On Sunday, January 26, 2020 at 10:23:27 AM UTC-8, Grant Taylor wrote:> 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.For digital and analog signals, the 'ground' concept relates to signal return currents, and completion of the electrical circuit. For digital outputs, the logic 'zero' refers to voltages at/near ground (negative ground for 5V or 3.3V logic), and 'one' to voltages far from ground. The 5V logic and 3.3V logic can share a ground connection, and interconnect, thus that negative ground is the common connection (so 'common' often means 'ground'). For analog outputs (such as gigabit Ethernet levels) a good solution is to have differential driven wires, with NO ground dependence, so that a voltage drop in ground wires due to power fluctuations does not interfere with the signal definition. For long wires, that is important. Alternately, a metal chassis that has to be bonded (for safety) so as not to be electrically active and cause a shock, has to be 'ground', and will connect at various points to (for instance) the shielding on a video cable. Some signal improvement results from such safety ground being either unconnected, or simply (in only ONE PLACE) connected to the signal ground/analog ground/digital ground. But, positive and negative power supply voltages are just... voltages that deliver power, and don't have shielding requirements, nor (in general) do they have well-defined immunity to noise and interference. That's why some logic (traditional ECL) uses negative 5.2V, the noise on a power rail would contaminate the signal if that signal were examined as a difference-from-positive-power-terminal, but not if that signal was difference-from-negative-power-terminal. Being confused is OK, but do NOT assume 'ground' is always the negative terminal of a power supply, that is NOT OK.
Negative 48 Volts DC
Started by ●January 25, 2020
Reply by ●January 26, 20202020-01-26
Reply by ●January 26, 20202020-01-26
On Sunday, January 26, 2020 at 7:43:42 PM UTC-5, whit3rd wrote:> On Sunday, January 26, 2020 at 10:23:27 AM UTC-8, Grant Taylor wrote: > > 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. > > For digital and analog signals, the 'ground' concept relates to signal return > currents, and completion of the electrical circuit. For digital outputs, > the logic 'zero' refers to voltages at/near ground > (negative ground for 5V or 3.3V logic), and 'one' to voltages far from ground. The > 5V logic and 3.3V logic can share a ground connection, and interconnect, > thus that negative ground is the common connection (so 'common' often means 'ground').You seem to be saying there is a difference in the concept of ground for analog and digital circuits. Digital circuits are still analog electrically. They just have a much higher noise tolerance. But noise is still a significant issue and should not be ignored.> For analog outputs (such as gigabit Ethernet levels) a good solution is to have > differential driven wires, with NO ground dependence, so that a voltage drop > in ground wires due to power fluctuations does not interfere with the signal > definition. For long wires, that is important.Exactly the same as digital. Differential pairs are commonly used to convey signals between boards or boxes.> Alternately, a metal chassis that has to be bonded (for safety) so as not to be > electrically active and cause a shock, has to be 'ground', and will connect > at various points to (for instance) the shielding on a video cable. Some signal > improvement results from such safety ground being either unconnected, or > simply (in only ONE PLACE) connected to the signal ground/analog ground/digital ground.Don't confuse the concepts of protective earth and signal ground. They are not always connected directly. When passing signals between boxes, even in the same rack, the "commonality" or protective ground is at question. Directly connecting grounds can cause large currents to flow in the ground conductor creating voltages that interfere with the signal. Most of this has little or nothing to do with getting the polarity right on negative voltage power supplies. No need to overload the guy. -- Rick C. -+- Get 1,000 miles of free Supercharging -+- Tesla referral code - https://ts.la/richard11209
Reply by ●January 26, 20202020-01-26
On 25/01/2020 8:31 pm, Sylvia Else 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. > > SylviaYears ago the Seeburg jukebox used a ferrite core memory to keep track of the selections of records to be played. It replaced a lot of electro-mechanical crap. It was all tube circuitry and the sense lead was was connected to a pulse pulse amplifier in it's own little plugin metal box with a 12AX7, IIRC, and a small ferrite looking pulse transformer contained therein. The module plugged into the main control chassis. It's the only +V grounded circuit I've ever seen except for some PNP germanium audio amplifiers and PNP computer stuff. I never found the reason for this. I suspect it was done to increase the noise immunity. I will say that the -V wire had quite a layer of dust attached to it. The later NPN solid state versions used a -V ground with the sense lead went to the base of a SCS, silicon controlled switch. Once it fired it stayed on until the current flow was interrupted. Other than convention, I never cared which end of the power supply was connected to ground. I never touch bare terminals to check their potential to ground. I don't care what color they are.
