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.So then there is -48V between the unlabeled terminal and the return. But you'd think they would label that unlabeled terminal -48V or supply.> > 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 blackThe red side would be positive, the black negative. Current flows from the positive side of the source to negative. So the return would be the black, but that terminology isn't frequently used.> > 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?Take a 12 V power supply. If you connect the red meter lead to the red on the power supply, black to black you'd read +12V. If you connect red to black, black to red, you'd read -12V.> > How should things be wired to a piece of equipment that has the ground > symbol on one terminal and the other terminal unlabeled?Carefully. It's a very bad idea to have things unlabeled. Better RTFM.> > 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? >You have what you say is a -48V supply and it has one terminal marked return, the other unlabeled. Let's say you have a 48V piece of eqpt and it has a red wire and black wire coming out of it or a red terminal and black terminal. Knowing only the above, the logical thing is that the unmarked supply terminal goes to the black/neg and the return terminal goes to the red/positive.
Negative 48 Volts DC
Started by ●January 25, 2020
Reply by ●January 25, 20202020-01-25
Reply by ●January 25, 20202020-01-25
On Saturday, January 25, 2020 at 2:28:05 PM UTC-5, George Herold 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.And the latter is his "positive ground" system. As someone else pointed out, ground in this case just means a system reference point. As an example, cars today have a negative ground system, the battery negative is connected to the car metal chassis, which is used as part of the return path for current. Some cars years ago, instead had a positive ground system, with the battery positive connected to the chassis instead. It's like driving on the wrong side of the road, some just had to be different. :) Fortunately with grounding, I think the weirdos wised up and AFAIK no cars have been built for decades that have positive ground.
Reply by ●January 25, 20202020-01-25
On 26/01/2020 6:21 am, 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? > > >In any system of connected wires at different potentials, you can arbitrarily label one of them "ground", and then measure the potentials of the other wires relative to your ground. You will then get some that are positive, and some that are negative. For some systems, such as a car, it can make some sense to label whatever is connected to the chassis as ground, but it is still pretty much an arbitrary choice. And of course, with a fixed system, one can connect one point to the soil under one's feet, and call that point ground. But it's a naming convention, and nothing more. In the absence of clear documentation on the system you're examining, the only practical option is to take a multimeter to it, and make measurements. Sylvia
Reply by ●January 26, 20202020-01-26
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? >A communications system that I worked on for the International Space Station ran on -48VDC.
Reply by ●January 26, 20202020-01-26
On Sat, 25 Jan 2020 23:10:35 -0800, Michael Terrell 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? >> >> > > A communications system that I worked on for the International Space > Station ran on -48VDC.I should imagine for much the same reasons used to standardise road vehicle ground reference polarity and telephone exchange equipment grounding to earth - to minimise galvanic corrosion in vital metallic structures - the inside would be a humid environment - it has to be for the sake of the astronaut's respiratory health, providing ample opportunity for the water vapour to condense out onto cold spots within the structure of the ISS. Incidentally, regarding the question of colour coding the polarity of telecoms DC supplies, the GPO (as it was when I joined that organisation as an apprentice in late '67) which is now known as BT (British Telecom), the -52v "hot" (aka "Battery") exchange equipment bus bars were insulated with blue plastic insulation (PVC afaicr) and the grounded (actually earthed) positive bus bars were all left bare. The fact that only the 'live' bus bars were insulated and the choice of blue rather than black, were sufficient reminder (if a reminder was ever needed) that the 'dangerous' pole of the 52v DC supply was negative with respect to anything (all the exposed metalwork including the ground return bus bars) at earth potential. This scheme neatly eliminated any possible confusion that could arise over which was the 'live' if the convention of red for positive and black for negative had been followed (red for danger and black for the safety of a conductor at ground potential failing to apply in this case). As to whether or not this colour coding scheme was followed outside of the UK and its dependencies (and the 48vdc power standards that came in with the later solid state comms equipment), I know not so I'll leave that as a question for old timers who've worked in telephone exchanges outside of the UK to answer. ;-) -- Johnny B Good
