Getting zapped off 2.1 speakers and sub

[eeviking]

If the equipment (smps) have Y caps they should be connected to earth ground.
If you get a zap and can measure high voltage they are not!

There are only two possible faults:
1. The equipment have a broken or not connected ground wire from the mains plug to chassis/psu. (return or fix the equipment)
2. Your mains power outlet / extension cord have a broken or not connected earth ground wire. (fix your mains installation)

We see this a lot in EU when people connect 3 pin equipment to 2 pin extension cords without earth.

[tooki]

Like it or not, it is common and is normal.

If I bought a metal cased device that didn't have an Earth I would point it out to trading standards.  As I understand it, it would not pass British safety standards for mains operated equipment.

Every MacBook made for years now is metal-cased, and when using the charger with the 2-prong plug, it's ungrounded, and sometimes can tingle. Do you seriously believe that Apple could get away with selling millions of units of product that violate the rules? And that Apple wouldn't have had it certified?

Or is it perhaps more likely that your understanding of the rules is incomplete?

[Shock]

Paul, double insulated devices often have no mains earth/ground wire attached but still can use a metal chassis. Again standards are country specific, look up your local standards.

Armadillo, you can be electrocuted by smartphones, the battery has little to do with it. Metal chassis pose an additional risk should things go bad.

Noone is saying that the device posted is necessarily safe, this is what investigation and testing is for (should you be skilled enough not to put yourself at additional risk during the process).

This post by Peter Green on stack exchange basically sums up what I'm talking about:

Switched mode power supplies use what is known as a "flyback converter" to provide voltage conversion and galvanic isolation. A core component of this converter is a high frequency transformer.

Practical transformers have some stray capacitance between primary and secondary windings. This capacitance interacts with the switching operation of the converter. If there is no other connection between input and output this will result in a high frequency voltage between the output and input.

This is really bad from an EMC perspective. The cables from the power brick are now essentially acting as an antenna transmitting the high frequency generated by the switching process.

To suppress the high frequency common mode is is necessary to put capacitors between the input and output side of the power supply with a capacitance substantially higher than the capacitance in the flyback transformer. This effectively shorts out the high frequency and prevents it escaping from the device.

When desinging a class 2 (unearthed) PSU we have no choice but to connect these capacitors to the input "live" and/or "neutral". Since most of the world doesn't enforce polarity on unearthed sockets we have to assume that either or both of the "live" and "neutral" terminals may be at a sinificant voltage relative to earth and we usually end up with a symmetrical design as a "least bad option". That is why if you measure the output of a class 2 PSU relative to mains earth with a high impedance meter you will usually see around half the mains voltage.

That means on a class 2 PSU we have a difficult tradeoff between safety and EMC. Making the capacitors bigger improves EMC but also results in higher "touch current" (the current that will flow through someone or something who touches the output of the PSU and mains earth). This tradeoff becomes more problematic as the PSU gets bigger (and hence the stray capacitance in the transformer gets bigger).

On a class 1 (earthed) PSU we can use the mains earth as a barrier between input and output either by connecting the output to mains earth (as is common in desktop PC PSUs) or by using two capacitors, one from the output to mains earth and one from mains earth to the input (this is what most laptop power bricks do). This avoids the touch current problem while still providing a high frequency path to control EMC.

Short circuit failure of these capacitors would be very bad. In a class 1 PSU failure of the capacitor between the mains supply and mains earth would mean a short to earth, (equivalent to a failure of "basic" insulation). This is bad but if the earthing system is functional it shouldn't be a major direct hazard to users. In a class 2 PSU a failure of the capacitor is much worse, it would mean a direct and serious safety hazard to the user (equivilent to a failure or "double" or "reinforced" insulation). To prevent hazards to the user the capacitors must be designed so that short circuit failure is very unlikely.

So special capacitors are used for this purpose. These capacitors are known as "Y capacitors" (X capacitors on the other hand are used between mains live and mains neutral). There are two main subtypes of "Y capacitor", "Y1" and "Y2" (with Y1 being the higher rated type). In general Y1 capacitors are used in class 2 equipment while Y2 capacitors are used in class 1 equipment.

So does that capacitor between the primary and secondary sides of the SMPS mean that the output is not isolated? I've seen lab supplies that can be connected in series to make double the voltage. How do they do that if it isn't isolated?

Some power supplies have their outputs hard-connected to earth. Obviously you can't take a pair of power supplies that have the same output terminal hard-connected to earth and put them in series.

