Explain SLI to me.

[Rich46yo]

Any opinion by you Gurus on whether or not 750 watts will be enough to run SLI GTX 580s?

I can afford another 580, "hopefully a used one", but do I also need to upgrade my power as well?

[Bizman]

Calculate by yourself: http://www.extreme.outervision.com/psucalculatorlite.jsp
I'd recommend setting the capacitor aging to at least 30% in the last slot for some headroom.

[Chalenge]

Minimum system requirements for the GTX 580 is 600 W, with 244 W for the card alone. This is one reason why I use two 750 W PSUs. The extra leads come in handy for additional devices and fans (and what ever). It's the same for the 780s, but even the 680s that are less power hungry are only a little lighter on the requirements.

I know you didn't ask, but:

One thing about using two PSUs is that you can split up the cables between two UPS devices, also. When matching up a UPS to a PSU you want to find the Output Watt Capacity, which in every case I have seen has been less than 2/3s the published VA rating.

So for a single 750 W PSU you will need a 1500 VA UPS, and for a 1500 W PSU you will need a 2200 VA UPS. That won't give you much battery time, and they are not cheap so there's even more to consider.

[MrRiplEy[H]]

Minimum system requirements for the GTX 580 is 600 W, with 244 W for the card alone. This is one reason why I use two 750 W PSUs. The extra leads come in handy for additional devices and fans (and what ever). It's the same for the 780s, but even the 680s that are less power hungry are only a little lighter on the requirements.

I know you didn't ask, but:

One thing about using two PSUs is that you can split up the cables between two UPS devices, also. When matching up a UPS to a PSU you want to find the Output Watt Capacity, which in every case I have seen has been less than 2/3s the published VA rating.

So for a single 750 W PSU you will need a 1500 VA UPS, and for a 1500 W PSU you will need a 2200 VA UPS. That won't give you much battery time, and they are not cheap so there's even more to consider.

UPS is usually necessary in only two use scenarios: 1) You're working and you must make sure you don't lose data in a case of power outage. This is easyest handled by using a power laptop instead of a desktop for most data intensive works. If you do CAD like Chalenge then a laptop may not be enough even with a firepro or quadro. 2) Your electricity is horribly bad and you need a quality UPS to filter it. This is not necessary anywhere I live anyway.

For the rest of the people losing power suddenly mostly just means the abruption of gameplay, no big deal.

[Chalenge]

I disagree with everything Ripley just posted.

[guncrasher]

I had a ups for about 5 years.  never actually used it, till the battery needed replacement.  by then I had a ps with power surge, so nothing happened to my computer and monitor when the power went out 4 months ago.


semp

[Bizman]

I disagree with everything Ripley just posted.

In this case I'm with MrRipley. I know the state and town and other public authorities as well as major companies have UPS, but I haven't seen one in any of the numerous smaller offices I have visited. Yet they may have been hidden from me, but I doubt not. As Ripley said, our electricity is quite clean and stable especially in town areas. Things may be different in the countryside where the milking machine may use the same major fuse as the computer and the transformer is in the middle of a thunder sensitive field. As a rule of thumb I've said to my customers asking about their need of a UPS and surge protector that if their lights flash often and/or they have power outages regularly during near or distant storms, such devices may prove useful. Otherwise the experience would be similar to what Semp said.

Chalenge, could you please argument your point about the necessarity of an UPS in regular household use just for me to learn and maybe change my opinion about it?

[Chalenge]

Okay, before this goes the rest of the page without anyone coming to agreement I will outline what happens in the event of a power crash. In this case I will discuss first the issue involving a transformer failure, because we just experienced this within the last week.

First off, this problem was caused by a squirrel stepping, rather than jumping, from line to tree. ZAP! Squirrel explodes into fried tidbits, fur flies, toenails are embedded into tree and wire. The power instantly fails. One UPS in my house dies immediately from electric surge (I'm protected by the electric companies own equipment from this happening). Because the battery dies the computer shuts off catastrophically and loses the data. The DSL line puts off smoke under the house, but we don't see it. The router melts down internally. Gone, but not before also taking one motherboard with it. One out of fourteen isn't bad, I guess.

