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Thanks, Mac. Really appreciate the info. Quick question: Is there anything out there (hardware or software) that will reliably let me test how much current a USB drive is drawing, instantly and/or over time -- and is there anything out there that will let me test how much current my various USB ports on different computers (and hubs) are supplying?



As an R&D and Testing EE, I use a USB cable that I tapped into such that I can insert my Digital Voltmeter and my Digital Ammeter into the line.

But if you have to ask that question, it is likely ou7tside the scope of what you should be doing. Very easy to toast the mobo with a wrong connection or a chance brushig fo that line to the chassis, things like that.

On top of that, we have no Current specs available for the various USB drives for the most part, which means that even after I've found out how much current a certain port can deliver, I have no way of translating that to a specific drive that would or would not run correctly without actually obtaining a sample of the drive and putting it on the testbench and measuring as per the above.

Since the drive is also starting and stopping at least two electromagnetic motors, there is also the inrush current to take into account, too. That is like a "burst" that is needed when the motor coils first fill up with electrons. Once the inrush is over, the Current settles down to a steady state that is typically much lower than the inrush state. If your port cannot handle just the amount of current needed during that critical inrush period, the motors may not start. By "motors" I am referring not only to the spinning one that turns the disks, but to the reciprocating headarm motor as well.


--Mac

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