Reply by ●January 26, 20202020-01-26
On 26/01/2020 3:42 pm, Grant Taylor wrote:> On 1/26/20 1:37 PM, Rick C wrote: >> Unfortunately that question is confusing to me. lol > > Sorry. I'll try restating. > > I naively agree with you that one terminal is positive with respect to the other > terminal. > > However, what this terminal is called, is confusing, particularly when dealing > with negative voltage. > > Aside: Yes, this equipment is powered by /negative/ 48 VDC. "Neg(ative) 48 > (V(DC))" or some close variant (including the "negative polarity) and "48" > volts) is quite common phrasing as an alternate power source in computer > (particularly servers) and networking equipment. > > Further Aside: I can't actually remember the last time I heard reference to > (positive) 48 VDC in computers & networking equipment. > > I believe that if I hook the positive / red lead of a voltmeter to the positive > / red lead of a power supply, and the negative / black lead of the volt meter to > the negative / black lead of a power supply, I expect the following voltages: > > Standard bench top 12 VDC power supply: + 12 VDC > Negative 48 VDC telephone power supply: - 48 VDC > > So what is called the positive or red lead actually is negative with respect to > what is called the negative or black lead. > > I /think/ this is accurate. But I'm not sure. Nor do I actually understand > /why/ this is the way that it is. This thread is my attempt to learn and > understand. …how can a positive power wire have a negative voltage on it? > >> One terminal is positive and the other negative. Unless there is an internal >> connection to ground (like the power line safety ground - which there >> shouldn't be) it doesn't make any real sense to call it a -48 volt supply. > > See above. > >> That's the part I'm not getting. > > I understand the confusion. Hence my trying to ask questions and learn. > >> Does the power supply actually say it is a -48 volt supply > > Simplistically, yes, the power supply does say that it's -48 VDC. > > Less simplistically, the labeling may not say it in those words. It may simply > say the output is (nominally) -48 VDC. Some actually are labeled as -48 VDC > supplies. > >> or just 48 volts? Or is the -48 volts just what you see in references to the >> supply elsewhere? > > Nope. To the best of my knowledge, the "negative" is an important part of the > description. I don't think it's simply how it's connected in relation to the 48 > VDC. > >> Bottom line is there's nothing unexpected going on. If it is wired for a -48 >> volt supply it will have the positive terminal wired to ground and the other >> terminal will be -48 volts. I can't tell you anything about how the terminals >> are labeled and I would not assume anything unless the labels on the supply >> are a bit more clear. >> >> The supply could very well be intended for -48 volt use with a positive ground >> and so the label "return" means positive. Or it could also be a typical >> supply with a positive output and a negative return. Is there a label with >> model number, maker's name, other identification? Find that and look up a data >> sheet. > > That is my plan. > >> When you say a better "understanding" you mean of the color code conventions? >> Technically it's all just wires and polarity, not much to understand. > > No. It's more than just color code. As you say, colors are immaterial and > simply chosen based on convention. > > I want to understand how the volt meter reading described above. > > I want to understand how the following AC-to-DC power supplies work: > > -⏚) AC-to-DC with a connection between neutral / ground and the - output. > +⏚) AC-to-DC with a connection between neutral / ground and the + output. > > If I don't know which, +⏚ or -⏚, the AC-to-DC supply is and I bond the - output > to ⏚, I'm either going to be safe (-⏚) or quite unhappy (+⏚). > >> That's what I'm asking, the wiring colors. Are they consistent? > > The equipment all uses red and black wires. I don't know what the potential is > between each of them to ⏚ is, much less how they are labeled. > > I will need to look when I get an opportunity to, probably on Tuesday. > >> Yes, you keep saying that, but you don't really say what is not clear. > > I hope this message has cleared some of this up. > >> Maybe rote memory is good enough for now and a light bulb will come on later. >> That has happened for me in many areas. > > Maybe. I dislike doing such. > >> I don't know what you mean by "blinders". > > I'm referring to the 48 VDC supply (negative omitted on purpose) coming in on > two wires to connect to a piece of equipment. I can ignore the color of the > wires, use a volt meter to