Psu Leaks Little Bit Of Ac To Gnd Pin, Normal?


urjaman

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Okay, this is my Pandora PSU (that IIRC craigix said is a good PSU), flypower PS12K0502000E5.

Relative to ground, my multimeter senses ~86VAC on the output GND pin (with the multimeters GND on the grounded socket's ground pin).
Of course this is very small current signal, nearly any at all route to gnd will zero it out, but still, it will flow into the pandora's GND net, and eventually to the gnd ring on the microphone socket, which has a bit of metal that your skin can contact when you hold your pandora up against bare skin. So, I get (very slightly, but feels a bit stingy) zapped by my pandora when I use it while its charging (and I'm shirtlessly at bed). Just asking if it's normal of this PSU type (I know some computer PSUs do this too, still they shouldnt), or if there's something weird going on?
 

mali

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That's not nice :( Does it do the same when you turn the plug 180 degrees in the wall socket?
 

urjaman

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mali said:
That's not nice :( Does it do the same when you turn the plug 180 degrees in the wall socket?
Tested that, same results.
 
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mali

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A few years ago I had a defective wall socket where the earth wire was broken, which was unfortunately the socket for my PC. Two mainboards were killed after a few months of use before I found the problem. IIRC, the headphone ground is somewhat isolated from the main ground, so this behaviour is very alarming.
I hope this doesn't affect all PSUs. It's not acceptable if it does.

edit:
MWeston said:
SirisC said:
Would it cause problems if I wired the L2 and R2 buttons to a stereo jack with their negatives/grounds going over the same wire? (Is there even enough room to fit an extra stereo jack in the case?)
No problem doing three wires for the spare shoulder buttons by taking just one ground from the spare pads. I know you aren't suggesting using the already present stereo jack as some people are mentioning here, but I will say that the ground on the headphone connector should not be used for a ground on digital signals such as these spare shoulders as it is an isolated ground around the audio circuitry before joining the main ground.

I'm not sure about finding room for a new jack but maybe you could creatively squeeze in a small 2.5mm jack somewhere. The smaller the better.
 
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urjaman

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mali said:
A few years ago I had a defective wall socket where the earth wire was broken, which was unfortunately the socket for my PC. Two mainboards were killed after a few months of use before I found the problem. IIRC, the headphone ground is somewhat isolated from the main ground, so this behaviour is very alarming.
I hope this doesn't affect all PSUs. It's not acceptable if it does.
It happens (i can feel it), on two sockets in totally different sides of the house (that was built/ready for moving in 01/2010). And to make it clear, I measured against the earth line (third, safety earth) on what you (talking to you germans atleast :p) would call a schuko socket, while the adapter is two-pronged (double-insulated), and doesnt actually use the third pin. The measurement gnd was just to get a stable reference point for the multimeter. It measured about 70VAC with ground in my finger (means that I'm not that stable, and will change charge level a little bit from the current flowing through the multimeter), so I think that the safety earth was the best available stable reference. And about the earthphone ground, it feels much less in there than at the tip of the charger head, but still I think the filtering is of the low-pass type (and the wall AC is 50Hz here), so it seems that atleast some will pass.
 
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tsh

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See Enclosure leakage current or touch current
http://www.ebme.co.uk/arts/safety/part6.htm (which is talking about medical devices, but I think this is for standard class II electronics.
Measuring the voltage with a Hi-Z DMM is meaningless - you may achieve the same result by placing one lead mid-way between live and neutral conductors!
The current from any exposed part of the PSU to protective earth must be less than 0.1mA, 0.5mA is permissible under a single component fault condition (for design approval). Keep a 100k power resistor in-circuit if you want to be safe of not blowing up your DMM!
 

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Well... you have HOT, NEUTRAL, and EARTH GROUND in a standard 3-prong AC socket. Earth Ground is NEVER used to measure potential difference (aka EMF aka "voltage") in a DC circuit and Neutral is no good either since this is AC and not DC so neither the Hot nor the Neutral is truly common or "ground" due to the very nature of AC.

Earth Ground is there for safety, and in a device with a metal chassis only the chassis would be at earth ground potential. And, as you know, the power supply for the Pandora DOESN'T use the Earth Ground nor does it have a metal chassis... so you're trying to measure a value in the circuit using a reference that ISN'T part of the circuit.

Try using the DC Common (aka "ground") off the end of the charger plug that goes into the Pandora and measure the potential difference between that and the part of the headphone jack you are getting shocked by.

I'm not saying that I don't believe you, I'm sure if you're feeling electricity then you probably are... but using Earth Ground as a reference potential is just junk science.

This is why I hate the term "ground" being used in place of the proper term, Common, for DC voltages... too many people don't understand the difference between "ground potential" and "common potential."

