| Author |
Message |
|
|
 Posted: Aug 03, 2009 - 07:42 PM |
|
Joined: Jan 12, 2002
Posts: 7829
Location: Canada
|
|
| whenever unsure, use an isolation transformer. In short, for a lab bench, you should always have an isolation transformer available to plug your mans supplied circuitry into until you know it is safe. |
|
|
| |
|
|
|
|
|
|
Posted: Aug 04, 2009 - 01:48 PM |
|
Joined: Jun 11, 2004
Posts: 2422
Location: Vilanova (Barcelona)
|
|
Check http://www.powerint.com/sites/default/f ... s/epr9.pdf
The infamous cap is C4. Too big, and you will 'feel the power of the dark side'. Too small, and you don't pass EC EMI compliance tests. |
_________________
Guillem.
"Common sense is the least common of the senses" Anonymous.
|
| |
|
|
|
|
|
|
Posted: Aug 04, 2009 - 02:25 PM |
|
Joined: Nov 01, 2005
Posts: 6326
Location: Hilversum - the Netherlands
|
|
| Guillem wrote:
Quote:
Too big, and you will 'feel the power of the dark side'
I tested that "in vitro" on the bunch of power supplies I posted about a few posts back: they appear to be of the right size. Got 70 uA as max, 40 uA in most of the cases. The transformer-versions are the ones to use for experiments.
Nard |
_________________
Dragon broken ? Or problems with the Parallel Port Programmer ? Scroll down on my projects-page http://www.aplomb.nl/TechStuff/TechStuff.html for tips
|
| |
|
|
|
|
|
|
Posted: Aug 04, 2009 - 04:56 PM |
|
Joined: Dec 11, 2007
Posts: 6854
Location: Cleveland, OH
|
|
HI Nard,
Nice job on the photos, testing, and results presentation.
It would be interesting to include at least one "old" transformer type, (non-regulated), wall wart, just to see what the leakage current was under the same test setup and measurement conditions, just for a comparison.
Sometimes the simple things that one takes for granted, like a wall wart, can be more complex than one at first appreciates!
JC |
|
|
| |
|
|
|
|
|
|
Posted: Aug 04, 2009 - 05:03 PM |
|
Joined: Nov 01, 2005
Posts: 6326
Location: Hilversum - the Netherlands
|
|
JC, that's what I did: you can find them on sheet/page 3. I tested 2 old-fashioned transformer-type wall warts. Very safe results, as you can see !
Nard |
_________________
Dragon broken ? Or problems with the Parallel Port Programmer ? Scroll down on my projects-page http://www.aplomb.nl/TechStuff/TechStuff.html for tips
|
| |
|
|
|
|
|
|
Posted: Aug 04, 2009 - 05:31 PM |
|
Joined: Dec 11, 2007
Posts: 6854
Location: Cleveland, OH
|
|
Opps, 
Got it. I was going back to look at all of the numbers more closely, and the difference is obvious!
Need more caffeine... 
JC |
|
|
| |
|
|
|
|
|
|
Posted: Aug 04, 2009 - 05:45 PM |
|
Joined: Nov 01, 2005
Posts: 6326
Location: Hilversum - the Netherlands
|
|
|
Quote:
Need more caffeine...
Nah .... take some more sleep instead. That's what I would recommend if I was a doc  |
_________________
Dragon broken ? Or problems with the Parallel Port Programmer ? Scroll down on my projects-page http://www.aplomb.nl/TechStuff/TechStuff.html for tips
|
| |
|
|
|
|
|
|
Posted: Aug 04, 2009 - 06:27 PM |
|
Joined: Nov 29, 2007
Posts: 3219
|
|
|
Plons wrote:
JC, that's what I did: you can find them on sheet/page 3. I tested 2 old-fashioned transformer-type wall warts. Very safe results, as you can see !
Bzzzzzzt, No.
As you have shown, the ones with the capacitor between the primary and secondary side don't kill you - if done right. The same argument holds for traditional transformers: they don't kill you - if done right.
Transformers have to be winded observing particular isolation requirements. Capacitors are to be build observing particular isolation requirements (the Y class).
To decide which one is in principle safer you would have to have statistics about breach of isolation. I don't have access to such statistics. However, the power that be deem the capacitors good enough (safe enough) for the consumer mass market. |
|
|
| |
|
|
|
|
|
|
Posted: Aug 04, 2009 - 07:48 PM |
|
Joined: Nov 01, 2005
Posts: 6326
Location: Hilversum - the Netherlands
|
|
|
Quote:
The same argument holds for traditional transformers: they don't kill you - if done right.
