modified GFCI

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JR.
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Re: modified GFCI

Post by JR. » Mon Nov 23, 2015 7:15 pm

OD1.png
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Just finished my 3rd cut layout... No jumpers and no vias, a single sided design.

I upgraded the diodes and mosfets to 400V with two in series for negative swings...

After i build a few I can see how they like my 480V test...

JR

PS added one more feature, if outlet voltage is 240V a neon lamp lights up,

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JR.
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Re: modified GFCI

Post by JR. » Sun Dec 06, 2015 2:45 pm

OD1trim.png
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Got Rev 3 working,,, it required a few minor circuit tweaks to not trip the GFCI, from the ground LED current.

Shown in the picture is a test outlet that I intentionally miswired RPBG (reverse polarity bootleg ground) where neutral and ground are both hot and line is cold.

On the left the blue LED indicates power present and the green LED indicates a ground connection is detected (even though it's bootleg).

The three LEDs on the right indicate which outlet leads are energized. In this case of RPBG fault both the neutral (yellow) and ground (red) LEDs are lit, indicating the two faults.

The commercial outlet tester plugged into the top outlet is dumb and happy, saying the RPBG wiring is good. (it clearly isn't) :oops:

Danger Will Robinson.

That circuit board fits inside the clear plastic plug housing and you touch the screw that holds the housing together to sample outlet voltages.

JR

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JR.
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don't try this at home

Post by JR. » Tue Feb 09, 2016 5:09 pm

To continue development of my outlet tester, I need to pass a 100M at 500V insulation resistance test..
highV.jpg
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To get close to 500V I rigged up 4 power transformers,,, I connected all the secondaries together in parallel, drove one primary with 120V and then stacked the other three on top of the first like an autoformer. It makes about 444 voltage which is close. In the picture you see a 10M series resistance but my VOM is only about 10M input Z so half the voltage is gone and ability to parse 100M from 5M source impedance isn't great.

Changing to current mode I can drive the device being tested with closer too the required voltage, but not sure I trust the results... I calc 40-60M which doesn't seem right due to 100M input R.

I friend is lending me a real Fluke insulation meter so when that arrives I should be able to make a real measurement..

=======
The good news is that banging the input with almost 450V didn't break it.. still works... but I used 400V parts inside and they shouldn't ever see close to the full test voltage across them.

JR

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JR.
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Re: modified GFCI

Post by JR. » Sat Feb 13, 2016 4:19 pm

Interesting... So much of my education in electronics is discovering what didn't work, and now I understand what was going on.

My crude Hi V insulation test was actually accurate enough to confirm that my nominal 100M resistor was not behaving. The real deal Fluke insulation tester confirmed my 60M impedance. :oops:

Like usual when something doesn't work you go back and read the instructions. The data sheet for the resistors suggest a working voltage more like 50V than 500V :o :o no wonder it wasn't 100M+. Apparently with SMD resistors there is a relationship between size and working voltage besides the obvious power dissipation, apparently something about the process and geometry.

I also notice an X working voltage a 2x overload voltage and in some cases a 2.5x dielectric breakdown voltage.

I found some SMD resistors rated for 600V but they were larger and much more expensive ($0.70 in quantity), so no deal. Even using through hole resistors were expensive at 100M

JR

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mediatechnology
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Re: modified GFCI

Post by mediatechnology » Sun Feb 14, 2016 6:15 pm

Apparently with SMD resistors there is a relationship between size and working voltage besides the obvious power dissipation, apparently something about the process and geometry.
Yeah, they're small as hell and not to be used at vacuum tube voltages due to flash-over.
Same reason you don't want to be under a transmission line when a grass fire is burning.
High voltage and carbon are two things I never like to see together LOL.

It's real easy to over-estimate SMT resistors.
I remember one high in-rush current application where, when the On button was pushed, an 0603 resistor glowed like a small lamp for a short duration.
The standby current was minuscule but the capacitor that resistor was charging was for all practical purposes, for a short time, a dead short.
A leaded 0.25W carbon film resistor would have gone unnoticed at turn-on.

