Top positive review
538 people found this helpful
For you EE propeller heads out there, here is some electrical data
on August 3, 2010
I have bought a LOT of the 2TB WD Caviar drives. I have had excellent results with them on my iMac. I use them primarily for data storage where fast data retrieval is not a consideration. I'm more concerned with plugging them into these USB-based drive docks when I need the data. However, I'm also interested in them from an electrical perspective, just because ... well, just because I'm interested in them. Over the years I have worked my way up the ladder of hard drive storage capacities. Like many of you, I've been rather appalled at how hot these older models would get. I swear, you could fry an egg on some of them. I never felt comfortable with their longevity, fearing that they would most likely burn themselves up. Fortunately, none did.
When the Caviar Green product line came out (1TB was when I first took notice), I was quite intrigued at the claimed power reduction. In electronics, heat is the main enemy of components. Usually every 10 degree C rise in temperature translates into a halving of component life. The Caviar brand looked like a way to get a much more reliable drive if the power reduction numbers actually panned out.
I took one of the drives in to work where I have fancy test gear at my disposal. In particular, I have some very good Tektronix current probes that let me measure DC and AC currents. I built a little cable that let me get to the +12V and +5V lines so that I could clamp my current probes around the wires to measure current consumption. I connected the two power leads to power supplies so that I could also vary the two voltages. In this fashion, I can accurately see and measure power consumption of the drive as I exercise the drive. I get far more accurate measurements this way than you can with a simple watt-meter, which seldom let you see fractional watts.
Since I can't (actually, don't know how to) embed scope photos in this review, all I can do is verbally describe my observations. My tests are far from extensive, but they will give you a good idea of how much power these drives draw, and when they draw it.
* When the drive is just sitting there, doing nothing but spinning, the +12V current drain is 0.24A and the +5V drain is 0.13A. That totals 4.2 watts of power during idle. I have not measured earlier, high-power drives, but I'm willing to bet the Caviar Greens draw at most half the power of traditional hard drives. I would not be surprised if it were 1/3 the power.
* If you shut off one voltage, the other supply stops drawing all power. It's a convenient way to power the drives on and off. I would suggest power cycling the +5V rail as the circuitry to shut off the +5V supply with a simple PFET is simpler than that for the +12V rail.
* When the drives are first powered up, +5V draws an almost constant 500-600 mA. +12V current is a ramp, starting at 200 mA and works its way up to 600 mA after about 10 seconds, when the drive is then up to speed. At this point, the +12V peak current drops down to idle spinning) current of 0.24A. It does not vary much after this, regardless of disk activity (erase, write, read, etc.). On the other hand, the +5V supply current gets busy. It's pretty clear that the head servo is driven from the +5V supply and not the +12V supply. It's hard to verbally describe the +5V current, but I would say the average current during head movement activity is about 400 mA. When there is no activity, the +5V current is about 0.13A. When the drive is done doing what it is doing, then it drops into the 4.2W idle power mode that I mentioned above. If you are a power supply designer, you should be aware that these DC currents I cite are averages, and that you have a "hash" of AC currents that result in the average values I list. The +5V current has a hash of about 300mA p-p, and the +12V current hash is maybe 400mA p-p.
* I have never succeeded in getting OSX to put the drives to sleep. I've tried all the utilities in the Mac universe (SpinDown, Cocktail), but no matter what you do, the drives never want to got to sleep, at least for me. If WD puts out a utility for the PC, they certainly offer no support for OSX. Even if you properly eject the drives from the desktop, they sit there spinning and drawing 4.2W. Hardly seems "fully green" to me.
* During the idle mode, my infrared thermometer measures a case temperature rise of 12 degrees C, which is a pretty low number. UL safety limits for human hand touch temperatures are usually between 50-55 degree C -- you'll begin to pull your hand back at that temperature range. So if the drive is 12 degrees above ambient, and you are sitting at normal room temperatures (25 degrees), then your drive temperature is only about 37 degrees (98.6 degrees F, just like a human!). This explains why people are reporting that the drive "feels pretty cool." As these things go, they do indeed run quite cool.
Here's hoping that some of you more technically-inclined customers out there find this data useful.