Existing USB ports may face trouble powering new breed of peripherals

Existing USB ports may face trouble powering new breed of peripherals

Summary: Contrary to popular belief, at least from a power perspective, not all USB ports are created equal. That's what I learned yesterday during an e-mail exchange with Buffalo Technology's Brian Verenkoff.


Contrary to popular belief, at least from a power perspective, not all USB ports are created equal. That's what I learned yesterday during an e-mail exchange with Buffalo Technology's Brian Verenkoff. Earlier this week, as a part of ZDNet's Deputy Tester of the Week program, I announced that the next person to be named a ZDNet deputy reviewer would get a free 80GB USB-based hard drive from Buffalo Technology.

There are tons of USB drives on the market. Buffalo's unique selling proposition for this particular drive, according to the box it comes in (the drive actually ships at the end of the month) is that, in its turbo mode that requires special software drivers, it can run up to 64 percent faster. It's a claim that whoever we name to be the ZDNet deputy tester will hopefully be able to confirm or deny. With everyone on vacation this week though, I had a tough time figuring out what one of the extra cables that came with the drive is for (you can see me mention this in the video attached to the aforementioned blog post). Included in the box was a regular USB cable for connecting the drive's USB port to a PC's USB port. But also included in the box was another cable with a USB jack on one end, and a power jack that fits the drive's power port on the other. The first obvious question to me was, isn't the first cable all that's needed for both data and power?

As it turns out, depending on your PC, maybe not. And that's because, as I said earlier, not all USB ports are created equal. Yes, they all offer 5 volts. But where they often differ, according to Verenkoff, is on amperage which could be equally important to the peripheral people are looking to power -- particular power hungry devices like hard drives.

Verenkoff did such a great job explaining this to me via e-mail, that I'm just going to cut and paste his explanation here into this blog post. It's a must read.

[The first issue] is Amps vs Volts. Amps is volume, volts is pressure. The best example is a garden hose. Volts is the pressure of the water coming out of a hose. You can raise the pressure by putting your finger over the end of the hose (increasing the pressure and making the water go further). However, the actual amount of water coming out of the hose doesn't change. The amount of water being supplied through the hose is amps. Amps or volume doesn't change as the pressure increases or decreases. Watts is actually the measure of amps and voltage combined, but it is not applicable to the discussion we're having.

Where as all USB ports support the 5 volt requirement in the USB specification, amperage varies from one system to the next. 500 milliamps (ma) appears to be the standard with many notebooks supporting more. You have to remember that originally, USB was designed for mice, flash memory, and other low power devices. Any device you plug into a USB port on a computer and do not plug into an AC adapter is running at 5v and generally low amperage.

Devices like USB keychain flash drives and mice run at 5v but only require limited amounts of power (or amperage). However, larger devices like 3.5" USB Drives, external speakers, etc. require significant power and often need to be plugged into the wall. The USB cable on those types of devices just uses the 5v USB as a communications protocol to send data, not to try and power the device.

A USB hard disk drive literally has a hard disk drive (HDD) inside of it. A HDD itself has a motor which spins the platters as well as another motor that moves the heads around the platters. This requires a lot of power since things are moving. A 2.5" USB HDD (portable HDD) is one of the few devices that has moving parts that can still be powered by the limited amperage of many USB ports.

Every computer has different amperage at their USB ports. For example, even in some of the new Macbooks, we've observed a low amperage of 500ma. USB HDDs happen to be the main device that really becomes a problem on low amperage USB ports. Today, most computer manufacturers realize that USB HDDs will be used and are taking measures to make sure there's enough amperage in their USB ports. [But, there are still some systems out there (new and old) whose USB amperage is too low to power USB HDDs.] Many older laptops for example were designed before USB HDDs were widely used.

All USB HDDs require different amounts of power. The variable here is the actual HDD inside. Generally, larger drives require more power because there are more platters inside. When there are more platters it takes more power for the motor to spin them. Also, more platters = more heads for the platters. Those heads are on their own motors as well. Finally, faster RPM drives require more power to spin their motors faster (just like running a car engine faster uses more gas). There are also slight variations in the amount of power between similar drives. For instance, a Western Digital 80GB 2.5" HDD may use more or less power than an almost identical Seagate 80GB 2.5" HDD.

As far as Buffalo, our experience shows that 80 and 120GB drives work fine without any additional power. We are just now producing the 160s and 250s and haven't tested them yet, but we will soon. However, there have been reported problems with other manufacturer's 80s and 120s NOT working without another form of power.It's also worth noting that many manufacturers do not provide ANY alternative way of increasing amperage.