identify which is + and - and wire it to the > equipment the way that it wants. But that ignores, or is blind to, the actual > colors of the wires and how it integrates to the rest of the system. > >> You seem to think there is some greater understanding, but in reality it's all >> just a matter of polarity and the conventions are just that, conventions. > > I /think/ that it is more than just polarity. See the +⏚ and -⏚ examples above. > >> Do you have a question? > > I think I've asked, or at least alluded to, many in this thread. It's difficult > to word smith a question about a concept that is still unclear to me. :-( I > think this email has some better ""questions in the form of "I want to > understand". They aren't worded as questions per say. But I hope they convey > what I want to learn. > >> Positive to positive and negative to negative. It's literally that simple. >> Since the vendors of the equipment seem to be fuzzy on labeling terminals, at >> least on the power supply, you should measure everything.I think you have a poor understanding of basic current flow theory and likely very little practical experience. This may be a good place to start. So your job is connecting equipment to other equipment and you have no idea how to do this?
Reply by ●January 27, 20202020-01-27
On Sunday, January 26, 2020 at 3:37:40 PM UTC-5, Rick C wrote:> On Sunday, January 26, 2020 at 1:36:16 PM UTC-5, Grant Taylor wrote: > > On 1/25/20 3:54 PM, Rick C wrote: > > > 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. > > > > I naively agree with you. But the negative part of -48 VDC confuses me > > on what the positive and negative lead is. :-/ > > Unfortunately that question is confusing to me. lol One terminal is positive and the other negative. Unless there is an internal connection to ground (like the power line safety ground - which there shouldn't be) it doesn't make any real sense to call it a -48 volt supply.Sure it does. It's intended for use in a SYSTEM that uses -48V as the power source.> > That's the part I'm not getting. Does the power supply actually say it is a -48 volt supply or just 48 volts? Or is the -48 volts just what you see in references to the supply elsewhere?He clearly stated that one terminal is marked -48V, the other return.
Reply by ●January 27, 20202020-01-27
On Sunday, January 26, 2020 at 4:42:38 PM UTC-5, Grant Taylor wrote:> On 1/26/20 1:37 PM, Rick C wrote: > > Unfortunately that question is confusing to me. lol > > Sorry. I'll try restating. > > I naively agree with you that one terminal is positive with respect to > the other terminal. > > However, what this terminal is called, is confusing, particularly when > dealing with negative voltage.Why is it confusing? One terminal is the negative polarity, the other the positive. On your supply, one terminal is marked -48V, the other return. I would also make the -48V black, the return one red. but even with just -48V on one and return on the other, it's clear which is negative, which is positive. If you had a 9V battery and one terminal was marked -9V, or 'neg", would you be confused about the polarity?> > Aside: Yes, this equipment is powered by /negative/ 48 VDC. > "Neg(ative) 48 (V(DC))" or some close variant (including the "negative > polarity) and "48" volts) is quite common phrasing as an alternate power > source in computer (particularly servers) and networking equipment. > > Further Aside: I can't actually remember the last time I heard > reference to (positive) 48 VDC in computers & networking equipment. > > I believe that if I hook the positive / red lead of a voltmeter to the > positive / red lead of a power supply, and the negative / black lead of > the volt meter to the negative / black lead of a power supply, I expect > the following voltages: > > Standard bench top 12 VDC power supply: + 12 VDC > Negative 48 VDC telephone power supply: - 48 VDCWoah there Pilgrim! Are you saying on that -48V supply has a RED terminal or wire for the -48V and BLACK for return? Now that I would agree would be confusing. I would expect black to be on the -48V, red on the return.> > So what is called the positive or red lead actually is negative with > respect to what is called the negative or black lead.It's either one polarity or the other, positive is never called negative. What is called the "hot", the "source" or the "return" could be either depending on the system polarity.> > I /think/ this is accurate. But I'm not sure. Nor do I actually > understand /why/ this is the way that it is. This thread is my attempt > to learn and understand. …how can a positive power wire have a > negative voltage on it?With one voltage, two wires like you have, it can't.