

No. The only way to decrease the amount of power a component needs is just not to use it.

Now, in your case, the 500 watt Basiq is actually a pretty good PSU.
http://www.hardwaresecrets.com/article/792

Total 12 volt capacity is 36 amps. Your PSU is powerful enough to run your system with your new video card. In fact, I estimate that your system will pull about 350 watts from your PSU.
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Related resources
November 19, 2010 10:19:03 PM

by lowering power consumption i mean using an alternate psu to run all fans independently.

I did the raptor x calc without the fans, just mobo, cpu, vga, hd and usb devices and it told me 2 things that stand out.

Typical gaming 12va draw 21.9 A. If this exceeds 18A, a dual 12V rail psu probably won’t work - psu will shut down while gaming. The only solution is to buy a non dual 12V rail psu*

actual power consumption when gaming 383 W 30.6 A

it recommended that I have 605 W / 1008 VA

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a b ) Power supply
November 19, 2010 10:28:39 PM



To answer your question, its generally max, but you can exceed it on quality PSU's, and sometimes the other way around on lesser PSU's. There are some 650w Raidmax PSU's that cant put out 400w, and some 400w Corsairs than can put out 650w.
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November 19, 2010 11:49:34 PM

I guess I'll try it as is and see how stable and what passmark score I can get. I looked at a review of the psu and it says they pulled up to 640w from it and the rectifying bridge on it could pull 736W theoretically.
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a b ) Power supply
November 19, 2010 11:55:56 PM

Let us know how it works out. You can also try using 3Dmark06, orthos, or OCCT. To stress your PC.
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November 27, 2010 4:31:57 AM

Alright, Ill let you know how it works out and after some help from you guys and some research I'm pretty sure the antec will hold, bump the thread or something if I forget, I do that untill I get a email, I'm going back to the crib tomorrow after thanksgiving with the family so Ill test it out. my boys got a 700w psu with leds and plexi windows that looks like a party inside and a brand I never heard of I can have but I think i'll stick with the quality antec 500 if I can, I'd rather have a fried antec hooked up to my system than some raidmax new out the box

I use passmark, 3dmark06 and furmark, I'll post some scores and voltage readings. What would be the best way to check voltage stability? Use the onboard sensor with speed fan or bios, check the p4 molex 12v with a multimeter or the video card vgpu to ground while benching? Guess I should google it... I just want to make sure its going to handle and a lot of these cards are becoming affordable to people with older systems now so its nice to know
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a b ) Power supply
November 27, 2010 5:51:12 AM

Best way to check voltage without using a multi-meter would be through the BIOS if you can or a free program called HWMonitor works really nice. There is a PSU stress test in a program call OCCT but it warns of possible damage if your PSU is not up to the task, I wont try it on my PC, but I figured I would mention it.
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December 3, 2010 10:24:31 AM

Everything seems to be working fine with the new parts. I the psu was lacking a 8pin connector but I figure I can make one for it, I don't really think its going to make a difference though for this cpu. The PSU is putting out a little heat which I'm not used to but all the voltages are stable in the bios. software while running says they are too but I wouldn't trust it much. 12.29v with hard drive, a case fan, and the heatsink has 2 fans on it (cooler master n520) pretty good system for cheap

Passmark score came out 2614.2 3d graphics mark 1221.6 passmark total. the amd 940 is upped from 3.0 to 3.2, the 667 ram from my old system is at 800 and the video card is overclocked a little bit. black ops runs perfect now with the highest settings, crysis pulled around 50fps

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a b ) Power supply
December 3, 2010 11:41:13 AM

tetsusaiga said:
I'd rather have a fried antec hooked up to my system than some raidmax new out the box


Interesting statement since I just had a friend give me a computer case, because it was the only thing the Antec power Supply he had in it didn't take with it when it blew.

It's a common senario question here at THGF after a power sucking graphics card has been added to the mix, seeing how much can we actually get away with and for how long, without spending any more money to really be sure and safe, and especially when overclocking is added to the mix.

Since my early SLI days and lessons learned the hard way, any power supply I buy first of all my minimum is 200w above the cruising load including the additional overclock load if it is to be overclocked for the entire hardware setup, and additionally, simply make sure the power supply was designed for what you're using it for.

Johnny Guru said it best, "Make sure the power supply you choose, has all the connectors you need so no adapters have to be used to connect it." best advice I've heard yet regarding your power supply choice.

If the time has come that adapters are required to connect something new, then it's time to replace the power supply with one that's been designed to handle what you're hooking up to it.

Or the next post will possibly be:

I pressed the power button this morning and nothing happened? Any ideas?

Or;

I pressed the power button and it sparked and went pfff't, and smells horrible, do you think my power supply blew?

Or; If you're extremely fortunate.

Man that 4ryan6 guy is clueless I've been running this rig for an additional 2 years now!

**************************************************************************************************

To sum it all up, it's better to be safe than sorry! Ryan
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a b ) Power supply
December 3, 2010 12:33:26 PM

^+1 ---- Since the PSU is the main component that provides stability for your system it is not a part to try to skimp on -- a cheaper MOBO,CPU, RAM, or GPU will only effect the overall performance of the system but a cheaper PSU has the potential to fry your entire investment or keep the entire system from running at all so why take a chance and risk $1000+\- investment with a $20 part -- If the budget calls for going cheap somewhere do it on the case or drop 1 level in GPU\CPU don't risk the entire investment by cutting quality where it matters the most !
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December 10, 2010 10:24:43 AM

the antec psu is handling pretty well now since I've got 2 running. temps went way down. Ill get one soon as i can afford a 120$ antec or corsair. This ones still going for 40 on ebay used so its a good start.

Do you happen to know if the antec that fried your friends system had overvolt protection?
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