Weird shock feeling

[_FatMann_]

So I recently bought this PSU from Msi it's the A550BN 80+bronze unit., it seemed promising from what I've read, not that I'm really good at understanding electric stuff, but mostly because I know dc to dc psu's are good and it being from msi and it having a 10 year warranty seemed great. So I replaced my old PSU which is not 80 plus certified and pretty sketchy in general, When I plugged in the pc, I Felt a tingle when touching the metal screw's when the psu is turned of and plugged in, and once the PSU is switch is set to ON, it seems to disappear, is this type of behavior normal?

and does plugging in the computer to an outlet extension not ground the PSU properly?, I noticed that it still gave me a slight tingle even when the PSU switch is turned on when plugged in to the extension, (note: it goes away when the specific plug is switched on, but when it's turned off, it show's these symptom's, my best guess is that when turning off the outlet of my extension it cut's off the ground. So is this type of behavior normal for a psu?

 

 

[mariushm]

The computer must be grounded - every component between the computer and the AC outlet in your wall must have grounding, that 3rd contact in the socket. So your extension cord should have the earthing pin and contacts on each socket, the cable between the power supply and the extension should have one and so on ...

 

A small tingle is possible and acceptable but it shouldn't feel like you're getting zapped every time you touch exposed metal bits of your case. 

Power supplies are designed to "leak" a bit of energy through the earthing pin of the AC socket , which also happens to be connected to the case of the power supply and in turn to the computer case. If you have good earthing/grounding, that energy leak discharges through the wire instead of through your body (which is what happens when you feel that tingle in your fingers, the electricity finds another path through your skin and your body down to ground)

[191x7]

Check if you have grounding on the socket (wall, power socket) and the extension cord.

[_FatMann_]

I just found out what a cheater's plug is.

I'm using it to connect to my 2 prong outlet, so my outlet's don't have ground.

 

[_FatMann_]

So Im basically attaching my extension cord with 3 pin's on to a 2 pin outlet.

Is that the problem, I also wanted to know if I should just use my old PSU power cord (it's a 2 prong connector) to my new PSU, and maybe that'll solve the problem?

 

 

[mariushm]

You need THREE  , the third is the grounding ... live, neutral (return) , ground/earthing ... find an AC socket in your house that has that earthing pin (and make sure it's functional)

If there's one cable or one plug/socket that doesn't have the third contact/prong/pin , the circuit is interrupted and doesn't work so it doesn't offer you protection.

[_FatMann_]

14 minutes ago, mariushm said:

You need THREE  , the third is the grounding ... live, neutral (return) , ground/earthing ... find an AC socket in your house that has that earthing pin (and make sure it's functional)

If there's one cable or one plug/socket that doesn't have the third contact/prong/pin , the circuit is interrupted and doesn't work so it doesn't offer you protection.

Is it safe if I just used a cheater's plug? Because the nearest one is like across my room.

[_FatMann_]

Im quite impressed by the fact on how fast the response's are here at ltt.

[mariushm]

Are you thick ... you need that third wire to carry the extra energy and dump it into the ground. A cheater plug as you describe it just makes it possible to power something from a 2 prong outlet , ignoring that extra protection and safety of the earthing prong ... so naturally the grounding/earthing is interrupted.

 

Is it safe ... it's recommended to have grounding/earthing on your computer all the time. No earthing and you can have erratic behavior like random resets, you can get zapped if you touch exposed metal parts. It's not good. 

 

Get a fucking long extension cord, 5-10 meters of cable, doesn't matter, put the cable along the walls and bring the extension cord to the back of your computer desk

.

[_FatMann_]

Ok got it. I'll do that as a temporary fix, and as soon as possible, ill try to get one installed. thank's for the help.

[mariushm]

Class Y capacitors are used in the EMC filter (input filtering) and those are between live and earth and neutral and earth. Due to this filtering, some current can "leak" to earth and if you measure with a multimeter you'd see AC voltage on the earth pin of the power supply...

See https://www.meanwelldirect.co.uk/glossary/what-is-leakage-current/

 

There's also stray capacitance between the windings of the transformer, due to high switching frequency that happens in switching power supplies (typically 60kHz and higher). To minimize emi, noise etc there's usually a Y class capacitor between the two windings.

 

Quoting from stackexchange explanation because can't be bothered to word it myself : ( stack link )

 

Quote

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 designing 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 significant 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.

 

Computer power supplies are allowed to leak up to 3.5mA of current, according to IEC-60950-1  ... but majority of power supplies are much lower, usually under 2mA.  For example, Techpowerup measures this current in their reviews, picked a random review see and you can scroll down to the bottom and see the Corsair HXi 1500w's leakage current at 1.77mA : https://www.techpowerup.com/review/corsair-hxi-series-1500-w/9.html

 

 

typos in the quote above belong to the original poster.