Other power supplies only have capactive coupling from the output to either the input or to mains earth. These can be connected in series since capacitors block DC.

Here is a double insulated device:

[Armadillo]

Paul, double insulated devices often have no mains earth/ground wire attached but still can use a metal chassis. Again standards are country specific, look up your local standards.

Armadillo, you can be electrocuted by smartphones, the battery has little to do with it. Metal chassis pose an additional risk should things go bad.

Noone is saying that the device posted is necessarily safe, this is what investigation and testing is for (should you be skilled enough not to put yourself at additional risk during the process).

Except PELV circuit which is also double insulated with earth/ground wire.
The codes regarding the SELV/PELV are similar in all parts of the world.
The exposed metal parts cannot exceed the SELV voltage and it may also be considered as "LIVE" if the charge exceed the value defined in the "Mandatory" codes of compliance

The focus must be on OP safety as he described as "Painful Shock" and not on anyone glory of knowledge. [that will includes myself].
May we channel our energy on that. 

[Armadillo]

Fluke call it stray ghost voltage;

http://en-us.fluke.com/community/fluke-news-plus/digital-multimeters/stray-ghost-voltages.html

So, I would advise OP to measure with analogue voltmeter having a impedance of about 20Kohm [though fluke uses 3Kohm] or wire a 3kohm resistor in parallel.

But since OP encounter painful shocks, this is not normal and not acceptable. I have not a single smps that exhibits such kind of a problem, no feeling whatsoever.

[amyk]

All this pseudo lawyering amongst almost no suggestions to measure how much current can be drawn...

People have differing levels of sensitivity to current. What may be imperceptible to some could be painful to others. But IIRC up to 300uA may be allowed by the standard.

Search this forum and the Internet for "touch current" for more information.

[Armadillo]

Firstly you determine whether it is "LIVE" or "Ghost" voltage as per fluke document above.

If it is LIVE, don't do any current draw, kind of silly and will damage your meter.

If it is Ghost, the voltage will drop to almost Zero volts, then you can safely proceed to do current draw if your want. It should range from about 90uA to 150uA region.

Can the Y cap be shorted? I don't know. But it's better to be safe.

[mikerj]

You should focus on the subject and context than finding skeletons to reply.

Smartphones are battery operated and even when it is connected to the charger, we don't get a electric shocks [metal case], so your story on the Y-cap cannot be substantiated.

100% incorrect.  Many smart phones will have ~100v AC on the metal case when charging.  The impedance is (or should be) very high, so touching it will cause the voltage to decrease significantly, though some people will be able to feel it (I can).  I thought my original genuine Apple iPhone and iPod chargers were faulty because I could measure similar voltage on the cases and it was unpleasant to touch (not a shock as such, but it felt like the surface was vibrating) but they were all like this.

[Neganur]

Charging an iPhone & listening to music via wired in-ear headphones at the same time can actually hurt quite a bit.

[Armadillo]

You should focus on the subject and context than finding skeletons to reply.

Smartphones are battery operated and even when it is connected to the charger, we don't get a electric shocks [metal case], so your story on the Y-cap cannot be substantiated.

100% incorrect.  Many smart phones will have ~100v AC on the metal case when charging.  The impedance is (or should be) very high, so touching it will cause the voltage to decrease significantly, though some people will be able to feel it (I can).  I thought my original genuine Apple iPhone and iPod chargers were faulty because I could measure similar voltage on the cases and it was unpleasant to touch (not a shock as such, but it felt like the surface was vibrating) but they were all like this.

Make it 110%..... hahahhahahahah 
Bin the phone, might be from china imitation rejects.   

...................... few phone chargers they may be SMPS.  If one of them gave me a shock or even a buzz I would bin it. 

[Armadillo]

Charging an iPhone & listening to music via wired in-ear headphones at the same time can actually hurt quite a bit.

Poor Child. Nowadays you got so many kinds of wield problems, you know, hurt everywhere... and in-ear headphones become conductive due to Y capacitor problems etc..   

[Neganur]

Charging an iPhone & listening to music via wired in-ear headphones at the same time can actually hurt quite a bit.

Poor Child. Nowadays you got so many kinds of wield problems, you know, hurt everywhere... and in-ear headphones become conductive due to Y capacitor problems etc..   

Excuse me, did you run into the door in the morning or something?