True. But what more can we do ? Stop designing circuits that require to be powered from the mains ? I mean .... where to draw the line ?
For medical electronics we use(d) either battery power or certified transformers and/or certified isolated DC/DC converters. What do you suggest for our freaks-circuits ?
Nard |
_________________
Dragon broken ? Or problems with the Parallel Port Programmer ? Scroll down on my projects-page http://www.aplomb.nl/TechStuff/TechStuff.html for tips
|
| |
|
|
|
|
|
|
Posted: Aug 05, 2009 - 05:32 AM |
|
Joined: Dec 30, 2004
Posts: 8788
Location: Melbourne,Australia
|
|
One solution if we wanted a simple bench power supply would be to wire the power supply output to some terminals and have the - side earthed.
For PC power supplies - due to the large current availability (>20A), I'd suggest using a fuse or polyswitch device to limit the current to say, 1A to minimise the risk of bits of wire going up in smoke and causing a fire.
I have noticed the leakage in mainly dvd played and set top boxes where they have a metal chassis but only a two pin plug. If you're earthed and touch the case of these devices when they're floating ( electrical wise) you'll get a tingle that will make you jump. |
|
|
| |
|
|
|
|
|
|
Posted: Aug 05, 2009 - 02:24 PM |
|
Joined: Jun 17, 2002
Posts: 300
Location: Melbourne, Australia
|
|
ArnoldB wrote:
Quote:
s you have shown, the ones with the capacitor between the primary and secondary side don't kill you - if done right. The same argument holds for traditional transformers: they don't kill you - if done right.
Ron:-->Agreed.
Kartman wrote:
Quote:
One solution if we wanted a simple bench power supply would be to wire the power supply output to some terminals and have the - side earthed.
Yes: This is the sort of thing that I have been trying to say.
The main problem with switchmode plugpacks with a capacitor from output to input rectifier is not necessarily the leakage current but the instantanious voltage on the capacitor when the plugpack is connected to one of our applications when there is a pre-existing grounded connection such as a CRO or PC Serial port.
Kartman's solution is valid and removes my hatred of un-earthed SMPS plugpacks. The transformer based variety have much less input to output capacitance and rarely provide a problem.
While I note that while Nard has performed extensive measurements and posted the results, (Thanks), I am still at a loss that no other poster has put their multimeter or CRO on their mobile phone charger to see what there is there. Its a 30 second test, not too much to ask, is it ?
I'm happy to see that for the first time in years, there there are some AVRfreaks willing to look into this pet issue of mine a bit deaper.
This all stems from loosing an expensive old programmer when one of my previous staff members connected a live SMPS plugpack instead of the transformer based one into the programmer which was already connected to a PC.
The programmer was irreplaceable.
Thanks, Ron. |
|
|
| |
|
|
|
|
|
|
Posted: Aug 05, 2009 - 03:02 PM |
|
Joined: Nov 01, 2005
Posts: 6326
Location: Hilversum - the Netherlands
|
|
Later today I will put some more SMPS's to the test, and will focus on mobile-phone chargers and other low-cost wall-warts.
I want to let you (all) know that I am very pleased with the thorough approach to this prblem.
Nard
Edit: I got my first "tickles" from one of the SMPS-wall-warts. And I need to have a closer look at the multimeter I am using for this: sometimes odd results. I will update when I sorted that out. |
_________________
Dragon broken ? Or problems with the Parallel Port Programmer ? Scroll down on my projects-page http://www.aplomb.nl/TechStuff/TechStuff.html for tips
|
| |
|
|
|
|
|
|
Posted: Aug 06, 2009 - 09:23 PM |
|
Joined: Nov 01, 2005
Posts: 6326
Location: Hilversum - the Netherlands
|
|
|
|
|
|
|
|
Posted: Aug 07, 2009 - 01:11 AM |
|
Joined: Jun 18, 2001
Posts: 1085
Location: Brisbane Queensland Australia
|
|
Nice report on your part Nard.
Thanks for your time & effort.
This does shed a different light on what suitable testing equipment is required.
The oscilloscope wins hand down with visual feedback.
Then again no reason a black box cannot do the same thing & transfer it optically to a PC for the result.
I have seen few wall wart units using like audio transformer inside as part of their switchmode setup.
