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

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Dec 22, 2006 by Mike Chin

It's less than three months since our last update to the power supply test rig; what would require yet another revision? Oh, nothing that serious. Just the need to increase the load test capability to 1,000 watts in preparation for a monster PSU from Enermax that's been awaiting our attention.

It was mentioned earlier that the 50W resistors had not arrived, and thus, our rig was still not capable of reaching much higher than about 650W. Once the resistors got here, it turned out that adding another >350W load capability to the setup required a few more changes.

The cables and connectors on the test rig already get mighty hot at high loads. It's not wise to send any more power through the existing connectors. The 2x12V connector is shown signs of heat damage, and the DBS 2100 is far to packed to hack into. The natural step was to add 6-pin PCIe power connectors to the load tester; this would help to distribute the load over more wires and connectors.

The big challenge was to find 6-pin PCIe power connectors. In Vancouver, neither female nor male versions could be found in any of the usual electronic supply stores I frequent. In the end, a DIY hack/mod was the answer, as it has been so often in the SPCR lab.

The Antec NeoHE power supply happens to use a bank of 6-pin power connectors as the output sockets for their modular cable system. We happened to have a NeoHE that Devon inadvertently killed some time ago. Its carcass was stripped, and the PCB with 6-pin connectors retrieved. Wiring this PCB and connector assembly for a simple 2-conductor pathway proved to be a royal pain because it was originally a 4-conductor circuit handling 12V, 5V and 3.3V outputs.

Once done, the banks of resistors were wired up to the 6-pin connectors and installed within the PSU test box. The connectors / PCB assembly was mounted on the side of the box.

Originally, the wiring and backside teminations were left exposed, but Devon expressed some concern over potential damage due to shorting or the possibility of testers burning or electrocuting themselves by touching the things accidentally. An insulating cover was devised by folding up a promotional plastic card from a restaurant and applying a bit of glue from a hot glue gun. That's how this PSU tester version became the Bonefish edition.

Recognize the PSU test rig?

The slogan on the card reads, "We get fish, you get fresh".

Here's a closeup of the 6-pin connectors.

Getting back to some semblance of business, that little switch on the side selects between one bank of three 3.3 ohm 50W resistors and two banks. Originally, I started with four resistors in the sandwiched aluminum plates, but after a quick test run, I felt just how hot these things became and decided that just three resistors per sandwich was wiser. With 12V input, the three resistors represent a load of 131W; 262W with both banks. After some pondering about how to integrate this into the PSU box, I decided to hang the two banks of heatsinked resistors directly behind the 120mm exhaust fan. This would ensure decent cooling.

Hanging resistor banks.

The total load capability is now in excess of 900W. However, it is still not enough. We need a kilowatt capability. Since testing at such high power will be rare, I decided not to load up the PSU test box any further, and make a detachable load bank instead. This one has four 3.3 ohm 50W resistors and will pose a load of 175W with 12V input. It will be sandwiched between two aluminum plates and a multifinned heatsink. It will rest atop the PSU box, and when in use, connect in parallel to the hanging resistor banks via one of the 6-pin connectors. Devon and the rest of the SPCR lab crew have been warned not to touch.

Before sandwiching.

The final assemly will be clamped together with bolts.

And that's our PSU tester, Bonefish edition. The end result is load capability of nearly 1.1 kilowatt. Hopefully, we won't be testing such loads often. No computer PSU could be quiet at that kind of output.

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