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. :-/> When you say "return" terminal, what do you see that distinguishes > the two terminals? Is one labeled "return"?Yes. One terminal is labeled "return" and the other terminal is unlabled.> 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?I have not yet done this test.> You may need to put a 1 kohm resistor across the meter to prevent > seeing stray voltage while you do this.Yep. I'm familiar with this.> In typical DC electronics, red is positive and black negative.This matches my experience.> I don't work with -48 volt circuits a lot, so I can't say that this > applies for that.My limited experience with -48 VDC makes me think that it does not. Hence my desire to get a better understanding of -48 VDC.> What is the existing system using? I would go with that unless you > want to rewire the whole thing.Sadly, the few pieces of -48 VDC equipment that I have are all using small AC to DC power supplies for each piece of -48 VDC equipment. Both the supplies and the equipment are unique. There's nothing really common to look at. Save for the red and black wires. But with nothing else common to match against, it's tough to tell.> Is the equipment designed for -48 volts?Yes.> If so connect accordingly. I guess you are asking about colors.I'm asking multiple questions in the hopes of getting a general understanding. I'd like to have more than simple wrote memory.> I don't know convention other than in smaller gear where red is > positive and black is negative.That's where the bulk of my experience is too.> 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.If I put on blinders and look at just the positive / negative and what each piece of equipment wants, I agree. I'm trying to learn more about how the multiple pieces of equipment work together as a system.> 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.Yep. I know that the equipment is -48 VDC. I know that the supply provides -48 VDC. I'm just not clear on which terminal needs to be connected to what. Yes the manuals will be involved. -- Grant. . . . unix || die
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 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. 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? 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.> > When you say "return" terminal, what do you see that distinguishes > > the two terminals? Is one labeled "return"? > > Yes. One terminal is labeled "return" and the other terminal is unlabled. > > > 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? > > I have not yet done this test.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.> > You may need to put a 1 kohm resistor across the meter to prevent > > seeing stray voltage while you do this. > > Yep. I'm familiar with this. > > > In typical DC electronics, red is positive and black negative. > > This matches my experience. > > > I don't work with -48 volt circuits a lot, so I can't say that this > > applies for that. > > My limited experience with -48 VDC makes me think that it does not. > Hence my desire to get a better understanding of -48 VDC.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.> > What is the existing system using? I would go with that unless you > > want to rewire the whole thing. > > Sadly, the few pieces of -48 VDC equipment that I have are all using > small AC to DC power supplies for each piece of -48 VDC equipment. Both > the supplies and the equipment are unique. There's nothing really > common to look at. Save for the red and black wires. But with nothing > else common to match against, it's tough to tell.That's what I'm asking, the wiring colors. Are they consistent?> > Is the equipment designed for -48 volts? > > Yes. > > > If so connect accordingly. I guess you are asking about colors. > > I'm asking multiple questions in the hopes of getting a general > understanding. I'd like to have more than simple wrote memory.Yes, you keep saying that, but you don't really say what is not clear. Maybe rote memory is good enough for now and a light bulb will come on later. That has happened for me in many areas.> > I don't know convention other than in smaller gear where red is > > positive and black is negative. > > That's where the bulk of my experience is too. > > > 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. > > If I put on blinders and look at just the positive / negative and what > each piece of equipment wants, I agree.I don't know what you mean by "blinders". 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'm trying to learn more about how the multiple pieces of equipment work > together as a system.Do you have a question?> > 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. > > Yep. I know that the equipment is -48 VDC. I know that the supply > provides -48 VDC. I'm just not clear on which terminal needs to be > connected to what. Yes the manuals will be involved.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. -- 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 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. :-/This seems to be the question you are asking I guess. If you are working with a -48 volt system, the ground will be positive and the power lead will be negative. If your power supply is intended for such a system the lead labeled "return" will be positive and the other output will be negative. It would be helpful to see some photos of the terminals and the power supply label. -- 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 1:23:27 PM UTC-5, 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. > > There are other, more skilled people between me and connecting equipment.OK, that makes sense. Good on you for trying to figure it out. probably you can get one of the tech guys to show you the voltage on a DMM (volt meter). (and even compare to ground on the ac plug.) George H.> > > > -- > Grant. . . . > unix || die
Reply by ●January 26, 20202020-01-26
