Power supply 'return' confusion

I

Igmar Palsenberg

Guest
Hi,

I've got a piece of equiptment lying around here which I need to bring
alive. However, the naming on the power supply confuses me.

It says :

-48 volt
-48 volt return
Ground connection to supply

The -48 volt return confuses me : What is that ? The PSU that I have
supplies -48 and +48 volt, and a ground. Can this PSU power that piece
of equiptment ?

Any hints are welcome.


Regards,

Igmar
 
It might be less confusing if the terminal labeled '-48 volt return' were
thought of as being 'common'.
On some power supplies, the 'common' terminal is at the same potential as
'ground' (chassis ground),
on others, like the one you have, it is isolated or floating from
(chassis)ground.

The replacement supply you have with +48, -48 and 'ground' is a dual supply.
That is.. +48 volts between the ground and + terminal, -48 from the ground
to the - terminal. There would be 96 volts between the + & - terminals. The
'ground' terminal is the common (return) and may or may not be actually
connected to chassis ground. You can use this supply for replacement by
using only the - and ground terminals taking into consideration that you may
have to physically isolate the 'ground' on it if it would cause a conflict.

Is that any hhelp or did I just confuse you more?
Kevin


"Igmar Palsenberg" <devnull@jdimedia.invalid> wrote in message
news:401a1092$0$321$e4fe514c@news.xs4all.nl...
Hi,

I've got a piece of equiptment lying around here which I need to bring
alive. However, the naming on the power supply confuses me.

It says :

-48 volt
-48 volt return
Ground connection to supply

The -48 volt return confuses me : What is that ? The PSU that I have
supplies -48 and +48 volt, and a ground. Can this PSU power that piece
of equiptment ?

Any hints are welcome.


Regards,

Igmar
Click to expand...
 
krikkit wrote:
It might be less confusing if the terminal labeled '-48 volt return' were
thought of as being 'common'.
On some power supplies, the 'common' terminal is at the same potential as
'ground' (chassis ground),
on others, like the one you have, it is isolated or floating from
(chassis)ground.
Click to expand...
Why are those labelled this way ? The reason I didn't hook it up is that
I can't be for sure it's wired OK, and i'll blow things up.

The replacement supply you have with +48, -48 and 'ground' is a dual supply.
That is.. +48 volts between the ground and + terminal, -48 from the ground
to the - terminal. There would be 96 volts between the + & - terminals. The
'ground' terminal is the common (return) and may or may not be actually
connected to chassis ground. You can use this supply for replacement by
using only the - and ground terminals taking into consideration that you may
have to physically isolate the 'ground' on it if it would cause a conflict.
Click to expand...
The PSU does have a real grounded common, so that should be OK. I'll
check for sure with a scope, not having a proper grounding should be
easely spottable with one.

Is that any hhelp or did I just confuse you more?
Click to expand...
Partly. I just wonder why they don't put +48 and ground on it instead of
-48 and 'return'.

Kevin
Click to expand...

Igmar
 
Phone system does not use +48 volts. It uses a -48 volts
relative to ground.

Igmar Palsenberg wrote:
Why are those labelled this way ? The reason I didn't hook it up
is that I can't be for sure it's wired OK, and i'll blow things up.

...

The PSU does have a real grounded common, so that should be OK.
I'll check for sure with a scope, not having a proper grounding
should be easely spottable with one.
...
Partly. I just wonder why they don't put +48 and ground on it
instead of -48 and 'return'.
Click to expand...
 
It might be less confusing if the terminal labeled '-48 volt return'
were thought of as being 'common'.
Kevin (krikkit)
Click to expand...
True. Other ways of saying this are
"zero volts" or "the return path for the -48 volt supply".
 
w_tom wrote:
Phone system does not use +48 volts. It uses a -48 volts
relative to ground.
Click to expand...
In other words : just -48 volts and ground. Now let's start the hunt for
the right connectors :)



Igmar
 
On Sat, 31 Jan 2004 18:35:48 +0100, Igmar Palsenberg
<igmar@nonexistant.local> Gave us:

w_tom wrote:
Phone system does not use +48 volts. It uses a -48 volts
relative to ground.

In other words : just -48 volts and ground. Now let's start the hunt for
the right connectors :)
Click to expand...
It's positive 48 volts with the positive leg grounded, if one wants
to be technical about it. It all about reference points.
 
DarkMatter wrote:
On Sat, 31 Jan 2004 18:35:48 +0100, Igmar Palsenberg
igmar@nonexistant.local> Gave us:

w_tom wrote:
Phone system does not use +48 volts. It uses a -48 volts
relative to ground.

In other words : just -48 volts and ground. Now let's start the hunt
for the right connectors :)


It's positive 48 volts with the positive leg grounded, if one wants
to be technical about it. It all about reference points.
Click to expand...


Have a look at

http://homepage.ntlworld.com/g.knott/elect110.htm
 
On Sat, 31 Jan 2004 19:15:03 -0000, "grahamk" <g.knott@ntlworld.com>
Gave us:

Have a look at

http://homepage.ntlworld.com/g.knott/elect110.htm
Click to expand...

With OUR HV supplies, the "black" lead is always ground.

That means that if one sees an HV supply with a red led, it is a
positive supply.

If the output lead is clear, it is a negative supply.

Black is always assumed as ground, and is never elevated in
potential with respect to ground. It can be negative or positive,
just not with respect to ground. ONLY with respect to the PS output
lead.
 
Igmar Palsenberg <devnull@jdimedia.invalid> wrote in message news:<401a1092$0$321$e4fe514c@news.xs4all.nl>...
Hi,

I've got a piece of equiptment lying around here which I need to bring
alive. However, the naming on the power supply confuses me.

It says :

-48 volt
-48 volt return
Ground connection to supply
Click to expand...
This Naming convention often is used to indicate that the -48V Return
is not tied to ground (or cannot be reliably thought of as being tied
to ground)
Telco equipment often keeps the 48V supply and chassis/shield Grounds
seperate so that the Telco can implement their own grounding regime.

Regards
Richard Freeman
 
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