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Electronics for Audiophiles: Voltage and Current (Video)

tomtoo

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At least he goes short into body resistance. But his analogy at the end is just wrong. There are many tsunamis in this world, none ever killed me. Couse the energy of to tsunami has to get transvered to me. But thanks to resistance, the water that carrys that energy did never come to me. Its the water that kills, not the tsunami. ;)

@amirm to get serious, i absolutly understand what you like to tell. High current sources are not dangerous, keep away from high voltage sources. Whats in this context is absolutly right. But just two or three sentence more, and it would be completly right. High standarts i know, but its ASR. :)

Btw. thouching 200000V.

Dont do this on your powerline. ;)
 
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Endibol

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I am starting a new educational series on simple but essential engineering concepts/lingo we use in discussing audio products. This is the introductory video on voltage, current and power supplies:


Please give feedback as to whether you find this type of video useful and I will make more of them.

Thanks.
Hi Amir,
I think these video's could be a good idea indeed. It is quite challenging though, because too much simplification can cause confusion.

A few remarks:
- In Germany (and other countries) they use U as symbol for the physical quantity "Electrical Tension", V (Volts) is the unit used to express the magnitude of this quantity. For example: U = 12 V. They do this to distinguish the quantity from the unit. For current this is not necessary since they have different symbols. The "electrical current" I = 5 A (amps).
- To understand the difference between voltage, current and resistance I always like the analogy with a garden hose. The pressure the faucet exerts on the entrance of the hose can be compared to the voltage, the amount of gallons per second that it puts out at the end to current and the cross section and length of the hose to resistance. This intuitively gives more insight. If you have a thicker hose (or a shorter one) more water will be put out per second.
We also know from experience that there is an end to this, making a hose thicker and thicker will not increase the amount of water per second endlessly: the water supply is clearly no "voltage source". The pressure sags when the resistance is getting too low.
 
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Suppa92

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Watched the entire episode and loved it. waiting for the next lesson.
 

anchan

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I think Amir was trying to tailor the video to audio consumers, and in an effort to dumb it down, the way current and voltage are described is not 100% accurate. I used to design exhibits for science museums, and did quite a few solid state high voltage static electricity exhibits in the range of 5-200kV. We had to consult experts and submit research papers to the museums along with our exhibits.

Yes, as a layman explanation, voltage is the one to watch out for, since generally we don't know if it is current limited. And current is drawn as necessary, so high current capacity at low voltage is not something to worry about.

But the real answer is that V / R(system) + R(body) = I (through our body). Some nuance is needed to determine if we are talking about current through our heart across 2 arms, or between voltage source and earth. But generally take the voltage, divide by your body's resistance, and make sure it is not more than 2-30mA max. You can actually hold 2 probes of a multimeter to get a reasonable resistance measurement. Try holding the multimeter probe with your hands wet vs dry. People use 2000 Ohms as as nominal resistance in the body, but it can actually be 10 - 100X this depending on humidity and other factors, including how big or small you are, what you're wearing, etc. Take 48V and divide by 2000 ohms and you get 24mA. That's why 48V is kinda sorta still low enough voltage to not be life threatening, but you still gotta be careful. Also don't do any work with your car battery if you are standing in a pool of water.

Generally, a safe guideline is that for physical contact to an electrical source of 2 seconds or less 2mA - 30mA is safe regarded as safe. For more than 10 seconds, which is regarded as continuous, 20-30mA is regarded as safe, but not advisable. There is actually a bit of variation here in terms of what may or not kill or hurt someone. But 2-30mA is generally the range that is discussed.

As a starting point the International Electrotechnical Commission (IEC) standards for Domestic Electrical Appliances 60335 "Safety for Domestic Electrical and Similar Electrical Appliances Safety General Requirements." Using clause 8.1.4, defines safe discharge of electricity in 2 levels: 1) @voltages from 45V to 450V shocks should be limited to the energy stored in capacitance of 0.1uF into 2000Ohms 2) At voltages up to 15kV, the delivered charge should not exceed 45uC into 2000 ohms (nominal human impedance). Ref is from IEC60335-1:2002. In addition, this reference goes on to say that for DC currents, peak should not exceed 2mA. These limits are regarded as "Safe Limits," for inadvertent or accidental contact and not necessarily for deliberate or prolonged contact.

