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Power supply 'return' confusion

I

Igmar Palsenberg

Jan 1, 1970
0
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
 
I

Igmar Palsenberg

Jan 1, 1970
0
krikkit said:
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.

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.

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?

Partly. I just wonder why they don't put +48 and ground on it instead of
-48 and 'return'.


Igmar
 
K

krikkit

Jan 1, 1970
0
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
 
W

w_tom

Jan 1, 1970
0
Phone system does not use +48 volts. It uses a -48 volts
relative to ground.
 
J

JeffM

Jan 1, 1970
0
It might be less confusing if the terminal labeled '-48 volt return'
were thought of as being 'common'.
Kevin (krikkit)

True. Other ways of saying this are
"zero volts" or "the return path for the -48 volt supply".
 
I

Igmar Palsenberg

Jan 1, 1970
0
w_tom said:
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 :)



Igmar
 
D

DarkMatter

Jan 1, 1970
0
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.
 
D

DarkMatter

Jan 1, 1970
0


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.
 
R

Richard Freeman

Jan 1, 1970
0
Igmar Palsenberg said:
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

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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