Line filter question

[Dannyx]

Re: Line filter question

Yeah, those are what I'm talking about - pretty pricey though, at least where I live. Here's an open one - rip out them Y caps - problem solved

[redwire]

Re: Line filter question

240VAC Outlet tester using three neon lamps. I'd have to think how to make an LED version, and just leave it plugged in all the time.
For my workbench I use a RCD, they don't require a ground connection.

[stj]

Re: Line filter question

i think one of those big clive video's has schematics of an led version.
but whats wrong with neons?

[redwire]

Re: Line filter question

Neons are fine, I have one tester like that but they need at least 60-75V to light up.
That's too much for a lamp to earth-ground, you could have 50V and nothin' lit (w/120VAC mains here).
Modern green LED's are super efficient and could light up with much less voltage I think. I'll check out Big Clive's one and see if it looks ok.

[eccerr0r]

Re: Line filter question

Not sure why bigclive dissed so much on the transistor current regulator... it will detect those 50V differences where a neon lamp will miss...

[redwire]

Re: Line filter question

It ran too hot, SOT-23 transistor dissipates 0.25W at 2mA/240VAC and 1/2 wave.
Almost all of these outlet/socket testers are just lamps in a delta configuration. Although the Fluke has a PIC MCU.

[eccerr0r]

Re: Line filter question

Right, it runs hot as it will dump heat (yes, they are underspecced for 100% duty cycle) but they do serve a function that a simple resistor can't do...

[redwire]

Re: Line filter question

Those LED CC sources are setup to regulate above 16V, I guess they wanted the LEDs dim below that.

OP is connecting outlet PE with Neutral which is really not a good way to go. Because it's supposed to be done at the main panel, and it's supposed to be able to handle lots of current (building's service size).
An open neutral could have (building) return current going through OP's wiring which is only adequate for those sockets - so the wiring would cook and melt.
This is why it's Neutral-PE bonding is heavier gauge wire and done at the service entrance.

[eccerr0r]

Re: Line filter question

op should just leave pe open and not modify the caps or internal wiring, and use a GFCI/RCD for safety. Not ideal but should not result in a fried Dannyx.

[Dannyx]

Re: Line filter question

Yeah, I'm not gonna mess around (too much) with the electrical wiring in my home/shop. I was mostly interested in how to design a proper power supply that's safe to install on lab equipment which comes in contact with electronics, even in the absence of a PE. Like chargers and even TVs that don't even have a 3-pin power plug.

For instance, I was planning to touch up the solder joints of the RAM slots on my MOBO. I'm not sure how much leakage current some components on that board would tolerate through them if the supply of my iron has no PE.

[redwire]

Re: Line filter question

The power supply you built I thought is a linear one with a big power transformer, so it possibly has low leakage current and can be run with no ground if you're confident about the wiring and insulation. Just measure ACV between its output/frame/chassis and PE, across say a 1MEG resistor or none at all.
Sure there are ungrounded devices like chargers and TV's stereo that are "double insulated" and have very low leakage current to PE or between devices. There's no Y-caps at all. But your soldering iron is not like that so it ain't gonna work.
Take multimeter ACV readings and see what the stray voltage is like on your work bench, soldering iron, test gear etc.
If your bench is metal/ESD mat, it is a current path. If the mobo is connected to anything, there is another path. It's not easy to know all paths.
I find an ungrounded (SMPS Y-cap) soldering iron will have 60-90VAC at the tip which is OK if you've got a wood bench top and you (roll of solder) is also insulated from everything. But the stray charge is from capacitance between you and something, the work bench too and IC's, MOSFET's getting 60-90VAC with a tiny zap...

[eccerr0r]

Re: Line filter question

Indeed the key thing is insulation - the only way you can get devices with only 2 prongs is that it's completely plastic on the outside for insulation as well as full isolation from the internal metal chassis if any -- hence "double insulated". Basically any metal cased item, if it's the primary encapsulation, does not qualify for double insulation and requires a ground connection.

Note that the ground issue gets complicated if the chassis ground is needed for RFI shielding. Like for 2-prong computers and laptops, the key aspect is that the wall wart/brick must be isolated from the power cord (which is the transformer), AND normal operation this ground must not be touching the chassis of the computer that you normally touch to work the computer - you must only be touching plastic of the computer.

