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Ordered new video card


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#1
fortune82

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I just ordered an EVGA 250 GTS, and I fear my power supply is inadequate.

I have a Thermaltake Purepower 500 NP. Its 500W max, but I'm more worried about amps. This PSU has +12v V2, and it says it has 15 amps going through it. If it turns out to be not enough, will the molex-to-6pin converter put through enough amps?
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#2
cbarnard

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Hello Fortune82,

I was just checking this out for you.
check out this link to EVGA:

EVGA says min amperage is 24 if you have a 15amp min. You will need to upgrade your PSU

Without it your computer will be unstable with constant shutdowns\errors due to a lack of power

Hope this helps. If you need anything else let me know.

Good luck

Cbarnard

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#3
stettybet0

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You only listed one of your +12V rails. Assuming you have this PSU, you also have a +12V1 rail with 14A on it. However, you can't just add together 14A and 15A to get 29A. You have to use a little bit of physics to determine how much 12V amperage you really have.

The equation we'll be working with is the equation for power which is:
P=IV, or Power (watts) = Current (amps) x Voltage (volts)

Now, in addition to the two +12V rails, the PSU has a +3.3V rail, a +5V rail, a -12V rail, and a +12VSB rail.

To determine how much power each of these rails is capable of using...

The +3.3V rail has 22A on it, so it has a maximum output of 72.6W (3.3 x 22).
The +5V rail has 32A on it, so it has a maximum output of 160W (5 x 32).
The -12V rail has 0.3A on it, so it has a maximum output of 3.6W (12 x 0.3).
The +5VSB rail has 2A on it, so it has a maximum out put of 10W (5 x 2).

Add all these outputs up, and you get 246.2W. Subtract that amount from the total maximum output of the entire PSU (500W), and you are left with 253.8W for the +12V rails.

Then, you simply divide 253.8W by 12V, to get 21.15A. So, the output on your +12V rails is 21.15A.

Of course, this is still not as much as EVGA recommends (24A), but it's pretty close, and those recommendations are always more than is what actually is required. If the video card is on its way, you might as well try it with your current PSU. If you experience system instability or graphical artifacts, then you know it's time to come back here for PSU recommendations.
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#4
fortune82

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Which brings me to the other question: would using the molex-to-6pin connector bring enough amps into the equation? Or would I just deal with the inadequate amperage?

Also, the PSU you provided was the exact one I have!

Edited by fortune82, 02 May 2009 - 09:05 PM.

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#5
cbarnard

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According to Thermaltake your PSU already has a 6pin installed you shouldn't need an adapter.

Unless of course it doesn't reach (but it should)

If you were to use an adapter, it will make a very minimal difference in amperage. The run is very short so I wouldn't be concerned about it.

If you made connection on top of connection etc... several times it would start to make a difference.

I hope this answered your question.

Good luck

Cbarnard

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#6
stettybet0

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cbarnard, fortune82 wasn't asking if he needed to use an adapter, nor was he asking if the adapter itself would have an impact on the amperage the video card would receive. Rather, he was asking if the molex connection, via an adapter, would provide more (or less) amps to the video card. To answer that question, the molex connectors also use the +12V rail, so there would be no difference in amperage.
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#7
cbarnard

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I'm sorry Stettybet0

I knew that it would not make a difference(amperage wise).

I was trying to point out (in case he didn't know) that the 6 pin plug came standard with the PSU
I always prefer not to use adapters unless it is necessary.

I misunderstood that he was trying to get more power by using a different branch in the wiring(utilizing the molex connectors). In my mind I knew they were based off the same 12v line so I missed the point.

Thank you for the clarification

Cbarnard

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#8
fortune82

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Well, if it were to come to buying a new PSU, what would the recommendations be?

All it would powering is:

AMD Athlon X2 5400+
4GB OCZ DDR2 800
500GB Maxtor Sata HDD
LG 20X IDE DVD/CD
EVGA nVidia 250 GTS

Also, it needs to be relatively cheap. After this video card, I don't have much left.

Edited by fortune82, 03 May 2009 - 05:00 AM.

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#9
stettybet0

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While it might seem counter-intuitive, getting this 450W Corsair PSU is probably the best upgrade you can make on the cheap. While it has a lower rated maximum output, it has a much higher efficiency and 33A on the +12V rail. So, this PSU would actually be capable of supplying much more power to the ~90% of your machine that runs off the 12V rail (including your new GPU). While it has less power on the 3.3V and 5V rails, the ~10% of your machine that use those rails only need a fraction of the available power anyways.
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#10
fortune82

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I will bookmark it, but for the time being, I'm stuck with my 500W. The only money I (will) have is $16, so I'll have to hope Newegg has a nice sale soon.
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#11
pertsavk

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I will bookmark it, but for the time being, I'm stuck with my 500W. The only money I (will) have is $16, so I'll have to hope Newegg has a nice sale soon.


A little hint if you are to get a new PSU: don't be fooled by some generic PSU's boasting with their rated amperages. There are many ways to measure them, e.g. the temperature: the amperages delivered are different (higher) if the temperature is lower, and that is the reason why some low-life leeches do their measurements in +20 centigrades instead of +50 which would be a lot closer to the real world situation. Pick some known brand and you have one less problem. It is the wrong spot to save money when selecting the PSU.
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#12
fortune82

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Card came today, and what an improvement! Power seems to be fine; ran the Crysis GPU benchmark for about 30 minutes, and no issues. Thanks for all the input!
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