Other references:
See IEC 60335, IEC 60664. In particular, see IEC 60990 column 1999 "Methods of Measurement of Touch Current and Protective Conductor Current." This is a very good paper, and it discusses a human body model. While measuring current through the body, this model is very good because it takes into account how different frequencies affect the body. Also see IEC 60479-1, part 2 "Special Aspects Involving Human Beings."

Bottom line though, it is current is what kills, but it's a long explanation so we usually shorten it and say watch out for high voltage.

Lastly, I'd like to give an imperfect analogy. Imagine you want to throw a brick off a cliff. The height is the voltage, and the fluid in which it is dropped is the resistance. If you drop a brick off a cliff in the air then that brick is going to hurt and kill someone. Now imagine that instead of air, the cliff is underwater and water is the fluid. That brick would not hurt someone. That's because there was sufficient resistance in the system, which rendered the voltage harmless.
 
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Multicore

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I love that video! Brilliant presentation. But Mehdi's use of the word energy is metaphorical not scientific and not a ideal choice for a explanation of Ohm's Law when current times voltage equals the time derivative of energy. Words with useful metaphorical value for voltage include push, force (but take care), potential (if you have a bit more time, like a body of water behind a dam).
 

tomtoo

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I think Amir was trying to tailor the video to audio consumers, and in an effort to dumb it down, the way current and voltage are described is not 100% accurate. I used to design exhibits for science museums, and did quite a few solid state high voltage static electricity exhibits in the range of 5-200kV. We had to consult experts and submit research papers to the museums along with our exhibits.

Yes, as a layman explanation, voltage is the one to watch out for, since generally we don't know if it is current limited. And current is drawn as necessary, so high current capacity at low voltage is not something to worry about.

But the real answer is that V / R(system) + R(body) = I (through our body). Some nuance is needed to determine if we are talking about current through our heart across 2 arms, or between voltage source and earth. But generally take the voltage, divide by your body's resistance, and make sure it is not more than 2-30mA max. You can actually hold 2 probes of a multimeter to get a reasonable resistance measurement. Try holding the multimeter probe with your hands wet vs dry. People use 2000 Ohms as as nominal resistance in the body, but it can actually be 10 - 100X this depending on humidity and other factors, including how big or small you are, what you're wearing, etc. Take 48V and divide by 2000 ohms and you get 24mA. That's why 48V is kinda sorta still low enough voltage to not be life threatening, but you still gotta be careful. Also don't do any work with your car battery if you are standing in a pool of water.

Generally, a safe guideline is that for physical contact to an electrical source of 2 seconds or less 2mA - 30mA is safe regarded as safe. For more than 10 seconds, which is regarded as continuous, 20-30mA is regarded as safe, but not advisable. There is actually a bit of variation here in terms of what may or not kill or hurt someone. But 2-30mA is generally the range that is discussed.

As a starting point the International Electrotechnical Commission (IEC) standards for Domestic Electrical Appliances 60335 "Safety for Domestic Electrical and Similar Electrical Appliances Safety General Requirements." Using clause 8.1.4, defines safe discharge of electricity in 2 levels: 1) @voltages from 45V to 450V shocks should be limited to the energy stored in capacitance of 0.1uF into 2000Ohms 2) At voltages up to 15kV, the delivered charge should not exceed 45uC into 2000 ohms (nominal human impedance). Ref is from IEC60335-1:2002. In addition, this reference goes on to say that for DC currents, peak should not exceed 2mA. These limits are regarded as "Safe Limits," for inadvertent or accidental contact and not necessarily for deliberate or prolonged contact.

Other references:
See IEC 60335, IEC 60664. In particular, see IEC 60990 column 1999 "Methods of Measurement of Touch Current and Protective Conductor Current." This is a very good paper, and it discusses a human body model. While measuring current through the body, this model is very good because it takes into account how different frequencies affect the body. Also see IEC 60479-1, part 2 "Special Aspects Involving Human Beings."

Bottom line though, it is current is what kills, but it's a long explanation so we usually shorten it and say watch out for high voltage.

Lastly, I'd like to give an imperfect analogy. Imagine you want to throw a brick off a cliff. The height is the voltage, and the fluid in which it is dropped is the resistance. If you drop a brick off a cliff in the air then that brick is going to hurt and kill someone. Now imagine that instead of air, the cliff is underwater and water is the fluid. That brick would not hurt someone. That's because there was sufficient resistance in the system, which rendered the voltage harmless.

