Efficiency, Differential Temperature and Noise
Efficiency is defined by the power output divided by the power input and is usually expressed as a percentage. If a PSU were a 100% efficient (which none are) 400 watts of AC power going in would result in 400 watts of DC power coming out (with no waste heat to dissipate). In the real world there are always inefficiencies and power is lost in the form of heat during the conversion process. Newer revisions to the ATX12V Power Supply Design Guide V 2.2 have continued to increase the efficiency recommendations for PC switching mode power supplies and now lists both required and recommended minimum efficiencies.
We measured the AC power input to the two SilverStone SFX power supplies with an Extech power analyzer while the total DC load was found by adding all the individual +3.3V, +5V, +12V, -12V and +5VSB loads together.
The overall efficiency of both SilverStone SFX power supplies were good and easily meets the 80 Plus Bronze guidelines, even when operating on 120VAC and at elevated temperatures.
80 Plus Program
Note: Tests conducted at room temperature (25°C)
Differential Temperature and Noise Levels
To simulate a demanding environment, some of the warm exhaust air from the PSU under test is recirculated back to the intake through a passive air duct, which allows the PSU air inlet temperature to increase with load, up to 40°C.
The differential temperature across the power supply was calculated by subtracting the internal case air temperature (T in) from the temperature of the warm exhaust air flowing out the back of the power supply (T out).
Thermocouples were placed at the air inlet and exhaust outlet. The ambient room air temperature was 23ºC (74ºF) +/- 0.5ºC during testing.
T out = temperature of air exhausting from power supply
T in = temperature of air entering power supply
Delta T = T out – T in
Sound pressure level readings were taken 3’ away from the rear of the case in an otherwise quiet room. The ambient noise level was ~27 dBA.
Both power supplies start out with the cooling fan spinning relatively slowly which results in very little noise. The fan speed started to ramp up once we hit the 50% load test but stayed very quiet through mid-power range. At full load with an elevated ambient temperature, the cooling fans did speed up and the noise became noticeable but never became really loud.
SilverStone ST30SF and ST45SF fan speed profile: (courtesy of SilverStone)
I disagree with the negative
I disagree with the negative comment on rerating of the operating temp.
Anyone trying to run high power apps in a small enclosure that is typical of a SFX power supply installation “is doing it wrong”. For small enclosures where SFX power supplies are used, the associated motherboard is typically mini-ITX. Anyone trying to run high power apps on a mini-ITX board “is doing it wrong”. I won’t comment on the “fringe users” that attempt to operate high end, heat-producing monster video cards on mini-ITX mobos strapped to a ridiculously overpriced (and maybe even overclocked) CPU in the absolute smallest case they can find just so they can brag about playing the lastest game at the absolute highest resolution possible in a multi-screen setup (with the largets screens possible, of course).
A major problem with “small form factor anything” is moving heat away from the heat-producing elements. The pictures of internals of these power supplies clearly show that these units are “packed” internally. Physical objects block or otherwise restrict airflow making cooling difficult, unless that device is mated to a high volume fan, but then “noise” can become a problem.
Now move this challenge (small size & heat) to a mini-ITX mobo. Pack any “high end” mini-ITX mobo, and there are just a few of those around, with a high power CPU and the problem changes to mounting an adequate CPU heatsink/fan due to component clearances. Since a lot of high power CPUs have extensive I/O options, the end user may even be trading off a lot of capability for small space. Said another way, if a high power CPU has lots of PCIe lanes, and most of those CPUs can power a pair of PCIe x16 Gen2 or even Gen3 slots, how does one access all of those lanes on a mini-ITX mobo? See my point about tradeoffs?
Now combine SFX power supplies and mini-ITX mobos into those small “cube like” cases. The problem of removing heat from the inside of the case becomes a problem of getting enough airflow across all of the heat-producing elements inside the case. If the intent is to build a relatively quiet PC, heat will build up because the high powered fans needed to move the heat away will not be used because they are too noisy. Such a small case could have “mesh” sides all over the place to help with airflow, but then case rigidity (not to mention appearance) could suffer. Again, there are tradeoffs due to size.