So, the reason we provide the power assist cable is to make sure that our customers have a backup if they need it. We've had this cable since our original drives, mainly so people with older notebooks could use them, however, now it's nice to have because of the 500ma Macbook limitation. This may come more into play as we see 250 and 300GB (and higher) USB Portable HDDs in the near future. The cable is completely optional and only required if you need more than 500ma.

Unfortunately [for those checking notebook data sheets to see if their USB amperage is enough to power all drives], we cannot say an exact mA number for what our drives use because it's ever changing based on the HDDs. Even HDDs with the same part number can have small internal changes that fluctuate that number. We're not a HDD manufacturer, but we've been closely testing the drives we select for our products to give them the best chance of working with only 500ma. In the event they don't, the power assist cable is available.

Using the power assist cable provides another 500ma over from the second port (for a total of 1000ma of power from both ports. It uses the first USB port for 500ma power and USB communication (data) and uses the second port ONLY for 500ma power (no data travels over that USB cable).

I recommend Googling the following string: "western digital passport not enough power" You can read forever about the problems they're having [DB's note: example here] and here's a thread from Apple's support forum that illustrates the 500ma problem.

The HDD manufacturers have been trying to reduce their power draw. Most people tend to be blaming the USB HDD manufacturers even though their not the ones who make the notebook or the USB port. It appears this problem is most significant on Apple's and most other notebooks haven't had this problem for years. In Buffalo's case, we don't make the notebook or the actual HDD inside so we look to find drives that draw the least power.

Wow. Interesting explanation and it certainly opens my eyes to some important issues having to do with USB ports. I wonder if this also explains why some AC adapters with a USB jack on one end won't charge just any USB-based rechargeable device. For example, I have a bunch of chargers that output their charge through a mini-USB jack, but some simply won't charge my Motorola Q or my wife's Motorola Razr.

In Buffalo's case, the net net is that you won't need second cable in all situations. But just in case you do, it's there. For those situations where you don't have a spare USB port to accommodate the second cable, I asked Verenkoff if one could get the drives with an AC adapter and the answer was not durrently.

Topics: Storage, Hardware, Networking

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  • Seagate uses this theory also

    I have noticed on my Seagate and Western Digital pocket drives that there were two USB Ports on them. WD only sent one cable with it's drive but Seagate actually sent 2 and labeled them (one says "Data" and the other "Power"). This is explained by the fact that if the user has a V1.1 USB Port then the second cable might need to be used for power but most V2.0 ports should provide enough power.
  • USB Spec says 500mA is the max

    The USB specification says that the maximum power that a single device should draw from a single USB port (1.1 or 2.0) is 500mA. If your device draws more than 500mA from a single port then it is the fault of the device, not the USB port!
    • Eek!

      Current IS NOT POWER.
      • But

        a device drawing 500mA maximum at constant 5V should draw 2.5 Watts maximum. No?

        Jack-Booted EULA
        • Max power allowed by spec.

          Here is a clear description of voltage drop allowed at max allowed current load. The 5v is allowed to droop a little so not quite 2.5W. Also at startup the draw allowed is a max of 100mA until the 500mA is negotiated:
    • not quite

      The USB spec says that the total current out of any USB port is 500mA, and then only if the device negociates with the USB controller and the controller allows the port to have it! The nominal total current is otherwise 100mA.

      What this means is that if you connect an unpowered hub to your port, then a couple devices off the hub, the total current going to that hub has to conform to the spec.
  • That's why Apple is TEH BESTEST EVAR!!!

    I get 1.21 gigawatts out of my USB ports!
    • SO YOU are the one

      that is causing all the rolling blackouts! Truth be told! ]:)
      Linux User 147560
    • I used to think you were 13

      No I don't think you are over the age of 10
  • Would this cover the problem I have with

    a computer that will not boot with the printer USB cable plugged in? It sits with a cursor flashing in the upper left hand corner until I unplug the USB cable from the printer, at which point it then proceeds boots up normally. I then plug the cable back into the printer and it functions as designed.

    Would a voltage drop of a sort at the USB port somehow keep the system from booting correctly? The printer had never caused this issue on the two other systems it was previously connected to, nor do the 2 other, externally supplied power USB devices cause this issue.
  • A consequence of...

