I have recently fought with a similar but a bit different supply. The fuse had failed because the switchig transistor has failed shorted, or else only shorts when power is applied. Diagnostics were challenging because of the tightly packed board. We found a suitabole supply with twice the current rating and adjustable to exactly the specified vokltage for $21 on line, and it arrived 3 days after the order was placed. Amazon prime is slightly useful. Fortunately a friend had an account and could order it.
Diagnostics of one of those supplies is very challenging at best. And the damaged component is usually the result of some other component that shows no sign of failure.
Be sure to save the output cablem noting which side is positive.. That is the hard part to replace, usually.

 

I have recently fought with a similar but a bit different supply. The fuse had failed because the switchig transistor has failed shorted, or else only shorts when power is applied. Diagnostics were challenging because of the tightly packed board. We found a suitabole supply with twice the current rating and adjustable to exactly the specified vokltage for $21 on line, and it arrived 3 days after the order was placed. Amazon prime is slightly useful. Fortunately a friend had an account and could order it.
Diagnostics of one of those supplies is very challenging at best. And the damaged component is usually the result of some other component that shows no sign of failure.
Be sure to save the output cablem noting which side is positive.. That is the hard part to replace, usually.

Yeah, I already thought of that. However, the PSU label tells you which one is the positiva and which one the negative, so all you have to do is look at the label and see that the positive icon is linked to the center pin/dot, while the negative is connected to the surrounding circle, which is the outside "shell"/"shield".



Oh, I remember one thing... I was one day discussing exactly this topic, and I claimed "well, the positive must be always the center pin, the inside pin, the inner dot". If you reverse that, you would have an exposed +19.5V DC in the cylinder metallic part, and that is wrong by design. Why would you want the outer part to be positive instead of 0V?

And shockingly, one guy mentioned that that's not always the case, neither the "best design". Sometimes is better to have the outer ring positive, and the inner covered contact at 0V. I am thinking about it and I can't understand why would someone say that. Wouldn't the positive +19.5V DC outer ring be dangerous if it touches something conductive?

 

The ONLY bad design feature of putting the positive on the outside ring is...everyone expects it to be the other way around.

Well except for those who know better.

 

The ONLY bad design feature of putting the positive on the outside ring is...everyone expects it to be the other way around.

Well except for those who know better.

Yeah, but besides that, isn't it technically worse?
Isn't it more dangerous to have the exposed ring with +19.5V instead of 0V?
Couldn't the current find it's way if the ring touches something conductive?

 

Define "something conductive" a nail?

What if the device in question has a positive ground?

There is no such thing as "0V" it's a reference nothing more.

Your 19.5 volt circuit has 19.5 volts from positive to negative and 19.5 volts from negative to positive so where is this 0V?

 

The only reason some make the outside positive is to be different and to try to foce folks to buy the OEM supply for $79 instead of an aftermarket supply for $15 or so. That is why all label printers use 9 volts center negative.
I am amazed that phone makers have not come up with a scheme to force folks to buy their $49 charger instead of any old cheap charger.

 

Something conductive means some piece of material that's conductive and can connect that outer ring to earth, so amps start to flow from the outer ring to earth. Correct me if I am missing something but I believe that's what would happen.

Well, I mean the same reason why the hot wire is the one you send to the switch and not the neutral wire, because neutral wire is the return path, which is almost like earth voltage (0V).

What kind of common object (or rare...) is positively charged and exposed to be touched by accident?
The most common (if not only) thing to find is earthed objects at 0V... If you have a positively charged exposed piece, you touch it and you are not insulated, get ready to get shocked, right?

I believe 0V is earth reference. One thing is to have 20V from point A to point B, and another thing to say that B is at 0V. In the first situation, A could be at 250V, B at 230V, and from A to B 20V. Still B is at 230V. From what? Obviously from earth.

May be I am missing something?

 

Something conductive means some piece of material that's conductive and can connect that outer ring to earth, so amps start to flow from the outer ring to earth. Correct me if I am missing something but I believe that's what would happen.

Well, I mean the same reason why the hot wire is the one you send to the switch and not the neutral wire, because neutral wire is the return path, which is almost like earth voltage (0V).

What kind of common object (or rare...) is positively charged and exposed to be touched by accident?
The most common (if not only) thing to find is earthed objects at 0V... If you have a positively charged exposed piece, you touch it and you are not insulated, get ready to get shocked, right?

