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Author Topic: 3-light tester RPBG upgrade  (Read 31299 times)

John Roberts {JR}

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Re: 3-light tester RPBG upgrade
« Reply #60 on: February 27, 2015, 09:48:34 AM »

If the neon bulb layout works well enough but we want more brightness,
My brightness concern is when neon lamps are connected to each other but the common lead is not probed, so we effectively have a voltage divider. This suggests the line lamp will get >60VAC and the ground-neutral lamps will get <60VAC. Some neon lamps may not like <60V.
Quote
it would be simple enough to use each neon bulb ito trigger a photo-transistor which in turn would drive an LED. That would give you many hundreds of volts of isolation on that side of the circuit, and the ballast resistors could be high enough to reduce touch plate "shock" current to sub-milliamp levels if we want.
My concern is:

A) wimpy indication when contact not touched (this all lamps on "idle" indication confirms lamps and tester are functional,  power and ground are present). 

B) ghost or phantom leakage currents in a floating ground lead (I've measured fractions of a mA) might be enough to illuminate a neon lamp. (Ghost voltage could be high enough even if ghost current is low. Lower impedance lamp circuitry could absorb ghost currents without false indications).

Of course I have yet to prove that my buffer idea even works. For RPBG connection my buffer PS is swinging 120VAC so buffer may saturate at extremes. This could impact display quality, input impedance would still be the input resistance so safe

Of course I still like the KISS neon lamps too. The ghost issue may be manageable with some shunt resistance, while that increases potential touch pad current during a fault (RPBG) condition.

JR

PS: I don't know if there are any special concerns about the frequency of neon light to effectively excite opto-osolators. Apparently there is an old classic guitar effect that used a neon lamp and LDR so perhaps light is just light. My inner engineer is channeling Missouri, wanting to be shown that specific components work together but this is not important. Normal mode brightness is not my concern.   

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Mike Sokol

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Re: 3-light tester RPBG upgrade
« Reply #61 on: February 27, 2015, 10:03:41 AM »

My brightness concern is when neon lamps are connected to each other but the common lead is not probed, so we effectively have a voltage divider. This suggests the line lamp will get >60VAC and the ground-neutral lamps will get <60VAC.

If there is too much cross-talk between the bulbs, my plan would be to add diodes in series with the ballast resistors which should stop the back-flow current you're referring to. Of course, only one side to the neon bulbs will light since it's only seeing half of the AC cycle. 

John Roberts {JR}

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Re: 3-light tester RPBG upgrade
« Reply #62 on: February 27, 2015, 10:44:16 AM »

If there is too much cross-talk between the bulbs, my plan would be to add diodes in series with the ballast resistors which should stop the back-flow current you're referring to. Of course, only one side to the neon bulbs will light since it's only seeing half of the AC cycle.

You will notice when I don't have parts so I can melt solder, I spend too much time over thinking stuff.

Yes, steering diodes will prevent lighting at idle. What I like about a lower voltage lamp system is that they can serve dual purpose, to indicate power is present, ground is connected, and that the tester lamps are all good.

I think I can overcome my frustration about not being able to bench test this. IIRC Some hi-efficiency LEDs are visible down to low single digit mA range. So I could make my LED based tester, scaled down to a couple mA without the buffer.

No more excuses, if you don't hear a report back from me, it means I stuck my fingers in an outlet.  ;D

JR
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Mike Sokol

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Re: 3-light tester RPBG upgrade
« Reply #63 on: February 27, 2015, 11:41:16 AM »

IIRC Some hi-efficiency LEDs are visible down to low single digit mA range. So I could make my LED based tester, scaled down to a couple mA without the buffer.

