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Modular Power Supplies Less Efficient Say Makers

By - Source: Tom's Hardware US | B 57 comments

It's all about power efficiency these days.

Up until the last few years, few paid any attention to the little box that actually powers a PC--the power supply. Now with certifications like the 80-Plus, we're able to at least distinguish efficient power supplies from the rest of the pack. But even with 80-Plus, more and more power supplies are jumping on the bandwagon, so while product quality goes up overall, things are still not where manufacturers want them to be.

There's more detail to power supplies than can fit in the scope of this article, but we spoke to several power supply manufacturers at Computex and the focus customers put on their units.

Despite modular power supplies being a hot product, don't be quick to grab the up-take. The companies we spoke to told us that modular power supplies are less efficient than those that have their cables hard-wired. The reason being that the extra connection you make, adds resistance, and hence, increases heat and reduces efficiency.

Enermax, Seasonic, and Corsair all told us that if you're looking to maximize efficiency, go for a non-modular PSU.

Are the differences great? No one gave us any hard numbers, but they did indicate that the numbers are measurable. PC Power & Cooling, now part of OCZ, says the same thing:

Due to their look, convenience, and cost savings for manufacturers, modular plugs have become a popular power supply feature. Unfortunately, there has been little or no discussion of the impact of this feature on overall performance and reliability. The fact is, modular plugs limit power by adding to electrical resistance. The voltage drop can be as much as would occur in 2 feet of standard wire. Worse yet, modular plugs utilize delicate pins that can easily loosen, corrode, and burn, creating the potential for a major system failure. That's why professional system builders specify uninterrupted wire!

So in the end, you have to choose: do you go with a modular PSU for cable management and appearance, or do you spring for a hard-wired PSU?

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  • 3 Hide
    B-Unit , June 7, 2009 10:31 AM
    Glad to see the major players getting behind this. I read a couple of articles online talking about this over a year ago and have avoided purchasing or recommending modular PSUs since.
  • 9 Hide
    stray_gator , June 7, 2009 10:52 AM
    PCP&C always discouraged modular psu's - which they also didn't make.
    Hearing similar claims from other manufacturers (some of which sell mainly modular units), though, give them more weight and credibility.
    I'd still love to see some hard numbers, anyway.
  • 0 Hide
    theone1 , June 7, 2009 11:20 AM
    If two connectors and pin (male female) add 1 ohm (total) then for a 20-40A current you loose 20-40 Watts.
  • Display all 57 comments.
  • 5 Hide
    theone1 , June 7, 2009 11:28 AM
    theone1If two connectors and pin (male female) add 1 ohm (total) then for a 20-40A current you loose 20-40 Watts.


    Sorry My mistake:

    R(loss) = 0.04Ohm (2 feet of 20 AWG wire + 2 feet for return ground)
    Power Loss = I*I*R(loss) = 40*40*0.04 = 64Watt

    This is a power loss of 10% for 650Watt PSU
  • -5 Hide
    The Lady Slayer , June 7, 2009 11:41 AM
    I'm not a spambot. Just to make that clear.

    Before I bought my modular PSU I did a fair amount of reading and research and in end I decided to go with a Coolermaster Silent Pro 600W. I had heard that Corsair were THE makers of modular PSUs, but in Australia you pay significantly more than the standard US to AU currency conversion due to their popularity. Anyway, in my searching for reviews I stumbled across Jonny Guru, an online reviewer who almost exclusively rates PSUs, and tests them based on many things including whether they are infact 80-Plus.

    He gives the Corsairs (MX620W up to MX1000W) between 9.5 and 10, off the top of my head, and gave the CM M600W a score of 9.0, which I was really happy with.

