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How We Test Power Supply Units

PSU Testing Equipment In Detail

Chroma Electronic Loads

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Reviewing PSUs

Some PSU reviewers use retail solutions (such as Sunmoon 268 - 5500 - 8800, Fast Auto, RedTech loaders, etc.), while others use the manufacturer's laboratories, which are usually equipped with fully automatic Chroma stations. We find this approach misguided, since we can't help but wonder how it's possible to do an impartial PSU review when testing in the competition's labs, and in most cases not being able to operate the equipment yourself. There are also reviewers who have managed to build their own loaders. However, their test results are questionable since they cannot be reproduced.

We consider reliable test results to be only those which can be reproduced in another lab using the same equipment. In order to conduct tests that can be reproduced, you need to use equipment that is widely available and not custom-made.

The electronic loads are the most essential, and the second-most expensive component in our lab. A load tester simulates the load (static or dynamic) and gives us the capability to stress a PSU to its limits.

All measurements are performed using two fully equipped Chroma stations. The first Chroma station is able to deliver up to 2500 W of load and consists of two 6314A mainframes equipped with the following electronic loads: six 63123A [350 W each], one 63102A [100 W x2], and one 63101A [200 W]. The second Chroma station can deliver more than 4 kW of load and consists of two 63601-5 and one 63600-2 mainframes. The aforementioned mainframes host ten 63640-80-80 [400 W] electronic loads in total along with a single 63610-80-20 [100 W x2] module.

The electronic loads would be useless if we didn't have the proper testing fixture at which the PSU's connectors are connected. In other words, this testing fixture is the bridge that links the PSU being tested with the electronic loads.

Monitor & Control Program

In order to monitor and control our Chroma loads, along with the rest of the equipment (oscilloscopes, temperature loggers, data loggers, power analyzer, hotbox heating elements etc.), we developed a software suite which can also record and analyze all output data.

The development of this program started in early 2010 and is still an ongoing process since new features are added on a regular basis, while old ones are improved. The software suite provides even more capabilities to the Chroma loads that we use, making the PSU testing procedure much easier and accurate at the same time. Another advantage of this software is that it can easily adapt to various types of electronic loads and testing equipment. So if, in the future, we decide to move to another testing platform, the transition process will be almost painless.

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Chroma 6530 AC Source

This is the most expensive part of our testing equipment, surpassing even the cost of both of our Chroma mainframes, along with their loads. Nonetheless, it fully justifies its high cost by providing us with the ability to simulate different power-line disturbance conditions. It allows us to simulate a complex mains supply waveform, if needed, while delivering a steady input voltage. It also filters most external noise from the power grid, which can seriously distort ripple measurements.

In addition, an AC source like the Chroma 6530 is capable of simulating all sorts of voltage dips, interruptions and variation waveforms showing the PSU's response under similar scenarios. Finally, this AC source can deliver up to 3kW of power, facilitating the evaluation of any PSU available on the market today (even Super Flower's 2kW unit) without the slightest problem.

Besides the Chroma 6530 AC Source, we also have the lower-end Chroma 61604 at our disposal, which provides up to 2kW of power. This AC source was pushed to its limits during the evaluation of PSUs with over 1.5kW capacity, so we replaced it with the stronger Chroma 6530. Our testing equipment also includes a variable transformer (variac), which is able to deliver up to 3kW.

Power Meter/Analyzer

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A power meter provides only basic functions, whereas a power analyzer is a highly sophisticated and expensive piece of equipment able to deliver accurate power and harmonics measurements. We use two N4L power analyzers (PPA1530 and PPA5530) to measure the exact (AC) wattage that the PSU pulls from the power grid, along with other crucial parameters like power factor and AC volts/amps. Given a known power consumption on the DC side, we can easily calculate the efficiency (DC watts/AC watts) of a PSU in real time through our testing software suite. Our backup power analyzer is a Yokogawa WT210.

Every PSU reviewer needs a good power meter, or, ideally, a power analyzer, with a high sampling rate. You see, sometimes the APFC stage of a PSU can be tricky, resulting in inaccurate readings with cheap Kill-a-Watts. Unfortunately, a power analyzer is pretty expensive. But if you want to have accurate readings, especially in light loads (<100W) or demanding ones (>1000W), then you have no other choice. As backups, we have a GW Instek GPM-8212, one of the best power meters for its price, and a Prova WM-01 power analyzer. Our main instrument for measuring the electrical characteristics of the  PSU is the Yokogawa WT210, which reports directly to the control/monitor program, allowing the calculation of a PSU's efficiency in real time.

