Lab bench instruments and laptop earthing

Greetings all! I need to consult you guys for a concern regarding lab bench instrument's a nd laptop grounding scheme. I'm using the laptop (which is a class-2 device, non earthed) together with the Pickit3 programmer/debugger. The Pickit3 is connected to the target ap plication which is powered by an external powersupply. Connected to the app lication board is one oscilliscope and two waveform generators. So, how should I earth all this to prevent anything to burn. Between the laptop "ground" (measured on an USB connector shield)and earth I have about 80VAC when the battery charges is connected to mains. This should be due to some Y-caps in the charger SMPS. The charger has no c onnection to earth so those Y-caps are probably connected between primary a nd secondary ground (laptop ground). I have had the oscilloscope floating, supplied from an isolation transforme r since I've worked on SMPS's lately. But now I rather have it earth connec ted to minimize the leakage current from the oscilloscope SMPS and it's Y-c aps to my application board. So, my question is: Is it safe for the laptop and Pickit3 to connect to th e application board if I earth all the instruments. What worries me is, wil l that 80VAC potential cause any damage to the Pickit3 or even worse, the l aptop? Thanks for your suggestions, and have a great weekend you all!

Reply to
powerampfreak
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On a sunny day (Fri, 12 Apr 2013 08:23:50 -0700 (PDT)) it happened powerampfreak wrote in :

I sort of permanently solved that problem by using Raspberry Pi and noppp as PIC programmer, and do ssh from the laptop to it via ethernet. Ethernet is 100% isolated, WiFi works too, even more isolated:

formatting link

But it is probably OK to connect all your stuff to the same ground. If the USB cable is OK it should ground your laptop too. I noticed at one USB cable here that does not connect ground YMMV.

Reply to
Jan Panteltje

"powerampfreak"

I have had the oscilloscope floating, supplied from an isolation transformer since I've worked on SMPS's lately.

** What a f****it thing to do.

Common sense says to use the ISO on the SMPS - not the damn scope.

But you have never shown any sign of sense.

... Phil

Reply to
Phil Allison

laptop grounding scheme.

the Pickit3 programmer/debugger. The Pickit3 is connected to the target application which is powered by an external powersupply. Connected to the application board is one oscilliscope and two waveform generators.

have about 80VAC when the battery charges is connected to mains.

connection to earth so those Y-caps are probably connected between primary and secondary ground (laptop ground).

since I've worked on SMPS's lately. But now I rather have it earth connected to minimize the leakage current from the oscilloscope SMPS and it's Y-caps to my application board.

application board if I earth all the instruments. What worries me is, will that

80VAC potential cause any damage to the Pickit3 or even worse, the laptop?

Stuff breaks...but if your stuff ain't broken, it's typically OK to connect the chassis/safety grounds together.

The problem happens when the safety ground is on the connector that your plugging/unplugging.

I have an external hard drive with eSATA connection. A cable can connect it directly to the motherboard. And it's FAST compared to USB. Problem is that I am unwilling to risk my motherboard on a glitch during plug/unpluging it. Or a static discharge that has too much inductance to the safety ground path.

I once trashed a motherboard by plugging in a printer cable with nothing on the other end. As a percentage of the times I'd plugged something in, it was about zero. But that's no consolation when your motherboard is dead.

You balance convenience with risk and take whatever chances you can live with.

As for floating the scope, don't do it. Use isolated probes or make a differential measurement with probes that can stand the worst case excursion.

The use of an isolation transformer when testing any equipment is a good idea for the same reason you use safety glasses...in case you screw up and accidentally touch something live. It's not a license to to connect a wire between ground and something with a lot of relative volts on it.

Reply to
mike

"mike"

** Or just float the circuitry with an ISO tranny.
** Not it isn't and there is no such comparison.

Routinely using an ISO tranny on *all* equipment under test /repair is STUPID and DANGEROUS !!!

This has been thrashed out here several times now and there is NO justification for the practice.

ONLY if you need to scope the AC line side of a device ( PSU etc) should an ISO tranny ever be used at all.

Technicians must never get the idea that it is safe to handle ( or ground ) the live parts of a circuit - or one day it will kill them.

Plus, using an ISO hides serious fault conditions in equipment, either pre existing or due to errors by the technician.

So, once the need for the ISO had gone, put the item back on the regular AC supply immediately and place the ISO out of sight so there is no confusion.

