On 25/01/2020 19:21, 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? > > >It's a very long time since I had anything to do with +ve earth British Post Office stuff but as I recall we used to talk about battery and earth. (Except the Irish guy I worked with, who used battery and ert.) I have one or two examples of things I designed then (approx 1980, as they (PO Telephones) were morphing into British Telecom) but no diagrams. Here's a link to what looks like a fairly typical diagram: http://finalselector.blogspot.com/2008/02/mystery-no-longer.html You can see the use of earth and battery symbols. This link is to a picture of a prototype relay tester (uses an Intel 8048 and designed to look as much like traditional relay based stuff as possible). I don't have a schematic but you can see the names we used and the on the front panle. The ETH wires are red. https://www.dropbox.com/s/to75xfo3ujdjraz/LF1470.JPG?dl=0 MK
Negative 48 Volts DC
Started by ●January 25, 2020
Reply by ●January 28, 20202020-01-28
Reply by ●January 28, 20202020-01-28
Michael Kellett <mk@mkesc.co.uk> wrote in news:e6SdnVob_YZ3m63DnZ2dnUU78aPNnZ2d@giganews.com:>> Is anyone willing to explain Negative 48 Volts DC? >>Lead acid batteries used in system UPS's are 12V. Series 4 together and get 48 Volts. Batteries are isolated sources, so either node can be 'fashioned' as 'ground'. The power supplies used to charge such battery back up systems had to make more than 48 Volts to make a charge condition occur on the bank. Whether they had individual battery watchdog circuits I do not know, but having a bad cell in a 4 battery 48 Volt system causes less of a droop than having a bad cell in a single battery 12 Volt system. So the supply could be a bit down in voltage yet still do the needed job. Whereas a single battery or parallel bank may not be as happy with a burned cell in play. So my guess is that the voltage was chosen to match the current storage cell technology of the times, and it simply stuck even though electrical demands to perform the same jobs reduced as solid state matured.
Reply by ●January 28, 20202020-01-28
On Monday, January 27, 2020 at 9:09:27 PM UTC-5, Grant Taylor wrote:> 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.Not okay. If you hook the red positive lead of a meter to the positive and the black negative lead to the neg of either power supply you will see +12V> > > 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.Weird and confusing to use red for the negative.> > > 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.Yes, because it's connected to -48V.
Reply by ●January 28, 20202020-01-28
On Monday, January 27, 2020 at 10:17:43 PM UTC-5, Rick C wrote:> On Monday, January 27, 2020 at 9:09:27 PM UTC-5, Grant Taylor wrote: > > 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 > > Positive and negative are electrical terms of physics. It has nothing to do with convention of colors or which polarity of common you use. Connect the positive meter probe to the positive power line and you will always measure a positive voltage no matter what. > > > > > "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. > > Let's forget color. If it is a -48 volt system the positive wire will be the common, but it will still be positive. > > > > > 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. > > Ok, so they are using the convention that red is "hot" and black is "common". They are also grounding their common to earth ground which is likely connected to a protective earth wire. > > > > > 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. > > I was talking about the voltmeter leads. But whatever. > > > > > 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. > > You just said above the positive power lead is common and connected to a grounded chassis. You can't get any more zero than that. Of course you have to use common or ground as your reference (e.g. connect the black meter lead to common). > > > > > 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. > > And that is the hazard. If the neutral connection to the panel is lost, there is no return path for the power circuit and anything touching neutral will be hot. The bond between protective earth and neutral must be connected in a way that no failure can cause the protective earth to be hot.There is no such way. If the ground wire becomes disconnected at the panel, or the wire is cut on it's way to the grounding electrode system and you also have your disconnected neutral, the eqpt grounding system will become energized through any loads.
