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Topic:
Understanding Voltage Drop
This thread has 39 replies. Displaying posts 16 through 30.
Post 16 made on Monday January 21, 2019 at 12:24
Ernie Gilman
Yes, That Ernie!
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On January 21, 2019 at 09:45, highfigh said...
Re my comment that doubling a wire gives you about the same resistance as a wire three numbers smaller (wire diameter larger, numbers smaller).
Really? Did you look at the chart for the resistance of 24ga vs 18ga? I did and that's why I wrote that the resistance would be ~25%. Jesus!

No need to bring him into it. He does everything wirelessly.
Read, don't skim! I have to tell myself to do the same but if you doubt my statements, the least you could do is look at the source!

I was remembering a similar discussion from some time ago. No, I didn't look and haven't looked for more than a year. But here's what I found upon looking:

My chart says the resistances of these wires are this:
24 gauge, 25.67 ohms per thousand feet
21 gauge, 12.8
18 gauge, 6.385
I claimed that two 24s in parallel have a resistance almost exactly the same as a 21 gauge wire. From the numbers above, two 24s in parallel have a resistance of 25.67/2 = 12.835 ohms per thousand feet.
I said that two of these paralleled pairs of 24s would have a resistance nearly the same as an 18 gauge wire. Two wires of 12.835 ohms in parallel have a resistance of 12.835/2 = 6.4175 ohms per thousand feet.
Those numbers are very very very close, close. Aren't they?

I think you understood me to mean something else. What did you think I was saying?

Will two power amps produce the same output into low impedance loads? Why not?

Because red herrings swim sideways. What does this have to do with the discussion? I assume you mean connecting two power amps to one load; this will cause interaction between the output stages that would likely damage the amplifiers, so it's not worth thinking about.
Power supply. If one power supply is more robust, the output will be more similar to connecting to a higher impedance load and if not, we'll see them rated for output @1KHz into 8 Ohms. Also, did you NOT see my comment about a regulated supply?

Yes, I saw that comment, and I wrote this. Perhaps we should both read everything:
Oops, that last assertion doesn't pan out.
A power supply rated for more current will be able to output more current than one rated for a lower current. But you're talking about somehow getting more current out of a supply at 12 volts than out of another supply at 12 volts, with the same load each time. That won't happen. 12 volts divided by the same load in two different setups will be the same current.

I missed one point -- if one supply is underrated for the job, then yes, a power supply that can do the job will work better. That has nothing to do with robustness. A robust supply might be one that can survive a short circuit, after all, which is not an issue here.

Maybe you should have responded to the original- you wasted time with your first comment about not having time and here you are, not responding to it again.

You're right.

On January 21, 2019 at 09:47, buzz said...
With respect to using a capacitor to augment available current for operating the gate lock:

First, there is the assumption that the lock operates from a DC drive. I have no depth of installer experience here, but just listening to the action as I enter various spaces, many locks operate from AC. Of course, as the installer you would have control over this point.

Good points.

Second, capacitor charging and support times are a consideration. One should not assume that the door operator (the human) will instantly yank the door open after the lock is enabled.

Hence my statement that the door should spring open, or something along that line.
My guess is that several seconds of support would be appropriate. Now, what happens if the person failed to meet the timing window and must then wait until the capacitor recharges before the next attempt?

The timing is likely to be less than a second. It needs to pop open a solenoid, and in a second, enough charge is likely to accumulate to make a pulse of several amps possible.

However, Highfig's suggestion of putting a battery there is BY FAR the better idea:
*Trickle charging, even on one 24 GA wire, (I said one wire instead of one pair because all the circuit grounds would be tied together) would be 24 hours per day with no large currents
*the battery would easily always be able to supply several amperes for several minutes, way beyond what's required to pop a solenoid.

Years ago in car audio we experienced the benefits of adding huge capacitors, in that if large enough, they almost behave like batteries. Batteries would be even better here.
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
Post 17 made on Monday January 21, 2019 at 19:01
davidcasemore
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Gee, Ernie. You haven't commented on my post right near the start of this thread.

I feel so ....... left out:-(
Fins: Still Slamming' His Trunk on pilgrim's Small Weenie - One Trunk at a Time!
Post 18 made on Monday January 21, 2019 at 20:19
Ernie Gilman
Yes, That Ernie!
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So so sooooo sorry.