On Sun, 26 Jan 2020 10:16:41 -0800 (PST), mpm <mpmillard@aol.com> wrote:>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.Hmmm... I guess the ISS doesn't need to worry about ground leakage.>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.In 1971, after graduating college directly into a recession, the only job I could find was working for the local 2-way radio shop. I spend 2 months installing Motorola Motrac radios in concrete trucks. I think they were either Mack or Peterbilt but I'm not sure. Most had positive ground system. There were also some 24 volt systems (2 batteries in series) but we were able to tap off one battery. Somewhat later, I found myself servicing and later selling marine radios. On larger metal hull vessels, both the positive and negative lines are floating. Therefore, all our early marine radios had floating grounds. Eventually, a separate 12V power system was introduced for powering radios and such, which had a negative ground. Eventually, we supplied positive ground 12V radios on special order, where all the electronics was grounded to the chassis though multiple capacitors.>I remember it because there was a circuit on the microphone hang-up >clip that would automatically un-squelch the receiver (it used ground).Ummm... if that were Motorola, it would be called a "hangup switch". It did have anything to do with the noise squelch but did turn off the PL (Private Line) tone squelch decoder. Usually, the button on the back of the microphone was connected to ground when the PL was enabled through the "microphone hanger". However, for positive ground system, there was an isolated leaf switch inside the "hangup switch" and the button on the back of the microphone was not used.>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.Sounds like a later model radio that didn't have a positive ground feature or option. I've seen radios installed on wooden platforms to provide the necessary insulation. A plastic case microphone, isolated hangup switch, and capacitor coupling the antenna coax ground were also common.>I think the antenna was also one of those Motorola NMO-type mounts >(also "grounded"), so we had to do something to that too.I've seen what happens when someone forgets about NOT ground the antenna shield. Things mostly work ok, until someone blows the fuse in the negative power line. That makes the only path to battery negative through the coax cable ground. It usually works ok, until someone keys the transmitter. The coax shield becomes hot enough to melt the outer jacket and possibly set fire to everything nearby.>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.)The corrosion aspect was important for telco plant, but less so for automotive. For cars, the manufacturers wanted to save money. Why waste money on copper "ground" wire when they can run the current though the body of the car. At high currents, that was also good for re-heating all the Unibody spot welds. Usually about 10% of these welds would fail, which was not enough to ruin the integrity of the chassis, but was sufficient to create enough squeaks and rattles to drive the owner nuts. With such an arrangement, it really doesn't matter whether the chassis is positive or negative polarity. Road salt is sufficient to guarantee that the body rots out at about the same time as the other major components fail. I don't know why negative ground was selected, but there are a variety of theories. Here's one that suggests it was because the original cloth insulation would leak current when wet and cause corrosion: <http://www.cruisersforum.com/forums/f14/negative-ground-vs-positive-ground-history-question-184600.html> Incidentally, Motorola decided to run two really heavy cables directly between the trunk mounted radio and the battery under the hood. However, they got cheap and lazy with their front and dash mounted radios by supplying fairly short power cables with the radios. Installers were tempted to just ground the negative to the car chassis and were then blessed with alternator whine, generator whine, and vibrator hash on transmit. Not wishing to repeat all the mistakes of past attempts to color code the power wiring, the solar power standard committees decided that it would be better to label these in English and use the colors in their original manner (red=danger, green=working, yellow=warning, black=all_else). So, it is now mandatory to attach stickers on everything including the DC power cables: <https://www.google.com/search?tbm=isch&q=solar+power+warning+labels> However, the DC power labels do not mention polarity. Instead the are yellow and say "Solar Circuit". Most (not all) of the panels I've seen use red and black color coded wires. NEC 2014 wasn't bad for a first attempt at labeling, but did require a rewrite in 2017 to make the English intelligible. <https://www.solarpowerworldonline.com/2016/03/new-nec-2017-brings-clarity-solar-pv-labeling/> I expect the next generation of labels might add multiple languages, hieroglyphics, and icons. -- 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 26, 20202020-01-26
On 1/26/20 1:37 PM, Rick C wrote:> Unfortunately that question is confusing to me. lolSorry. 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 supplySimplistically, 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.-- Grant. . . . unix || die
Reply by ●January 26, 20202020-01-26
On 1/26/20 1:41 PM, Rick C wrote:> This seems to be the question you are asking I guess. > > If you are working with a -48 volt system, the ground will be positive > and the power lead will be negative.Okay. So what colors would you expect / assume the ground and power leads to be? Black and red, respectively? Or red and black, respectively?> If your power supply is intended for such a system the lead labeled > "return" will be positive and the other output will be negative.Okay. Do you think it would be acceptable for the negative power lead to be referred to as "hot"? This does seem to answer part of what I'm wanting to know. I say "part" because I think your answer likely does provide the wrote memory type of information. And in a round about way makes it easier for me to point to the other part that I'm trying to learn. 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? That other information / knowledge is the other part of what I'm wanting to learn and understand. The intention being for me to learn the foundational knowledge to deduce statements like you did without needing to rely on wrote memory. Does that make sense?> It would be helpful to see some photos of the terminals and the power > supply label.Agreed. I'm at home, and the equipment in question is at work. I doubt that I'll be able to get any pictures before Tuesday. -- Grant. . . . unix || die
