Negative 48 Volts DC

On 1/25/20 12:57 PM, Jeff Liebermann wrote:
> Please note that red=positive and black=negative is an color automotive 
> standard.  Color codes are VERY different in other industries.

All of the -48 VDC equipment that I've seen used have used red, black, 
and maybe green for a safety ground.

I think that red is the "hot" wire with -48 VDC with reference to the 
black "common" wire.  But I'm not sure.

See my other message ~5 minutes ago for more details.



-- 
Grant. . . .
unix || die

On 1/25/20 1:42 PM, Steve Wilson wrote:
> Telephone companies can drive a large ground rod into the soil to take 
> care of the loss of ions at the positive terminal. This protects the 
> positive copper terminal from corrosion. Since there is no corrosion 
> at the negative terminal, the copper wires are protected and can 
> remain buried forever.

Interesting.  So the ground rod is for more than just safety.  It's 
actually used to control / prevent corrosion too.



-- 
Grant. . . .
unix || die

On 1/25/20 2:42 PM, Steve Wilson wrote:
> jlarkin@highlandsniptechnology.com wrote:
> 
>> I think positive ground has some sort of corrosion advantage.
> 
> Not in cars. For telephone wires, it's a different story.
> 
> It's simnple high school chemistry. Electrolysis liberates metal ions at the
> positive terminal and produces OH- at the negative terminal.
> 
> when copper is at the positive terminal, copper ions are released. This
> corrodes the copper.
> 
> When copper is at the negative terminal, there is only OH- produced. There is
> no corrosion.
> 
> Telephone companies can drive a large ground rod into the soil to take care
> of the loss of ions at the positive terminal. This protects the positive
> copper terminal from corrosion. Since there is no corrosion at the negative
> terminal, the copper wires are protected and can remain buried forever.
> 
      I guess pipeline companies bury old pipe out in fields then send 
some current out to the buried pipe.  That protects the actual pipeline 
they want to use.

On Saturday, January 25, 2020 at 3:38:40 PM UTC-5, Grant Taylor wrote:
> On 1/25/20 12:28 PM, George Herold wrote:
> > Right, Say you have a 48V battery.
> 
> Okay.
> 
> > You hook up the neg. terminal to ground, you've got +48V at the 
> > positive terminal.
> > You hook up the pos. terminal to ground and it's -48V at the negative 
> > terminal.
> 
> This seems to assume that you hook the negative terminal of your meter 
> to ground and the positive terminal of your meter to the other battery 
> terminal.
> 
> So with a positive ground system, the meter's negative terminal is 
> hooked to the batteries positive terminal and the meter's positive 
> terminal is hooked to the batteries negative terminal.
> 
> This I think that "ground" / "common" is largely irreverent in this 
> scenario.  The only way that I think it starts to make any difference is 
> if you don't measure at the batteries terminals and instead measure off 
> of a different circuit in the car reference to common.
> 
> 
> 
> -- 
> Grant. . . .
> unix || die

Voltages are about differences.  You have to set 'zero' somewhere... 
or we can't really talk about it.  Ground is a common point (NPI) 
you can float everything above ground... but it gets dangerous to touch 
above ~60V (depends on source impedance)
GH. 
Are you an EE?  

On Saturday, January 25, 2020 at 3:44:27 PM UTC-5, Grant Taylor wrote:
> On 1/25/20 12:33 PM, Rick C wrote:
> > I'm at a loss to understand what you are confused about.  Do you have 
> > any specific questions???
> 
> I have a -48 VDC power supply with an unlabeled terminal and a return 
> terminal.
> 
> Other sets of DC equipment & associated supplies (multiple small sets of 
> different supplies and equipment used for various things) use red and 
> black wire.
> 
> What is return? red or black
> 
> What voltage should be read when connecting the meter's positive / red 
> lead and negative / black lead to the red & black wires from the DC supply?
> 
> How should things be wired to a piece of equipment that has the ground 
> symbol on one terminal and the other terminal unlabeled?
> 
> My brain is having problems aggregating all of these and making 
> associations.
> 
> > How does any of this impact using the 48 volts to supply the equipment 
> > you list?  In other words, why are you confused?
> 
> Which terminal of the DC source; unlabled and return, connects to the 
> ground terminal on the DC load equipment?
> 
> 
> 
> -- 
> Grant. . . .
> unix || die