Reply by ●January 28, 20202020-01-28
On Monday, January 27, 2020 at 9:28:39 PM UTC-5, Grant Taylor wrote:> On 1/27/20 9:46 AM, Whoey Louie wrote: > > 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. > > Having looked at the equipment earlier today, you'd be wrong. > > Negative had the red wires. > Positive / ground had the black wires. > > The confusion is understanding why things are wired the way that they are.Yes, I see you said that in another post now too. And I agree, it is confusing. I would not expect red to be the negative supply side and black to be positive. That is confusing and asking for trouble.> > > 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? > > In a negative ground system, no, I would not be confused. > > In a positive ground system, I apparently am.Which end is designated the ground/return doesn't change the polarity of the terminals at the power source.> > > Woah there Pilgrim! Are you saying on that -48V supply has a > > RED terminal or wire for the -48V and BLACK for return? > > Yes!!! > > That is EXACTLY what I'm saying. (See above.) > > > Now that I would agree would be confusing. > > Hence this thread.Yes, so then it's just a color choice thing. Which raises an interesting question. In the small minority of cars that decades ago used a positive ground, I wonder what color the supply wires were? Possible they were red too. I've never seen one, IDK.> > > I would expect black to be on the -48V, red on the return. > > Nope. > > I don't know what I would have expected / guessed this time last week. > I'm loath to guess, lest I confuse myself more this week.Well, knowing that, just consider the red to be the supply side, black to be the return. In the case of your -48V system, the red then is the negative polarity.> > > 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'm slowly coming to the conclusion that I have naively assumed that red > ≈ positive. Which is obviously wrong for positive ground systems.Red is positive in everything I've seen, but then all of that has been negative ground, so I share your confusion. But some of it might become obvious, even without looking at the power supply. If there are breakers or fuses for example, they would be on the supply/hot side, so if those wires were red and I knew it was a -48V system, I'd start wondering.> > I think I need to retrain myself that red = hot and that what is hot is > dependent on the type of system it is; negative ground or positive ground.Yes, at least for that particular system. The question is that what all positive ground systems do?> > > With one voltage, two wires like you have, it can't. > > I think that I need to reword my statement to be "a hot wire has a > negative voltage … in a positive ground system".Yes, you've got it now.> > > 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. > > I checked, and one terminal is labeled "negative" and the other terminal > is labeled "positive". > > > 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. > > There is no color (save for polished / chrome steal). > > The red wire was connected to negative. The black wire was connected to > positive. > > I've not had the opportunity to measure the voltage yet. I'm planing on > doing that tomorrow. > > > Why are you now adding neutral to this? Neutral is on the AC side. > > I'm fairly certain that neutral and ground are bonded together somewhere > upstream. Thus I typed "neutral / ground" as "neutral or ground". > Because, from an electrical conductivity standpoint, they are at the > same potential and in some ways the same. >Yes, you have that correct too. Very normal for the return side of eqpt to be connected to earth ground, for lightning, in case an AC line side conductor somewhere gets shorted to the DC/low voltage side, etc.> > > -- > Grant. . . . > unix || die
Reply by ●January 28, 20202020-01-28
On Tuesday, 28 January 2020 18:56:17 UTC, Whoey Louie wrote: A couple of years ago I helped choose colours for the input connectors of a networking product that had 12V (automotive range) and 48V versions. The 12V choice was easy. We were using Anderson Powerpole connectors, so we followed the amateur radio convention for these connectors with red for positive and black for negative in a specific configuration. For 48V, I looked at every standard I could find and found a mass of conflicting recommendations. An additional constraint was that we wanted to use the "finger safe" version of the connectors and could only use colours available from Anderson. Most customers would use positive ground, but some had negative ground systems. The final outcome was that the input was isolated with no connection between either power terminal and chassis and the positive terminal was red and the negative terminal was blue. This seemed to be in keeping with the spirit of most of the standards and less likely to cause confusion than any other combination. Pictures at the bottom of the page: https://www.firebrick.co.uk/fb2900/ John