I believe 0V is earth reference. One thing is to have 20V from point A to point B, and another thing to say that B is at 0V. In the first situation, A could be at 250V, B at 230V, and from A to B 20V. Still B is at 230V. From what? Obviously from earth.

May be I am missing something?

YES, You are missing the fact that the supply output is supposed to be isolated from the mains. The result of that isolation is that whereber the negative from the output connects to, including "ground", NO CURRENT WILL FLOW because there is no circuit to the positive isolated output. Basic electricity tells us that withouta closed circuit no current will flow.

 

I believe 0V is earth reference. One thing is to have 20V from point A to point B, and another thing to say that B is at 0V. In the first situation, A could be at 250V, B at 230V, and from A to B 20V. Still B is at 230V. From what? Obviously from earth.

May be I am missing something?

Hello there!

People display bias beliefs when they select information that supports their views.
Dismissing one's well-educated advice due to what are perceived to be more important,(your misguided beliefs) ignoring contrary information.
You are missing something!
When earth ground is used as a common ground or a 0V reference. This is a bit misleading because a 0V reference is not actually connected to earth ground. Ohm's law can care less about your beliefs or anyone's else's for that matter. I hope this helps!
https://www.allaboutcircuits.com/technical-articles/an-introduction-to-ground/

 

Once again, the part that is missed is the isolation!!The zero volts point on the output side of the isolated computer power supply IS NOT CONNECTED to the input side of the supply at all.
This means that no current will flow to any point connected to the input from the output.

Believing something different does not make it different, and wishing something was different does not make it different, no matter what Jim Moore says.

 

YES, You are missing the fact that the supply output is supposed to be isolated from the mains. The result of that isolation is that whereber the negative from the output connects to, including "ground", NO CURRENT WILL FLOW because there is no circuit to the positive isolated output. Basic electricity tells us that withouta closed circuit no current will flow.

I know I am not an expert when it come to these kind of details but... if hot wire and neutral wire are isolated from ground, and when you touch the hot wire you get shocked, how are we closing there the circuit with earth, but in my DC adapter example we aren't?
I don't understand.

"The result of that isolation is that wherever the negative from the output connects to"
But I didn't say the negative, I said the positive. If you touch a positive with your hand and you are "earthed", isn't that a path from the positive to earth?
I think this is exactly what happens with hot mains.

We are not discussing if 20V DC are enough to make current flow, imagine instead of 20V DC we have 2000V DC or AC. I am thinking about the general rule.

 

Hello there!

People display bias beliefs when they select information that supports their views.
Dismissing one's well-educated advice due to what are perceived to be more important,(your misguided beliefs) ignoring contrary information.
You are missing something!
When earth ground is used as a common ground or a 0V reference. This is a bit misleading because a 0V reference is not actually connected to earth ground. Ohm's law can care less about your beliefs or anyone's else's for that matter. I hope this helps!
https://www.allaboutcircuits.com/technical-articles/an-introduction-to-ground/

I am not trying to ignore facts and choose whatever I want, Jesus... I am trying to learn, that's why I am asking questions and proposing examples that show my view on this topic, so you can correct me if I am wrong or agree with me if I am right.

 

I know I am not an expert when it come to these kind of details but... if hot wire and neutral wire are isolated from ground, and when you touch the hot wire you get shocked, how are we closing there the circuit with earth, but in my DC adapter example we aren't?
I don't understand.

"The result of that isolation is that wherever the negative from the output connects to"
But I didn't say the negative, I said the positive. If you touch a positive with your hand and you are "earthed", isn't that a path from the positive to earth?
I think this is exactly what happens with hot mains.

We are not discussing if 20V DC are enough to make current flow, imagine instead of 20V DC we have 2000V DC or AC. I am thinking about the general rule.

I AM an expert on electrical things. Not a master but an actual engineer wit years of experience designing electrical equipment that was found buy those who purchased it to meet their requirements very well. AND that equipment was determined by their safety people to be quite safe and to meet the safety requirements. So I understand very well about circuits and current flows and where current does not flow.
And you are quite welcome to ignore all of my good advice if you do not like it. My requirement then is to not blame me when things go wrong.

 

Jesus, why are you defending yourself?
I am neither attacking nor ignoring your comments!