...you've gotta keep in mind that so called "voltage" is just a relative thing. Voltage is the measurement of potential difference in the EMF (Electro-Motive Force) relative to a common level. So when you say "9 volts" that means nothing... "9 volts" relative to what? is what immediately pops into my mind. 'Cause really, if we were able to somehow find a "universal common potential reference" we'd all probably be a hundred or so volts off from it.
 

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tsh said:
Keep a 100k power resistor in-circuit if you want to be safe of not blowing up your DMM!
Hmm, how high would the current need to be to blow my DMM? (I'm just thinking that if the current were over 10mA (which i think shouldnt cause a problem) then I should be having serious issues touching it, not a tiny zap...) Well I'll measure later today (and find some 100k resistor, I think i prolly dont have a 100k power resistor but what the heck, the resistor will act as a fuse in case stuff fail)
 
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mali

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A current that is able to cause a zap is too much anyway. Try a "Phasenprüfer"(those little screwdrivers with integrated lamp to test wall sockets). On the tip the DC plug from the PSU and on the other side your finger. It shouldn't light up.

Fun note: I licked several two prong PSUs I had lying around, my tongue is still ok, no zapping at all :p
 

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^ Fearless electrician :p Forgot your Duspol and too lazy to climb down the ladder? A wet finger is the poor man's Duspol ;) Btw, a resistor "in line" wouldn't help anyway, you'd need a weird looking shunt construction :D
 

urjaman

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Now it has been experimentally proven that I can feel 0.05mA (note: atleast with my nipple *ouch* (dunno, I had to test...) )... duh. (So yeah it is within specifications, but ...)
 

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I don't know a whole lot, but mitosis is on to something about earth ground not being a proper reference. The reference should be the body that is getting shocked, since it's based on the potential difference between you and the pandora. I don't think the DC common "ground" would be too reliable here, since he could be getting shocked due to a voltage between the common and his body, or something. Just seems to make sense based on the small bit I know and whatever's going on in my head.
 

urjaman

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paulguy said:
I don't know a whole lot, but mitosis is on to something about earth ground not being a proper reference. The reference should be the body that is getting shocked, since it's based on the potential difference between you and the pandora. I don't think the DC common "ground" would be too reliable here, since he could be getting shocked due to a voltage between the common and his body, or something. Just seems to make sense based on the small bit I know and whatever's going on in my head.
Hmm, it's the common pin that's shocking me you know (I was alarmed to this by the headphone jack, but I could (atleast at one point of time) just touch the common (outside of the DC jack) with my finger and feel it). I'm mostly thinking that the current that exists when I get zapped is the 1. common pin changing my potential (against some very very small capacitance that i must have, thus current between pin and me) plus any current that flows from from the common pin to me and then to earth (via some very resistive route, I was not touching earth ground directly at any point). So that's why my first action was to take the Hi-Z DMM in AC mode with some stable reference point (=earth) against the common pin to see if there is any activity (and it measures a voltage that I think can zap, so...). It can be that this signal has no real reference point to begin with, eg.(in a theoretical sense) some charge is being added to and removed from the common pin (and propably the +5V pin dances in the same way, just stably 5V above the common) at propably the line frequency (only time base I know the adapter should have, and that is AC), so introducing a stable resistance to any reference point (even the very high Z that the DMM has does this, because it must draw _some_ current to make the measurement) makes the signal swing around that reference point... Anyways this is just my fuzzy ideas about this and I'm not that educated in matters of AC.
 
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WizardStan

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Are you sure it's the Pandora that's shocking you and not you shocking the Pandora? Perhaps you've got a natural propensity for static electricity.
 

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WizardStan said:
Are you sure it's the Pandora that's shocking you and not you shocking the Pandora? Perhaps you've got a natural propensity for static electricity.
Perhaps his bed is made of nylon and cats.
 
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tsh

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urjaman said:
tsh said:
Keep a 100k power resistor in-circuit if you want to be safe of not blowing up your DMM!
Hmm, how high would the current need to be to blow my DMM? (I'm just thinking that if the current were over 10mA (which i think shouldnt cause a problem) then I should be having serious issues touching it, not a tiny zap...) Well I'll measure later today (and find some 100k resistor, I think i prolly dont have a 100k power resistor but what the heck, the resistor will act as a fuse in case stuff fail)
I was being cautious just in case someone takes this thread out of context. My 100k value was assuming the fault condition of a direct short to live (which is 110/240V AC above the rock we're standing on at the transformer, with an impedance of a few ohms) so limiting the current to a couple of mA. The issue would be the heat dissipation in that resistor (which would then catch fire, and possibly scar your Pandora)
 
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urjaman said:
Now it has been experimentally proven that I can feel 0.05mA (note: atleast with my nipple *ouch* (dunno, I had to test...) )... duh. (So yeah it is within specifications, but ...)
you kinky bastard... hahahaha
 
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