I don't know if they have HV/high-value but have you looked at MELF resistors?
They're good for high peak current applications.

You might have to "breakdown" (pun intended) and use a leaded part.

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JR.
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Re: modified GFCI

Post by JR. » Sun Feb 14, 2016 10:16 pm

The problem is not flash over at only 500V, or heat dissipation, but something about the very small geometry technology...

I looked at pricing for through-hole parts and at 100M they are a little exotic too... and not any cheaper than a specialty (600V) SMD. Pretty much same price so not worth the bother. I'm too cheap to spend $0.70 for any resistor in high volume, so my plan B or plan C for "cheap", is to use two in series that add up to > 100M and between them offer 400V operating voltage (200V+200V) and 800V overload (400V+400V). I understand the hypothetical that if they don't share equally one could over-voltage, but the parts I measured drop resistance at higher voltage, so should share nicely, in series. 8-)

FWIW my 100M-50V technology part only drops down to 60M @ 500V so while it fails UL insulation resistance, it doesn't catch fire or even release smoke.

The bigger parts to get up to handling hundreds of volts takes up more PCB real estate (2012s) than the former small parts.

It's nice to still be learning new stuff at my advanced age and crustyness. :lol:

JR

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JR.
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Re: modified GFCI

Post by JR. » Wed Mar 16, 2016 8:13 pm

I have decided to not impose my engineering judgement on UL... While I absolutely believe 2x 400V max resistors in series will work fine at 500V, I do not trust UL to accept my judgement. :o

I have sourced a proper 600V resistor in 2012 package but is costs >$0.70 in quantity. This may be a quirk of distribution since 100M resistors are not stocked very deep, I can buy a 600V 100M resistor in 1W package for only $0.14 in quantity... The 2512 1W resistor is huge on my 1" round PCB but I like the price. (Did I mention I'm cheap?)

The second company I was talking to about partnering on this bailed... so I may have to submit it to UL for approval myself. I'm not looking forward to that (did I mention I am cheap?)
=====
I have set up a web page to tell my OD-1 outlet tester story. http://circularscience.com/home/terms-a ... tions/od-1 Hopefully I can use this to explain why I think this is important. Share with anybody you know who might have interest.

JR

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Re: modified GFCI

Post by emrr » Thu Mar 17, 2016 8:37 am

Thanks JR, got it marked.
Best,

Doug Williams
Electromagnetic Radiation Recorders

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JR.
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Re: modified GFCI

Post by JR. » Tue Mar 22, 2016 5:25 pm

OD1pcb.jpg
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Here's a picture of the latest layout with a 1W resistor in series with touch contact. I stuck a 1/4W resistor layout in the middle of it that 1W (just above the middle hole) I can use if I find the 1/4W for the right price... A 1W resistor should never cost 1/5 the price of a 1/4 W resistor all else equal.

JR

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JR.
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Re: modified GFCI

Post by JR. » Sun May 22, 2016 6:36 pm

RPBG_trim.jpg
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I have just finished one more generation (hopefully the last) of my outlet tester... I hand soldered 4 PCB this weekend with 28 SMD parts on each... I am too f'n old for hand popping SMD. :lol: I generally use two layers of magnification, but to read the cathode marks on the small diodes I had to use a 3rd magnifying lens in series with the other two.

In the picture I show my outlet tester correctly catching a RPBG (reverse polarity bootleg ground) mis-wired outlet that the commercial 3 -lamp tester thinks is good. :oops: :oops: The red LED on my tester is saying danger the safety ground is hot, there is also a yellow LED warning that neutral is hot (not very dangerous by itself).

I figured out a way to get the touch probe input impedance (insulation resistance) even higher. I now read more than 550M @ 500V which is off-scale high for the Fluke insulation test equipment.

JR

PS: I updated my OD-1 webpage http://circularscience.com/home/terms-a ... tions/od-1

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