Author Topic: Getting zapped off 2.1 speakers and sub  (Read 9981 times)

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Offline zetsubouTopic starter

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Getting zapped off 2.1 speakers and sub
« on: January 22, 2018, 02:40:51 am »
Hi everyone, I'm trying to figure out where to begin troubleshooting this issue.
My speaker setup has under performed from day 1, confirmed by the retailer, but they wanted me to pay the $70 return shipping fee and I decided to just deal with it.

I realised today that I get painful shocks from touching the metal parts on both the sub and speakers. They're powered independently by transformers.
Speakers -   18VDC 3.3A
Sub -   +-30VDC 2A
The sharp tingling occurs regardless of ON/OFF switch position on both the sub and speakers.

Am I onto something here or do I just not know how to use a multimeter? |O



« Last Edit: January 22, 2018, 02:43:01 am by zetsubou »
 

Offline Bushougoma

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Re: Getting zapped off 2.1 speakers and sub
« Reply #1 on: January 22, 2018, 03:01:36 am »
Any change when taking that measurement in LoZ mode?
« Last Edit: January 22, 2018, 03:18:54 am by Bushougoma »
 

Offline iampoor

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Re: Getting zapped off 2.1 speakers and sub
« Reply #2 on: January 22, 2018, 04:59:06 am »
Is your outlet wired the right way??
 
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Offline Armadillo

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Re: Getting zapped off 2.1 speakers and sub
« Reply #3 on: January 22, 2018, 05:38:27 am »
2 Situations; Identify the faulty one.

1) 18VDC faulty - unplug it and test metal surface with test pen
2) +/-30VDC faulty - unplug it and test metal surface with test pen

The ground fault interrupter should trip if the leakage current has exceeded trip threshold [e.g. direct shorts].
 
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Offline shakalnokturn

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Re: Getting zapped off 2.1 speakers and sub
« Reply #4 on: January 22, 2018, 09:52:10 am »
This is a common problem due to the way SMPS are built, they always have some leakage current from primary to secondary and when all equipment is unearthed you can feel it tickle you, it is usually not dangerous though (measure AC amps from ground to earth) it is quite annoying.

The answer is to earth at least one point of the common ground, but then earthing one piece of equipment only can run you into other problems when disconnecting cables between them: The typical example is having one piece of equipment un-earthed and one earthed, when connecting an RCA jack the center pin will touch before the shield (ground) sending the floating 100V or so you're measuring to the ground through an IC's input, that is sometimes enough to destroy the IC.
« Last Edit: January 22, 2018, 09:55:09 am by shakalnokturn »
 
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Offline paulca

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Re: Getting zapped off 2.1 speakers and sub
« Reply #5 on: January 22, 2018, 11:35:31 am »
Would this not just pop an RCD trip instantly?
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Offline mikerj

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Re: Getting zapped off 2.1 speakers and sub
« Reply #6 on: January 22, 2018, 12:33:58 pm »
Would this not just pop an RCD trip instantly?

No, you need quite a bit of earth leakage current to trigger an RCD, at least 5mA and maybe as much as 30mA for the type used in homes.  The leakage you get from the interference suppression Y capacitors on SMPS should be less than 0.5mA.
 
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Offline Armadillo

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Re: Getting zapped off 2.1 speakers and sub
« Reply #7 on: January 22, 2018, 12:38:59 pm »
The measurement is in AC mode. Not normal.
 

Offline madires

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Re: Getting zapped off 2.1 speakers and sub
« Reply #8 on: January 22, 2018, 02:25:59 pm »
Yay! You just found the EMI suppression cap of the SMPSU ;)
 
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Offline Armadillo

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Re: Getting zapped off 2.1 speakers and sub
« Reply #9 on: January 22, 2018, 03:02:59 pm »
Yah, that's a normal misconception.
The nominal Y cap is at least 1.2Mohms hence you should not be able to measure that magnitude of AC voltage at the output. No way. It's a fault.
 

Offline Bashstreet

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Re: Getting zapped off 2.1 speakers and sub
« Reply #10 on: January 22, 2018, 04:36:31 pm »
100+ AC through SMPSU is not normal it is faulty i would not use it nor poke around.
Get new one not much point try repairing it unless you know what you doing  :-\
 

Offline shakalnokturn

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Re: Getting zapped off 2.1 speakers and sub
« Reply #11 on: January 23, 2018, 01:51:57 am »
Just for comparison I made the measurement on an unearthed, unloaded Toshiba PA2444U laptop PSU.
I'm in a 230V country. Secondary ground to earth voltage is 96V (distorted half sine AC of course) into a 10Mohm meter, leakage current available is 80µA.
Don't believe what you're told however, look a SMPS schematic and think for yourself.

