Larger PSU's extra heat when not neede?

[LoneWolf_53]

I just thought I'd post this to get some feedback from the community.

I have begun to notice that though all other components are the same as well as the level of over clock on two of my i7 920 PC's that one runs warmer.

On the one unit I use a 550W power supply which is more than sufficient for my needs as I only have one optical drive, the hard drive, and a 9800GT graphics card.

On the other unit I have all the same items except the PSU is a 850W unit as I got a good deal on it and thought maybe I'd try to future proof a bit.

Both machines are under the same load, same operating system, and same 3.6Ghz OC but you can clearly notice that the machine with the larger PSU kicks out far more heat at the back even though both machines should be putting the same load on their PSU.

I have to say I hadn't honestly considered that happening when I purchased the larger PSU or I doubt I would have bothered.

Has anyone else noticed the same behavior?

I'm finding it food for thought when considering what size of a PSU to purchase.

 

[GhislainG]

What is the efficiency of both PSUs at average power requirements (150W-300W)? Your 550W PSU probably is more efficient than your 850W PSU. Less efficiency means more heat. Another factor is PSU cooling. A PSU with a better airflow should keep the system cooler.

 

[LoneWolf_53]

What is the efficiency of both PSUs at average power requirements (150W-300W)? Your 550W PSU probably is more efficient than your 850W PSU. Less efficiency means more heat. Another factor is PSU cooling. A PSU with a better airflow should keep the system cooler.

Both these PC's have the same case, same heatsink/fan combo on the CPU and same size fan in the PSU not to mention in the same location.

If anything I would actually have thought the larger PSU would be better since it is a Zalman HP model that employs heatpipe technology in its cooling.

The cases are designed with the PSU located at the top and I'm actually beginning to think that the larger PSU would be better suited to the style of case that locates it at the bottom in its own compartment.

 

[GhislainG]

Since it has excellent cooling, the Zalman probably pulls less air from the case, keeping it warmer.

 

[jsc]

I have two similar systems:
GA-EP45-UD3P | Q9550 OC'd to 3.6 GHz (425 MHz X 8.5) | GTX260| Corsair 750TX
GA-EP45-UD3L | Q6600 OC'd to 3.6 GHz (400 MHz X 9) | XFX4870 | Antec 550 TP3,
both in Antec 900 cases.

In both systems, under the maximum load I can put on them (3DMark and three instances of Prime95), the PSU exhaust air is about 3 C over ambient, as measured with an electronic cooking thermometer.

Admittedly, one could say that both are operating up in the efficient area of the output curve. But when the system is idling (nothing but the desktop running), the temperature difference for both is still about 2 - 3 C.\

Maybe if the nominal output difference (200 watts) were larger, I would see difference results.

 

[LoneWolf_53]

I think GhislainG might be on to something.

The Zalman is the only one I'm aware of that utilizes the heatpipe technology to cool so probably has different characteristics.

All I know is when I put my hands on the tops of the cases the one with the 550W PSU feels just slightly above room temperature whereas the 850W unit is much warmer.

I also had experimented with the GPU loaded and at idle and at idle the case drops back to feeling about the same as the 550W unit.

Thing is the 550W unit uses the same GPU and it is under full load.

 

[LoneWolf_53]

What is the efficiency of both PSUs at average power requirements (150W-300W)? Your 550W PSU probably is more efficient than your 850W PSU. Less efficiency means more heat. Another factor is PSU cooling. A PSU with a better airflow should keep the system cooler.

86% efficiency for the Zalman according to specifications.

85% for the BFG Tech according to specifications.

I do note that the BFG uses a 140mm fan for cooling.

The Zalman uses dual heatpipes and a 120mm fan.

 

[JDFan]

SInce the Zalman has heatpipes if it is like the XG magnum that I have the fan probably only runs at a very low speed just to move a little air to keep the heatpipes efficient as they are designed to use mostly the passive cooling so they are much quieter until they are under enough stress to kick the fan up in speed - so they do tend to stay a bit warmer to the touch than a PSU that uses just the airflow for cooling !!

 

[shovenose]

the hottest running i own is a 350w Mad Dog MultiMedia lousy psu. it always has extremely hot air coming out the back...

 

[LoneWolf_53]

Best answer selected by LoneWolf_53.