I think you might be right. There's a variety of low-current LEDs rated for 2mA current draw at full power. That's right in the range you're looking for.

http://www.vishay.com/leds/low-current/
« Last Edit: February 27, 2015, 11:47:12 AM by Mike Sokol »
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Mike Sokol

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Re: 3-light tester RPBG upgrade
« Reply #64 on: February 27, 2015, 11:49:49 AM »

I think you might be right. There's a variety of low-current LEDs rated for 2mA current draw at full power. That's right in the range you're looking for.

http://www.vishay.com/leds/low-current/

If I add 100K build-out resistors and steering diodes these might just work in place of Neon bulbs for my 6-light tester. I'll have to compare brightness.

John Roberts {JR}

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Re: 3-light tester RPBG upgrade
« Reply #65 on: February 27, 2015, 12:22:54 PM »

If I add 100K build-out resistors and steering diodes these might just work in place of Neon bulbs for my 6-light tester. I'll have to compare brightness.

Good news bad news...  Using my decades old LEDs I had laying around, they work as expected to confirm power present and ground present (on my bootleg rig), but.... even running <2 mA touching the common node, does not turn off the ground/neutral LEDs. Even if I lick my fingers I am not enough of a current sink to shunt off the other LEDs.

Need to retest with steering diodes in series with the LEDs. To see if I can get an indication from touching without the shunt path to other lamps.

I can confirm the power present and ground connection with additional LEDs, but would lose the lamp self test feature.

JR
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John Roberts {JR}

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Re: 3-light tester RPBG upgrade
« Reply #66 on: February 27, 2015, 12:46:50 PM »

OK, success kind of. Using my decades old LEDs, and 2mA to real ground resistor current limit, with steering diodes I can just see a very slight glow in my neutral LED.... Which confirms what I already know, that this outlet is miswired.

perhaps I need to repeat with just a singer cap in series sized for more current worst case....

JR

[edit] bummer now I can't recreate that first weak result.

Another concern about using a human for the touch reference, the human is probably more like a capacitor than a resistor (actually both depending on clothes-footwear). With steering diodes, the cap portion would probably get charged up to voltage and stop drawing current.

I am back to thinking buffer, but need to get some modern LEDs and buy some damn parts....

OK according to WWW human body is only 100-200pF so 13M Ohm at 60 Hz... Resistance can be lower if body is grounded  but that can not be counted on not to mention capacitance needs to be relative to something too.

I'm leaning toward MOSFET buffer now... 

With my VOM I measure 40 VAC using my body as a ground, so my body impedance to ground (neutral) is 2x the VOM circuitry input impedance.

JR  [/edit]
« Last Edit: February 27, 2015, 01:37:41 PM by John Roberts {JR} »
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Stephen Swaffer

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Re: 3-light tester RPBG upgrade
« Reply #67 on: February 27, 2015, 04:09:27 PM »

FWIW, I routinely wear EH rated footwear-don't count on it ever, but I will rarely be "grounded" when using a tester.

JR, it seems a 2 light tester should work just fine in your home (IF your receptacles are polarized-if not polaarized then testing is probably pointless).  Just thought I'd give you something else to consider:)!
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Mike Sokol

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Re: 3-light tester RPBG upgrade
« Reply #68 on: February 27, 2015, 04:14:59 PM »

FWIW, I routinely wear EH rated footwear-don't count on it ever, but I will rarely be "grounded" when using a tester.

Steve, the 4th "hot-ground" bulb on my test last week was done standing on a wood floor in timberline boots, so I wasn't grounded but still was able to light the bulb via my capacitive connection to the earth. Of course, none of these proposed testers are perfect, but should at least warn the technician or electrician that something is wrong that requires further testing.

Mike Sokol

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Re: 3-light tester RPBG upgrade
« Reply #69 on: February 27, 2015, 06:24:58 PM »

Just received my Neon handle screwdriver testers from China. IIRC the cost was less than $2 each including shipping. As you can see, they actually work pretty well in a dimly lit room, but you wouldn't be able to see the Neon bulb in a bright room or outside in the sun. Still, an interesting test and confirmation of an old-school voltage tester.

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Re: 3-light tester RPBG upgrade
« Reply #69 on: February 27, 2015, 06:24:58 PM »


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