The calm, reasonable, correct, incontrovertible, non-exaggerated and pretty damn thorough posts never get any attention, do they?

At this moment I can't think of any smartass thing to say, except thanks for cracking me up.

On the terms of it, though, I'd be really wary of increasing the voltage for the reasons you cited, but you also have to beware of succession sucking. This happens when the guy who comes after you to work on the system several years from now sucks because he doesn't measure the power supply voltage (be honest: how often do you measure the voltage of a working power supply?) before disconnecting half of the cameras with 200 foot runs, thus blowing some of the ones that are left.

It would be nice if camera sellers over here knew the voltage limits of their product, but as I said, they don't even understand the question. (And of course this goes for all other products, too.)
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
Post 19 made on Tuesday January 22, 2019 at 09:21
highfigh
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On January 21, 2019 at 12:24, Ernie Gilman said...
Re my comment that doubling a wire gives you about the same resistance as a wire three numbers smaller (wire diameter larger, numbers smaller).
I was remembering a similar discussion from some time ago. No, I didn't look and haven't looked for more than a year. But here's what I found upon looking:

My chart says the resistances of these wires are this:
24 gauge, 25.67 ohms per thousand feet
21 gauge, 12.8
18 gauge, 6.385
I claimed that two 24s in parallel have a resistance almost exactly the same as a 21 gauge wire. From the numbers above, two 24s in parallel have a resistance of 25.67/2 = 12.835 ohms per thousand feet.
I said that two of these paralleled pairs of 24s would have a resistance nearly the same as an 18 gauge wire. Two wires of 12.835 ohms in parallel have a resistance of 12.835/2 = 6.4175 ohms per thousand feet.
Those numbers are very very very close, close. Aren't they?

I think you understood me to mean something else. What did you think I was saying?

That's well known- why go into such detail when it's shown in the chart?


Because red herrings swim sideways. What does this have to do with the discussion? I assume you mean connecting two power amps to one load; this will cause interaction between the output stages that would likely damage the amplifiers, so it's not worth thinking about.

You assume too much and here, you assume incorrectly.


Yes, I saw that comment, and I wrote this. Perhaps we should both read everything:
I missed one point -- if one supply is underrated for the job, then yes, a power supply that can do the job will work better. That has nothing to do with robustness. A robust supply might be one that can survive a short circuit, after all, which is not an issue here.

Robust would also mean it can handle high demand without failure, but it doesn't need to be a dead short.
However, Highfig's suggestion of putting a battery there is BY FAR the better idea:
*Trickle charging, even on one 24 GA wire, (I said one wire instead of one pair because all the circuit grounds would be tied together) would be 24 hours per day with no large currents
*the battery would easily always be able to supply several amperes for several minutes, way beyond what's required to pop a solenoid.

Years ago in car audio we experienced the benefits of adding huge capacitors, in that if large enough, they almost behave like batteries. Batteries would be even better here.

The demo I saw in about 1982, around the time stiffening caps began to be used widely for car audio had a cap connected to a light bulb and a battery connected to another, with a voltmeter and ammeter connected to each. The current needed for the bulbs was fairly high and it was a decent demo of peak power demand and how each would supply what was needed in order to maintain output and supply voltage. The battery won, easily. IIRC, three paralleled half Farad caps were needed to match the ability of the battery.
My mechanic told me, "I couldn't repair your brakes, so I made your horn louder."
Post 20 made on Wednesday January 23, 2019 at 02:18
Ernie Gilman
Yes, That Ernie!
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You're not keeping up with what you write.
On January 22, 2019 at 09:21, highfigh said...
That's well known- why go into such detail when it's shown in the chart?

That huge amount of detail was for your benefit. I wrote this, in which I just now saw the typo in orange:

On January 20, 2019 at 21:59, Ernie Gilman said...
The resistance of two of the same conductor in parallel roughly equals the resistance of a wire three numbers larger on the chart. Frinstance, two #4 (error-- should have been 24) in parallel are about the same as a #21. Take two such setups and parallel them, and you'll effectively have 18 gauge. It's worth sticking in your brain somewhere that a CAT5 cable, using all conductors, is roughly equivalent to an 18 gauge pair.

So, you got it, right? I claim that combining two wires of the same gauge in parallel a)halves their resistance and b)comes to the resistance of a wire of a gauge number three smaller, that is, for instance, 24 to 21.

