Efficiency, Differential Temperature and Noise
Efficiency

The overall efficiency of a power supply is very important.  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.

OCZ ModXStream Pro 600W Power Supply Review - Cases and Cooling  1

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.

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I measured the AC power input to the ModXStream 600W 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. 

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(click to enlarge)

The overall efficiency of the ModXStream power supply is very good.  The efficiency appears to peak around 250W and remains consistently above 80% throughout the curve. 

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And yes, the ModXStream 600W PSU is 80+ Certified.

Differential Temperature and Noise Levels

To simulate real world operation the ModXStream 600W power supply was mounted in a modified mid tower case (Lian Li PC60) during 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. 

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 ~28 dBA. 

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Below 300W output and 30°C inlet air temperature, the ModXStream 600W PSU is virtually silent.  Temperatures slowly build as the load increases and above 400W; the cooling fan starts to speed up to where it becomes noticeable but not loud.  Overall, very good results.  Note: I was not able to take SPL readings at the maximum load due to all the programmable DC load cooling fans running.


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