Go to harbor freight (assuming you live in US) buy the cheap DMM 
and measure it!  Otherwise you have no idea how red and black are set.
GH

On Saturday, January 25, 2020 at 3:49:25 PM UTC-5, Grant Taylor wrote:
> On 1/25/20 12:57 PM, Jeff Liebermann wrote:
> > Please note that red=positive and black=negative is an color automotive 
> > standard.  Color codes are VERY different in other industries.
> 
> All of the -48 VDC equipment that I've seen used have used red, black, 
> and maybe green for a safety ground.
> 
> I think that red is the "hot" wire with -48 VDC with reference to the 
> black "common" wire.  But I'm not sure.
> 

Here is the DC color code used by two very large US wireless carriers (i.e., cell phone providers) at their cell sites (and, signal sources like HetNet that act like "mini-cell sites"):

Coming off the batteries to the rectifier: (Input to the rectifier)
(The rectifier keeps the batteries charged.)
Black = Negative 
Red = +48 VDC

Output of the rectifier feeding all the radio & other cell site equipment:
(Note:  This is usually the input to a PDU, which is a fused Power Distribution Unit - a fancy name for a fused distribution block, panel-mount.)
And everything at many cell sites is 48 VDC, including the overhead lights, and sometimes even the air conditioning.

Black = Negative 48 VDC
There is a saying in the industry:  "Black to the breaker."

Grey (or White) = Return (this is 0-VDC potential relative to Earth ground), and at the rectifier, is bonded to..

Green = Earth Ground  (i.e., the main facility ground bus bar)
The equipment racks are also connected to ground using Green cable.

The cables used are typically TelcoFlex-III, 600 Volt. ($$ expensive cable)
I've seen anywhere from #10 AWG to #2 AWG, depending on how many cell site radios are installed.

On Sat, 25 Jan 2020 13:38:41 -0700, Grant Taylor
<gtaylor@tnetconsulting.net> wrote:

>On 1/25/20 12:28 PM, George Herold wrote:
>> Right, Say you have a 48V battery.
>
>Okay.
>
>> You hook up the neg. terminal to ground, you've got +48V at the 
>> positive terminal.
>> You hook up the pos. terminal to ground and it's -48V at the negative 
>> terminal.
>
>This seems to assume that you hook the negative terminal of your meter 
>to ground and the positive terminal of your meter to the other battery 
>terminal.
>
>So with a positive ground system, the meter's negative terminal is 
>hooked to the batteries positive terminal and the meter's positive 
>terminal is hooked to the batteries negative terminal.
>
>This I think that "ground" / "common" is largely irreverent in this 
>scenario.  The only way that I think it starts to make any difference is 
>if you don't measure at the batteries terminals and instead measure off 
>of a different circuit in the car reference to common.

One almost always connects a meter negative terminal to ground. That
way, you can see if the voltage you're measuring is positive or
ground.



-- 

John Larkin         Highland Technology, Inc

The cork popped merrily, and Lord Peter rose to his feet. 
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"

On Sat, 25 Jan 2020 13:44:29 -0700, Grant Taylor
<gtaylor@tnetconsulting.net> wrote:

>On 1/25/20 12:33 PM, Rick C wrote:
>> I'm at a loss to understand what you are confused about.  Do you have 
>> any specific questions???
>
>I have a -48 VDC power supply with an unlabeled terminal and a return 
>terminal.
>
>Other sets of DC equipment & associated supplies (multiple small sets of 
>different supplies and equipment used for various things) use red and 
>black wire.
>
>What is return? red or black
>
>What voltage should be read when connecting the meter's positive / red 
>lead and negative / black lead to the red & black wires from the DC supply?
>
>How should things be wired to a piece of equipment that has the ground 
>symbol on one terminal and the other terminal unlabeled?
>
>My brain is having problems aggregating all of these and making 
>associations.
>
>> How does any of this impact using the 48 volts to supply the equipment 
>> you list?  In other words, why are you confused?
>
>Which terminal of the DC source; unlabled and return, connects to the 
>ground terminal on the DC load equipment?

