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90V AC on hard disk?!?

Discussion in 'Beginner Electronics' started by Major Scott, May 1, 2013.

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  1. Major Scott

    Major Scott Guest

    I have a USB hard disk enclosure, and I'm running it without it's case as I'm testing another drive with it. When I touched the hard disk with my hand and the case of the computer (which is earthed) with my arm, I felt a tickle. So I connected a multimeter to it, and the hard disk is at 90 volts AC with a short circuit current of 0.136 mA. Is this normal? Is this a good idea when working with delicate computer electronics? I suppose the ground of the USB lead will get rid of it but it seems a bit odd. The USB disk unit is powered by a cheap wall wart that came with it, rated 12V DC 1.5A.
  2. Major Scott

    Major Scott Guest

    It works though.

    I've had a similar voltage out of the composite output of a VCR. That's the trouble with these double insulated things that aren't earthed.
  3. Major Scott

    Major Scott Guest

    That sounds rather strange to me. Especially where delicate electronics are involved. Imagine I connected the USB hard disk, while it was powered up, to the computer, and the USB plug's grounded chassis managed to touch one of the signal contacts.
  4. Major Scott

    Major Scott Guest

    If Ian is correct it won't help. I'd have to find one in my huge box of them with the right output then change the plug. I'll just be careful with it.
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