So, this got me interested in going back and reading up on the possibilities of electrical problems. They are:

Surge: Power outside of the design limitations of equipment will cause premature failure, possibly complete failure of all electronics.
Sag: (most common) power dropouts that do not lead to power failures will still lead to data loss, corrupted data, and reduce efficiency and life span (particularly hard drive motors).
Blackout (total loss of electric): Data loss. Potential for FAT to be lost and all data on a hard drive to be lost.
Spike: Catastrophic hardware damage. Data will be lost.
Noise: A noisy line leads to glitches and errors in running programs and data files.

Noise will usually have the same affect as a failing PSU. Note that in all cases data is lost, or potentially lost.

What a UPS provides is another level of protection from these problems, as well as allowing for a graceful exit from Windows in the case of power issues.

Pretty much that's a big deal.

[Bizman]

Thanks, that explained a lot. I believe there are variables in each country, though. IIRC that there's more than what's evident in the 120 or 240 volts and 60 or 50 amperes. Like fried squirrels... Never actually heard about one causing such trouble even inside a transformer here, although some have been found inside them! Birds sometimes die in the power current cables (380 V) but they usually don't cause major troubles either. Underground cables from transformers to houses have further diminished problems like falling trees.

[Chalenge]

What I said about surges, sags, spikes, and so on are universal to electricity. Your area may have a delivery system that is more stable, but it's those things you have no way to measure that lead to sudden failures. Noise for instance, or power sags can in some instances have no visible indicator that there is an issue, but then suddenly you have a dead hard drive. I would prefer to lose a UPS over a motherboard, because I know it won't stop there.

[Chalenge]

Another thing about UPS systems. The local "Geek Squad" will sell you a UPS that is barely adequate. Their idea of efficiency is to sell you something rated very closely to your systems maximum power requirement, or something like an 80-90% load factor. So, at full load your system will run on batteries from four to eight minutes. However, UPS devices are designed to run efficiently at as little as 30% load. So, there is nothing wrong with buying a UPS that provides more than you need. Your pocket book is the only limiting factor, aside from the amount of space the unit will take up.

[Skuzzy]

Challenge is quite correct about this.  Brief power interruptions (on-off-on) can cause massive amounts of damage to electronic devices.  None of them are designed for an open ended surge of power.  Mobile devices are even more susceptible to damage.

[Bizman]

Understood and agreed about spikes and other anomalies causing damages. That wasn't exactly what I was talking about, though. What I was after is, if UPS gave significant advantage in areas where power is stable except for human errors.

[MrRiplEy[H]]

A simple surge protector is enough in most cases, UPS is just overkill. Most motherboards are configured to return to power off state in case of a loss of electricity so they're not exposed to the dangerous power cycle Skuzzy mentioned.

I've owned literally dozens of PCs and Macs during the years and I have never lost a single one to a power spike. Even if I did it would be far cheaper to just replace the component or two that may get damaged instead of getting an expensive UPS and having to replace its batteries regularly.

[Bizman]

"Literally dozens" sounds like you have had the opportunity to get rid of them before their possible faults were starting to show... I'm on my fifth build/upgrade since Jan 1997, this one dating from about six years ago upgraded on the way with a new psu (preparing for future upgrades) and second hand cpu and gpu. No surge protector nor ups, and I have several times been surfing during a thunderstorm roaring within a mile. We have never lost any electric equipment here due to spikes, surge or anything else than normal aging.  Even the amount of replaced nic's can be counted with my fingers during these nine years I've been doing my techie thing inside a circle of 10 miles or so, most of the cases having been deep in the countryside.

BTW how does this help anyone understanding SLI?