Oscilloscope

To measure voltage ripple on the DC rails with static or dynamic (transient) loads, an oscilloscope is a one-way road. Back in the early days, most PSU reviewers used the limited bandwidth (250kHz) Stingray DS1M12 because it was affordable and did a pretty good job. However, for high-speed transient response tests, a higher-bandwidth oscilloscope is needed. We use a Picoscope 3424 scope and a Picoscope 4444 differential scope for ripple- and transient-response measurements, while our hold-up tests are conducted with the help of a Keysight DSOX3024A scope.

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Spectrum Analyzer

A spectrum analyzer (SA) is a piece of equipment that measures the magnitude of an input signal versus frequency and its main purpose is to measure signal power. In a SA the horizontal axis is for frequency while the amplitude is shown on the vertical axis. We have an SA in our lab to perform some basic EMC Pre-Compliance testing. Our main SA is a Signal Hound BB60C which features excellent performance and at the same time it doesn't break the bank. The BB60C has a pretty wide range, at least for our purpose, from 9 KHz to 6 GHz, and its dynamic range is from -158 dBm to +10 dBm. The provided software, called Spike, is easy to use and provides many interesting functions. Besides the SA we also got two Aaronia antennas, one omnidirectional (OmniLOG 70600) and one directional (HyperLOG 7060). We want to thank Aaronia for providing us these antennas at a significant discount. We need lots of expensive equipment to conduct proper PSU reviews and we really appreciate when a company supports us.

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We would like to note here that the BB60C Spectrum Analyzer was kindly provided by Signal Hound and the least we can say to them is a huge "thank you" for their support.

We also have in our disposal a Rigol DSA815-TG which might not be fully compatible with the CISRP 16-1-1 requirements, but still can be used to effectively check the EMC of a device. The DSA815-TG is among the best bang for the buck EMI receivers available on the market today and provides options that some years ago could be found only in super-expensive equipment. We would like to thank Rigol for providing us the EMI option, which will allow us to perform all relevant tests easily.

LISN Device And EMC Probes

In order to perform correctly the EMC Pre-Compliance tests we need a LISN (Line Impedance Stabilization Network) device, which very briefly is a low-pass filter that removes all unwanted noise from the AC line that feeds the under test device (in this case a PSU). In addition, a LISN device provides a stable line impedance along with an RF (Radio Frequency) noise measurement jack, to which we can connect our SA to measure EMI noise. Besides a LISN we also have in our disposal an EMC probe set which came set with a wideband amplifier. With these probes we are able to locate interference sources inside any device, since they act as antennas picking radiated emissions from electronic components, even PCB traces.

Both the LISN device and the EMC probe set were kindly provided by Tekbox Digital Solutions and we thank them very much for their support.

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Multimeter

Although almost all load testers are equipped with their own current/voltage meters, a good multimeter is always useful in a PSU review. It doesn't need to be a 4.5-digit one. However, it needs to be recently calibrated in order to provide accurate values.

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We have a large number of multimeters at our disposal, including a high-end Fluke model with 4.5 digits (289), a mid-range one (175) and a high-end bench multimeter with 5.5-digit precision (Keithley 2015 TDH). We also have a Labjack U3-HV multifunction data acquisition (DAQ) device to obtain some real-time readings from the PSU being tested. Finally, we have a DMMCHECK Plus device, through which we are able to check the accuracy of all equipment we use for measurements.

Hotbox

We strongly believe that there is no point in measuring a PSU at room temperature since it will spend all its life inside a case where temperatures will be much higher. So, the most interesting test results are the ones obtained with the PSU operating at temperatures above 40 degrees Celsius (104 degrees Fahrenheit) ambient. The ATX specification states that a PSU should be able to operate at ambient temperatures of 10 to 50 °C (50 to 122 °F) at full load, with a maximum temperature change rate of 5 °C (41 °F) per 10 minutes, but no more than 10 °C (50 °F) per hour.

The 80 PLUS organization tests efficiency at only 23 °C (73.4 °F) ambient, which, in our opinion, is way too low for this purpose. Performance at high operating temperatures is what separates the good PSUs from the mediocre and bad ones. A well-built power supply should be able to output its full power continuously at up to 50 °C (122 °F), while lower-grade ones can only hang at up to 40 °C. Finally, low-quality PSUs are restricted to 25 °C (77 °F).

In order to set a standard for our PSU reviews, we decided to conduct our full load tests at 45 °C (113 °F). In case a PSU explodes or delivers a really poor performance under the above conditions, we note this in the review and subtract the corresponding performance points from its overall performance score.

To be able to test at high ambient temperatures, an environmental chamber is needed. We constructed our own hotbox with heating elements that are software-controlled and can operate in a fully automatic mode. That is, we set the desired temperature and the heating elements operate accordingly in order to keep it within a specified range.

