Testing (Cont’d)

Power Factor (PF)


Power factor is one of those mysterious properties of AC that even most electrical engineers have a hard time explaining.  A thorough technical discussion goes beyond the scope of this review (not to mention this author’s understanding).  For a more detailed discussion about PF, please look here.


Three Ultra ATX Power Supplies Reviewed: X-Pro and X-Finity - Cases and Cooling 57


AC Volts x AC Amps = VA (Volt Amp)


Purely Resistive AC Load: VA = Watts (same as DC circuits)

Inductive/Reactive AC Load: VA x PF = Watts


AC Volts x AC Amps x PF = Watts


Power factor is defined as the ratio of true power (measured in watts) to apparent power (measured in Volt Amps).  It measures how effectively AC power is being used by a device.  The difference between true power and apparent power is expressed as the power factor and results from the way true power and apparent power are measured.  Ideally we would like to have true power and apparent power equal to one another, which would result in a PF of 1.00 or 100% effective power utilization. 


I measured the AC Power Factor with an Extech power analyzer.  All three of the Ultra power supplies incorporate active power factor correction circuits, which resulted in all PF readings being at or close to 1.0. 


Three Ultra ATX Power Supplies Reviewed: X-Pro and X-Finity - Cases and Cooling 58


Note: A power supply with active PFC is more environmentally friendly (doesn’t pollute the AC transmission grid) and will draw less current, but it will not save you money on your monthly electric bill unless you are a commercial user whose bill is based on PF and usage.  




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) 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.


Three Ultra ATX Power Supplies Reviewed: X-Pro and X-Finity - Cases and Cooling 59


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 the latest revision (Ver 2.2) now lists both required and recommended minimum efficiencies.


Three Ultra ATX Power Supplies Reviewed: X-Pro and X-Finity - Cases and Cooling 60


I measured the AC power input to the Ultra PSUs with the Extech power analyzer and calculated the combined DC power output by summing the products of all the DC outputs (volts x amps) for five different DC loads.


Three Ultra ATX Power Supplies Reviewed: X-Pro and X-Finity - Cases and Cooling 61


The overall efficiency of the three Ultra power supplies is very good and the X-Pro EE 600W in particular, meets the latest recommendations with ease.  As expected, the high efficiency X-Pro EE 600W unit exhibited the best efficiency numbers of all, especially in the 200W to 300W range where most users will be running.  The efficiencies would most likely be even higher when operating on 230 VAC instead of 115 VAC, which would put the X-Pro EE 600W PSU very close to Ultra Product’s claim of up to 85% efficiency under a typical load. 


Three Ultra ATX Power Supplies Reviewed: X-Pro and X-Finity - Cases and Cooling 62


The 80 Plus Computer Power Supply Program



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 buying a 600W to 800W power supply.


Differential Temperature and Noise Levels


The differential temperature across the three Ultra power supplies was calculated by subtracting the ambient room air temperature (T in) from the temperature of the warm exhaust air flowing out of the power supply (T out). 


Thermocouples were placed at the air inlet and exhaust outlet. The ambient room air temperature was 24ºC (75ºF) +/- 1ºC during testing.


T in = temperature of air entering power supply

T out = temperature of air exhausting from power supply

ΔT = T out – T in


Sound pressure level readings were taken 3′ in front of each PSU in an otherwise quiet room.  The power supplies were placed on a foam rubber mouse pad during testing.  The ambient noise level was ~30 dBA. 


Three Ultra ATX Power Supplies Reviewed: X-Pro and X-Finity - Cases and Cooling 63


I was expecting the X-Pro EE 600W power supply with its large 135mm fan and efficient design to run relatively cool-n-quiet, which it certainly did, but I was not expecting the larger 800W power supplies with dual 80mm fans to be as quiet as they were.  Here again, higher efficiency can help lower operating temperatures.  Although I was not able to take SPL readings at the two highest output levels for the 800 watt units (the cooling fans in all the DC programmable loads had kicked in by that point), they really didn’t seem to get all that noisy (mid 40’s dBA range, maybe) even at full outp[ut.


After Spin Technology (AST) fan control


To test the AST feature of the X-Pro 800W and X-Finity 800W power supplies (the X-Pro EE 600W does not include AST) I connected two 80mm fans to the AST fan leads marked CPU cooler and Case fan during testing.  The CPU fan is powered up anytime the power supply is turned on but the attached case fan only turns on once the PSU reaches a certain temperature and gradually speeds up as the power supply temperature increases.


When the PC and power supply is turned off the two fans inside the power supply keep spinning for 4 to 5 minutes to help cool the system down.  Both the attached CPU and Case fans stopped however as soon as the power supply was switched off, which appears contrary to what the AST literature says (I assumed they would keep spinning like the PSU fans).


« PreviousNext »