    Just google his name if you haven't heard of him.
  • 8 Hide
    EQPlayer , June 7, 2009 11:43 AM
    I'm not worried about giving up a few % of efficiency in order to get modular cabling. *shrugs*
  • 1 Hide
    brendano257 , June 7, 2009 11:51 AM
    I've had two modular power supplies in the past, one of them did fail, although I'm not sure it was because it was modular or not. But if you get something like the Corsair 750TX all you need is a little nook or cranny at the bottom or top of the case to put unneeded wires. (Bottom/Top depending on PSU placement.) In my Antec 900 they actually all fit under the bottom drive bays, which put them completely out of the way and didn't take up any usable space.
  • 1 Hide
    Pei-chen , June 7, 2009 12:42 PM
    Make sense. Didn't manufactures also said a single jumble rail is better than multiple smaller rail as multiple rail often creates unbalanced load on the PSU.
  • 3 Hide
    shades_aus , June 7, 2009 12:47 PM
    Add a few % more then for the connector to your mainboard and HDDs, floppy, let's not forget the data cables also, I mean, everything takes power. What about the tin legs for the chips and solder used to conduct between the copper tracks and the chips themselves?
    You would think they are talking about rubbing two sticks together here!.

    Have you actually mesured the difference with a good multimeter? I have, and it says there is no difference. This sounds like bs to me. IF there is any merrit, perhaps manufactures should look at trying different connectors or metals like silver/gold plating.

    I think this all started because one manufacturer has the patent on a form of the modular connector and the others don't want to pay.
    Why not just design one that isn't patented and standardise it.
    All for modular. Cleans up the case nicely.
  • -3 Hide
    baddad , June 7, 2009 1:10 PM
    0 Ohm's in one inch of wire is the same as 0 Ohm's in ten feet of wire no significant resistance.If there is any lost in modular PSU 's it's so small it's of no impact, sounds to me like they don't want to make them to cut cost.
  • 7 Hide
    fletchoid , June 7, 2009 1:24 PM
    Before everyone starts ripping out their modular power supplies, it would be helpful to have some objective testing to determine the actual effect on efficiency of the modular vs standard power supplies. Even then, if the loss of efficiency is minimal, I will stick with modular power supplies. They allow for a much cleaner case, with better air flow, and if a power supply does fail, or you decide to get a more powerful supply, you just unplug the back of the PS, unscrew the PS mounts, put the new one in, and replug the connections. Much easier.
  • 1 Hide
    Anonymous , June 7, 2009 1:42 PM
    I think I'd prefer the possibility to upgrade or replace my powersupply in case of failure. Also, the resistance added by plugs instead of a hard wire is less than 0,05ohms. Not 1 ohms.
    Second: I've been running pc's from 1999 and older. None of these ever had a corroded pin. If they did, the impedance wouldn't go up, because as you plug or unplug the plug, the corrosion gets scraped off, and newer metal will be exposed giving a good connection again.

    Though it is true those mod pins are not very surdy, and could break. Especially for testing mobo's that regularly get hooked up on different hardware like PSU's.

    If modular pins last 5 to 10 years, about as long as a powersupply does, then I'd say go for modular.
    The chances are greater that you'd upgrade your rig with an extra DVD/blueray player, harddisk, cpu, more USB devices, or newer gaming videocard, and need the extra power; or,perhaps, buy a lower power PSU, as newer technology comes out, and smaller die ram/CPU, or newer SSD drives reduces the overall powerdraw.
  • 6 Hide
    dirtmountain , June 7, 2009 2:17 PM
    This is what Jonnyguru says (in part)

    "There’s been a lot of scare tactics used to convince people to not go with a modular power supply. But the reality is, even at high loads the resistance is quite minimal if the correct measures are taken."

    Give us hard numbers, especially since so many modern modular PSUs have the ATX/PCIe/and primary SATA cables hardwired and only have extra peripherals/additional PCIe using the modular cables if they're needed
  • 0 Hide
    scook9 , June 7, 2009 2:41 PM
    This is interestting given that Corsair just released two modular models that are 80plus Silver rated, that is ths highest ANY of their power supplies have been to date. And as for reliability, they also come with 7 year warranties, also the best ever from corsair. The little inefficiency due to the extra contact is not that bad actually....unless they go with REALLY cheap materials for the connections. Besides, these losses already exist at the component end of the wire anyway, where ALL the computer parts connect.