Reply by ●January 26, 20202020-01-26
On Sun, 26 Jan 2020 13:31:52 +1100, Sylvia Else <sylvia@email.invalid> wrote:>On 26/01/2020 6:21 am, 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? >> >> >> > >In any system of connected wires at different potentials, you can >arbitrarily label one of them "ground", and then measure the potentials >of the other wires relative to your ground. You will then get some that >are positive, and some that are negative. > >For some systems, such as a car, it can make some sense to label >whatever is connected to the chassis as ground, but it is still pretty >much an arbitrary choice. > >And of course, with a fixed system, one can connect one point to the >soil under one's feet, and call that point ground. > >But it's a naming convention, and nothing more. > >In the absence of clear documentation on the system you're examining, >the only practical option is to take a multimeter to it, and make >measurements. > >SylviaThe universe is probably absolute ground, and also defines absolute zero velocity. -- 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 26, 20202020-01-26
On Sat, 25 Jan 2020 12:21:25 -0700, 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?In a DC system, red is positive, black is negative, by convention. Terms such as hot, return and ground are simply descriptive, and usually applied in distributed AC in North America, where black is hot.
Reply by ●January 26, 20202020-01-26
On Sunday, January 26, 2020 at 10:58:11 AM UTC-5, jla...@highlandsniptechnology.com wrote:> On Sun, 26 Jan 2020 13:31:52 +1100, Sylvia Else <sylvia@email.invalid> > wrote: > > >On 26/01/2020 6:21 am, 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? > >> > >> > >> > > > >In any system of connected wires at different potentials, you can > >arbitrarily label one of them "ground", and then measure the potentials > >of the other wires relative to your ground. You will then get some that > >are positive, and some that are negative. > > > >For some systems, such as a car, it can make some sense to label > >whatever is connected to the chassis as ground, but it is still pretty > >much an arbitrary choice. > > > >And of course, with a fixed system, one can connect one point to the > >soil under one's feet, and call that point ground. > > > >But it's a naming convention, and nothing more. > > > >In the absence of clear documentation on the system you're examining, > >the only practical option is to take a multimeter to it, and make > >measurements. > > > >Sylvia > > The universe is probably absolute ground, and also defines absolute > zero velocity.Yeah, if we could just find the middle of it. Well, the part we can see anyway. What if we are off in a corner of the universe expanding away from the center at greater than the speed of light? So if the universe started as a singularity and expanded from there, how could any part of it speed away and become invisible by exceeding the speed of light? -- Rick C. -+ Get 1,000 miles of free Supercharging -+ Tesla referral code - https://ts.la/richard11209
Reply by ●January 26, 20202020-01-26
On Sunday, January 26, 2020 at 2:10:41 AM UTC-5, Michael Terrell wrote:> A communications system that I worked on for the International Space Station ran on -48VDC.I don't know if it is still the case, but that last (and probably only) time I had to install a two-way radio into a backhoe or bulldozer - that was a "positive ground" system. I remember it because there was a circuit on the microphone hang-up clip that would automatically un-squelch the receiver (it used ground). But in this case, we had to isolate the chassis of the two-way radio from "ground", as to avoid a short. I forget what we did as a workaround. I think the antenna was also one of those Motorola NMO-type mounts (also "grounded"), so we had to do something to that too. Someone earlier mentioned that "positive ground" systems tend to slow down corrosion. I don't know if that's true with backhoes, but they do spend their lives outdoors in the elements? (But so do cars, mostly.)
Reply by ●January 26, 20202020-01-26
On 1/25/20 2:34 PM, George Herold wrote:> 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?No. I'm a systems / network administrator by trade. I'm just trying to understand (more than wrote memory) how some of the equipment I administer works. There are other, more skilled people between me and connecting equipment. -- Grant. . . . unix || die
