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Author Topic: brain storm an optimal human safety system for back line  (Read 105608 times)

Mike Sokol

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Re: brain storm an optimal human safety system for back line
« Reply #440 on: February 05, 2016, 03:38:15 pm »

I think they would slide up to one another and the next thing you know there is a little teardrop trailer.

Sort of like a bigger version of how synthesizers are made.
« Last Edit: February 05, 2016, 03:46:24 pm by Mike Sokol »
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #441 on: February 05, 2016, 06:57:13 pm »

Uhmmmm.... Here I am doing exactly that in a video. You can see me standing on the steps of an RV electrified with a hot-skin potential of 120-volts AC using a NCVT to test for a hot ground. Starts around 4:45 or so in the video.

https://www.youtube.com/watch?v=Y8h64X33aKg&list=PLbNmdE7sBb0dt0zyv6ULMeacIcqvxwuNO

Yeah, I have too much fun with this...
Thanx... that's pretty much what I expected...

JR
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #442 on: February 07, 2016, 01:58:23 pm »

Well I just tried the the neon 240V detector and A) the resistor ratio I used doesn't drop the normal 120V enough (only 50%) so it's lighting up even with 120V, and B) it doesn't fit inside that plug... (unless I completely redesign the PCB with a cut out to make room). 

I may just drop this feature for now (well see).   :'(

Next step is to rig up a 500VAC supply to test insulation resistance. Don't try this at home.  :o :o

JR

PS: Yesterday I repaired the OD-1 I blew up with my first attempt to reduce the ground current. Fried two LEDs and the mosfet... working again now....  8)
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Rob Spence

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Re: brain storm an optimal human safety system for back line
« Reply #443 on: February 07, 2016, 05:59:46 pm »

John, I have a Fluke 1503 insulation tester you could borrow if it would help you.


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Tim McCulloch

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Re: brain storm an optimal human safety system for back line
« Reply #444 on: February 07, 2016, 07:17:07 pm »

Well I just tried the the neon 240V detector and A) the resistor ratio I used doesn't drop the normal 120V enough (only 50%) so it's lighting up even with 120V, and B) it doesn't fit inside that plug... (unless I completely redesign the PCB with a cut out to make room). 

I may just drop this feature for now (well see).   :'(

Next step is to rig up a 500VAC supply to test insulation resistance. Don't try this at home.  :o :o

JR

PS: Yesterday I repaired the OD-1 I blew up with my first attempt to reduce the ground current. Fried two LEDs and the mosfet... working again now....  8)

Obligatory topic swerve:  what do you have fermenting whilst you're playing with electricity?
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #445 on: February 07, 2016, 07:19:06 pm »

John, I have a Fluke 1503 insulation tester you could borrow if it would help you.


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I may take you up on that. I'm too cheap to buy one.

UL requires 100M insulation at 500V... I just looked up the Fluke and looks like the perfect tool for the job.

I'll contact you off list, thanx.

=======

I just finished my jury rigged DIY insulation test and my test results were not definitively concise.

From the attached picture I used 4x mains transformers I had laying around, the voltage doesn't much matter.  I connect mains voltage to the primary of one, then wire all the secondaries in parallel, so the first one drives the other three. Last, I stack the primaries on top of the first one, making a kind of auto-former that should deliver 4x mains voltage.

I measure 444V at the output so close enough for government work.

Part 2 I added a 10M resistor in series with this voltage output so I can measure the drop across it to impute my insulation resistance as a voltage divider with the 10M. But for the bad news my Rat Shack meter exhibits a roughly 10M input impedance, not bad for a 15 year old $25 meter, but my no load test voltage measurement is already scrubbing off about half my test voltage (220V).

Part 3, In theory, I can measure the drop with the OD-1 being probed (one lead at a time) and then calculate a resistance in parallel with the meter's 10M.

OK, I got results and they come in right around 100M but now I'm already testing the OD-1 at less than 1/2 the proscribed test voltage, and trying to parse out a resistance that is 20x my source resistance (5M) so not very accurate.

The good news is no smoke was released, and I didn't kill myself... but I can't stick a fork in this spec yet... Since I have a 100M resistor in series with my probe input it is hard to image resistance ever being less than that.. but this is all about empirical measurement, not my speculation.   

I need to soak this in beer over night for other angles of attack...

I expect my scope's 10x probe is higher input impedance (100M?)  than my rat shack meter but I will need to be careful about how I ground it since my 500V supply is not isolated from the mains. I guess I could add another transformer to my rig and completely float the 500V.

DON'T TRY THIS AT HOME... danger Will Robinson.

I'll count this as a half step forward, it clearly didn't fail... just didn't pass with a fat margin of certainty.

JR
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #446 on: February 07, 2016, 07:21:41 pm »

Obligatory topic swerve:  what do you have fermenting whilst you're playing with electricity?
Johnny Stout,,, but I don't partake of the hopped refreshment while messing with 450VAC on the bench...