Look at the problem this way:
“high power, small size, low noise, low operating temps – pick any 2”
So I fail to see the value in knocking a manufacturer for derating the operating temps of it’s SFX products to something more inline with “common sense” and “reasonable for typical applications”.
Now, the warranty “knock” seems reasonable in view of the general trend in the industry towards longer warranties on power supplies, but again, consider the platform. SFX is a small chassis compared to typical ATX power supplies, so heat buildup may still be an issue here, unless a noisy high airflow fan is used (but then other mechanical engineering issues related to airflow have to be considered), and heat degrades the lifetime of any quality part no matter who makes it.
Also consider the MSRP prices cited in the article itself. At those prices, expecting a longer warranty seems unreasonable nowadays. Longer warranties typically translate to higher product prices because manufacturers will spend more on longer warranty products, both to produce them and to support them through their warranty lifecycles.
So, while I find Lee’s power supplies reviews to be balanced and informative, I think his negative comments in this review are an attempt to “stir up a tempest inside a teapot”.
Talk about stirring up a
Talk about stirring up a tempest inside a teapot! Your rant about people who max out their mini ITX motherboards is over the top. First of all no one is “doing it wrong” except you. Some of us “fringe users” successfully run “high end” mini ITX motherboards inside of those “cube like” cases without problem “even overclocked”. In fact I have been doing it daily for about three years now using the ST45SF power supply without a single component failure. You do it with water cooling and three Cougar Vortex hydro-dynamic bearing fans. High power, small size, low noise, low operating temps – pick all 4! See my point about trade-offs? Oh and I also have 2 8GB GSkill TridentX overclocked DIMMS, 2 4TB WD enterprise 3.5 HDs in RAID-0 (8TB), two Samsung 256GB SSDs, a Swiftech MCP35X water pump, a Black Ice Xtreme 120mm x 38mm radiator, and room for a double slot mini ITX GPU, all running off a high performance ASUS Maximus VI Impact mini ITX motherboard, inside a version 1.0 NCase M1 chassis. At full load for one hour my chassis, mobo, and quad core CPU temps remain under 40C, and at idle are under 32C and totally silent. With modern parts it would be even better. I don’t see your “trade offs due to size” argument, or your “appearance” argument for that matter. You just don’t know how to do it yet.
Ironically, making a case
Ironically, making a case smaller makes it EASIER to get fresh air to components (and hot air out). You don’t even need a battery of case fans lie you do with a 42L ATX Overcompensator: with good design, the fans on individual components are placed right next to the case intakes, so they will pull in their own fresh air directly.
The previous two comments
The previous two comments have small form factor (SFF) builds figured out.
Stop spouting your theories about SFF builds and comment on the power supplies being reviewed.
SFX Joule worrier?
SFX Joule worrier?
As someone who has done
As someone who has done everything you’re moaning about – what’s your issue?
I have a very nice, very quiet HTPC/gaming PC rigged up that’s entirely water-cooled and using one of the older SFX PSUs from Silverstone. Granted it’s very hard to max the PSU even under load with limited component space, but the PSU fan is inaudible or quieter than the already quiet radiator fans.
I think “ease of building” is the main concern – getting everything in neatly was a nightmare, but entirely possible in the FTZ01.
However, at this wattage, most high end users will go for the 500 or 600W versions, so while your gripes miss the mark in general, in this specific case I’d say they’re fair.
I actually found the 40/50degC rating confusing.
WHY is the home unit rated at a lower temperature if the NAS unit would run longer and be more prone to wear out?
Is that the DERATING concern?
Does the derating concern apply or is there some confusion between the NAS and HOME units?
Version 2 is the NAS unit.
Version 3 is the HOME unit.
“450W continuous power output at 50℃ temperature rated for 24/7 operation (V2.0)
450W continuous power output at 40℃ temperature rated for 24/7 operation (V3.0)”
The site next to the FAN PROFILES also says the SAME thing for both units (“perfect for quiet home or office use”) which doesn’t quite make sense since it says above that V3 is quieter and meant for HOME with V2 meant for NAS/IPC.