Hi,
which kind (size, Material) and value of resistor should i use to connect GND and PE?
Hi Noy,
Apology for the late reply but this looks like a question intended for the original author of the "Lo-Z static drain resistive connection between the PE and the BNC ground" modification, which would be my good self.
The "Lo-Z static drain" resistance value being, in this case, a matter of 3K3 to 10K rather than the typical anti-static drain value of one or two megohms. A quarter or half watt rated carbon or carbon film or metal film (take your pick - it's not critical) 4K7 resistor will suffice and allow DC offsets of up to 32 and 48 volts respectively between PE and BNC ground.
I recently converted three UK wallwarts with a similar half mains touch voltage suppression mod using 4K7 ohm resistors so had a reason to calculate the maximum DC offset voltage that could be applied between the 0v connection and mains earth.
In two of these mods, I'd simply used gutted wallwarts which happened to have proper (but unused) earth pins to rehouse the innards of a 12v wallwart and a 20v wallwart that had come supplied with an Aldi 4 watt LED desk lamp not so blessed with earth pins. I'd already gutted these older wallwarts and kept their housings for just such jobs as this.
For those of us living in regions where the use of an earthed wall socket is mandatory such as here in the UK, the next time you're going through your box of ancient wallwarts, keep hold of any with a real earth pin since they've now become as precious as gold dust in the quest to eliminate the rather cheap 'n' nasty half mains voltage tingle of the later and current models that rely on a plastic earth pin merely to act as a safety shutter opener on such sockets.
The other low standby power 12v 1A rated wallwart was already blessed with a real earth pin (unused) so only required to be cracked open in order to fit a quarter watt 4K7 metal film resistor between the accessible and solder-able earth pin contact[1] and the 0v rail of its 12v DC output.
The reason for this sudden spurt of wallwart modification activity was my experiencing the ESD induced lockups of my FY6600 as a result of grounding it to an already grounded DUT or DSO prior to my solving this half mains voltage on the BNC grounds issue. Now I was seeing the same effect but this time as a result of the half live mains voltage of the 12v wallwart powering my GPSDO.
Although it's a simple enough matter to arrange a separate GPSDO earth connection, independent of its 7 to 24 volt dc supply connection, I'd decided that I'd had more than enough of this nonsense of wallwarts cursed with this half live mains voltage issue and it was high time that I actually did something about it.
The desk lamp wallwart had been an annoyance for some considerable time (LV current carrying telescopic arms making the use of such wallwarts unacceptable in this case) so, quite naturally, it had gotten included in my 'de-tingling' of the primary and spare 12v GPSDO wallwarts project.
[1] Solderable they might be but you do need to take precaution against softening the plastic whilst applying some 70 watts' worth of heat for the 20 to 30 seconds typically required to form a reliable solder joint using lead/tin solder. I used a broken digitally programmable on/off timer switch held by its earth pin in a vice into which I plugged the wallwart to act both as a heatsink and as a stabilising jig to prevent the earth pin canting out of alignment (I knew I'd eventually get some use out of that crappy timer switch if I held onto it long enough
).
JBG