> > > One terminal is positive and the other negative. Unless there is an > > internal connection to ground (like the power line safety ground - > > which there shouldn't be) it doesn't make any real sense to call it > > a -48 volt supply. > > See above. > > > That's the part I'm not getting. > > I understand the confusion. Hence my trying to ask questions and learn.But it does make sense. That power supply is designed to be used in a positive ground system. So the supply terminal is labeled -48V.> > > Does the power supply actually say it is a -48 volt supply > > Simplistically, yes, the power supply does say that it's -48 VDC. > > Less simplistically, the labeling may not say it in those words. It may > simply say the output is (nominally) -48 VDC. Some actually are labeled > as -48 VDC supplies. > > > or just 48 volts? Or is the -48 volts just what you see in references > > to the supply elsewhere? > > Nope. To the best of my knowledge, the "negative" is an important part > of the description. I don't think it's simply how it's connected in > relation to the 48 VDC. > > > Bottom line is there's nothing unexpected going on. If it is wired > > for a -48 volt supply it will have the positive terminal wired to > > ground and the other terminal will be -48 volts. I can't tell you > > anything about how the terminals are labeled and I would not assume > > anything unless the labels on the supply are a bit more clear. > > > > The supply could very well be intended for -48 volt use with a positive > > ground and so the label "return" means positive. Or it could also > > be a typical supply with a positive output and a negative return. > > Is there a label with model number, maker's name, other identification? > > Find that and look up a data sheet. > > That is my plan. > > > When you say a better "understanding" you mean of the color code > > conventions? Technically it's all just wires and polarity, not much > > to understand. > > No. It's more than just color code. As you say, colors are immaterial > and simply chosen based on convention.So what color is the -48V terminal? Is there a color? I would expect it to be either black or no color identification and the return to be either red or no color.> > I want to understand how the volt meter reading described above. > > I want to understand how the following AC-to-DC power supplies work: > > -⏚) AC-to-DC with a connection between neutral / ground and the - output. > +⏚) AC-to-DC with a connection between neutral / ground and the + output.Why are you now adding neutral to this? Neutral is on the AC side.
Reply by ●January 27, 20202020-01-27
On Monday, January 27, 2020 at 11:31:43 AM UTC-5, Whoey Louie wrote:> On Sunday, January 26, 2020 at 3:37:40 PM UTC-5, Rick C wrote: > > On Sunday, January 26, 2020 at 1:36:16 PM UTC-5, Grant Taylor wrote: > > > On 1/25/20 3:54 PM, Rick C wrote: > > > > 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. > > > > > > I naively agree with you. But the negative part of -48 VDC confuses me > > > on what the positive and negative lead is. :-/ > > > > Unfortunately that question is confusing to me. lol One terminal is positive and the other negative. Unless there is an internal connection to ground (like the power line safety ground - which there shouldn't be) it doesn't make any real sense to call it a -48 volt supply. > > > Sure it does. It's intended for use in a SYSTEM that uses -48V as > the power source. > > > > > > That's the part I'm not getting. Does the power supply actually say it is a -48 volt supply or just 48 volts? Or is the -48 volts just what you see in references to the supply elsewhere? > > He clearly stated that one terminal is marked -48V, the other return.As usual, you are wrong again, always wrong. -- Rick C. -++ Get 1,000 miles of free Supercharging -++ Tesla referral code - https://ts.la/richard11209
Reply by ●January 27, 20202020-01-27
On Monday, January 27, 2020 at 11:59:28 AM UTC-5, Whoey Louie wrote:> On Sunday, January 26, 2020 at 4:50:41 PM UTC-5, Grant Taylor wrote: > > > > How did you come to saying that -48 the ground will be positive and the > > power lead will be negative? What other information / knowledge did you > > rely on to make that statement? > > Did he say that? I hope not. > > > With your -48V supply, the -48V terminal would be called the "hot" > the "supply", but not the positive.Please don't confuse the guy by not reading what he writes. -- Rick C. +-- Get 1,000 miles of free Supercharging +-- Tesla referral code - https://ts.la/richard11209
Reply by ●January 27, 20202020-01-27