Then you wrote this:

On January 21, 2019 at 09:45, highfigh said...
Really? Did you look at the chart for the resistance of 24ga vs 18ga? I did and that's why I wrote that the resistance would be ~25%. Jesus! Read, don't skim! I have to tell myself to do the same but if you doubt my statements, the least you could do is look at the source!

AND JUST NOW, after reading this, yes, rapidly several times over the last couple of days, I see that you said the resistance would be 25%... so yes, you said the same thing. I gave the numbers showing it would halve, then halve again. Expressing anything as a percentage was the furthest thing from my mind.  When you cited a percentage, I TOTALLY missed that you were on the same subject. As I've said before, you and I talk about things differently. Sorry I missed that!
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
Post 21 made on Wednesday January 23, 2019 at 10:04
highfigh
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On January 23, 2019 at 02:18, Ernie Gilman said...
You're not keeping up with what you write.

I need to keep up? You're the one who's confused.

That huge amount of detail was for your benefit. I wrote this, in which I just now saw the typo in orange:

And yet, I didn't benefit from it because I already knew it. My post showed that the resistance would be about 25% and I wrote that before I located the chart. Been doing this for a while, OK?

So, you got it, right? I claim that combining two wires of the same gauge in parallel a)halves their resistance and b)comes to the resistance of a wire of a gauge number three smaller, that is, for instance, 24 to 21.

I used 24ga for the wire because, well, that's what Cat5e is made of. You need to make the leap from 24ga to 18ga without needing to have a layover at 21ga.

AND JUST NOW, after reading this, yes, rapidly several times over the last couple of days, I see that you said the resistance would be 25%... so yes, you said the same thing. I gave the numbers showing it would halve, then halve again. Expressing anything as a percentage was the furthest thing from my mind.  When you cited a percentage, I TOTALLY missed that you were on the same subject. As I've said before, you and I talk about things differently. Sorry I missed that!

No difference. We learn fractions before decimal and percentages- we should be able to do any or all of these, interchangeably. Be happy I didn't convert to Metric.

You would think I'm insane if you ever see the diagrams I use when I design things to build, myself. I mix fractions and decimal, mainly because it's a bit faster to express 23/32" (or some other fine increment) than the decimal equivalent. I studied Architecture, which is all fractions, but I have done work where machining was used, which is usually decimal. I'm comfortable with both and, having serviced boats & cars, I don't have a problem if Metric is used. If I need to make a drawing for someone else to use, I stay with one type.
My mechanic told me, "I couldn't repair your brakes, so I made your horn louder."
Post 22 made on Wednesday January 23, 2019 at 22:12
Ernie Gilman
Yes, That Ernie!
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On January 23, 2019 at 10:04, highfigh said...
I studied Architecture, which is all fractions,

Ah. All is explained. Architects are the guys who very often try to sell their work by making a drawing showing the finished building, often drawn as though at a distance impossibly far from the building, because, hey, there are buildings on the other side of the street. Many times architect's renderings do not include people, maybe because that messes up the look. And, of course, the joke:

Why can't architects get into heaven?
Because Jesus was a carpenter.

For any who don't get it, this is a comment on architects designing things that are at least clumsy, and sometimes impossible, to build.


As for me and dimensions, I prefer one system at a time. And inches, not feet and inches. It's all about instant usability. I feel that if I have to multiply something by twelve and add it to a remainder before I can divide it by three, then the dimension is given in the wrong units.

BTW, during our first meeting with the Saudi engineers who were involved in the huge theater project we did last decade, one of my functions was to throw out the metric/feet conversions so the other half of the people would have a sense of the dimensions.

Which reminds me of a funny moment, when we told them that a structure could be made out of plain 2x4s, and they wrote down 2".
By 4".
And I blew them away by telling them that 2x4s measure 1 1/2" x 3 1/2" (3.8 x 8.9).
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
Post 23 made on Thursday January 24, 2019 at 01:33
highfigh
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On January 23, 2019 at 22:12, Ernie Gilman said...
Ah. All is explained. Architects are the guys who very often try to sell their work by making a drawing showing the finished building, often drawn as though at a distance impossibly far from the building, because, hey, there are buildings on the other side of the street. Many times architect's renderings do not include people, maybe because that messes up the look. And, of course, the joke:

Why can't architects get into heaven?
Because Jesus was a carpenter.