Reply by ●January 28, 20202020-01-28
On Tuesday, January 28, 2020 at 2:33:22 PM UTC-5, jrwal...@gmail.com wrote:> On Tuesday, 28 January 2020 18:56:17 UTC, Whoey Louie wrote: > > A couple of years ago I helped choose colours for the input connectors > of a networking product that had 12V (automotive range) and 48V > versions. The 12V choice was easy. We were using Anderson Powerpole > connectors, so we followed the amateur radio convention for these > connectors with red for positive and black for negative in a specific > configuration. > For 48V, I looked at every standard I could find and found a mass of > conflicting recommendations. An additional constraint was that we wanted > to use the "finger safe" version of the connectors and could only use > colours available from Anderson. Most customers would use positive > ground, but some had negative ground systems. > The final outcome was that the input was isolated with no connection > between either power terminal and chassis and the positive terminal > was red and the negative terminal was blue. This seemed to be in keeping > with the spirit of most of the standards and less likely to cause > confusion than any other combination. > Pictures at the bottom of the page: > https://www.firebrick.co.uk/fb2900/ > > JohnThat's what I would have done too. I sure would not use red for negative and black for positive. I was thinking about saying in the other reply that if I decided to use black for the return in a positive ground system, then I sure would not use red for the supply. I would use some other color that would at least give someone looking at it reason to further look into what's going on. When one sees just red and black in low voltage DC system, one naturally assumes red is positive.
Reply by ●January 28, 20202020-01-28
Whoey Louie <trader4@optonline.net> wrote:> On Tuesday, January 28, 2020 at 2:33:22 PM UTC-5, jrwal...@gmail.com wrote: >> On Tuesday, 28 January 2020 18:56:17 UTC, Whoey Louie wrote: >> >> A couple of years ago I helped choose colours for the input connectors >> of a networking product that had 12V (automotive range) and 48V >> versions. The 12V choice was easy. We were using Anderson Powerpole >> connectors, so we followed the amateur radio convention for these >> connectors with red for positive and black for negative in a specific >> configuration. >> For 48V, I looked at every standard I could find and found a mass of >> conflicting recommendations. An additional constraint was that we wanted >> to use the "finger safe" version of the connectors and could only use >> colours available from Anderson. Most customers would use positive >> ground, but some had negative ground systems. >> The final outcome was that the input was isolated with no connection >> between either power terminal and chassis and the positive terminal >> was red and the negative terminal was blue. This seemed to be in keeping >> with the spirit of most of the standards and less likely to cause >> confusion than any other combination. >> Pictures at the bottom of the page: >> https://www.firebrick.co.uk/fb2900/ > > That's what I would have done too. I sure would not use red for negative > and black for positive. I was thinking about saying in the other reply > that if I decided to use black for the return in a positive ground system, > then I sure would not use red for the supply. I would use some other > color that would at least give someone looking at it reason to further > look into what's going on. When one sees just red and black in low > voltage DC system, one naturally assumes red is positive.This schematic shows red assigned to the higher potential and black assigned to the lower, more negative, potential: https://resources.secamerica.com/hs-fs/hubfs/Blog_Images/48vdc_for_telecom.jpg Red is assigned to the relatively positive power rail, at least in this schematic. What installers choose to do in the field's a whole nother story. That schematic originates with communications vendor: https://www.secamerica.com/applications/communications/ Presumably the vendor knows more than most about color code usage in the industry. In regards to ground: "Ground is a fantasy invented by engineers to simply their work." - Bill Whitlock The ground fantasy as applied to this thread seems to complicate instead of simplify. It's probably best to leave it out. Thank you, -- Don Kuenz KB7RPU There was a young lady named Bright Whose speed was far faster than light; She set out one day In a relative way And returned on the previous night.
