PSU damage?

[cookybiscuit]

I've heard that running a PSU close to its max rating is bad for the PSU, for example running a system that takes 480w on a 500w PSU. Is this true? If so, what kind of damage can it take? Just wondering because I was planning on running a R7950 (with a factory OC) on a Sliverstone ST50F-ES and I'm worried it can result in a less than pleasant fire.

Thanks.

 

[luciferano]

Wattage of the PSU is almost irrelevant. Look at the +12V amperage because that is what is important. This does not necessarily directly correlate with the wattage rating. For example, a 430W PSU might have a 35 amp rating while a 500W has a 28 amp rating and the reverse can be true, depending on the model.

PSUs that are run at very high load are running less efficiently and yes, this does cause additional wear and tear damage to the PSUs.

 

[geekapproved]

What? A 7950 uses 150w.

Your 500w psu is plenty fine for that video card.

Your entire computer likely draws around 250-275w under max load, depending on your other components which you didn't list.

 

[djscribbles]

Wattage of the PSU is almost irrelevant. Look at the +12V amperage because that is what is important. This does not necessarily directly correlate with the wattage rating. For example, a 430W PSU might have a 35 amp rating while a 500W has a 28 amp rating and the reverse can be true, depending on the model.

PSUs that are run at very high load are running less efficiently and yes, this does cause additional wear and tear damage to the PSUs.

You are right that the important factor is the 12V supply; a crappy power supply will sometimes supply large amounts of power on the 5V and 3.3V rails in order to reach higher ratings.

However I'm not sure if I follow what you are saying about efficiency, so I'm going to clarify some for the OP.
In theory, a 500W PSU will supply 500W to you components; it's efficiency does not matter whatsoever, an 80+gold is no more capable of supplying 500W to components than a PSU that cannot achieve 80+ certification at all. The efficiency rating only affects whether your 500W PSU pulls 550W or 600W of AC power from the wall.

However, the ratings of a PSU can really vary in what they mean (even the current ratings of the 12/5/3.3V rails). A 500W PSU from seasonic you could likely run at or near the max ratings for all 3 rails for a long long time; however a 500W PSU from ChiefMax may only be able to sustain it's max ratings for 30 seconds.

If the PSU fails due to being over-loaded for too long, nobody can really predict how it would fail (except possibly the engineers who designed it). I would expect you to see some warning signs before it outright failed, but I wouldn't put my own theory to the test either.

From looking around, it seems like recommendations are to have 25A on the 12V rail (source: http://forum-en.msi.com/faq/article/printer/power-requirements-for-graphics-cards) for a standard 7950; your PSU supplies 34A at 12V so to me it seems pretty safe, you've got a good amount of headroom on your 12V supply to account for any overclocking and extra system usage. (basic components are accounted for by the 25A recommendation, but if you've got several extra HDDs or massive overclocks, you will use more at full load).

If you are still nervous though, I would pick up a larger PSU of similar quality (http://www.eggxpert.com/forums/thread/323050.aspx), Seasonic, Corsair, XFX, PC Power & Cooling are typically all good brands; Silverstone appears to be quite good at a glance, though it's not one I typically recommend (for reasons of ignorance, not because of anything against that brand).

 

[InvalidError]

The quality of individual outputs is far more important than their individual ratings. A 450W PSU with 35A on 12V is worthless if any output drifts too far out of specs or is too noisy. Output ratings are also worthless if the output capacitor bank has insufficient AC ripple rating to survive reasonably long exposure to AC ripple at anywhere near that level of output.

I would much prefer a solidly built 25A output than a marginally well built 35A output unless I actually needed more than 25A.

 

[luciferano]

You are right that the important factor is the 12V supply; a crappy power supply will sometimes supply large amounts of power on the 5V and 3.3V rails in order to reach higher ratings.

However I'm not sure if I follow what you are saying about efficiency, so I'm going to clarify some for the OP.
In theory, a 500W PSU will supply 500W to you components; it's efficiency does not matter whatsoever, an 80+gold is no more capable of supplying 500W to components than a PSU that cannot achieve 80+ certification at all. The efficiency rating only affects whether your 500W PSU pulls 550W or 600W of AC power from the wall.

However, the ratings of a PSU can really vary in what they mean (even the current ratings of the 12/5/3.3V rails). A 500W PSU from seasonic you could likely run at or near the max ratings for all 3 rails for a long long time; however a 500W PSU from ChiefMax may only be able to sustain it's max ratings for 30 seconds.

If the PSU fails due to being over-loaded for too long, nobody can really predict how it would fail (except possibly the engineers who designed it). I would expect you to see some warning signs before it outright failed, but I wouldn't put my own theory to the test either.

From looking around, it seems like recommendations are to have 25A on the 12V rail (source: http://forum-en.msi.com/faq/article/printer/power-requirements-for-graphics-cards) for a standard 7950; your PSU supplies 34A at 12V so to me it seems pretty safe, you've got a good amount of headroom on your 12V supply to account for any overclocking and extra system usage. (basic components are accounted for by the 25A recommendation, but if you've got several extra HDDs or massive overclocks, you will use more at full load).

If you are still nervous though, I would pick up a larger PSU of similar quality (http://www.eggxpert.com/forums/thread/323050.aspx), Seasonic, Corsair, XFX, PC Power & Cooling are typically all good brands; Silverstone appears to be quite good at a glance, though it's not one I typically recommend (for reasons of ignorance, not because of anything against that brand).

A 500W PSU running at 50% load runs more efficiently than the same PSU in the same condition running at 100% load. It will also degrade most faster when run at load in both stability, longevity, efficiency, and maximum power delivery.

