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I have an old gaming PC which I'm going to overhaul and turn into some much better. I'm interested to know whether anyone can help me understand what the PSU is capable of. Here's the spec:



I completely appreciate that this is a crappy old PSU and I'm definitely going to be replacing it I just need to know whether it's capable of supporting the video card I want to fit which is:

EVGA GeForce GTX 760 Superclocked Graphics Card - 2GB http://eu.evga.com/products/moreInfo.asp?pn=02G-P4-2762-KR&family=GeForce%20700%20Series%20Family&uc=EUR

Apparently the power requirements for this card look like this:

Requirements
Minimum of a 500 Watt power supply.
(Minimum recommended power supply with +12 Volt current rating of 30 Amps.)
Maximum Power Draw 170

Apart from supplying power to the motherboard I have a DVD, SSD and HDD in there drawing power.

The question is, can my PSU support this card? I don't really understand the power outputs and any advice would be gratefully received. Thanks.

Modern PCs pull almost all of their power through the +12V rail.
550 watts minus 185 minus (12x0.3) minus (5x2) leaves 351 watts (29.3 amperes) available on your +12 volt power line. That should be sufficient, if you trust this power supply to produce its rated capacity.

JustAnEngineer wrote:

Modern PCs pull almost all of their power through the +12V rail.
550 watts minus 185 minus (12x0.3) minus (5x2) leaves 351 watts (29.3 amperes) available on your +12 volt power line. That should be sufficient, if you trust this power supply to produce its rated capacity.

Thanks for that.

Trying to understand those calculations so I don't have to keep bugging people to explain all the time. Could you give a little more workings of how the numbers add up?

That sounds pretty tight to me. If the card needs at least 30 Amps and I have 29.3 Amps available isn't that on the cusp of being too low?

What would happen if I fit the card and there isn't enough power. Would would the effect be?

The effect would probably be to lighten your wallet by £69½, £66, £63 or £84.

Most power supplies have a listing for the combined power of all of the +12 volt rails. Power is the product of voltage and current, so 30 amperes (A) at 12 volts (V) equals 360 watts (W). NVidia lists fairly conservative power requirement ratings because some manufacturers flat-out lie about the capacities of their PSUs and others under-engineer them so that they won't survive at maximum capacity.

This Antec EA-380D can provide 336 watts (28 amperes) on the +12 V rail. That's pretty much the same as your existing 550-watt HEC power supply.

JustAnEngineer wrote:

The effect would probably be to lighten your wallet by £69½, £66, £63 or £84.

I realise it's not a huge expense.

I see where the numbers come from now. Turned my brain on a little.

Thanks.

Seriously, your old power supply should be OK. Try it out. You can always choose to spend more money on more upgrades later.

JustAnEngineer wrote:

Seriously, your old power supply should be OK. Try it out. You can always choose to spend more money on more upgrades later.

That sounds like good advice. Thanks.

If the PSU can't supply the power what will the effect be? Will the system crash or shutdown.

As my PSU quotes 2 12v supplies do I need to be careful where I connect the card to?

I will need to order a power cable adapter because it doesn't have any 8pin PCIE connectors. Is that an issue?

UltraFlynn wrote:

I will need to order a power cable adapter because it doesn't have any 8pin PCIE connectors.

EVGA includes 8-pin and a 6-pin PCIe power adapters in the box with your graphics card.

If your power supply is inadequate, the system will probably crash or shut down when you start playing a game or benchmark demo. I expect that it will be OK. TR observed sustained system average power usage (from the wall) of 253 watts under load in their review of the GeForce GTX760. Figure in the ≈82% efficiency of the power supply that they used in the review and that's only 208 watts being used for the entire system inside the case. You've got more than 140 watts of headroom above that with your existing PSU to handle higher instantaneous loads.

Try a power supply calculator if you're very concerned.

UltraFlynn wrote:

If the PSU can't supply the power what will the effect be? Will the system crash or shutdown.

Yes. Either the PSU will detect the overload and shut itself off, or the voltages will start to sag, resulting in system instability.

UltraFlynn wrote:

As my PSU quotes 2 12v supplies do I need to be careful where I connect the card to?