... Phil

Reply to
Phil Allison

Den lördagen den 13:e april 2013 kl. 04:29:07 UTC+2 skrev Phil Allison:

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Phil - give me a break! You talk about sense... please direct your rude com ments to those who deserve it. I must say you don't show much of a sense yourself really Reason for ISO the scope is simply I have not a ISO tranny of 20kW which wo uld be needed to power the SMPS. But that's not what the topic was all about in this thred, maybe you got th at wrong. In order to connect my class-2 laptop together with the pickit3 debugger wh ich connects to my application board which has several instruments hooked u p to it. What is the best way to earth everything to minimize the risk of d amage to the laptop or instruments, was the meaning of this thred.

Reply to
powerampfreak

I thought this was a place of engineering knowledge spreading, not a place to throw sand on each other in the kindergarden. :) Of course my intention was not be gain enemies here... Phil, I don't think you could judge me being an idiot or not. Anyway, John it was interesting to hear about your high power UUT testing. An USB isolator sounds good, but still I need to power my debugger from USB power, so I cannot use it. Anyway, I will figure out something. Thanks guys

Reply to
powerampfreak

"powerampfreak" Phil, I don't think you could judge me being an idiot or not.

** ROTFLMAO !!!!!!!!!!

Your idiotic fake name, your "hotmail" addy and

VERY SINGLE THING you post

SCREAMS:

Warning: NUT CASE ON the LOOSE !!!

Fuck off.

Reply to
Phil Allison

Oh we do both here.

Don't take it personally, there is indeed a lot of engineering knowledge to be had.

power, so I cannot use it.

--

John Devereux
Reply to
John Devereux

It's quite humoristic how angry you are Phil. I hope it's not affecting your blood pressure too much, because I believe you are, after all, quite a nice guy :)

Cheers

Reply to
powerampfreak

e to throw sand on each other in the kindergarden. :)

.

SB power, so I cannot use it.

any real usb isolator would also isolate the power

-Lasse

Reply to
langwadt

to th=

wil=

e l=

as PIC programmer,

still need to power the pi so you are likely to get similar problems

the laptop you can just unplug and run on battery

-Lasse

Reply to
langwadt

laptop grounding scheme.

Pickit3 programmer/debugger. The Pickit3 is connected to the target application which is powered by an external powersupply. Connected to the application board is one oscilliscope and two waveform generators.

have about 80VAC when the battery charges is connected to mains.

connection to earth so those Y-caps are probably connected between primary and secondary ground (laptop ground).

since I've worked on SMPS's lately. But now I rather have it earth connected to minimize the leakage current from the oscilloscope SMPS and it's Y-caps to my application board.

We have a Tek 4-channel isolated-input scope, TPS2024. Even the trigger input is separately isolated. It's wonderful for working on switchers and power amps and things. You can measure the small voltage drop waveform across something that's

400 volts off ground, and do that in four different places simultaneously.
--
John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    
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Reply to
John Larkin

On a sunny day (Sun, 14 Apr 2013 13:18:43 -0700 (PDT)) it happened " snipped-for-privacy@fonz.dk" wrote in :

That is true, but I hope there are plenty of good micro USB adaptors that the idiots did not put in caps to the mains... (Why do they do that???). And I can imagine situations where it is more convenient to have the laptop elsewhere (as I often do), this may especially be the case in HV environments, or radiation environments etc... also where a Raspberry Pi is only 35 $ and the laptop

50x more expensive,,,,

And the remote programming (ssh -Y) is really cool, Pi was on 12 hours a day for a whole week last week programming stuff etc, and I am surprised at the stability, more worried about write cycles to my SDcard. I have an other interesting setup with GPIO use for it here in the making,

And, last but no least, you can make Pi run from battery too, I have build a small switcher with USB 5V out that will accept anything above about 8 V as input, an 11 V 2200 mAh Lipo should almost last a work day, not all laptops do.

It all depends. It is just an other instrument (Pi) added to the scala, I am happy with it,

Reply to
Jan Panteltje

input,

Beaglebone gives you an easy isolated power over ethenet option, rPi not so much.

--
?? 100% natural 

--- news://freenews.netfront.net/ - complaints: news@netfront.net ---
Reply to
Jasen Betts

On a sunny day (15 Apr 2013 10:03:04 GMT) it happened Jasen Betts wrote in :

input,

much.

Was not that beagle thing much more expensive? Hard to get too probably, why raspis march past all the time, easy to catch one. And then there is support... My little switchers was less than 8 $ alltogether. beaglebomb is dead dead dead

Freaking H*LL this is a design group, take some ferrite core, put 2 x 20 turns around it, add a tranistor and stabiliser, and you have you mains isolation.

Reply to
Jan Panteltje

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