For your homemade PSU that was meant as a general purpose PSU things get tricky. Ideally your PSU's case is also isolated - if one of the primary/hot wires insulation breaks and touches the chassis you should not get a shock. If you have a plastic case you should be fine, but if it's shared with the GND pin of your output for noise shielding, things can get electrified...

[redwire]

Re: Line filter question

I checked the safety standards and basic insulation hi-pot test is about 1,500VAC for 1 minute.
Double-insulated 3,000VAC, they just doubled the test voltage for ungrounded equipment.
This flushes out any poorly done spacings/clearances or insulation. Also Y-caps have to pass as well, sometimes two in series are used to meet the 3kV requirement.

That cheap chinese laptop brick that failed, it was really bad - Big Clive did a vid on it. Secondary-side inductor touched and arced to the primary-side DC hot heatsink. Fuse was in Neutral (not Line) and did not blow. Traces melted, killed a Microsoft Surface tablet and I think the LCD monitor too. Easily could have killed someone.

Just an example of worst case scenario and a basic hi-pot test would have caught the spacing and insulation fail, if china ever tested their goods for safety.

[Dannyx]

Re: Line filter question

Can't remember right now how TV power supplies without the third PE conductor are arranged (double insulated). I've worked on quite a few of them over the years, but can't recall the arrangement of the primary right now because I never had to dissect the AC side too much - things only failed from the bridge rectifier onward

Although the case is plastic, you still have exposed metal on the connectors you have to take into account. The connectors are secondary (cold) GND on their outer shell (I'd often use them for my meter's negative lead), so they're also tied to chassis GND via the screws (since I'd also use the case for the same purpose). There's a Y cap between primary and secondary GND and the case is not connected to PE because it doesn't have a third prong on the mains inlet. This means there must be some leakage between pri and sec, although it probably still counts as double insulated because it's very low and is up to the standards of safety ?

Side story: I DID kill a TV once and I'm pretty sure it's related to this, at least to some extent. Funnily enough, it was my own TV at home ('twas a Philips ). I went to connect an HDMI lead between my desktop PC and the telly. I connected it to the TV first. When I went ahead and tried to plug the other end into the graphics card, I suddenly felt this massive surge of current through my body ! It was shockingly (pun intended) powerful, especially since it seemed to result from virtually nothing - it's not like I had just touched a live wire ! In fact, I'd go as far as to call it similar to touching live 230v....which I've done quite a few times, despite my young age compared to others' ! Shock aside, now the TV no longer displayed anything on any of the HDMI inputs (can't remember if the tuner still worked), so it was virtually useless. Further more, when I had a peek around the back, I started to realize just how much static must've built up in that one zap, just waiting, BEGGING to be released by a grubby finger The back plastic cover was now covered in dust, and not just regular dust buildup, since it was very clean, but honest to God Lichtenberg patterns formed from airborne dust which was instantly attracted and stuck to the back of the telly ! You wouldn't believe it until you see it, but it's true - too bad I was still dazed and didn't snap a picture. Fortunately, it was still under warranty at this time, so we had its main board replaced....ironically enough, by the service center I ended up working for a few years later and still am to this day (the one I've told you stories about before) . Looking back now, I'm still not sure what caused it. Either simple static build up on my body, or some rather high leakage currents in one of the supplies (TV or PC). The TV, as discussed, had no PE pin and the PC, though it has a PE pin, the outlet didn't, so they were both floating at different GND potentials and when my hand bridged the gap between them *ZAP*.

It's completely beside the point - more of a discussion.

[stj]

Re: Line filter question

tv's are a bitch, you CAN get a shock off the antenna connector etc.

[Dannyx]

Re: Line filter question

I did some tests today: I took a power transformer that outputs 24VAC, enough to power my soldering iron through a bridge rectifier and DC-DC converter to limit it to 24v and measured ACV between the negative (GND) leg of the DC-DC converter's output and PE at the wall socket. I got 12v. If I touch my finger on the GND wire (so the iron's tip), the reading dropped to 0. I then tried clipping the PE prong of the socket to the GND directly, which of course resulted in 0v PE-to-GND. The 12v I was getting when unearthed is probably the primary to secondary "something" of the transformer. Capacitive coupling ? What's it called ?