You can either:

-Live with getting zapped.
-Earth the equipment.
-Substitute the SMPS for something equivalent with an iron core transformer.
 
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Offline tooki

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Re: Getting zapped off 2.1 speakers and sub
« Reply #12 on: January 23, 2018, 02:40:48 am »
100+ AC through SMPSU is not normal it is faulty i would not use it nor poke around.
Get new one not much point try repairing it unless you know what you doing  :-\
Yes it is! 100V is on the high side, but not at all unusual. (I could swear Bigclive did a comparison of a bunch of USB chargers, measuring this, but for the life of me I can't find it.)

https://www.eevblog.com/forum/beginners/phone-charger-gives-electric-shocks-how-to-measure-voltage/25/
https://www.eevblog.com/forum/beginners/y-capacitor-current-leakage-electromagnetic-interference-(emi)-problem/

Use a multimeter to measure the current of the leakage. It should be under 85uA, according to one source I read.
 

Offline Shock

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Re: Getting zapped off 2.1 speakers and sub
« Reply #13 on: January 23, 2018, 05:27:23 am »
According to the AS/NZS 3760:2010
Class II
Measure the current flowing between accessible unearthed metal and earth
Maximum leakage should be no greater than 1mA
Soldering/Rework: Pace ADS200, Pace MBT350
Multimeters: Fluke 189, 87V, 117, 112   >>> WANTED STUFF <<<
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Offline Armadillo

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Re: Getting zapped off 2.1 speakers and sub
« Reply #14 on: January 23, 2018, 06:03:08 am »
 

Offline Armadillo

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Re: Getting zapped off 2.1 speakers and sub
« Reply #15 on: January 23, 2018, 08:03:35 am »
Layman view or standards?
https://en.wikipedia.org/wiki/Extra-low_voltage

Wikipedia is not a reliable source for standards, also standards can be country specific.
The one I refereed to AS/NZS 3760:2010 is specific to Australia/New Zealand.

I was not replying to your message. Your view was sound.
Regarding reliability, refer to the actual standards referred therein.
 

Offline Armadillo

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Re: Getting zapped off 2.1 speakers and sub
« Reply #16 on: January 23, 2018, 09:05:49 am »
care-less laymen speech may cause life.
if you want to err, always err on the safer side.
Look at the way it was hooked up to the equipment and the way it was measured [Not open, not unloaded].
Cheers;


 

Offline shakalnokturn

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Re: Getting zapped off 2.1 speakers and sub
« Reply #17 on: January 23, 2018, 11:24:21 am »
The standards define a maximum voltage that should be safe to touch.  They also specify safe leakage current limits. (Having a 10kV source with an internal resistance of 1Gohm is not dangerous to touch although 10kV sounds scary.)

Then on top of the standards there are RCD/GFCI devices for further protection, I'm not saying getting zapped by your subwoofer is not a concern and that it should be overlooked, failing to understand the problem is IMHO at least as dangerous as overlooking a possible fault.
 

Offline madires

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Re: Getting zapped off 2.1 speakers and sub
« Reply #18 on: January 23, 2018, 11:52:12 am »
Yah, that's a normal misconception.
The nominal Y cap is at least 1.2Mohms hence you should not be able to measure that magnitude of AC voltage at the output. No way. It's a fault.

Doesn't that depend on the input impedance of the DMM? The higher the input impedance the lower the current, the lower the voltage drop across the cap, the higher the measured voltage?
 

Offline Armadillo

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Re: Getting zapped off 2.1 speakers and sub
« Reply #19 on: January 23, 2018, 12:03:44 pm »
Armadillo please provide exact details instead of saying "look" and words like "open" and "unloaded" which could mean anything.

it meant the power supply not connected to anything, left floating.
If you noticed, the word "unloaded" was used by shakalnokturn ???

OP power supply is connected to the equipment. The metal part exposes 100 over volts AC.

