Efficient Power Supply Units

I have a Bitfenix Prodigy mini-itx build (sidenote, it’s not worth it - go full ATX!):
i5 3550,
8GB DDR1600
Samsung 830 256GB SSD
Seagate 2TB 7200RPM HD
Sapphire HD7870
2005 OCZ Modstream 450W PSU.

I bought a 3TB Toshiba HDD and an SATA DVD-RW only to find that my PSU had no more SATA connectors, and rather than pay ~$20 to get two molex>sata adapters, decided to buy a new Antec Earthwatts ‘Platinum’ rated 450W PSU.
I measured power consumption @ Idle with 0% CPU/HDD usage, and with Furmark doing a torture test, I then repeated with the new Antec PSU and the extra HDD/DVDRW hooked up - figures in brackets are the consumption with the old PSU:
Idle: 51w(63w)
Furmark torture test: 197w(230w)

Idle uses 20% less power, heavy load uses 16% less power. Will save me at least $30 per year as I leave it on 24/7 and pay itself back in just over 2. Not bad!

Your PSU is underpowered for your build and you are probably going to have all kinds of floating voltage under max load due to it unable to regulated it above certain load. Eyeballing your build - it needs at least 600W, unless both GPUs and CPUs cut power consumption by 50% or more since I checked last.

Run your numbers:


This is my preferred calculator.

i5 max TDP: 77w
7870 max TDP: 170w(by default it runs at 140w, 170w is to give AMD Overdrive headroom)
SSD + 2 7200RPM HDDs: 10w (being generous)
2 modules of DDR3 RAM @ 1.5v: ~8w
2 120mm system fans and 120mm PSU fan: 4w
Stock CPU cooler: 1w

Max load ~300w, actual load under torture test gaming: 197w

How is a 450w underpowered for the build? Also, anandtech tested a heavily overclocked i7 with an overlocked HD7870 and power consumption didn’t break 350w.

Amusingly, I just posted on RPS that people tend to overspend and overspec on PSUs.

@Greatatlantic: That suggests a minimum of 275w, and recommends at least 325w, which seems pretty accurate.

That suggests a minimum of 275w, and recommends at least 325w, which seems pretty accurate.

Bear in mind that PSU output does drop over time, so a reasonable amount of headroom is good. But yea, people are still thinking in terms of the old power-gulping cards, and speccing for that. Without SLI, well, yes my 650 is complete overkill >< I should have gone for a 450 or 500, but I was running a power-gulper before my 7750.

I overbought my PSU on purpose. It has multiple fan speeds (including a silent mode) and I wanted it running under a modest load even when going all out.

Iirc, power supplies are most efficient at high load. Also, heat generated is related to power generated, buying a 600w PSU hoping it will generate less heat than 450w PSU while doing the same tasks doesn’t seem to make sense to me?

Who said anything about heat? I said noise. Doesn’t it seem possible that a power supply running at less than half capacity might produce less noise than one at max, even at the same wattage, if the fans can run at lower speed?

Fans run in a PSU to dissipate heat, what other purpose would they be serving? A 450w PSU delivering 300w will need the same amount of heat dissipated as an 800w PSU delivering 300w, all else being equal - so if both have the same fan, the noise will be exactly the same.

The two tables on this site should give you an idea of what I mean: http://www.silentpcreview.com/article1313-page4.html

Kedaha, was your post due to you having a problem with your set up? Or just for peace of mind? Anyway my thoughts are as long as you check on the various ‘power-checking’ sites, run your own power draw tests etc, you will be in the best position to determine if that Antec 450W PSU will be enough. A long time ago i used to aim high, to give myself lots of headroom, but these days i prefer to run as low power a PSU as possible (given that some of the latest CPU’s and GPU’s are getting very efficient).

I was honestly surprised by how much of a difference a platinum rated PSU made on power being drawn - even when idling. Considering my old PSU lasted me 7 years and the new one will have paid for itself in 2, I figured some people might be interested.

Especially when there’s so many misconceptions about them flying about! :)

One curiosity for PSU gurus: if I o/c a CPU and pump some higher voltage into it, will this wear out a PSU quicker?

Not significantly, unless you’re above 80% load.

How modern is your PSU? My OCZ one was 450w but only 312w across the 12v rails (which powers CPU+GFX), whereas my new 450w gives 408w across the 12v rails.

The wattage a PSU is rated at is what it’s guaranteed to run at. With a decent PSU, the worst that will happen if you overload it is that it will shut down with no harm done. With a cheap one, I dunno!

kedaha, this thread is certainly informative. My existing PSU is 1100W, I had it for last 8 years and it was at one point needed for a power-hungry SLI build. Surprisingly, it is also 80+, but I didn’t care about that when I purchased the beast. Now most of the rails are disconnected and sit in the cable box. I could probably get by with a 450W PSU like you. I also realized that I held on to preconceived notion that anything below 500W in PSU is “cheap crap”. This thread and a bit of research made me realize this is no longer true.

I can answer that! Back in 2006, I tried to make a gaming rig out of an eMachine desktop (true story!) They had a sale on the base tower unit for $185, which included an Athlon XP 3700+, Win XP, 512 ram, 200 GB hard drive, and to power the thing, it had a Bestec 300 watt PSU. Not knowing anything about PSUs at the time, I thought 300 watts would be plenty, brand name be damned.

I added an nVidia 7900GT, upgraded to 2 GB ram, an additional hard drive, and a few fans, among other little things like an illuminated Logitech G15 keyboard and a G7 mouse.

To be fair, it was a beautiful little machine when I was done with it, and I actually completed Crysis on it (at 1440 x 768 or whatever the stock (17" LCD) eMachine monitor ran at). It was kind of a project where I wanted to see how far I could go with an eMachine.

It ran a whole year before the PSU died, taking out the motherboard with it. Cost me $169 to find an exact replacement motherboard (which came with a warning sticker NOT to use the Bestec PSU).
So I upgraded the PSU at that point to a brand-name 550 watt.

Total cost of the machine, including matching monitor and all that other stuff, and replacement parts: $1,200. All of which began with a “great” deal of a $185 base unit.

Never again. Although the machine has been rock-solid ever since, and I still use it for my older 32 bit Win XP games.
My main point is this: A cheap PSU can take out your motherboard. I was lucky that that’s the only damage it did.