Re: Calling electrical experts - Din rail PSU 240vac to LV dc

[David Yeend <david.yeend@xxxxxxxxx>]

Thanks for your comments Keith - some very important considerations
there. I'll certainly do a bit of investigation with this in mind.

Ta.

David


On Wed, 24 Nov 2004 20:44:33 -0000, Keith Doxey <ukha@xxxxxxx> wrote:
>
> Hi David
>
>
>
> > -----Original Message-----
> > From: uktiggs [mailto:david.yeend@xxxxxxx]
> > Subject: [ukha_d] Calling electrical experts - Din rail PSU
240vac to LV
> > dc
> >
> > I am fed up with the number of plug pack PSUs which require
numerous
> > mains sockets and take up so much space.....
> >
> > I have thought about using one big powerful DC PSU to drive a
> > concoction of regulators giving individual outputs at multiple
(maybe
> > adjustable) voltages.
> >
> > Anyone got any comments on this?
> >
>
> Just a few things to watch for....
>
> ... equipment that uses Wall Wart power supplies *USUALLY* has the
negative
> side of the power socket connected to the ground of its circuitry and
all
> voltages within it are positive with respect to ground.
>
> BUT... there are some pieces of equipment that will have the POSITIVE
side
> of the power supply connected to its ground rail and all its circuitry
is
> negative with respect to ground.
>
> There are also pieces of equipment that generate a psuedo ground rail
> internally which is connected to the ground of inputs and outputs. In
this
> case the ground of the unit is actually half the supply voltage. ie
you feed
> it a 12V supply from which it regulates a 6V rail. This can be refered
to as
> 0 +6 +12 supply but only if ground is actually connected to the most
> negative rail.
> If ground was connected to the middle rail it is then a -6 0 +6 supply
and
> you will be in trouble if you then connect this to other equipment
powered
> from the same source if that equiment gronds the most negative rail.
>
> Whilst using individual wall warts, all these rails are floating so
there is
> no problem interconnecting different bits of kit then connects there
> respective grounds together and if one is positive ground and the
other is
> negative ground you have a short circuit across your power supply
which if
> meaty enough could result in some serious damage.
>
> As long as all bits of kit use negative ground you wont blow anything
up but
> you can introduce ground loops via the grounds of the kit and the
negative
> of the supply rail.
>
> Dont forget to add some inline fuses to each lead particulary if it is
a
> really hefty supply, partly to protect the devices but also to prevent
one
> piece of kit blowing the power supply for all the other items.
>
> Hope that helps
>
> Keith
>
>
>
>
>
>
>
> Yahoo! Groups Links
>
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