Reply by ●January 28, 20202020-01-28
On Tuesday, January 28, 2020 at 2:50:00 PM UTC-5, whit3rd wrote:> On Tuesday, January 28, 2020 at 10:56:17 AM UTC-8, Whoey Louie wrote: > > > ... I agree, it is > > confusing. I would not expect red to be the negative supply side and > > black to be positive. That is confusing and asking for trouble. > > Alas, the innards of an automobile won't teach you anything bur red = positive. > There are LOTS of color conventions, many with legal enforcement, and > one must learn not to generalize. > > In US house wiring, red would be AC high voltage.If you mean by high voltage 240/120 AC then yes that's true, red could be used. But Grant's example is DC and 48V. You could also have red and black in house wiring in other applications, eg HVAC,thermostats, alarm wiring. But red for positive and black for negative in DC was the issue and this is the first application where I've heard of red being used for neg, black for positive. In a computer, red is +5V,> and yellow is +12V.In every low voltage DC anything where there is just one voltage, I've never seen red and black be anything other than positive and negative. Apparently it exists, but it's not common and the convention is not limited to cars. Buy a DC, low voltage, one speed motor, I've never seen one where red and black did not mean pos and neg, have you?
Reply by ●January 28, 20202020-01-28
On Tuesday, January 28, 2020 at 3:42:55 PM UTC-5, Don Kuenz wrote:> Whoey Louie <trader4@optonline.net> wrote: > > On Tuesday, January 28, 2020 at 2:33:22 PM UTC-5, jrwal...@gmail.com wrote: > >> On Tuesday, 28 January 2020 18:56:17 UTC, Whoey Louie wrote: > >> > >> A couple of years ago I helped choose colours for the input connectors > >> of a networking product that had 12V (automotive range) and 48V > >> versions. The 12V choice was easy. We were using Anderson Powerpole > >> connectors, so we followed the amateur radio convention for these > >> connectors with red for positive and black for negative in a specific > >> configuration. > >> For 48V, I looked at every standard I could find and found a mass of > >> conflicting recommendations. An additional constraint was that we wanted > >> to use the "finger safe" version of the connectors and could only use > >> colours available from Anderson. Most customers would use positive > >> ground, but some had negative ground systems. > >> The final outcome was that the input was isolated with no connection > >> between either power terminal and chassis and the positive terminal > >> was red and the negative terminal was blue. This seemed to be in keeping > >> with the spirit of most of the standards and less likely to cause > >> confusion than any other combination. > >> Pictures at the bottom of the page: > >> https://www.firebrick.co.uk/fb2900/ > > > > That's what I would have done too. I sure would not use red for negative > > and black for positive. I was thinking about saying in the other reply > > that if I decided to use black for the return in a positive ground system, > > then I sure would not use red for the supply. I would use some other > > color that would at least give someone looking at it reason to further > > look into what's going on. When one sees just red and black in low > > voltage DC system, one naturally assumes red is positive. > > This schematic shows red assigned to the higher potential and black > assigned to the lower, more negative, potential: > > https://resources.secamerica.com/hs-fs/hubfs/Blog_Images/48vdc_for_telecom.jpg > > Red is assigned to the relatively positive power rail, at least in this > schematic. What installers choose to do in the field's a whole nother > story. > > That schematic originates with communications vendor: > > https://www.secamerica.com/applications/communications/ > > Presumably the vendor knows more than most about color code usage in > the industry.I'm wondering what color was used on the negative/supply side of the wiring in early cars that used a positive ground? I took a quick google, couldn't find anything.> > In regards to ground: > > "Ground is a fantasy invented by engineers to simply > their work." - Bill Whitlock > > The ground fantasy as applied to this thread seems to complicate instead > of simplify. It's probably best to leave it out.Earth ground, I would agree is just a further complication here. But ground in general is just a system reference point and typically the return. So if someone was working on Grant's system and hooked a meter between -48V wiring and the return wiring, it would be common to say that he's measuring between supply and ground.> > Thank you, > > -- > Don Kuenz KB7RPU > There was a young lady named Bright Whose speed was far faster than light; > She set out one day In a relative way And returned on the previous night.
