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

["Keith Doxey" <ukha@xxxxxxxxxxx>]

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