These do not have the "C Tick" Australian Standard & we do not use them.(cheap & comes from Ch---)
Ken |
|
|
| |
|
|
|
|
|
|
Posted: Aug 07, 2009 - 01:45 AM |
|
Joined: Dec 07, 2008
Posts: 347
Location: germany
|
|
I've put my scope at the 12V line of my pc power supply. While the GND was connected I meassured nothing. If I leave the GND of the scope away I get something like a 50 Hz sine and it's magnitude is way too high to measure. Like more than 400 V.
I get the same signal if I put the probe at the 12V-GND. (always leaving scope gnd in the air)
I don't know how to think about this. Is this only some "caught in voltage" from "long" wires? Or is it some serios commom mode leakage?
PS: my multimeter has only an "auto V" option. So no possibility to get an AC meassurement  |
_________________
Jan Kießling
74HC Overview
Flowchart CAD
schematic CAD
|
| |
|
|
|
|
|
|
Posted: Aug 07, 2009 - 08:11 AM |
|
Joined: Jun 11, 2004
Posts: 2422
Location: Vilanova (Barcelona)
|
|
The problem with ground, earh and similar appear when one wants to measure voltages of electronic systems enclosed in a metallic box. That is translated as the shield of the 'scope probe being earthed (law issues...), while some other part of the metallic enclosure of the device under test is also earthed (PC SMPS).
That leads to these high voltages measured with the 'scope, and that is only solved properly grouding both. The term 'properly grounding' can mean the use of isolation transformers, differential probles, isolating earth, etc. |
_________________
Guillem.
"Common sense is the least common of the senses" Anonymous.
|
| |
|
|
|
|
|
|
Posted: Aug 07, 2009 - 02:06 PM |
|
Joined: Dec 30, 2004
Posts: 8788
Location: Melbourne,Australia
|
|
Ok, I took the Pepsi challenge.
Just got a Dlink router to hack around with so I measured its plug-pack(wall wart etc).
- to earth 105vac
- to earth 130uA
This one has an earth pin, but I'm not sure it does anything.
Another router power pack - this time from a Edimax BR6204Wg
- to earth 98vac
- to earth 71uA
This one only had two power pins.
I've been going router hack mad lately. On my way to becoming an embedded Linux guru. |
|
|
| |
|
|
|
|
|
|
Posted: Aug 07, 2009 - 02:27 PM |
|
Joined: Nov 01, 2005
Posts: 6326
Location: Hilversum - the Netherlands
|
|
| Kartman wrote:
Quote:
I've been going router hack mad lately. On my way to becoming an embedded Linux guru.
Enjoying yourself ?
Your measurements confirm what I have found so far.
Since the scope-pictures tell so much more, I tested 4 selected wallwarts. Results:
http://www.aplomb.nl/SMPS_leakage/Doc_ie.html#August_7_scoped
It ain't half hot mum .... as it's about 30 degrees C in the shack
Nard |
_________________
Dragon broken ? Or problems with the Parallel Port Programmer ? Scroll down on my projects-page http://www.aplomb.nl/TechStuff/TechStuff.html for tips
|
| |
|
|
|
|
|
|
Posted: Aug 07, 2009 - 03:30 PM |
|
Joined: Jun 11, 2004
Posts: 2422
Location: Vilanova (Barcelona)
|
|
Impressive job, Nard!!
That confirms that for precisse instrumentation, classic transformer rocks much more than wallwarts. Anyway, that Samsung one also impresses me, and leads the path to follow.
Mmmmm, that makes me think about to test certain SMPS I have at home, but I wouldn't post any results if they are bad, may be I will be ashamed.
Oh, and all this also makes me wonder about the current output SMPS that showed me "the paths of the dark side" for my first time. It left me breathing like Darth Vader, and seeing everything black for few minutes. |
_________________
Guillem.
"Common sense is the least common of the senses" Anonymous.
|
| |
|
|
|
|
|
|
Posted: Aug 07, 2009 - 04:05 PM |
|
Joined: Nov 01, 2005
Posts: 6326
Location: Hilversum - the Netherlands
|
|
Thanks !
I have a question for the experts (which I am not):
Code:
What is the purpose of that Y-class capacitor ? EMI regulations have been mentioned, but what is the explanation .... what does it do ?
And what are the risks of removing it ?
And please don't shoot me for asking this ! I simply want to learn.
Nard |
_________________
Dragon broken ? Or problems with the Parallel Port Programmer ? Scroll down on my projects-page http://www.aplomb.nl/TechStuff/TechStuff.html for tips
|
| |
|
|
|
|
|
FAQ
Search
Register
Log in to check your private messages
Log in
Maximize
RSS