Digital Thermometer/Temperature Logger

An accurate digital thermometer or temperature logger is essential for the measurement of the PSU's intake and exhaust temperatures. For this purpose we use a Pico TC-08 temperature logger with eight probe inputs, and a CHY 502 thermometer as a backup, with two thermocouple inputs.

Sound Meter/Analyzer

Similar to the power meter and the power analyzer case, the difference between a sound meter and a sound analyzer is huge. A sound meter can only report basic sound measurements, while a sound analyzer provides a detailed look at the output noise, including frequency analysis, FFT sound and vibration, sound recording, and so on.

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The American National Standards Institute (ANSI) classifies sound level meters in three different types: 0, 1 and 2. Type 0 is used in laboratories, while Type 1 is used for precision measurements in the field and Type 2 for general-purpose measurements. The better Type 2 sound meters usually have an accuracy of ±2 dB(A), while a Type 1 sound meter usually has ±1 dB(A) accuracy. IEC standards divide sound level meters into two "classes." Class 1 instruments have a wider frequency range and a tighter tolerance for error than the lower-cost Class 2 units.

Another important factor in noise measurement is how "low" a sound meter can go. For example, most inexpensive sound meters simply cannot measure anything below 30 dB(A) because of their low-quality microphones. To be able to measure below this, you need to invest in a good Type 1 or Class 1 meter with a decent mic.

Our Class 1 Brüel & Kjaer 2250-L G4 Sound Analyzer is equipped with a type 4189 microphone that allows it to measure noise down to 16.6 dB(A). To fully exploit its capabilities, we built a mini-anechoic chamber, inside which we were able to measure down to 17 dB(A) during quiet hours. However, a good sound analyzer is worthless if it's not calibrated regularly (ideally, before any sound measurement). For this reason, we use a Brüel & Kjaer type 4231 sound calibrator, which provides a calibration accuracy of ± 0.2 dB(A).

Infrared Camera

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An infrared (IR) camera isn't an essential piece of equipment for a PSU review, but it can be useful if you need to check the thermal dissipation and the cooling fan's performance. We use a Flir E4 and, thanks to the ingenious folks at EEVblog, we managed to raise its resolution to 320x240 pixels.

Soldering and De-Soldering Tools

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In addition to the required testing equipment, we also have the tools to fully dismantle a PSU for a build quality check. We use a Thermaltronics TMT-9000S soldering and rework station. We also have a Hakko 808 desoldering gun, an AOYUE 474A desoldering station and a Weller WSD 81 soldering station.

  • JPNpower
    Nobody can fault you guys for not being thorough enough! All we can wish for is that you do these tests a bit more often. I'm at a loss how to navigate the PSU field, and a "Best Picks" section for PSU's would be tremendously helpful.
    Reply
  • Nuckles_56
    Really good article, it is now nice and clear how you guys go and test the power supplies, and as JPNpower said, no one can fault you guys for not being thorough enough.
    Reply
  • ykki
    @JPNpower= I also think a best psu for the money article would be nice but the power supplies in the market pretty much stay the same. We may go for months before seeing any change in the list.
    Reply
  • Kewlx25
    Interesting!
    Reply
  • damric
    Looks legit, Aris.

    THW used to be the laughing stock of PSU reviews, but your recent reviews have changed all of that.

    Keep up the good work!
    Reply
  • damric
    Nobody can fault you guys for not being thorough enough! All we can wish for is that you do these tests a bit more often. I'm at a loss how to navigate the PSU field, and a "Best Picks" section for PSU's would be tremendously helpful.
    @JPNpower= I also think a best psu for the money article would be nice but the power supplies in the market pretty much stay the same. We may go for months before seeing any change in the list.

    I'll make one and submit it through bb-71 to get stickied.
    Reply
  • ykki
    15570872 said:
    I'll make one and submit it through bb-71 to get stickied.

    OK. If someone makes a psu list I'd rather see it from you (or the mods). Good luck.
    Reply
  • damric
    15570891 said:
    15570872 said:
    I'll make one and submit it through bb-71 to get stickied.

    OK. If someone makes a psu list I'd rather see it from you (or the mods). Good luck.

    It will be a group effort for sure :)
    Reply
  • iam2thecrowe
    It would be nice if all manufacturers could do this testing and publish results when they build the things, or even better for it to be a requirement. Then at least there would be less junk PSU's on the market.
    Reply
  • ykki
    15571045 said:
    It would be nice if all manufacturers could do this testing and publish results when they build the things, or even better for it to be a requirement. Then at least there would be less junk PSU's on the market.
    Or more fake reviews.

    Reply