    This in no way discourages me from the Corsair 850HX I am planning on buying as soon as my paycheck comes in. And as others have mentioned, all of the high current connectors are almost always hard wired anyways, so the loss (if any) is VERY minimized as it is.
  • -3 Hide
    Shadow703793 , June 7, 2009 3:40 PM
    Quote:
    It's all about power efficiency these days.

    Nahh... it's about POWER & efficiency.
  • 0 Hide
    nickcardwell , June 7, 2009 3:50 PM
    It is hard to find quality non-modular power supplies these days. PC Power & Cooling is a great company for this. I have a Corsair non-modular 450w PSU that works great. Any higher from Corsair and they are all modular. I recently took my rig into a local custom system builder shop to see if they would be interested in purchasing it from me. They told me they were surprised I hadn't melted the little 450w PSU. It's just an E8400 and a single 9800GTX+. The whole system fully loaded only draws around 220w at the plug from my Kill A Watt meter. I can't believe even these seemingly pros buy into the whole 1Kw power supply idea. Most power supplies are most efficient when loaded about 50%.
  • -3 Hide
    tipoo , June 7, 2009 3:50 PM
    This has been known for years, has it not?
  • 7 Hide
    GenKhan2 , June 7, 2009 4:07 PM
    Complete shenanigans! They are likely complaining about the additional cost of making a modular supply. Preying on people's need to be "green" is popular and profitable these days. Allow me to demonstrate.

    -I have an Enermax Modu82+ 525W.

    -It’s rated at 40A combined draw out of the 12V rails (480W).

    -Two of those rails are dedicated to graphics cards.

    -Those rails connect to the graphics cards via twelve pairs of 18AWG wire into what is roughly a Molex Mini-Fit Jr connector.

    -I looked up the average resistance through mated connectors after 20 insertion/extraction operations from Molex. Here’s the results arranged by type of pin:

    Resistance per connected pin pair
    Gold plated brass = 2.62 mohms
    Tin plated brass = 3.09 mohms
    Tin plated phosphor bronze = 2.45 mohms

    So the modular nature of my power supply adds two times the resistance listed above to each circuit. However, there are twelve circuits in parallel. So the resulting added resistance is the figure listed above divided by a factor of six, as shown below:

    Total added resistance
    Gold plated brass = 0.437 mohms
    Tin plated brass = 0.515 mohms
    Tin plated phosphor bronze = 0.408 mohms

    Let’s assume I’m able to pull 100% of the total rated 12V current for my graphics cards. So here’s how much power is consumed by the pins:

    Power wasted due to resistance of pins
    Gold plated brass = 0.699 W
    Tin plated brass = 0.824 W
    Tin plated phosphor bronze = 0.653 W

    Now for the nail in the coffin of their argument. Out of the imaginary 480W total power consumed in my example what percentage is wasted by the pins?

    Percentage of total power wasted
    Gold plated brass = 0.146%
    Tin plated brass = 0.172%
    Tin plated phosphor bronze = 0.136%

    Yes, a modular supply is less efficient. It’s less efficient, in my example case, by a massive 0.227% on average. Completely negligible. By modular kids. Get your money's worth.
  • 0 Hide
    computabug , June 7, 2009 4:18 PM
    To me, it's not about efficiency... it's about reducing the chances of failure in my system :) . I just hide the extra wires behind my mobo tray. Besides, I'm so forgetful that I'd loose those extra wires when I need them :p 
  • -1 Hide
    mogle , June 7, 2009 5:21 PM
    well here are two thoughts that i'm sure everyone else was thinking. either put more power to the modular lines to compensate for the drop or make the common lines that 98% of us will use in every build an uninteruppted wire. then make the rest modular. all someone realistically needs is a couple mobo wires and a few for our sata devices. add a couple uninterupted pci express wires to the high wattage supplies and that should do it. if its something that you wouldnt want then read about the psu before you buy it. not a big deal.
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