RE: [OT] USB voltages and grounds

["Paul Gale" <groups@xxxxxxxxxxxxxxxx>]

Thanks Keith & Nick :)

I think I'll pull the maze of wiring out and have a bit of a tidy and
re-organisation.

Oh, I forgot to also mention that this PC (two different mainboards now)
sometimes doesn't power up - hangs at the detecting USB controllers stage.
If I disconnect some of the USB peripherals (seems to mainly be a printer
on a long run of cable) that it mostly boots - but not all the time - a bit
hit and miss.

Paul.



> -----Original Message-----
> From: ukha_d@xxxxxxx [mailto:ukha_d@xxxxxxx] On Behalf Of
> Keith Doxey
> Sent: 19 September 2006 19:46
> To: ukha_d@xxxxxxx
> Subject: RE: [ukha_d] [OT] USB voltages and grounds
>
> Hi Paul
>
> > I've caused Windows to hang a number of times when plugging in
> > USB cables and had the spark :(
> >
> > Is there nothing else that can be done? Seems pretty poor design?
> >
> > Some of my kit is powered from sockets on opposite sides of the
> > room (some through UPS's, filtered power strips etc - quite a
> > mess of 50+ plugs and transformers!!!). Will this contribute to
> > the problem?
> >
>
> It shouldnt matter because all your sockets are on the same ring main
so
> have the same earth. The problem is caused by floating Switch Mode
power
> supplies which are double insulated which means they dont have an
earth
> connection so any leakage just appears on the output. They should be
easy
> to
> spot as they will have a logo with a square inside a square and if
they
> are
> wall wart types will almost certainly have a plastic earth pin.
>
> Thinking about this a bit more, if you have several such items linked
> together the leakage will be accumulative to the point where it can
give
> you
> nasty nip, if you were then to try connecting this to something
grounded
> the
> spark would be more intense.
>
> The only possible solution I can think of is to have all the USB
> connections
> permanently made, or use a USB switch box which will at least maintain
the
> grounding of the shields even the the device is effectively
"unplugged"
>
> One other thing you can try.... because the PC is grounded it is
almost
> certainly the kit you are connecting that is floating. Perhaps you
could
> connect up the USB connection between Kit and PC with the KIT
DISCONNECTED
> FROM MAINS. Once the two items are bonded together reconnect the mains
to
> the piece of kit and power it up. Inconvienient I know but I cant
think of
> any other alternative other than bonding the chassis of each item
together
> prior to connecting them up by USB
>
> Keith
>
>
>
>
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