On 1/26/20 3:28 PM, Rick C wrote:> That's why I would look at the documentation for the equipment/supply.That is the plan. I've not had the opportunity to do so yet.> If it is a -48 volt system it certainly would be ok to call the > positive terminal "return" or "common". It would be ok to call the > negative terminal "hot".Okay.> I have seen some systems use a negative ground with a 48 volt power > source.Fair enough. I've not had the exposure to (positive) 48 volt power.> Now you are talking color codes. I can't tell you what the color > code is for a -48 volt system.I wasn't meaning to focus on the color code. Allow me to modify my statement slightly by removing the colors from it. I believe that if I hook the positive lead of a voltmeter to the positive lead of a power supply, and the negative lead of the volt meter to the negative lead of a power supply, I expect the following voltages: Standard bench top 12 VDC power supply: + 12 VDC Negative 48 VDC telephone power supply: - 48 VDC> "Called" vs. "looks" I can't say. I never talk about the "red" lead > when dealing with power circuits. I use the other terms listed above.Okay.> Now you have me confused again. Who talked about a positive wire with > a negative voltage??? Positive/negative are electric polarities and > don't change when your definition of the common or ground changes.I believe it was a permutation of "hot" -> "red" -> "positive" in a system that has negative voltage.> Ok, if they say it's a -48 volt supply with a minus sign in front > of the voltage, then it is safe to believe the hot wire will be the > negative the return/common wire will be the positive.Okay.> Ok, because I'm willing to bet the supply is not grounded, but it > may be. If not grounded they are only calling it a -48 volt supply > because that is how most people use it. There is nothing inherent > that makes it minus vs. positive.I had a few minutes to look at the -48 VDC power supply today. · The negative terminal was connected to the red wires. · The positive terminal was connected to the black wires. · The positive terminal was connected to the chassis. · The chassis will make electrical contact with a rack that is connected to earth ground.> The volt meter will always tell you the voltage between the two > probes assuming the red will be positive and the black negative.The implication of polarity with volt meter leads doesn't help this thread. But I generally agree with your statement.> If that is correct the meter will show a positive voltage. I the > red lead is negative it will show a negative voltage.I believe the red lead does show a negative voltage.> That will give you a positive voltage on the positive lead with > respect to (wrt) ground.I still need to measure, but I believe the positive lead has 0 volts to ground.> That will give you a negative voltage on the negative lead wrt ground.Agreed.> BTW, none of these supplies should have any connection to power line > neutral. That is dangerous situation and can kill. Neutral is not > ground (protective earth).I agree that ground and neutral (in typical 120/240 VAC 1ɸ wiring) are separate conductors and should not be used interchangeably. However, ground and neutral are bonded together in the main electrical panel. (At least every main panel that I've ever looked in. Sub-panels are decidedly different with ground and neutral isolated from each other.) So, there is a conductive path between ground and neutral.> Why would you bond any voltage line to earth? Do your equipment > systems use actual grounds anywhere? It's easy enough to measure > the voltages and see if the power is connected to ground.Ground is quite prevalent in networking equipment and servers. Some vendors refuse to honor warranty if the equipment is not properly grounded. Static is a (big) concern. So ground is used to dissipate static before it builds up and causes problems.> I'd say a measurement is in order... with the resistor I mentioned.After looking at the -48 VDC power supply earlier today, I am quite convinced that the positive terminal has electrical conductivity with the building's earth ground. (Positive terminal strapped to chassis which is bare metal connecting to the rack it mounts in (also bare metal) which is earth grounded.)> That's the part I don't get. Once you measure the voltages on the > wires and know what the terminals of your equipment need, what else > is there to know about the "system"??? The only problem that could > happen is if one of the power leads is grounded to the chassis and > a piece of equipment connects power to the chassis, but they are > different connections. That's why you read the documentation. > > That is all polarity, no? I'm not getting it. > > I hope that helps.-- Grant. . . . unix || die
Reply by ●January 27, 20202020-01-27
