Is anyone willing to explain Negative 48 Volts DC? I'm trying to learn about it because we're using it for a few things at work (servers and switch equipment) and I'd like to better understand what we're working with than simply going through the motions that someone else dictates. Read: I want to understand and not simply rely on wrote memory. I've learned that -48 VDC uses what is called "Positive Ground" and that what I'm used to is called "Negative Ground". I'm trying to correlate and understand the typical red and black wires with them being ground / return / common / hot / etc. I suspect that there is more to it than simply reversing the + and - lead from a battery or meter. But I can't wrap my head around it. Can ~> will someone offer any comments that might help me understand better? -- Grant. . . . unix || die
Negative 48 Volts DC
Started by ●January 25, 2020
Reply by ●January 25, 20202020-01-25
On Saturday, January 25, 2020 at 2:21:25 PM UTC-5, Grant Taylor wrote:> Is anyone willing to explain Negative 48 Volts DC? > > I'm trying to learn about it because we're using it for a few things at > work (servers and switch equipment) and I'd like to better understand > what we're working with than simply going through the motions that > someone else dictates. Read: I want to understand and not simply rely > on wrote memory. > > I've learned that -48 VDC uses what is called "Positive Ground" and that > what I'm used to is called "Negative Ground". > > I'm trying to correlate and understand the typical red and black wires > with them being ground / return / common / hot / etc. > > I suspect that there is more to it than simply reversing the + and - > lead from a battery or meter. But I can't wrap my head around it. > > Can ~> will someone offer any comments that might help me understand > better? > > > > -- > Grant. . . . > unix || dieRight, Say you have a 48V battery. 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. George H.
Reply by ●January 25, 20202020-01-25
On Saturday, January 25, 2020 at 2:21:25 PM UTC-5, Grant Taylor wrote:> Is anyone willing to explain Negative 48 Volts DC? > > I'm trying to learn about it because we're using it for a few things at > work (servers and switch equipment) and I'd like to better understand > what we're working with than simply going through the motions that > someone else dictates. Read: I want to understand and not simply rely > on wrote memory. > > I've learned that -48 VDC uses what is called "Positive Ground" and that > what I'm used to is called "Negative Ground". > > I'm trying to correlate and understand the typical red and black wires > with them being ground / return / common / hot / etc. > > I suspect that there is more to it than simply reversing the + and - > lead from a battery or meter. But I can't wrap my head around it. > > Can ~> will someone offer any comments that might help me understand > better?I'm at a loss to understand what you are confused about. Do you have any specific questions??? How does any of this impact using the 48 volts to supply the equipment you list? In other words, why are you confused? -- Rick C. - Get 1,000 miles of free Supercharging - Tesla referral code - https://ts.la/richard11209
Reply by ●January 25, 20202020-01-25
On Sat, 25 Jan 2020 12:21:25 -0700, Grant Taylor <gtaylor@tnetconsulting.net> wrote:>Is anyone willing to explain Negative 48 Volts DC?Sure. It goes back to telegraphy and telephony. The power to run the telegraphs and telephones came from batteries. One terminal of the battery went to earth ground. The other terminal went to the wires between stations. The problem was, which is better? Positive ground or negative ground. It was decided to use positive ground. The battery positive terminal went to ground, while the negative terminal went to the stations and wires resulting in a -48VDC system. The selection of polarity was NOT arbitrary. A positive ground offers better protection against corrosion: <https://en.wikipedia.org/wiki/Tip_and_ring#Polarity> To provide cathodic protection against corrosion of line wires, operating potential of telephone lines is typically negative with respect to ground, and the tip side is generally close to the ground potential. Thus, all power supplies for telecommunication equipment are designated to supply a negative voltage. When the internet was being built, data communications went via telephone company services and lived in telephone company owned central offices. These offices were powered by -48VDC power. It made sense for the new internet services, switches, muxs, termination equipment, PoE, etc to be powered by the same -48VDC power. Please note that red=positive and black=negative is an color automotive standard. Color codes are VERY different in other industries. Also, 48VDC is considered "safe" and suitable for using "low voltage insulation". Any higher voltage requires additional protection. However, in the electric power industry less than 50V is consider "extra low voltage" while anything under 1000V is considered "low voltage". Sigh. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Reply by ●January 25, 20202020-01-25