For any who don't get it, this is a comment on architects designing things that are at least clumsy, and sometimes impossible, to build.

I didn't study at a school where they teach people to draw pretty buildings, it was MSOE. We learned how to make them stand and why, not to hope they don't fall over or collapse.

Most architects don't do their own renderings, but they do need to show the new building in place, so why would they make it seem that the viewer is 3' away from it?

As for me and dimensions, I prefer one system at a time. And inches, not feet and inches. It's all about instant usability. I feel that if I have to multiply something by twelve and add it to a remainder before I can divide it by three, then the dimension is given in the wrong units.

You would use 170" instead of 14'-2"? Why? If you were working with plans and elevations, I would be surprised if the builders don't give you a hard time for that. In a classroom situation, it would never pass.

BTW, during our first meeting with the Saudi engineers who were involved in the huge theater project we did last decade, one of my functions was to throw out the metric/feet conversions so the other half of the people would have a sense of the dimensions.

Which reminds me of a funny moment, when we told them that a structure could be made out of plain 2x4s, and they wrote down 2".
By 4".
And I blew them away by telling them that 2x4s measure 1 1/2" x 3 1/2" (3.8 x 8.9).

OUR 2x4s are 1-1/2" x 3-1/3", but what's available in Saudi Arabia? (I could find out, but I would have to wake a friend in order to ask)

Throw out metric. Typical American.
My mechanic told me, "I couldn't repair your brakes, so I made your horn louder."
Post 24 made on Thursday January 24, 2019 at 12:48
Ernie Gilman
Yes, That Ernie!
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On January 24, 2019 at 01:33, highfigh said...
I didn't study at a school where they teach people to draw pretty buildings, it was MSOE. We learned how to make them stand and why, not to hope they don't fall over or collapse.

If this method takes into account actual building materials and methods, and doesn't end up with designs that can't be built, then, great.
Most architects don't do their own renderings, but they do need to show the new building in place, so why would they make it seem that the viewer is 3' away from it?

Your use of exaggeration (citing three feet as a reasonable distance) makes it look like you don't understand, so, here: Let's say the building is to be on a two-lane street in an old neighborhood near a metro downtown, built soon after 1900. The street is two lanes. But to show the design elements of a new building, the rendering shows the building from a hundred feet... which is about twenty feet inside the building across the street. It is not possible to see the view that is shown in the rendering.
You would use 170" instead of 14'-2"?

Yes.
Why? If you were working with plans and elevations, I would be surprised if the builders don't give you a hard time for that. In a classroom situation, it would never pass.

I agree that it would never pass in a classroom situation. I stopped going to college after I got my BA because it was becoming increasingly obvious that college was an artificial world, and I'd better get out here before becoming trapped in the academic world. Remember, when people say "It's all academic, anyway," they mean it's not realistic and it doesn't matter.
OUR 2x4s are 1-1/2" x 3-1/3", but what's available in Saudi Arabia? (I could find out, but I would have to wake a friend in order to ask)

Our 2x4s are 1 1/2" x 3 1/2", not 3 1/3". (Does your tape measure have thirds? Relax, I know it was a typo.)

But we were defining how we wanted something built. We asked them what the standard wood sizes were and they had blank looks. We had just barely started working with them and we had not learned that pretty much everything in Saudi Arabia is made with steel and some variety or agglutination of sand and stone.

While every construction worker in the US is likely to carry a Skil Saw, in SA they all carry grinders.

Back to the wood: They basically had to import any wood that would be used, with its major cost being shipping (since we weren't going to be specifying walnut plywood or anything nuts like that). This was wood for the structure that seating was to go on, and it was a component of the audio characteristics of the room, so our designer decided to specify what he had worked with for years, to minimize errors due to unfamiliarity with materials.

As for 170", yes, that's what I'd use. It's very easy to divide 14'2" by two, but divide it by three. Or mentally divide 15'7" by two. That's easy, it's 7'6" + 3 1/2" so 7'9 1/2". I think. Or add several numbers that are feet and inches. Adding inches alone is simpler.

I think this is one more example of real world versus academic world. The guys I see measuring on the job measure and calculate in inches.


Throw out metric. Typical American.