Reply by ●January 26, 20202020-01-26
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.That's why I would look at the documentation for the equipment/supply. 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".> 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 have seen some systems use a negative ground with a 48 volt power source.> 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 VDCNow you are talking color codes. I can't tell you what the color code is for a -48 volt system.> So what is called the positive or red lead actually is negative with > respect to what is called the negative or black lead."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.> 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?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.> > 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.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.> > 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.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.> > 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.The volt meter will always tell you the voltage between the two probes assuming the red will be positive and the black negative. If that is correct the meter will show a positive voltage. I the red lead is negative it will show a negative voltage.> 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.That will give you a positive voltage on the positive lead with respect to (wrt) ground.> +⏚) AC-to-DC with a connection between neutral / ground and the + output.That will give you a negative voltage on the negative lead wrt ground. 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).> 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 (+⏚).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.> > 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'd say a measurement is in order... with the resistor I mentioned.> 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.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.> > 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.That is all polarity, no? I'm not getting it.> > 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 hope that helps. -- 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 4:50:41 PM UTC-5, Grant Taylor wrote:> On 1/26/20 1:41 PM, Rick C wrote: > > This seems to be the question you are asking I guess. > > > > If you are working with a -48 volt system, the ground will be positive > > and the power lead will be negative. > > Okay. > > So what colors would you expect / assume the ground and power leads to > be? Black and red, respectively? Or red and black, respectively?I don't assume something I don't know about. You'll have to measure.> > If your power supply is intended for such a system the lead labeled > > "return" will be positive and the other output will be negative. > > Okay. > > Do you think it would be acceptable for the negative power lead to be > referred to as "hot"?Hot or power. Ground/common is typically used for the "reference" of the power. So the other lead will be positive in this system and so, hot.> This does seem to answer part of what I'm wanting to know. I say "part" > because I think your answer likely does provide the wrote memory type of > information. And in a round about way makes it easier for me to point > to the other part that I'm trying to learn. > > 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?Just that the definition of -48 volt power is that the negative is the power or hot lead and the positive is common. I really shouldn't use "ground" for the common lead since ground is often used for "protective earth" which is a different concept. They may be connected, but are not the same thing, just as neutral and protective earth are connected (if all is well) but not the same thing. If I mean protective earth I will say protective earth, otherwise ground will mean common.> That other information / knowledge is > the other part of what I'm wanting to learn and understand. The > intention being for me to learn the foundational knowledge to deduce > statements like you did without needing to rely on wrote memory. Does > that make sense?Not really. I think you are making this a bit too complicated than it is. I'm not complaining, just stating an observation.> > It would be helpful to see some photos of the terminals and the power > > supply label. > > Agreed. I'm at home, and the equipment in question is at work. I doubt > that I'll be able to get any pictures before Tuesday.I expect that by the time you get to the equipment this will all be much more clear to you. -- 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 4:42:38 PM UTC-5, Grant Taylor wrote: Grant, let me just offer this as consolation: A few months back, we got a job to wire-up a Verizon rack. The rectifier was an Emerson NetSure 502. (Pretty generic, in that industry). Well.... You need a Ph.D. to understand the Installation Manual. That manual covers so many different options and configurations it will make your head spin. The manuals (plural)are at least 3-inches thick, loaded with schematics and wiring diagrams to cover any situation and options packages known to mankind. We sat there for about an hour with the manuals just trying to figure out where to connect the two leads from the battery. (A "-48 VDC" system.) Getting nowhere - we finally called Emerson Tech Support. I was mortified - how embarrassing to have to call in for this kind of stuff?! You may as well wear a hat on your head that reads "I eat paint chips." AN HOUR LATER - the rep was FINALLY able to tell us where to hook up! Because even though Verizon probably buys these rectifiers by the 1000's, it's some special bus arrangement requiring the aforementioned Ph.D. to decipher the fucking manual. Great product. Horrible manuals! Unless all you do in life is focus on authoring manuals like that, and then of course, it's terrific. But who has the time for that? I guess I'm saying, don't feel bad about being confused. Even the big guys fuck it up.