On Sat, 25 Jan 2020 11:28:01 -0800 (PST), George Herold <ggherold@gmail.com> wrote:>On Saturday, January 25, 2020 at 2:21:25 PM UTC-5, Grant Taylor wrote: >> Is anyone willing to explain Negative 48 Volts DC? >> >> I'm trying to learn about it because we're using it for a few things at >> work (servers and switch equipment) and I'd like to better understand >> what we're working with than simply going through the motions that >> someone else dictates. Read: I want to understand and not simply rely >> on wrote memory. >> >> I've learned that -48 VDC uses what is called "Positive Ground" and that >> what I'm used to is called "Negative Ground". >> >> I'm trying to correlate and understand the typical red and black wires >> with them being ground / return / common / hot / etc. >> >> I suspect that there is more to it than simply reversing the + and - >> lead from a battery or meter. But I can't wrap my head around it. >> >> Can ~> will someone offer any comments that might help me understand >> better? >> >> >> >> -- >> Grant. . . . >> unix || die > >Right, Say you have a 48V battery. >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. > >George H.I had a British car once with positive ground. I had to replace the battery and, instinctively, strapped the negative lug to the chassis. When I connected the other cable and got a big spark, I understood the situation in milliseconds. Too many milliseconds! I blew out all the diodes in the alternator, and replaced them with a couple of big Motorola bridge rectifiers. Luckily, the radio was off at the time. I'm working with alternators again, FADEC power supplies. You short a PM alternator to regulate the output. I think positive ground has some sort of corrosion advantage. -- 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"
Reply by ●January 25, 20202020-01-25
Am 25.01.20 um 20:57 schrieb Jeff Liebermann:> On Sat, 25 Jan 2020 12:21:25 -0700, Grant Taylor > <gtaylor@tnetconsulting.net> wrote: > >> Is anyone willing to explain Negative 48 Volts DC? > > Sure. It goes back to telegraphy and telephony. The power to run the > telegraphs and telephones came from batteries. One terminal of the > battery went to earth ground. The other terminal went to the wires > between stations. The problem was, which is better? Positive ground > or negative ground. > > It was decided to use positive ground. The battery positive terminal > went to ground, while the negative terminal went to the stations and > wires resulting in a -48VDC system. The selection of polarity was NOT > arbitrary. A positive ground offers better protection against > corrosion: > <https://en.wikipedia.org/wiki/Tip_and_ring#Polarity> > To provide cathodic protection against corrosion of line > wires, operating potential of telephone lines is typically > negative with respect to ground, and the tip side is > generally close to the ground potential. Thus, all power > supplies for telecommunication equipment are designated to > supply a negative voltage. > > When the internet was being built, data communications went via > telephone company services and lived in telephone company owned > central offices. These offices were powered by -48VDC power. It made > sense for the new internet services, switches, muxs, termination > equipment, PoE, etc to be powered by the same -48VDC power. > > Please note that red=positive and black=negative is an color > automotive standard. Color codes are VERY different in other > industries. > > Also, 48VDC is considered "safe" and suitable for using "low voltage > insulation". Any higher voltage requires additional protection. > However, in the electric power industry less than 50V is consider > "extra low voltage" while anything under 1000V is considered "low > voltage". Sigh.Amen. A few additions: The terminology is TNV-x (TNV-1 or TNV-2 or TNV-3). Here is a nice tutorial: https://www.ewh.ieee.org/r6/scv/pses/ieee_scv_pses_jun07.pdf The IEC/EC/UL 60950-1 is past its DoW. It has been replaced with the IEC 62368-1. Many standards still refer to the 60950-1 and it will take at least another decade until this has changed. Michael
Reply by ●January 25, 20202020-01-25
Michael Nagel <m_nagel@muenchen [remove this] -mail.de> wrote in news:r0i8pk$eq9$1@news-1.m-online.net:> Am 25.01.20 um 20:57 schrieb Jeff Liebermann: >> On Sat, 25 Jan 2020 12:21:25 -0700, Grant Taylor >> <gtaylor@tnetconsulting.net> wrote: >> >>> Is anyone willing to explain Negative 48 Volts DC? >> >> Sure. It goes back to telegraphy and telephony. The power to >> run the telegraphs and telephones came from batteries. One >> terminal of the battery went to earth ground. The other terminal >> went to the wires between stations. The problem was, which is >> better? Positive ground or negative ground. >> >> It was decided to use positive ground. The battery positive >> terminal went to ground, while the negative terminal went to the >> stations and wires resulting in a -48VDC system. The selection >> of polarity was NOT arbitrary. A positive ground offers better >> protection against corrosion: >> <https://en.wikipedia.org/wiki/Tip_and_ring#Polarity> >> To provide cathodic protection against corrosion of line >> wires, operating potential of telephone lines is typically >> negative with respect to ground, and the tip side is >> generally close to the ground potential. Thus, all power >> supplies for telecommunication equipment are designated to >> supply a negative voltage. >> >> When the internet was being built, data communications went via >> telephone company services and lived in telephone company owned >> central offices. These offices were powered by -48VDC power. It >> made sense for the new internet services, switches, muxs, >> termination equipment, PoE, etc to be powered by the same -48VDC >> power. >> >> Please note that red=positive and black=negative is an color >> automotive standard. Color codes are VERY different in other >> industries. >> >> Also, 48VDC is considered "safe" and suitable for using "low >> voltage insulation". Any higher voltage requires additional >> protection. However, in the electric power industry less than 50V >> is consider "extra low voltage" while anything under 1000V is >> considered "low voltage". Sigh. > > Amen. > > A few additions: > > The terminology is TNV-x (TNV-1 or TNV-2 or TNV-3). > Here is a nice tutorial: > https://www.ewh.ieee.org/r6/scv/pses/ieee_scv_pses_jun07.pdf > > The IEC/EC/UL 60950-1 is past its DoW. > It has been replaced with the IEC 62368-1. > Many standards still refer to the 60950-1 and it will take at > least another decade until this has changed. > > Michael > >Great link... thanks.
Reply by ●January 25, 20202020-01-25
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
Reply by ●January 25, 20202020-01-25
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.
Reply by ●January 25, 20202020-01-25
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