I was using a bit of slang and I was not clear. Someone would give a dimension in inches, and I would yell out -- which I characterized as "throw out" -- the equivalent dimension in metric. It started with temperature, when I saw American eyebrows go up when someone said 35 degrees was too hot to work in.
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
Post 25 made on Thursday January 24, 2019 at 20:31
davidcasemore
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On January 24, 2019 at 12:48, Ernie Gilman said...
As for 170", yes, that's what I'd use. It's very easy to divide 14'2" by two, but divide it by three. Or mentally divide 15'7" by two. That's easy, it's 7'6" + 3 1/2" so 7'9 1/2". I think. Or add several numbers that are feet and inches. Adding inches alone is simpler.

The reason we have ten fingers (I'm counting a thumb as a finger) and ten toes is so we can easily work with divisions of ten. God figured, in all its wisdom, to give us these groups of ten digits because it assumed that the entire world would be smart enough to come up with, and use, the Metric System. So much for all-powerful and all-knowing!
Fins: Still Slamming' His Trunk on pilgrim's Small Weenie - One Trunk at a Time!
Post 26 made on Thursday January 24, 2019 at 21:21
buzz
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Turns out that we would be much better off if we had eight or sixteen appendages. Our number systems would be much better aligned with modern technology.

I always thought that I came through a rather backward school system, but for some seemingly unfathomable reason in 6th grade we were forced to learn the 16's times table. We wanted to smack the teacher. I'm not sure that anyone in the school system knew why this might be an advantage. Later, when I was in intern in a mainframe programming shop, Hex notation hit and the old timers were struggling, I was instantly at home.
Post 27 made on Thursday January 24, 2019 at 23:45
Ernie Gilman
Yes, That Ernie!
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On January 24, 2019 at 20:31, davidcasemore said...
The reason we have ten fingers (I'm counting a thumb as a finger) and ten toes is so we can easily work with divisions of ten. God figured, in all its wisdom, to give us these groups of ten digits because it assumed that the entire world would be smart enough to come up with, and use, the Metric System. So much for all-powerful and all-knowing!

I don't think it went im that direction. I think we got, developed, were blessed with, were forced to have, whatever you want to call it, ten fingers and ten toes, and it was then natural to use them to count, so we developed counting systems based on what we were carrying around:ten digits. Hell, the word is even DIGIT! (I can't say why twenty wasn't used.)

Apparent, but not, non sequitur:

There used to be a free engineering publication in Southern California, printed on newsprint paper. One of the features was the caption contest. Here's one of the artworks and its winning caption, from the early 80s:



          The Sales Department Counting to 21
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
Post 28 made on Friday January 25, 2019 at 10:49
highfigh
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On January 21, 2019 at 20:19, Ernie Gilman said...
It would be nice if camera sellers over here knew the voltage limits of their product, but as I said, they don't even understand the question. (And of course this goes for all other products, too.)

Good case for regulated power supplies, eh?
My mechanic told me, "I couldn't repair your brakes, so I made your horn louder."
Post 29 made on Friday January 25, 2019 at 10:51
highfigh
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On January 24, 2019 at 20:31, davidcasemore said...
The reason we have ten fingers (I'm counting a thumb as a finger) and ten toes is so we can easily work with divisions of ten. God figured, in all its wisdom, to give us these groups of ten digits because it assumed that the entire world would be smart enough to come up with, and use, the Metric System. So much for all-powerful and all-knowing!

I remember learning Metric in 7th Grade, in the late-'70s and hearing people say that it would never take off here, in the US. I could never understand why they were so resistant to it.
My mechanic told me, "I couldn't repair your brakes, so I made your horn louder."
Post 30 made on Friday January 25, 2019 at 10:56
Ernie Gilman
Yes, That Ernie!
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On January 25, 2019 at 10:49, highfigh said...
Good case for regulated power supplies, eh?

Not necessarily. If you have a regulated 12 volt supply and three volts of IR drop on your power wires... does the camera work at 9 volts? Since the manufacturers can't tell you, maybe an unregulated supply that floats up higher than the target voltage would work better.

Not that I'd use an unregulated power supply... I'd rather learn that the camera won't work with that amount of voltage drop, and then have to fix it, than use an unregulated supply. See, if the regulated supply didn't work, then I'd learn some things that, as said, the camera company couldn't tell me.
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
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