FSP Hydro PTM 650W PSU Review: Clean, Quiet Power for Mid-Range PCs

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Efficiency, Temperature and Noise


Our efficiency testing procedure is detailed here.

Using results from the previous page, we plotted a chart showing the HPT650M’s efficiency at low loads, and loads from 10 to 110 percent of its maximum-rated capacity.

Subjected to normal loads, the HPT650M stands up well to its competition. However, it lands second from the bottom in our chart of performance under light loads. With that said, an efficiency result of almost 81% isn't bad. The competition is simply tough in this category.

Efficiency At Low Loads

In the following tests, we measure the HPT650M's efficiency at loads significantly lower than 10 percent of its maximum capacity (the lowest load the 80 PLUS standard measures). The loads we dial are 20, 40, 60, and 80W. This is important for representing when a PC is idle, with power-saving features turned on.

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Test #12V5V3.3V5VSBDC/AC (Watts)EfficiencyFan SpeedPSU Noise (dB[A])PF/AC Volts
11.189A0.490A0.471A0.196A19.50670.143%708 RPM17.1 dB(A)0.660
22.440A0.981A0.979A0.392A39.87480.839%708 RPM17.1 dB(A)0.739
33.627A1.473A1.453A5.089A59.37585.294%710 RPM17.1 dB(A)0.803
44.884A1.964A1.960A0.787A79.78887.503%708 RPM17.1 dB(A)0.861

We measured >70% efficiency under 20W of load. In the other three tests, FSP broke the 80% threshold. Better still, the Moreover, the HPT650M's fan spins slowly, keeping noise to a minimum.

5VSB Efficiency

The ATX specification (revision 1.4), along with CEC, ErP Lot 3 2014 and ErP Lot 6 2010/2013, states that 5VSB standby supply efficiency should be as high as possible, recommending 75 percent or higher with 550mA, 1A, and 1.5A of load. The PSU should also achieve higher than 75% efficiency at 5VSB under full load, or with 3A if its max current output on this rail is higher than 3A.

We take six measurements: one each at 100, 250, 550, 1000, and 1500mA, and one with the full load the 5VSB rail can handle.   

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Test #5VSBDC/AC (Watts)EfficiencyPF/AC Volts

This is one of the most efficient 5VSB circuits that we've ever measured. FSP did a great job in its design, setting an example for other manufacturers to follow.

Power Consumption In Idle And Standby

In the table below, you'll find the power consumption and voltage values of all rails (except -12V) when the PSU is idle (powered on, but without any load on its rails), and the power consumption when the PSU is in standby mode (without any load, at 5VSB).

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Mode12V5V3.3V5VSBWattsPF/AC Volts

Vampire power is low with 115V input and a little higher than we'd like to see with 230V input.

Fan RPM, Delta Temperature, And Output Noise

Our mixed noise testing is described in detail here.

The first chart below illustrates the cooling fan's speed (in RPM), and the delta between input and output temperature. The results were obtained at 37°C (98.6°F) to 47°C (116.6°F) ambient temperature.   

The next chart shows the cooling fan's speed (again, in RPM) and output noise. We measure acoustics from one meter away, inside a hemi-anechoic chamber. Background noise inside the chamber is below 6 dB(A) during testing (it's actually much lower, but our sound meter’s microphone hits its floor), and the results are obtained with the PSU operating at 37°C (98.6°F) to 47°C (116.6°F) ambient temperature. 

The following graph illustrates the fan's output noise over the PSU's operating range. The same conditions of the above graph apply to our measurements, though the ambient temperature is between 30°C (86°F) to 32°C (89.6°F).  

Through most of its operating range, the HPT650M is very quiet. You have to push it with more than 530W of load to land in the 30-35 dB(A) range. Even then, that's hardly an annoying amount of noise.

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Contributing Editor

Aris Mpitziopoulos is a Contributing Editor at Tom's Hardware US, covering PSUs.