This works like this: I think what would happen if the outer ring is the positive, and explain it here. I already said that it must not be safe because of the same reason you get shocked and current flows through your body if you touch the hot wire. If you touch it, amps can flow from the hot to the ground.

If you know I am wrong, kindly point where I am wrong and what's wrong about my analogy between the hot wire and the outer ring. I have never EVER said anything similar to "nah, I don't like your explanation".
What? Where the heck did you induced that from my words?

IF you explain the reason to me, 2 things can happen, which indeed happened: one, I understand my error, or two, I don't understand your point. You said there would be no closed circuit and no current would flow, and that the circuit is isolated from the mains.

So what do I do?
I say, ok, let's think about that... and still didn't understand your explanation. The outer ring and and inner ring are also isolated from the mains, and there is a closed circuit, or a path: from the positive outer ring to ground. Pretty much like a lightning.

This is NOT ignoring your explanation, it is NOT discarding your explanation because I don't "like" it (what, now I learn science by my feelings?)... this is reading your explanation and trying to apply it. I did and it didn't work because I still say "well here's the path for the current to flow", and "it is isolated as well from mains".

If I am wrong you should say "No, the circuit is not closed because of this and this, think about this, etc", and "you are assuming this which is wrong because it wouldn't work like that because of this and that". You know, your regular average correction when someone is wrong.

 

The only reason some make the outside positive is to be different and to try to foce folks to buy the OEM supply for $79 instead of an aftermarket supply for $15 or so. That is why all label printers use 9 volts center negative.
I am amazed that phone makers have not come up with a scheme to force folks to buy their $49 charger instead of any old cheap charger.

They used to do that. The EU outlawed it.

Bob

 

Jesus, why are you defending yourself?
I am neither attacking nor ignoring your comments!

It has been explained to you in post #38, #41, #42, and #43. You have ignored them all and keep asking why you would not get shocked.

Bob

 

IGNORE: fail to consider (something significant), refuse to take notice of or acknowledge.

I am CLEARLY not ignoring the messages because I am applying their explanations, I AM using them and still don't understand, and I explain why I don't understand them, so if I am wrong in that explanation, point it out instead of saying nonsense like I am ignoring, which is completely false.

To sum up, I've seen 2 explanations:

"The circuit is not closed"
I already said there is a path from the positive to earth through your body if you touch the outer ring, I think like a lightning. If that is not what is happening, explain why, I've asked that several times. What is wrong with that argument? Is not that a path? Why not? Why is it for the hot? (I made it clear that imagine instead of 20V there are 1000V, in case it's just a matter of numbers)

I am asking what's the difference between touching a hot wire, which is as isolated from earth as the outer ring of, and touching the positive outer ring.

You are the ones ignoring my answer to your explanation, that I still don't understand.

 

No, I understand DC goes from positive to negative, or better, from higher to lower voltage.

In AC, it is exactly like that, from higher to lower voltage, but the hot follows a sinusoidal wave that peaks from +325V to -325V, RMS 230V. That, 50Hz, 50 positive peaks each second, 50 negative.

So, to answer your question, I understand current flows from higher to lower, so "creating" negative voltage would be like creating vacuum, and you would get shocked, I think. I know to understand this really well you have to be a quantum physicist, because we are taught that there are "balls, electrons flowing", which is not true. I have the idea that electricity is more like a shock wave, a force wave, it's not actual mass traveling through cables.

To sum up, 20V are higher, hence my reasoning. I don't understand neither the difference between that outer ring and a hot wire in terms of shocking you.

And thank you for actually caring for what I said instead of talking nonsense and claiming false insulting things such as assuming I like or dislike an argument and based on my feeling I apply that to science. No, I either understand them or do not, but I don't like or feel arguments. Much less ignore them.

 

For clarity I believe Rambo is responding to a question I waited too long to delete.

Sorry, my bad.

 

No, I understand DC goes from positive to negative, or better, from higher to lower voltage

In terms of DC circuit analysis, we normally consider the direction of electric current from positive to negative. Mathematically, negative charge flowing in one direction is equivalent to positive charges flowing in the opposite direction. Hence it does not make a difference. One can either consider the flow of current from positive to negative or vice versa during circuit analysis. In fact, positively charged ions can be attracted by negatively charged electrons