SPCR Power Supply Test Rig, v.4 (and v.4.1)

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Here's a list of all the gear we use currently for PSU testing:

  • Thermometers. There are several ordinary mercury thermometers in the lab as well as several digital ones. (Like DigiDoc.) They measure within ~1°C of each other, which is good enough for our purposes. The digital meters are usually powered by the PSU being tested. (<0.5W power draw.)
  • Extech MultiMaster 560 True RMS Multimeter, a high precision multimeter, is used particularly to double-check low voltage readings across the current shunt resistors. It's a great reference tool. A couple of ordinary digital multimeters are also used to measure DC voltage.

USB Instruments DS1M12 digital oscilloscope and high resolution Extech 560 digital multimeter.

Onscreen oscilloscope display.

  • DBS-2100 PSU load tester. Made specifically for load-testing computer power supplies, it consists of a large bank of high power precision resistors along with an extensive selection of switches on the front panel calibrated in Amps (current) and grouped into 6 voltage lines: +5V, +12, -12V, +3.3V, -5V, +5SBV. Leads from the PSU plug into the front panel.

    We've also enhanced its accuracy by installing 0.01 ohm shunt resistors across the three main voltages to monitor current accurately. This is discussed in detail on page 4 of SPCR's PSU Test Platform V.3.

Front panel of DBS-2100 PSU load tester nestled into PSU thermal simulation box.
Note digital displays on both; they show current across the various voltage lines.
A rotary switch selects the current display between 12V, 5V and 3.3V lines on the DBS-2100.

  • Additional 12V Loading for High Power Testing (up to 864W on 12V alone). The DBS-2100 can provide up to ~23A load on the 12V line, which is 276W. This is not adequate for current >400W PSUs, which provide the vast majority of their power on the 12V lines. To increase 12V loading, banks of resistors were combined into a series / parallel network to provide five individually switchable loads of 1.7A, 1.7A. 3.2A. 6.4A and 6.4A at 12V, and any combination thereof, up to a total of 19.4A. The network was wired to a 4-pin 2x12V (AUX12V) connector.

    As the resistors would have to dissipate up to 230W, the network was divided into two banks. Six resistors are clamped between a pair of heavy aluminum plates that act as heatsinks. There is enough space between the resistors to allow airflow between them.

    For Version 4 of the PSU test rig, we're adding 8 more 4.7 ohm, 50W power resistors to obtain an additional 348W in four 82W increments. This is to accommodate the highest loads for the highest rated power supplies (in excess of 1,000W total). The photos and captions below explain better than words alone.

    On left: One of the resistor banks, placed on bottom aluminum plate. The wiring was recycled from old, dead PSUs. On right: three of four 50W 3.3 ohm resistors being prepared the same way.

    The resistors are clamped between the aluminum plates, with screws raising the structure for airflow below. To ensure good thermal conduction, a small thermal interface pad was placed between the resistors and the plates. This material acts much like TIM goop for CPUs and heatsinks, filling gaps and evening the contact.

    The finished resistor banks are at the bottom of the PSU simulation box, in the flow of air from the fans in the DBS-2100 load tester. There is an inch of space behind each bank so the airflow can pass through between the resistors. All wiring connections are soldered. (NOTE: New 50W resistor banks not yet installed; to be done next week when resistor parts come in.)

    Note 5-switch "front panel" with 2x12V and 4x12V connectors. Unfortunately, an error was made with the latter — it's a "male" 4x12V plug that was laboriously soldered in place, but what's required is a "female", which I have not been able to locate since discovering this error. Ah well... at least it does no harm.

How the DBS-2100 and PSU thermal simulation box go together.

The end result is that the PSU can now be loaded up to ~23A on +12V1 using the DBS-2100 (with the main ATX cable and 4-pin Molex plugs), ~19A on +12V2 using this one of the additional resistor banks (via the 2x12V AUX connector), and ~30A on the 50W resistor banks (via EPS12V and PCIe x16 6-pin power connectors) for a total of about 72A, or 864W total on the 12V lines. The three resistive load banks are entirely independent, so the current and power to each can be reported separately.

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