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Inverters, Laptop Power Supplies and Earth Leakage

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Blaize110 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Blaize110 Quote  Post ReplyReply Direct Link To This Post Topic: Inverters, Laptop Power Supplies and Earth Leakage
    Posted: 22 September 2011 at 8:10pm
I've just bought myself a little 200W inverter for the purpose of powering a few LED parcans and a laptop PSU.

The LED parcans run fine without any hitches. However the when I plug the laptop PSU in (even with no laptop connected), the inverter 'fault' light comes on and it stops working. Now the PSU is about 70W so its not like its overloading it.

After some experimenting, I found that if I plugged the laptop PSU in the 'wrong' way around so that it had no earth, the inverter would keep working. The PSU makes a louder buzzing sound but it works. I have used this laptop with a friend's higher power inverter with no problems (the buzzing was still there but it worked fine).

I guess it is the earth leakage from the PSU that is causing the problem but it cant be that much as it still works on mains and also on the larger inverter, so I am putting it down to an over sensitive protection circuit. I was actually surprised that the earth was connected at all!

The obvious solution seems to be to plug in the laptop so that the earth pin is not connected. However I am reluctant to do this and have always warned people against it. If it has an earth, it must be there for a purpose... However in this case, is the earth that important, given that the inverter isnt grounded anyway?

Thoughts and opinions on the matter would be greatly received.


Edited by Blaize110 - 22 September 2011 at 8:12pm
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shagnasty View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote shagnasty Quote  Post ReplyReply Direct Link To This Post Posted: 22 September 2011 at 9:40pm
I have a Tecra M5 that has a buzz issue if I use the onboard sound card (which I only do in dire emergencies, I truely beleive anyone that connects anything to a pro sound system via a 3.5mm stereo jack should shot in the face and buried in shallow grave, yes I particularly mean iPods/Phones!!) so I just carry a second mains lead with no earth in it, a bit dodgy but TBH I am not seeing why the PSU has an earth anyway, my old Tecra has a 2 pole mains lead and the adapter works fine with the new laptop, I am guessing some CE crap has caused the to earth the PSU for EM emsisions and your inverters "moddified sinewave" output has so many harmonics on it they couple to ground reather well..
 
I wouldn't do the back to front plug thing, having the source of the problem on an exposed pin is a bit short sighted, but a "custom" c6 mains cable with no earth wired seems safe enough to me for inverter use, lets be honest, the inverter out is hardly earth referenced anyway so you would need to do some fairly batty wiring to make the whole rig a true hazzard....
 
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Edited by shagnasty - 22 September 2011 at 9:40pm
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kedwardsleisure View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 23 September 2011 at 12:05am
Not a good idea to get rid of an earth on a laptop adapter. The earth forms a physical barrier between high and low voltage parts, and provides a path for the filter leakage current. It minimises the effects of insulation breakdown between primary and secondary, ie mains in and low voltage out.

Commercially approved laptop adapters that are supplied with 2-core mains flex have enhanced insulation, creepage distances and filtering that obviates the need for the earth. 3-core laptop adapters don't, and are dangerous to use with the earth disconnected.

Look at the maximum permissible leakage currents between class 1 and class 2 equipment.

There is enough filter leakage in a class-1 adapter that has its earth lead cut off to zap any mixer or amp input or anything in the path from the laptop audio or usb output and the mains source, be it earth, neutral, inverter casing, car body, battery terminal, or you.
Kevin

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Saturnus View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Saturnus Quote  Post ReplyReply Direct Link To This Post Posted: 23 September 2011 at 12:34am
I have no idea why earth is there in the first place. No modern home installations in Denmark, and I suspect most of mainland Europe, have earth connection anywhere expect on 3-phase power. Often the hole is there to accommodate 3 connector plugs but the earth connector isn't connected to anything as there's only 2 wires.  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SamV Quote  Post ReplyReply Direct Link To This Post Posted: 23 September 2011 at 2:20am
If the laptop is 12v, forget the PSU :)
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shagnasty View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote shagnasty Quote  Post ReplyReply Direct Link To This Post Posted: 23 September 2011 at 2:25am
As I said earlier, if some thing has an earth you need to be VERY careful if you decide not to use it, I do a lot of work all over the world and TBH once you have used a BS1363 (IE UK) system anything else is simply 3rd world, we have the best system on the planet and you need to very sure what are doing before you mess with it.
With an inverter sytem and laptop, I'd would run without an earth if I needed to, but as soon as the mains proper get involved, forget it...
If you wanna be really safe just drop the 240v from your inverter to 120V via an isolating transformer, most laptop supplies will run 90-240V so there you have total safety and no probs!!!!
 