Ignore ricky. He doesn't want to help, he wants to insult.

Most of what he says translates to "you are stupid."



-- 

John Larkin         Highland Technology, Inc

The cork popped merrily, and Lord Peter rose to his feet. 
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"

On Saturday, January 25, 2020 at 3:44:27 PM UTC-5, Grant Taylor wrote:
> On 1/25/20 12:33 PM, Rick C wrote:
> > I'm at a loss to understand what you are confused about.  Do you have 
> > any specific questions???
> 
> I have a -48 VDC power supply with an unlabeled terminal and a return 
> terminal.

Unless there is a connection within the power supply to earth ground or some other reference point such as a ground for a control signal, the power supply is just a 48 volt power supply.  One terminal is positive and the other negative.  

When you say "return" terminal, what do you see that distinguishes the two terminals?  Is one labeled "return"?  Is that the positive terminal?  If you plug it in and measure the terminals to earth ground, what do you get?  If one approximately zero volts and the other positive or negative?  You may need to put a 1 kohm resistor across the meter to prevent seeing stray voltage while you do this. 


> Other sets of DC equipment & associated supplies (multiple small sets of 
> different supplies and equipment used for various things) use red and 
> black wire.
> 
> What is return? red or black

In typical DC electronics, red is positive and black negative.  I don't work with -48 volt circuits a lot, so I can't say that this applies for that. 


> What voltage should be read when connecting the meter's positive / red 
> lead and negative / black lead to the red & black wires from the DC supply?

What is the existing system using?  I would go with that unless you want to rewire the whole thing. 


> How should things be wired to a piece of equipment that has the ground 
> symbol on one terminal and the other terminal unlabeled?

Is the equipment designed for -48 volts?  If so connect accordingly.  I guess you are asking about colors.  I don't know convention other than in smaller gear where red is positive and black is negative. 


> My brain is having problems aggregating all of these and making 
> associations.

The main thing is to not think in terms of "reference" or "ground" but positive and negative.  You won't blow up things if you keep polarity straight. 


> > How does any of this impact using the 48 volts to supply the equipment 
> > you list?  In other words, why are you confused?
> 
> Which terminal of the DC source; unlabled and return, connects to the 
> ground terminal on the DC load equipment?

If the equipment is not presently connected (for you to measure and copy), I recommend you get a manual for the equipment and find out what polarity they are expecting.  Getting that wrong can destroy the equipment. 

-- 

  Rick C.

  + Get 1,000 miles of free Supercharging
  + Tesla referral code - https://ts.la/richard11209

On Saturday, January 25, 2020 at 5:31:54 PM UTC-5, jla...@highlandsniptechnology.com wrote:
> On Sat, 25 Jan 2020 13:44:29 -0700, Grant Taylor
> <gtaylor@tnetconsulting.net> wrote:
> 
> >On 1/25/20 12:33 PM, Rick C wrote:
> >> I'm at a loss to understand what you are confused about.  Do you have 
> >> any specific questions???
> >
> >I have a -48 VDC power supply with an unlabeled terminal and a return 
> >terminal.
> >
> >Other sets of DC equipment & associated supplies (multiple small sets of 
> >different supplies and equipment used for various things) use red and 
> >black wire.
> >
> >What is return? red or black
> >
> >What voltage should be read when connecting the meter's positive / red 
> >lead and negative / black lead to the red & black wires from the DC supply?
> >
> >How should things be wired to a piece of equipment that has the ground 
> >symbol on one terminal and the other terminal unlabeled?
> >
> >My brain is having problems aggregating all of these and making 
> >associations.
> >
> >> How does any of this impact using the 48 volts to supply the equipment 
> >> you list?  In other words, why are you confused?
> >
> >Which terminal of the DC source; unlabled and return, connects to the 
> >ground terminal on the DC load equipment?
> 
> Ignore ricky. He doesn't want to help, he wants to insult.
> 
> Most of what he says translates to "you are stupid."

Notice the troll likes to demean and doesn't actually help much himself.  

-- 

  Rick C.

  -- Get 1,000 miles of free Supercharging
  -- Tesla referral code - https://ts.la/richard11209