Edit: I supposed Australian codes are very consumer protective? Will you accept 100 over volts AC on metal parts and it bites? and come some wise crackos point to the Y cap and says is normal???
« Last Edit: January 23, 2018, 12:18:16 pm by Armadillo »
 

Offline Armadillo

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Re: Getting zapped off 2.1 speakers and sub
« Reply #20 on: January 23, 2018, 12:08:39 pm »
Yah, that's a normal misconception.
The nominal Y cap is at least 1.2Mohms hence you should not be able to measure that magnitude of AC voltage at the output. No way. It's a fault.

Doesn't that depend on the input impedance of the DMM? The higher the input impedance the lower the current, the lower the voltage drop across the cap, the higher the measured voltage?

Yeah, you are right. But the context is the OP photo as above.

Edit; it means a modicum of current draw will drop the voltage e.g. filter caps. If the exposed metal part is connected to the earth, will it read the same? Should check the earth continuity then, or the power supply.
« Last Edit: January 23, 2018, 12:31:27 pm by Armadillo »
 

Offline paulca

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Re: Getting zapped off 2.1 speakers and sub
« Reply #21 on: January 23, 2018, 01:07:36 pm »
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.

Regardless of standards, if I got a mains zap off a metal cased product it would be returned to the vendor with a letter of complaint and a threat of containing trading standards or naming and shaming them in the press if they didn't pay all postage costs and replace the unit with a safe one.

I don't care what amount of mains voltage American's or Australian's accept to get zapped by, nor do I really care what mains voltage/current leakage the British standards allow, I do not expect to get zapped by a mains device and then expect to keep it attached to any plug socket!

Here is a sensible question.

Would you want this device to be sitting on your living room floor while your child plays on the carpet next to it?  A child with wet hands.
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Offline madires

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Re: Getting zapped off 2.1 speakers and sub
« Reply #22 on: January 23, 2018, 02:10:15 pm »
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.

Like smartphones with a metal case?

Regardless of standards, if I got a mains zap off a metal cased product it would be returned to the vendor with a letter of complaint and a threat of containing trading standards or naming and shaming them in the press if they didn't pay all postage costs and replace the unit with a safe one.

Basically I'm with you, but the EMI suppression cap in SMPSUs is needed to comply with CE. A side effect is the mains referenced low current passing the cap. The cap should be a Y class type for safety and should also have a low capacitance to limit the current. Of course there are cheap SMPSUs which don't adhere to the rules. A metal case or case with exposed connectors isn't the problem, it could be a class II device (double insulated). You get zapped by the SMPSU.

I don't care what amount of mains voltage American's or Australian's accept to get zapped by, nor do I really care what mains voltage/current leakage the British standards allow, I do not expect to get zapped by a mains device and then expect to keep it attached to any plug socket!

You are free to replace all SMPSU wall warts and bricks with classic transformers.

Would you want this device to be sitting on your living room floor while your child plays on the carpet next to it?  A child with wet hands.

If you have the active speaker system connected to a PC it would be grounded via the PC.
 

Offline Armadillo

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Re: Getting zapped off 2.1 speakers and sub
« Reply #23 on: January 23, 2018, 02:40:32 pm »
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.

In any case, where the exposed metal surfaces exceed the safety extra low voltage, you failed the electric codes, regardless of what you want to say.

It would be almost not wise to say the current is limited. The shock though not lethal fatal may create a involuntary action that caused it to belethal fatal.

No, I am not impressed with your EMI or Y-cap knowledge.

https://www.edn.com/electronics-blogs/power-supply-notes/4414411/What-does-SELV-mean-for-power-supplies
« Last Edit: January 23, 2018, 04:04:41 pm by Armadillo »
 

Offline paulca

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Re: Getting zapped off 2.1 speakers and sub
« Reply #24 on: January 23, 2018, 03:19:16 pm »
I have NEVER received a shock or even a buzz off a mains powered device.  At least not one I hadn't opened and wasn't poking around inside while it was switched on.

I haven't checked my wall warts but based purely on the size of a few phone chargers they may be SMPS.  If one of them gave me a shock or even a buzz I would bin it.  If it was brand new I would send it back.

A mild buzz while using something like a deep fat fryer or kettle could result in someone jumping and pulling the hot oil / water down round themselves.

Mains devices should NOT, EVER, buzz or shock you unless they are broken or crap.  It's simply dangerous.  Most people I know would return it or bin it.

Again.  Would you like your child to be crawling around the floor with devices that might shock them sitting around?

If it buzzed me, I would not be connecting it to my PC.
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