Finished with the High Voltage bench for now, so Johnny beer it is.

JR

[edit] I revisited using VOM in current range and measured between 7 and 11 uA... on paper calculates to 40-60 Meg so < 100M.  :-\   Not sure I can trust that measurement.  [/edit]

« Last Edit: February 08, 2016, 07:21:12 pm by John Roberts {JR} »
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Rob Spence

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Re: brain storm an optimal human safety system for back line
« Reply #447 on: February 08, 2016, 11:14:45 pm »

I may take you up on that. I'm too cheap to buy one.

UL requires 100M insulation at 500V... I just looked up the Fluke and looks like the perfect tool for the job.

I'll contact you off list, thanx.

=======

I just finished my jury rigged DIY insulation test and my test results were not definitively concise.

From the attached picture I used 4x mains transformers I had laying around, the voltage doesn't much matter.  I connect mains voltage to the primary of one, then wire all the secondaries in parallel, so the first one drives the other three. Last, I stack the primaries on top of the first one, making a kind of auto-former that should deliver 4x mains voltage.

I measure 444V at the output so close enough for government work.

Part 2 I added a 10M resistor in series with this voltage output so I can measure the drop across it to impute my insulation resistance as a voltage divider with the 10M. But for the bad news my Rat Shack meter exhibits a roughly 10M input impedance, not bad for a 15 year old $25 meter, but my no load test voltage measurement is already scrubbing off about half my test voltage (220V).

Part 3, In theory, I can measure the drop with the OD-1 being probed (one lead at a time) and then calculate a resistance in parallel with the meter's 10M.

OK, I got results and they come in right around 100M but now I'm already testing the OD-1 at less than 1/2 the proscribed test voltage, and trying to parse out a resistance that is 20x my source resistance (5M) so not very accurate.

The good news is no smoke was released, and I didn't kill myself... but I can't stick a fork in this spec yet... Since I have a 100M resistor in series with my probe input it is hard to image resistance ever being less than that.. but this is all about empirical measurement, not my speculation.   

I need to soak this in beer over night for other angles of attack...

I expect my scope's 10x probe is higher input impedance (100M?)  than my rat shack meter but I will need to be careful about how I ground it since my 500V supply is not isolated from the mains. I guess I could add another transformer to my rig and completely float the 500V.

DON'T TRY THIS AT HOME... danger Will Robinson.

I'll count this as a half step forward, it clearly didn't fail... just didn't pass with a fat margin of certainty.

JR

Tester is on the way. While it can be dangerous too , not so much as the diy rig 😀


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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #448 on: February 11, 2016, 02:26:05 pm »

Thanks to Rob I now have a reliable and safer way to measure insulation resistance... The interesting thing is his proper (FLUKE) tester confirmed my crude estimate of 60M, so kinda good/bad news.  ???

Digging a little deeper there are voltage issues with small SMD resistors (my parts are only rated for something like 50V.

I can find a single SMD resistor that handles 600V but it cost $0.70 in thousands several dollars in small quantity, so i think I will cover that base with two $0.07 resistors in series. Looks like one more cut of PCB to fit in the extra parts.

Just for chuckles I stacked up two of my small 100M resistors in series, and confirm that my probe delivers  160M of insulation resistance at 500V so that is a PASS... and it still works with 160M (probably 200M at low voltage) in series with input... for production I'll probably target closer to 100M but comfortably above.

Another step closer... This would have been much more expensive for me if UL tested and found this. So all good and thanks again to Rob for the loan... nothing like using the right tool for the job.  8)

JR
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #449 on: February 18, 2016, 12:30:13 pm »

I just ordered what should be my final prototype PCB (from China).

I have fixed all known issues, and bailed on the 240V indication (not enough room).

I fixed one problem, that in hindsight I am not sure I should fix.

When testing a RPBG wired GFCI outlet (with ground bootstrap to the input side of the GFCI) the combined current of red ground hot fault LED + the normal ground present green LED, would equal more than 5mA and trip the GFCI. I can reduce the current of both so it can indicate RPBG without tripping the GFCI, but I am not sure that is necessary or even desirable. If the outlet tester trips the GFCI that should be a good indication that something is wrong.

My earlier version would trip GFCI just from the ground LED but that is now fixed (UL spec's that ground current to be less than 2mA so well below the 5mA trip current by itself). What I am debating now is should the OD-1 indicate properly with RPBG wired GFCI or just trip the GFCI?  My preference now is leaning toward trip it. The red and yellow LEDs flash momentarily before it trips...

This is just a matter of using different resistor values so i can make this decision later, but I would like to ask this well informed interest group for preferences??   

Trip or not trip a RPBG wired GFCI... ? (these should be pretty rare).

JR
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Re: brain storm an optimal human safety system for back line
« Reply #449 on: February 18, 2016, 12:30:13 pm »


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