"..Bottom line though, it is current is what kills, but it's a long explanation so we usually shorten it and say watch out for high voltage..."


Exactly, but is it realy the right thing to do?? If two sentence more could get it right?
 

anchan

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"..Bottom line though, it is current is what kills, but it's a long explanation so we usually shorten it and say watch out for high voltage..."


Exactly, but is it realy the right thing to do?? If two sentence more could get it right?

I don’t think there are any magic two sentences. Rather I think a video for beginners about voltage and current that uses a lot of imperfect analogies would help people to understand the nature of electricity and its terms. And from there people can get a more intuitive understanding. A little bit like the brick dropped from a cliff analogy that I mentioned above. There are many others and some people respond to different ones. Usually people use pipes with water, although I don’t personally love those.

I think the video needs to framed a little differently. It’s really just a video to give people a rough idea of some electrical terms and approximately how they relate to equipment. It’s not a definitive video.
In contrast I think Amir’s other videos regarding distortion, noise, etc are more clarifying.
 

Here2Learn

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@amirm +1 on these. IDK know how far you want to go, but it might be good to get to the point of going over Veritasium's YT video:


FWIW, Veritasium's video still feels highly counter-intuitive as one of the people in the video mention. Viewing the way electrical energy flows to a load outside the conductors seems like magic. When we look at circuits with the lumped element model, we don't view things this way. It would be interesting to look at various devices and to do just that, although illustrating it would be very tricky.

As we're interested in audio, maybe we can swap Veritasium's battery source for an amp, and his load for a loudspeaker and use speaker cables to complete the circuit - the same rules are going to apply.
 

AdamG

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Excellent Professor @amirm .edu Stuff! Well done Sir. Just missing a white lab coat with pocket protector/slide rule. :D

Hell Yes! Want MORE…………..And your Presentation is perfectly titled.
 
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lc6

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No, it is right for this type of video and context. Touch a high voltage source and you risk electrocution. Touch a low voltage source and you are fine. Touch a high current/low voltage source, and again, you are fine. Anyway this is a side comment so not sure how it became the core of your criticism.

Sure, but...

tomtoo said:
Its not right that the voltage kills you, its the current through you body that kills you.

electrical shock
"The effects of electric shock on the human body depend on the current that flows—the amperage—rather than on the force of the current, or voltage. The electrical resistance of the human body is variable and may in fact alter considerably during the passage of an electric shock. Therefore, except in broad terms, applied voltage is not a consideration. This leads to difficulties in the investigation of accidents, for the electrical engineer is often able to state only the voltage applied, but the physician thinks in terms of the current that flowed."
 
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amirm

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Its the basics that your internal resistance determines the current if not the resistance of the voltage source determinse it.
That is the wrong way to look at it as I explained. For any fixed body resistance, it is the voltage that determines current flow: I = V/R. Keep R constant and the current becomes directly proportional to voltage. Your body's resistance stays constant whether you touch high voltage mains or a battery. It is therefore the voltage that determines how lethal that experiment is.
 
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amirm

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I believe in little knowledge is a dangerous thing. I think such over simplification of EE principals will confuse people more than educate them. You will have ad infinitum of arguments on trivial things while they are completely missing the general principals.
Sorry no. There are infinite number of youtube videos about every aspect of voltage and current. No need for me to duplicate any of them.

An audiophile would have no interest in watching those videos as they don't care about the fundamentals but what it means to them. That is the purpose of these videos. You can talk about electron flow, EM fields, Maxwell equations all you want but they were will be of zero value to audiophiles. This is why every other week I get a question about whether it is OK to use a higher current power supply or not.

There is a practical aspect of electronical engineering which I use everyday. That is what I am trying to convey to people. If they want to learn more, they can seek out other information sources.

And nothing was dangerous here. Nothing was oversimplified to that level. The reverse was true actually as someone can watch those elementary videos on voltage and current and still not know if they can swap one power supply for another.
 
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amirm

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We also know from experience that there is an end to this, making a hose thicker and thicker will not increase the amount of water per second endlessly: the water supply is clearly no "voltage source".
Nothing generates more grief in these videos than talking about water analogy! Next thing you know people will argue about true electron flow as opposed to how engineers look at it, etc. Just check out the comments in videos produced with this analogy.
 

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