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90V AC on hard disk?!?

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Major Scott
Guest

Wed May 01, 2013 9:40 am   



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.

David Moorman
Guest

Wed May 01, 2013 2:59 pm   



In article <op.wweftxev2eh2io_at_red.lan>, "Major Scott" <no_at_spam.com>
wrote:

Quote:
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.

Something is effed up.

Major Scott
Guest

Wed May 01, 2013 3:14 pm   



On Wed, 01 May 2013 15:59:33 +0100, David Moorman <dmoorman4_at_comcast.net> wrote:

Quote:
In article <op.wweftxev2eh2io_at_red.lan>, "Major Scott" <no_at_spam.com
wrote:

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.

Something is effed up.

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.

--
I had some words with my wife, and she had some paragraphs with me.

Ian Field
Guest

Wed May 01, 2013 9:38 pm   



"Major Scott" <no_at_spam.com> wrote in message
news:op.wwevayr22eh2io_at_red.lan...
Quote:
On Wed, 01 May 2013 15:59:33 +0100, David Moorman <dmoorman4_at_comcast.net
wrote:

In article <op.wweftxev2eh2io_at_red.lan>, "Major Scott" <no_at_spam.com
wrote:

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.

Something is effed up.

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.


Any double insulated SMPSU has filter caps from each mains pole to the
equipment 'ground' - they form a capacitive voltage divider (Xc + Xc).

Major Scott
Guest

Wed May 01, 2013 9:46 pm   



On Wed, 01 May 2013 22:38:58 +0100, Ian Field <gangprobing.alien_at_ntlworld.com> wrote:

Quote:


"Major Scott" <no_at_spam.com> wrote in message
news:op.wwevayr22eh2io_at_red.lan...
On Wed, 01 May 2013 15:59:33 +0100, David Moorman <dmoorman4_at_comcast.net
wrote:

In article <op.wweftxev2eh2io_at_red.lan>, "Major Scott" <no_at_spam.com
wrote:

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.

Something is effed up.

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.

Any double insulated SMPSU has filter caps from each mains pole to the
equipment 'ground' - they form a capacitive voltage divider (Xc + Xc).

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.

--
H lp! S m b d st l ll th v w ls fr m m k yb rd!

Rheilly Phoull
Guest

Wed May 01, 2013 11:48 pm   



On 02/05/13 05:46, Major Scott wrote:
Quote:
On Wed, 01 May 2013 22:38:58 +0100, Ian Field
gangprobing.alien_at_ntlworld.com> wrote:



"Major Scott" <no_at_spam.com> wrote in message
news:op.wwevayr22eh2io_at_red.lan...
On Wed, 01 May 2013 15:59:33 +0100, David Moorman
dmoorman4_at_comcast.net
wrote:

In article <op.wweftxev2eh2io_at_red.lan>, "Major Scott" <no_at_spam.com
wrote:

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.

Something is effed up.

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.

Any double insulated SMPSU has filter caps from each mains pole to the
equipment 'ground' - they form a capacitive voltage divider (Xc + Xc).

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.

Could be time to try another PSU ??


Major Scott
Guest

Wed May 01, 2013 11:51 pm   



On Thu, 02 May 2013 00:48:23 +0100, Rheilly Phoull <rheilly_at_bigslong.com> wrote:

Quote:
On 02/05/13 05:46, Major Scott wrote:
On Wed, 01 May 2013 22:38:58 +0100, Ian Field
gangprobing.alien_at_ntlworld.com> wrote:



"Major Scott" <no_at_spam.com> wrote in message
news:op.wwevayr22eh2io_at_red.lan...
On Wed, 01 May 2013 15:59:33 +0100, David Moorman
dmoorman4_at_comcast.net
wrote:

In article <op.wweftxev2eh2io_at_red.lan>, "Major Scott" <no_at_spam.com
wrote:



Something is effed up.

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.

Any double insulated SMPSU has filter caps from each mains pole to the
equipment 'ground' - they form a capacitive voltage divider (Xc + Xc).

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.

Could be time to try another PSU ??

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.

--
New here? Pull up a chair and we'll plug you in.

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