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May be this is a weird question. But I am little curios to know why my 12V DC adapter is giving shock when the circuit is complete.

I purchased couple of these 1 AMP 200V AC to 12V DC adapter. Unfortunately they didn't come up with a 'data sheet' as such except the specs written on the enclosure of the adpater. It is for sure not a transformer-less adapter. I verified that. When I connect it with as input to my DC to DC converter, the converter parts give electron shock. Well, I must say it never seemed as strong as 220V AC shock. A mild shock, but everytime.

What might be the reason for this? To my knowledge if it's pure 12V DC, I am not supposed to get shock. Is it possible that the DC is not well filtered and some AC components are still left in the adapter's output which is causing the shock. The other day I say a Youtube video where the presenter demonstrated that 12V AC exceeds the comfort level of human being, and one would feel the shock. Is this the case happening here?

If yes, then my last question would be how can I get rid of that? Would a capacitor filter work?

sribasu
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  • Please see [Laptop surface vibrating because of ungrounded adapter](http://superuser.com/a/1103702/272824) and come back to us if you have further information. – Andrew Morton Jul 24 '16 at 19:31
  • There might be a little ripple on the adapter. I think you should make a calculation considering your load and put the calculated capacitor to the output to bypass the ripple. – Alper91 Jul 24 '16 at 19:32
  • Andrew, my question is still open. Because my adapter has 3 pins :( – sribasu Jul 24 '16 at 19:37
  • Alper91 even if I consider, I am going to consume nearly 1 AMP (fully utilize), what should be the recommended CAP value? 1000uF/Ampere - logic? – sribasu Jul 24 '16 at 19:38
  • @sribasu Just because the adapter plug has three pins does not mean it has the DC output ground connected to the mains ground. You can easily check that with a continuity tester. Also, if you are referring to a particular part (i.e your mains adapter) in the question, it would be good to give a link to it. – Andrew Morton Jul 24 '16 at 19:41
  • @Andrew that's a good point for me to work on. I will verify if the DC output is grounded or not. I purchased the adapter from a local electronics store, not online. – sribasu Jul 24 '16 at 19:47
  • Y-capacitor leakage. – winny Jul 24 '16 at 22:53

2 Answers2

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The most probable reason for the electrical shock is the value of the (Y-rated) capacitor that sits between the mains side of the adapter and the low voltage output.

This capacitor is needed to provide a return path for the high-frequency (about 100 - 200 kHz, not that high) with which the isolation transformer is fed.

If the value of this capacitor is higher than what is usual (1 nF) then you might feel a "tingle" when touching the output of the adapter.

Also see this question and perhaps this question as well because it shows a picture of a mains adapter PCB where you can clearly see the blue capacitor C5 across the yellow transformer.

As long as the shock is just a "tingle" then it should not harm. But properly designed adapters should not give this "tingle" !

Bimpelrekkie
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    what does mwah stand for? – bitshift Jul 24 '16 at 20:56
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    It's not a word, it's the sound an experienced engineer makes when commenting on if something is low/high/large or small. – Bimpelrekkie Jul 24 '16 at 20:58
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    I see. Wasn't sure if you were blowing the OP a kiss or not :) – bitshift Jul 24 '16 at 20:58
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    Haha, no, wasn't doing that :-) – Bimpelrekkie Jul 24 '16 at 21:00
  • You were correct. It's the Y-cap. Thanks @FakeMoustache With relation to this another problem came in my mind. I am little worried after measuring my body resistance (finger tip - left hand to right hand) - it's approx 300KOhm when I am dry. I think it's too low for human beings. Isn't it? Probably this is why the tingles are not comfortable for me at all :) – sribasu Jul 29 '16 at 21:21
  • The resistance of the human body does not vary so much, what does vary is the resistance of your **skin** and the contact between your skin and the metal part you're touching. If you have sweaty hands, resistance will go down. If you would wear isolated (rubber) shoes that might also help. **BUT** stop thinking that it is **you** causing the problem of feeling a tingle because it isn't. It is the problem of the **design of the power supply** , it should have been designed such that you feel no tingle. Again: not you, it's the supply !!! – Bimpelrekkie Jul 29 '16 at 21:29
  • I first read "mwah" as milliwatt-ampere-hours. On second thought that kind of unit should only appear when you accidentally multiply by charge when you meant to divide and your calculator starts giving you subtle hits about it. – John Dvorak Apr 12 '19 at 17:11
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240/300000=0.8mA SO THIS IS AROUND THE 1mA AC threshold for feeling a tingle. So you are getting the 240v AC not the 12V DC current. so be carefull as you have a short (wire exposure) or doggie earth bonding! Touching this with "wet hands" could throw or kill you! unplug it cut the wire on it and get rid of it(in that order).

user175329
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