You're right in that we can't predict when it would fail, but running at or around full load increases chances of failure greatly. Also, we can in fact predict how a PSU fails when it fails. A PSU that is constantly at load when it's not designed for that can fail because of overheating or capacitor damage. They're not the only reasons, but it's really not difficult to find out (although it can be difficult to find out without voiding the warranty).

The 80+ certification has more to do with than just the efficiency and different PSUs can supply power better even if its the same amount of power. For example, a PSU that can keep its 12V rail extremely stable can supply 500W better than another PSU with the same wattage/amperage ratings that can't keep it as stable.

 

[cookybiscuit]

Right thanks guys. I've only had the PSU a month so I don't want to just chuck it straight away. Was just wondering if its safe as is.

What? A 7950 uses 150w.

Your 500w psu is plenty fine for that video card.

Your entire computer likely draws around 250-275w under max load, depending on your other components which you didn't list.

I meant 480w draw as an example of a system for a 500w PSU. Sorry about not listing the other components but I didn't because honestly I don't know, I just have a prebuilt PC I stuck a GPU and better PSU in.

 

[djscribbles]

To the OPs original question, I think you are fine. The only change in load to your power supply is the new GPU consumes more power from the 12V rail; your PSU supplies 34A, that's a healthy amount and is plenty for the your components (assuming a powerful cpu with no overclock, and nothing crazy in the setup). You likely won't come close to 500w, as geekapproved stated.

 

[djscribbles]

A 500W PSU running at 50% load runs more efficiently than the same PSU in the same condition running at 100% load. It will also degrade most faster when run at load in both stability, longevity, efficiency, and maximum power delivery.

The problem comes back to rating. Some PSUs are designed to deliver 600W as their peak output for short periods of time, and are rated as 500W because they can maintain a 500W output reliably for their designed life, while another PSU is designed to deliver 500W as their peak output and can only deliver 400W sustained; both of these PSUs can be sold as 500W power supplies. If you look at the efficiency of the first supply, it's going to be approximately as efficient at 500W as it is at 200W; a typical efficiency curve is relatively stable until you start pushing towards the peak output.

You don't really get into wearing down your components until you drive them at or near their peak output for sustained periods. The problem comes from whether the supply is labeled conservatively or optimistically. In manufactured electronics (such as a TV or an appliance), you don't build a bigger power supply than you need, you build it the right size; if you over-engineer the supply, it isn't going to last any longer, it will just cost more.

 

[geekapproved]

Right thanks guys. I've only had the PSU a month so I don't want to just chuck it straight away. Was just wondering if its safe as is.

I meant 480w draw as an example of a system for a 500w PSU. Sorry about not listing the other components but I didn't because honestly I don't know, I just have a prebuilt PC I stuck a GPU and better PSU in.

Having a 500w psu with a system that draws 480w would be really bad. However, your system draws nowhere near that much power.

 

[Kursun]

If you look at the efficiency of the first supply, it's going to be approximately as efficient at 500W as it is at 200W; a typical efficiency curve is relatively stable until you start pushing towards the peak output.

You don't really get into wearing down your components until you drive them at or near their peak output for sustained periods. The problem comes from whether the supply is labeled conservatively or optimistically. In manufactured electronics (such as a TV or an appliance), you don't build a bigger power supply than you need, you build it the right size; if you over-engineer the supply, it isn't going to last any longer, it will just cost more.

Not so:
Energy efficiency is highly dependent on the loading.
"The energy efficiency of a power supply drops significantly at low loads. Therefore it is important to match the capacity of a power supply to the power needs of the computer. Efficiency generally peaks at about 50–75% load. The curve varies from model to model (examples of how this curve looks can be seen on test reports of energy efficient models found on the 80 PLUS website)."
http://en.wikipedia.org/wiki/Power_supply_unit_(computer)

On the other hand a lower capacity power supply will produce more heat. Heat is enemy number one of electronic circuits.

 

[djscribbles]

Not so:
Energy efficiency is highly dependent on the loading.
"The energy efficiency of a power supply drops significantly at low loads. Therefore it is important to match the capacity of a power supply to the power needs of the computer. Efficiency generally peaks at about 50–75% load. The curve varies from model to model (examples of how this curve looks can be seen on test reports of energy efficient models found on the 80 PLUS website)."
http://en.wikipedia.org/wiki/Power_supply_unit_(computer)

On the other hand a lower capacity power supply will produce more heat. Heat is enemy number one of electronic circuits.

http://www.hardwaresecrets.com/article/Understanding-the-80-Plus-Certification/742/3

80 plus is tested at 20%, 50%, and 100% load levels. An 80 plus basic has 80% or better efficiency at those levels; an 80 plus bronze has 82% efficiency at 20% and 100% loads and 85% efficiency at 50% load or better.

Yes, there is a curve; but it only looks like a curve if your graph is zoomed in to show it, that is why I said it was 'relatively' flat; it's subjective, but I don't think a variation of 2 or 3% is drastic enough that it's not very important to an individual user (in my opinion).

 

[InvalidError]

Yes, there is a curve; but it only looks like a curve if your graph is zoomed in to show it, that is why I said it was 'relatively' flat; it's subjective, but I don't think a variation of 2 or 3% is drastic enough that it's not very important to an individual user (in my opinion).

Hehe. Zoomed graphics to emphasize small variations are indeed misleading. I know I personally wouldn't take offense with an 80+ Bronze PSU peaking at 87% somewhere between 40% and 70% as long as it stays above 82% across most of its claimed range since that is what I sign up for when I buy something certified 80+ Bronze. Anything higher is a bonus/freebie.