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shagnasty View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote shagnasty Quote  Post ReplyReply Direct Link To This Post Posted: 23 September 2011 at 2:32am
Originally posted by SamV SamV wrote:

If the laptop is 12v, forget the PSU :)
 
Brave, and err, no, 13.8V may kill a 12V laptop, but good point, well made, bin the 240V bit and get a "car" laptop PSU, thus negating all the safety issues..
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Saturnus Quote  Post ReplyReply Direct Link To This Post Posted: 23 September 2011 at 9:50am

 

Originally posted by shagnasty shagnasty wrote:

As I said earlier, if some thing has an earth you need to be VERY careful if you decide not to use it, I do a lot of work all over the world and TBH once you have used a BS1363 (IE UK) system anything else is simply 3rd world, we have the best system on the planet and you need to very sure what are doing before you mess with it.Smile

That is funny. We see the British standards as 3rd worldish and vastly outdated but I guess different strokes, eh? ;)

But it's hardly surprising seeing that the British standard was introduced in 1947 and the current European mainland standard was introduced in 1995. Almost 50 years of experience and vastly changed requirements in difference.



Edited by Saturnus - 23 September 2011 at 11:09am
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Blaize110 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Blaize110 Quote  Post ReplyReply Direct Link To This Post Posted: 23 September 2011 at 10:33am
Thanks for all the advice.

Like I said, im normally the one telling people off for cutting the earth out of laptop power supplies so I am very hesitant to do it myself. However, if the current leakage is going down the earth, where does the inverter then send that leakage to 'get rid of it'.

I have also tried another laptop that only has a 2 pin connector and for some reason this also puts the inverter into 'fault' and I cant work out why... Any ideas?

EDIT: The laptop isnt being used for much, just music for a little Lepai 12V jobby. Normally i'd use by ipod but I need the battery to last a bit longer. I guess I could charge up the laptop battery when its not connected to anything and then run it off battery when doing audio to minimise the risk of earth-leakage frying anything.


Edited by Blaize110 - 23 September 2011 at 10:44am
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slaz View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slaz Quote  Post ReplyReply Direct Link To This Post Posted: 23 September 2011 at 11:05am
Originally posted by shagnasty shagnasty wrote:

Originally posted by SamV SamV wrote:

If the laptop is 12v, forget the PSU :)
 
Brave, and err, no, 13.8V may kill a 12V laptop, but good point, well made, bin the 240V bit and get a "car" laptop PSU, thus negating all the safety issues..
 
Smile


Hmm ... I'd be very surprised if 13.8V would kill a "12V" laptop. Only if its a _very_ cheap/nasty design ... (which is possible of course).

From what I can find out, the only laptop running natively from 12V is a EEE-PC 901 Asus netbook jobbie. I'd like to try one of these myself actually .... not sure about that 1024 x 600 screen mode for Virtual DJ though (anyone tried this ?).

But - yeah - for a regular laptop (most are 19V, a few like older IBM and Toshiba-made Toshiba are 16 or 15V) - a car laptop adapter (its a DC up-converter) might solve the problem. The cheapie ones claim efficiency of 85-90% .... dunno. They come with about 10 typical DC connectors to fit vast majority of laptops. I have one that seems to work OK, but not used extensively, so I can't comment on reliability. They come with a cigar-lighter plug .... could obviously be chopped off, or if you weant to retain car functionality just get a in-line cigar-lighter socket and customise to your connections ....
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slaz View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slaz Quote  Post ReplyReply Direct Link To This Post Posted: 23 September 2011 at 11:11am
Originally posted by Blaize110 Blaize110 wrote:

Thanks for all the advice.

Like I said, im normally the one telling people off for cutting the earth out of laptop power supplies so I am very hesitant to do it myself. However, if the current leakage is going down the earth, where does the inverter then send that leakage to 'get rid of it'.

I have also tried another laptop that only has a 2 pin connector and for some reason this also puts the inverter into 'fault' and I cant work out why... Any ideas?

EDIT: The laptop isnt being used for much, just music for a little Lepai 12V jobby. Normally i'd use by ipod but I need the battery to last a bit longer. I guess I could charge up the laptop battery when its not connected to anything and then run it off battery when doing audio to minimise the risk of earth-leakage frying anything.


Could be that the DC inrush when you first connect the AC adapter is upsetting the inverter. Out of curiosity, try briefly connecting the AC adapter to wall AC (without powering the laptop) - so its caps get charged - then connect to the inverter - then connect the laptop. If this "fixes" things things, it would confirm the above theory about inrush current. Won't help much, but you'd be a little wiser :-)


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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 23 September 2011 at 12:23pm
according to my research, Denmark has abandoned unearthed outlets and must fit earthed outlets by law to all new installations.
Looks like they finally caught up with us.
Kevin

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