Articles :: Modular Power Supplies: The Reality of the Resistance. :: Motherboards.org

Jon Gerow · 08-10-2006 · Category: Guides

Conclusion


Hopefully you all found my little experiment entertaining and informative, if not monotonous and overly in depth. Obviously, it's fighting a losing battle trying to convince anyone that modular connectors don't create any significant resistance, but I think there's a few things here we can all learn from.

Someone once said that a modular connector's pins have as much resistance as two feet of wire. I can't recall where that came from, but I think our five subjects have shown us that there's actually as much as four times as much voltage lost in a mere 18 inches of cable than there is in a modular connector. And when thinking about a loss in voltage in a modular connector, one shouldn't look just at the fact that a power supply has a modular connector, but perhaps how that modular connector is made.

The power supply that showed the most drop in voltage at the modular connector was the Corsair. I'm not really sure why this was since the connector was a one to one with a standard 6-pin PCI-e type connector. I could understand seeing this kind of drop with the other modular connectors on the Corsair because relatively small pins are used in the five pin connectors that plug into the power supply housing. Below is a close up picture of one of the Corsair modular peripheral power connectors.



Regardless of why there was this drop when the Corsair was under load, one has to keep in mind that this drop was only .03V even when there was an 11A load applied to a single connector. That's only a 0.25% drop in voltage during a very exaggerated static load.

The power supply that showed the most drop in voltage through the cable was the Antec. This probably has nothing to do with the gage and length of the wire, but because there are four conductors splitting off into six wires. Two of these wires meet into one contact, creating twice the resistance as the other conductor. Below is a close up of the back of the Antec connector...



Note how only four of the potential six pins are used. If you take a look at the photo below, you can see why. The connector on the right is the one used for PCI express. The one on the left is used for a four pin peripheral power connector. The 12V lead in the lower right is missing, but now there is a 5V in the upper right that the PCI express connector did not have. The upper left would house a 3.3V conductor for use with SATA drives.



Again, we have to admit that the drop was only .19V, even with an 11A load, as opposed to the .11V drop we saw on the Silverstone power supply's cable which had no modular connectors at all.

Now please keep in mind that this article is in no way a power supply review. You have not just witnessed some sort of weird five-way power supply shootout. There are so many good things to say about ALL of the power supplies I used today. For example, the voltage drop going from 0A to 11A on both the Antec NeoHE and Corsair HX620W was actually LESS than the FSP600-80GLC power supply with fixed cables. But the focus of today's article was to simply clarify some of the fuzzy math used to create fud over modular power supplies, therefore we focused primarily on the drop from the power supply's PCB to the load.

Of course, despite today's findings, we still can't ignore some KNOWN ISSUES with modular power supplies that we all need to be mindful of. Any physical connection point, whether you're talking about the modular connector on a power supply or a lug nut on your car's wheel, is a potential point of failure. Connections can work loose. But in some applications they don't work loose once they are in place because, unlike your car's wheel, your power supply is not a moving part. But many times I have seen people assemble builds with modular power supplies, tie things up all neat and tidy, and then NOT go back to double check the security of the modular connections at the power supply. This can, and DOES, cause HUGE problems. Please double check ALL of your connections whenever you open your case, shove your hands inside and start bumping and yanking on different cables.

And if you're the type of person that moves their stuff around inside their case, or even moves their stuff from case to case, be aware that by repeatedly plugging and unplugging your cables you may be working them loose. A loose cable is going to have more resistance than a nice firm one. If you feel your cable is working loose throw it away and replace it!

Contents

  1. Introduction
  2. Testing Methodology / Testing Corsair HX620W
  3. Testing Corsair HX620W (continued)
  4. Testing Corsair HX620W (results)
  5. Testing Ultra X2 550W
  6. Testing Antec NeoHE 430W
  7. Testing Fortron Source FSP600-80GLC
  8. Testing Silverstone ST65ZF
  9. Charting voltage output results for all five load tests
  10. Side by side comparison charts of voltage output
  11. Conclusion

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