[Armadillo]

Thesis KNNB, Anywhere in your reference did it denies the existence of the leakage current.? I would bin the thesis if it would portray such low level of perception ability.

The purpose of the Y cap is to act as a return path to the EMI current caused by poor manufactured uncoupled inductance of the transformer. It suppose to be doing its job especially when loaded. Current flow, voltage drop.
A single value cap selection cannot be expected to meet all tolerances of manufactured transformer.
I am not interested to debate the human perceptible level of leakage current, neither.

If you can feel the bite, bin the product.

It should range from about 90uA to 150uA region.

[Armadillo]

I have NEVER received a shock or even a buzz ...............

[Armadillo]

Devoid yourself from technicality for a moment and revert back to common sense.

You pay not to get bitten, not even a tiny bit.
With that, you set a higher standard for the manufacturers and help improve the level of safety and comfort for the human mankind.
Your level of education is supposed to be different, in the proper direction.

Many don't even feel a buzz. Work on it.

[Armadillo]

I think this is the part you missed.;
the "mandatory" requirement for less than 0.1uF circuit capacitance limit on protective impedance circuit.

And are you against the codes "carefully" researched and written by those professional members of the board? Think about it...."carefully".

BTW, I am interested to know how the headphones become conductive? Are there any conductive parts? I am not a headphones user.

[Armadillo]

Read it, understand it, and if you are not satisfied, you can write to the board to query their intents.

I consider the vibrating sensation normal as it happens at as low as a few tens of uA, and I'm totally fine with it.

You may have the rare anxiety disorder or maybe rare sensitivity ability?, but do check your doc. 

[paulca]

Given the graph presented, which is available from other sources which suggest that pretty low figures can cause muscle contraction, defibrillation and death.

Then given that some standards are allowing leakage current that can be higher than those figures and could potentially in a weaker person, a person with a heart condition or a pace maker cause heart failure one might be scared.

However are we all not forgetting the resistance of the skin is usually measured in mega ohms?  Dry skin circa 100M, wet/broken skin 1M.  If you get shocked by high voltage arc'ing burnt skin becomes much lower resistance down to 500Ohms. 

https://en.wikipedia.org/wiki/Electrical_injury

So while 600mA can kill you, it requires you experience a shock where 600mA actually flows through your body, including the skin resistance and the full resistance through your body to the current exit point.  Then it becomes a matter of ohms law.  It's difficult to get even ball park figures for a complete shock path.  I have seen internal resistance of 600-1000Ohms, but the initial resistance of the skin can be 100 times that.

So worse case of only 600Ohms, you would need V=IR ... V=0.6A * 600Ohm  ... V=360V

That is awfully close to mains voltage.

[amyk]

I am not interested to debate the human perceptible level of leakage current, neither.

Someone who deliberately ignores the facts is not worth arguing with.

Now would the OP please measure the leakage current and tell us...?

[shakalnokturn]

OP has unsubscribed by now, scared of chaos caused by such an innocent question...
He's decided it was less painful getting zapped than trying to follow the answers to his post.

[zetsubou]

OP has unsubscribed by now, scared of chaos caused by such an innocent question...
He's decided it was less painful getting zapped than trying to follow the answers to his post.

  Sorry everyone, I worked 33 hours in the past 2 days and haven't had time to check in.. Looks like I sparked some interest with this post! I appreciate the replies and will get back soon with my results. Happy to open things up if anyone would like a better look. Cheers!

[Armadillo]

Here we see the Armadillo c............

@Shock; That is the worse shameless rubbish I have seen to date, wrecking OP Posting with irrelevances.
I think you must be furious of being deprived the opportunity to self glorifies yourself with someone elses posting, yeah!.
if someone will to graffiti the silly picture with 2 soldering irons in the nose, you know that's an idiot rude lowdown!.. hahahahahaha LOL
I will take you on technically anytime..... other than that I won't be wasting anymore times on rubbish.

[zetsubou]

Some results..









I think it's safe to say this isn't *dangerous* but does it indicate a fault that would cause the sub to produce nearly no sound when turned all the way up?

[Armadillo]

That is definitely a dangerous faulty equipment @180mA leakage current. Not only painful shock, it could have been fatal if the shock persisted for over 1 sec.
You should send it back and demand for compensation on loss and expenses. But how do you exactly go about it, better seek some others views.

[zetsubou]

Can you please confirm if I have my test equipment set properly? Supply to the device is DC, through a transformer. My results AC reading and testing to earth.