    Intel choosing to introduce USB2 when the greatly superior FireWire standard was
    already available and in general use. Did Intel really find it so repulsive to put
    someone else's technology on their motherboards that they found it necessary to foist
    an inferior product on unsuspecting users, then use their market share muscle to
    make it ubiquitous?
    Fred Fredrickson
    • 1.21 Gigawatts and Firewire

      Well lets see...1.21 Gigawatts /5 Volts = 250 million Amps. Now that Apple's gonna blow one heckuva fuse :)

      As for Intel not adopting firewire, my undrestanding is that OEM's didn't want to pay a per unit license to Apple to use it so Intel offered an alternative. And as is usually the case in consumer tech wars, the inferior technology won.
      • Funny about royalties

        The FireWire licence fee was a trivial amount - $0.25. The cost of the hardware was
        $1 to $2. Had it been implemented as widely as USB, it would likely have cost much
        less. The difference at the point of sale may have been $10.

        If Intel had implemented it on the motherboard, OEMs wouldn't have cared, as long as
        they [b]all[/b] paid the same amount (which is what happens with USB). FireWire has
        been available since 1995, it seems absurd that its reign should have been usurped by
        USB. Even iPods now use it.
        Fred Fredrickson
    • Superior Firewire?

      I can walk into just about any store in the world and buy USB devices, while firewire is nowhere to be seen, except maybe on video cameras. USB is the defacto standard. While firewire is a little faster, most devices don't need the extra speed. For those that do, like external hard drives, there is ESATA.
    • One problem with your theory.

      Most Intel motherboards do have firewire on them as well as USB. Just exacyly how is 1394 superior?
  • External hard drives

    I have two external hard drives, an older Maxtor that I upgraded from 40 GB to 250 GB, and a newer ESATA 250 GB drive (AZIO case, WD drive). Both came with external power supplies, which I insist upon. Early on, I noticed that when connecting multiple USB devices that I would run into trouble if I had several devices drawing their power from the USB ports (ie, the motherboard). One solution to this is to use a USB hub that is self powered, thus shifting the power draw off of the motherboard. For heavy current users, like hard drives, a separate power supply makes sense.
  • Maxtor OneTouch™ III Mini Edition has a 'Y' USB cable also

    One end in the ext. drive, the other two in the computer's USB ports. Great if the drive requires more power, sucks to use two USB ports up...

    Mind you, the alternative of drive failure (read: WD Passport drives) is a whole lot worse..
  • The reason your Motorola Q won't charge ...

    ... is an entirely different issue. Motorola purposely turns off charging for all but Motorola approved devices. It is called vendoe lock-in.
  • Old story...

    Lacie's Porsche drives have had the extra power cable for years. It was needed on my old Dell Inspiron 8600. In fact, even *with* the extra cable, the Dell failed to drive the Lacie about 1 time in 5. The Dell had such puny USB power it wouldn't even drive most HP inkjet printers. At the time (2004) Dell Support seemed unaware of the problem - or, more likely was in denial.
  • USB 500 mA Limit is NOT by Port, but by Host-Adapter !!!


    When you connect your Mouse Printer HDD etc. to USB then any such Device has to identify, telling what kind of Device etc. etc. etc. AND telling how much POWER in Milli Amperes would be needed in MAXIMUM by this Device. Then the USB-Component on the Host- (= PC, Mac etc.) -Side calculates the Sum of Power already requested by OTHER USB-Devices attached ON THE SAME HOST-CONTROLLER. And now, when the newly attaching Device would EXHAUST 500 mA with his Power-Hunger - then the Host-Controller would say: sorry, not enough juce available to satisfy you.

    So when requesting Power with TWO (ore more) USB-Cables for the same Device, it could depend if you attach those Cables ON THE SAME HOST-CONTROLLER or on DIFFERENT HOST-CONTROLLERS of your PC, if you get the Power you ask for of if you dont get it.

    But, normally you would NOT know to which Host-Controller you are hooking in - in your Eyes its just a USB-Connector - and normally you would NOT look inside your Computer-Electronics to find out if its good to plug there or not.

    Badly concepted Devices do not tell the truth - for example saying they need 25 mA - but in Reality they eat much more. This could severly harm the Host-Controller concerned, or also other Parts of your Computer.

    Consuming lot's of Power over USB is NOT good at all.

    Ther is a new Standard in the Sky - Power USB. It's the same Adapter to plug In CONCERNING THE DATA LINES, but the Adapter has bonded a SECOND Part for POWER (5 Volt, 12 Volt and 24 Volt; Color coded; Pin secured). If you buy a new PC etc. and if you have the Option to chose, then take the Computer WITH Power-USB - because you will be able to attach ANY Device (Power-USB and the old one).

    Good luck, Simon