Efficiency, Differential Temperature and Noise



The overall efficiency of a power supply is very important, especially when operating at higher power levels.  The less waste heat generated the better!  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) 600 watts of AC power going in would result in 600 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.


PC Power & Cooling Turbo-Cool 1200W PSU Review - Cases and Cooling 48 


The latest 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.


PC Power & Cooling Turbo-Cool 1200W PSU Review - Cases and Cooling 49 


I measured the AC power input to the Turbo-Cool 1200W PSU with the Extech power analyzer while the total DC load was found by adding all the individual +3.3V, +5V, +12V, -12V and +5VSB loads together. 


PC Power & Cooling Turbo-Cool 1200W PSU Review - Cases and Cooling 50 


PC Power & Cooling Turbo-Cool 1200W PSU Review - Cases and Cooling 51
(click to enlarge)


The mid-to-upper-range efficiencies are very good and actually exceed PC Power & Cooling’s claims of 83%; even when operating on 115VAC.  But the lower end efficiencies were a bit of a disappointment.  Apparently the new design has more overhead at lower power levels than a conventional PC switching PSU.  The Turbo-Cool 1200W’s efficiency seems to peak out at around 600-700W. 


Note: The Turbo-Cool 1200W PSU was designed to produce +12V very efficiently but takes a hit on efficiency from the +3.3V and +5V outputs due to double conversion losses.  Having higher loads on the +12V outputs with lower loads on the +3.3V and +5V outputs will result in the best efficiencies. 


PC Power & Cooling Turbo-Cool 1200W PSU Review - Cases and Cooling 52 


There is a growing awareness among users, PC manufacturers and electric utilities regarding the money and natural resources that could be saved by adopting higher efficiency power supplies.  One group that is spearheading this new movement is Ecos Consulting.  You can learn more about their efforts to promote power supplies with better than 80% efficiency by visiting the 80 Plus Program website.


Spending a little more money up front to purchase a high efficiency power supply may very well pay for itself over the lifetime of the PC, especially when you are using this much power…  🙂


Differential Temperature and Noise Levels


To simulate real world operation the Turbo-Cool 1200W power supply was mounted in a modified mid tower case (Lian Li PC60) for testing.  Some of the warm exhaust air from the PSU under test is recirculated back into the case, which allows the internal case air temperature to increase with load, just like it would in a real PC.  The internal case air temperature is allowed to increase up to 40ºC and then held constant from then on at 40ºC. 


The differential temperature across the Turbo-Cool 1200W 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

DeltaT = 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 ~28 dBA. 


PC Power & Cooling Turbo-Cool 1200W PSU Review - Cases and Cooling 53 


The single 80mm fan appears to do a very good job of keeping all the internal bits cool.  It moves a relatively large amount of air that will also assist with case cooling.


The Turbo-Cool 1200W power supply was not designed to be quiet; and its not.  The primary design goals were to deliver stable, clean outputs with high reliability for high-end workstations and servers.  To accomplish that you need good cooling, which in this case, requires a relatively high-speed fan.  If you need a 1200W power supply, you will most likely be dealing with noise from numerous other component cooling solutions dissipating all that power.  However, if you are looking for a quiet power supply, then look to one of PC Power & Cooling’s Silencer series units.


I was not able to measure the SPL when the power supply was running at the higher loads because all the cooling fans on the programmable DC loads were also running at this point.  *There was one brief moment during the final 1,200W load test when all the DC load fans happened to cycle off at the same time and I grabbed a quick SPL reading.

« PreviousNext »