Strange Neon. Stays on after being unplugged. Why?

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,130
I have this warm steam vaporizer. It consists of some very simple elements. A power cord that connects to a resistor and a neon lamp (don't know the sorts). The neon lamp and resistor form a series circuit from line to neutral. Parallel to that are two electrodes that sit in water. The water is the heating element in that current passes through the water and generates the steam. This morning I unplugged it. Immediately the steam stopped but the neon lamp continued to glow dimly. It took about 30 seconds to fully extinguish (or to dim so low I couldn't see it). I've never seen a neon lamp do that. Any explanations?

Nothing to be fixed, just asking if anyone else has observed such phenomena.
Neon.png
 
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Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,130
I thought about that. So I pulled the electrodes (the whole head unit) out of the water but the neon continued to glow.

The water is ordinary tap water. It's only treatment is that it is run through a water softener. Otherwise the mineral count is pretty high in the water, something like 400 PPB dissolved minerals (and metals and other junk I'm sure). I have an RO drinking system and I've attempted to use the drinking water with a dissolved mineral count of 12 PPB. The unit would not produce steam. The instructions said to add a pinch of salt to the water. Thereafter it produced steam. I've decided to use ordinary tap water since then.

[edit] I opened the head unit to clean it once. I didn't take note of the resistor value, only that it is there as shown in the illustration. {end edit}
 

kubeek

Joined Sep 20, 2005
5,678
I could imagine the bubbles of ionized oxygen and hydrogen staying at the electrodes just after the halfwave is interrupted, and then recombining after you disconnect it to regain electron balance.
 

nsaspook

Joined Aug 27, 2009
6,900
I thought about that. So I pulled the electrodes (the whole head unit) out of the water but the neon continued to glow.

The water is ordinary tap water. It's only treatment is that it is run through a water softener. Otherwise the mineral count is pretty high in the water, something like 400 PPB dissolved minerals (and metals and other junk I'm sure). I have an RO drinking system and I've attempted to use the drinking water with a dissolved mineral count of 12 PPB. The unit would not produce steam. The instructions said to add a pinch of salt to the water. Thereafter it produced steam. I've decided to use ordinary tap water since then.
Then there must be some sort of energy storage system (intentional circuit or not) associated with the neon bulb circuit.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,130
@nsaspook When I cleaned it I thought I'd find a far more complicated circuit. The ONLY thing I saw was as I've drawn. The electrodes are about a half inch in diameter, approximately 4 inches long and they LOOK like they're made of carbon. As I said, I opened it to clean it. Not to investigate the materials used to construct it. I was surprised to see such a simple circuit. No caps, no chips, no logic, no nothing other than a neon and a resistor parallel to the electrodes.
 

AlbertHall

Joined Jun 4, 2014
9,276
I could imagine the bubbles of ionized oxygen and hydrogen staying at the electrodes just after the halfwave is interrupted, and then recombining after you disconnect it to regain electron balance.
That would imply a single electrolytic cell producing something like 70V to light the neon.
 

AlbertHall

Joined Jun 4, 2014
9,276
@kubeek Do you think it would go out if I shorted the plug? If so - could there be a dangerous voltage present at the unplugged plug?
Definitely worth doing the experiment.
You might also measure the voltage there. That might also turn off the neon - they need very, very little current for a visible glow.

You didn't keep any of those everlasting LEDs near it did you?
 

nsaspook

Joined Aug 27, 2009
6,900
@nsaspook When I cleaned it I thought I'd find a far more complicated circuit. The ONLY thing I saw was as I've drawn. The electrodes are about a half inch in diameter, approximately 4 inches long and they LOOK like they're made of carbon. As I said, I opened it to clean it. Not to investigate the materials used to construct it. I was surprised to see such a simple circuit. No caps, no chips, no logic, no nothing other than a neon and a resistor parallel to the electrodes.
I don't mean the lamp circuit. If there is a voltage present across the neon bulb when the unit is unplugged it's in the form of an electric field generated from charge separation somewhere. That source might be you.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,130
It's hard to see in daylight but I can barely see it glowing after I unplug it. I've shorted the two leads of the plug together and the neon did not go out immediately. I'm wondering if the neon glowing is causing the electrodes to heat up and continue to glow after power is removed. As they cool they slowly extinguish.

Keep in mind the vaporizer runs all night. This morning while it was still dark I noticed a distinct glow. Minutes ago when I plugged it in and unplugged it - the lamp did NOT glow after being unplugged. So I plugged it in and let it sit on for about a minute. Then when I pulled the plug it continued to glow briefly, about 15 seconds.

I'm sure none of this is important. Just wondering why a neon lamp would (could) continue to glow after power is interrupted. I've played with neon's and RC circuits to make a relaxation oscillator (I think that's what it's called), but I've never seen neon have an after-glow.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,130
You didn't keep any of those everlasting LEDs near it did you?
No. Surprised you remember that experiment. Guess I do a lot of weird things.

But speaking of LED's, my Christmas tree had an LED go out. The rest of the string continued to glow. When I pulled the bad LED out the whole string went out (half of it actually). Wondering why current can pass through a burned out LED too. But I'm not asking that here.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,130
Are you sure it's really a NE2 type 'neon' bulb?
It's about the right size BUT when I had it open I didn't examine anything particular. Only took note that it is a neon with a resistor in series across mains. I couldn't tell you exactly what sort of neon it is. If memory serves, the resistor is 1/8 watt. Would have to open it again to confirm that though.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,130
@Analog Ground Interesting theory. I don't think there's any color to it other than the typical orange neon glow, and I don't know that I've ever heard of a neon bulb having anything in it that fluoresces; unless the process of electrons jumping from electrode to electrode within the bulb counts as fluorescence. The lens that covers the bulb is green plastic. The WHOLE THING is plastic. The reservoir, the boiler chamber, the head unit. Only things that are not plastic are the cord, the neon, the resistor and the elements that contact the water.

Have to run to an appointment. Will be back in about two hours.
 

SLK001

Joined Nov 29, 2011
1,543
There's no discharge path for the neon. When you unplug it, it retains the charge and slowly bleeds off (as the remaining energy is consumed) until it extinguishes. It is an electrostatic charge that is on the neon and since a neon consumes basically zero current, the surrounding air and the very high impedance paths slowly dissipate the charge.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,130
Thanks @SLK001 Sounds like a reasonable explanation.

@thegamebusterpl the wire is only about 5 feet long. Not much capacitance in that I don't think. And depending on where in the sine wave I unplug it - that capacitance can be anything from zero to max positive or negative. Certainly not enough capacitance to keep a neon lit for 30 seconds or so.
 

Reloadron

Joined Jan 15, 2015
5,114
In the below image is a NE2 lamp.
neon lamps.png

Working from left to right the first image has DC applied and the element on the right inside the bulb is the negative. The center image also has DC applied and the element on the left is negative. The last image on the right has AC applied so note that both elements are glowing or actually only appear that way in the image because the elements are changing which one glows 60 times a second with 60 Hz power or 50 times a second with 50 Hz power. When a neon lamp reaches its "strike" voltage the gas in the envelop is ionized and the lamp is pretty much a short circuit, thus the need for the series resistor. Matter of fact before high voltage zener diodes neon lamps were used as voltage regulators, well neon and other gases.

So here is the question. Once AC power is removed, the vaporizer unplugged, how does the lamp look? One element remains glowing which would infer a DC presence or both elements glowing which would be a presence of AC and if the lamp continues to glow with both elements where is AC coming from?

Ron
 
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