You probably don't have a choice; one rail probably feeds the CPU, and the other one feeds everything else.

UltraFlynn wrote:

I will need to order a power cable adapter because it doesn't have any 8pin PCIE connectors. Is that an issue?

Probably not. Make sure you connect the two Molex connectors on the adapter to two different connector strings on the PSU, to reduce resistive losses.

Time for the required readings refresh:

viewtopic.php?t=38038
http://www.silentpcreview.com/article28-page1.html

Flying Fox wrote:

Time for the required readings refresh:

viewtopic.php?t=38038
http://www.silentpcreview.com/article28-page1.html

I was hoping that someone might point me towards a PSU 101. Thanks for that.

I'm reading a bit of bad press with twin molex to 8 pin PCIE adapters. Do they really have problems?


Here's what I'd replace my cruddy PSU with:

Corsair CX 600W 80 PLUS Bronze Certified ATX12V (http://goo.gl/kTW8Y)

Would that seem like a decent replacement or could anyone recommend better.

Flying Fox wrote:

Time for the required readings refresh:

viewtopic.php?t=38038
http://www.silentpcreview.com/article28-page1.html

Great article Fox, very informative and I discovered why my old Antec/Asus system failed to start on occasion.

UltraFlynn wrote:

I'm reading a bit of bad press with twin molex to 8 pin PCIE adapters. Do they really have problems?

Provided the PSU has enough power on the +12V rail to begin with, and you hook the adapter up to 2 different wiring strings, it should be OK. As a guess, some people are using them incorrectly (both Molex connectors on the same wiring string), and/or the PSUs they're being used with don't have enough juice on the +12V rail.

JustAnEngineer wrote:

UltraFlynn wrote:

I will need to order a power cable adapter because it doesn't have any 8pin PCIE connectors.

EVGA includes 8-pin and a 6-pin PCIe power adapters in the box with your graphics card.

If your power supply is inadequate, the system will probably crash or shut down when you start playing a game or benchmark demo. I expect that it will be OK. TR observed sustained system average power usage (from the wall) of 253 watts under load in their review of the GeForce GTX760. Figure in the ≈82% efficiency of the power supply that they used in the review and that's only 208 watts being used for the entire system inside the case. You've got more than 140 watts of headroom above that with your existing PSU to handle higher instantaneous loads.

Try a power supply calculator if you're very concerned.

l

Are the adapters supplied by EVGA 6-pin and 8-pin to molex?

Thanks for the review link.

I found the information on the PCIe power adapters by looking at the image gallery and at the PDF spec sheet's accessories list on the EVGA product page that you linked in your first post.

JustAnEngineer wrote:

I found the information on the PCIe power adapters by looking at the image gallery and at the PDF spec sheet's accessories list on the EVGA product page that you linked in your first post.

Apologies. I should have checked. Answering my own question: No it isn't.

Thanks for all your help. I feel my understanding of PSUs has increased a little bit.

I have decided to purchase a new PSU though. I don't trust this old PSU and connecting it to my shiny new £200 graphics card via molex adapters seems silly.

UltraFlynn wrote:

I have decided to purchase a new PSU though. I don't trust this old PSU and connecting it to my shiny new £200 graphics card via molex adapters seems silly.

A wise move. Even though electricity is cheap in the UK, the efficiency is good for reducing heat and noise, plus it's not just your £200 graphics card at risk - it's your old motherboard, RAM and processor. Even if they're not worth much, you could need to spend another £200 on Mobo/CPU/RAM too, if the PSU assploded.

Chrispy_ wrote:

UltraFlynn wrote:

I have decided to purchase a new PSU though. I don't trust this old PSU and connecting it to my shiny new £200 graphics card via molex adapters seems silly.

A wise move. Even though electricity is cheap in the UK, the efficiency is good for reducing heat and noise, plus it's not just your £200 graphics card at risk - it's your old motherboard, RAM and processor. Even if they're not worth much, you could need to spend another £200 on Mobo/CPU/RAM too, if the PSU assploded.

My thoughts exactly. I see a replacement reliable PSU as an insurance policy. Very short-sighted not to get it replaced.

I realise my current Mobo/CPU/RAM are old and need replacing and that will come in time, just not at the moment.