Neon Beer Sign -Shocking-

[dave*99]

I have a very old neon beer sign that works well - just be careful touching it. The orange tube around the sign perimeter sits in front of a metalized plastic reflector. There is a gold colored metallization to reflect the light. It's spotty but mostly intact. If you touch that reflector, you receive a mild continuous electric shock.

I carefully cleaned the reflector and tubes. Saw no improvement.
The ground wire to power plug is intact. It has good continuity to the sign frame and transformer housing.
The transformer is intact, the high voltage leads are in good shape. I can touch all the white tubing with no issue.
I can also touch the orange tube without incident. Just not the reflector behind it.

On startup, I hear occasional faint arcing between the orange tube and the gold reflector. It stops after about a minute.

I suspect the high voltage plasma in the tube is coupling to the metalized reflector.

The sign is plugged into a GFCI, and it does not trip. I tried 3 outlets on 3 different GFCI's (all less than a year old)
I suspect the transformer provides enough isolation therefore the GFCI does not trip. I measured about 200 VAC between the reflector and ground. High voltage - but no current capacity.

Any thoughts on how to reduce the shock hazard? I already figured out that if I don't touch it, I don't get a shock......

 

[Metal-Marc]

"Secondary Mid-Point grounded"

Picture of plug? Should be a three prong plug.
Check ground continuity.
Check proper ground at wall receptacle.

 

[wyliesdiesels]

You should have continuity between the secondary mid-point and the ground pin on the plug... if not then there is a wiring issue inside the transformer

 

[dave*99]

It has a 3 prong plug.
I verified continuity between the ground pin and the transformer case and the metal frame.
The outlet is properly grounded.
I checked the mid-point ground. I can't physically get to the mid-point lead from the secondary winding, but I did verify:
The total secondary resistance is 12.8 k ohm
From 1 secondary lead to ground is 6.42 k ohm
From the other secondary lead to ground is 6.38 k ohm
It seems the mid-point ground is intact.

 

[nadogail]

Is the sign reflector grounded?

 

[dave*99]

Is the sign reflector grounded?

There are at least 6 screws holding it to the grounded frame. But I don’t think the metalization is solid enough to call it grounded

 

[kbuhagiar]

Just curious - are you able to measure any current/voltage going from the reflector to ground?

If so, how much?

 

[dave*99]

Yes I measured about 200vac from reflector to ground. That’s with a high impedance voltmeter. I have not tried a load on that measurement. I think I will give it a try.

 

[b-boy]

I've restored a bunch of these things.

Your best bet is to pickup a new transformer. If it is buzzing or getting hot, you should replace the device.

You can get them for about $30-$40. They are about 1/2 the size of the old ones, and weigh about 70% less.

You'll need to do a little minor surgery to attach it to the sign, but that fixes 99% of problems with these. I've opened up a few transformers that were black on the inside from running super-hot. It's a bit scary to see one of those.

Are there rubber boots where the glass pieces connect? Any tears in them? They can be replaced. Maybe a connecting wire is broken or loose and you're getting some arcing?

If it's not the transformer, you're probably out of luck. However, there are sites that specialize in vintage replacement glass and other parts.

One idea - They make a neon tube tester that will light up a tube if it's good. They're pretty cheap on Amazon. It would be interesting to see if you still get a shock while using one of these. It would probably tell you whether the issue lies with the tubes.

 

[larry4406]

 

[dave*99]

Transformer is not buzzing or hot - but I'm not opposed to replacing it.

I put a 3" long piece of aluminum foil on the backside of the reflector and grounded it with a clip lead.. That seemed to eliminate the shocks. I'm considering using copper foil with an adhesive to form a ground plane on the back of the reflector.

The metallization on the reflector is spotty. I get the feeling if it was in better shape, the potential on it would not develop. The back side ground plane would be a substitute and the test piece seemed to work.

 

[walta]

There are at least 6 screws holding it to the grounded frame. But I don’t think the metalization is solid enough to call it grounded

I would add a thin bare copper wire to the back of the reflector.

 

[dogdog]

just go get another neon transformer with the same VA and secondary voltage ?

 

[dave*99]

just go get another neon transformer with the same VA and secondary voltage ?

I don’t think the transformer is the issue. I can touch all of the glass tube and the grounded frame with no issue. The GFCI is not tripping.

The metallized reflector has gaps in the metallization. I think these metal islands are energized because the high electric field from the energized neon gas is coupling to the metal.

I have some copper foil that has a conductive pressure sensitive adhesive on it.
This product is made for shielding applications.

I’m going to try adding a grounded shielding strip on the back of the reflector to bleed off the charge and make all the islands be at the same potential (grounded).

We shall see……

 

[wyliesdiesels]

EDIT: capacitive coupling

 

[dave*99]

Induced currents

Technically it's capacitive coupling through the electric field. Induction would be through magnetic field. There are high electric fields from the excited neon gas.

 

[wyliesdiesels]

Technically it's capacitive coupling through the electric field. Induction would be through magnetic field. There are high electric fields from the excited neon gas.

oh yeah duh ... need some more coffee

 

[dave*99]

So here is an update - I think it's fixed.

As I mentioned, the metallization on the reflector is in poor condition - that may lead to small sections being energized through capacitive coupling.



I applied product called CHO-FOIL to the back of the reflector. CHO-FOIL is an EMI shielding foil with a conductive pressure sensitive adhesive. I ran it around the frame and also hit all the screws that go into the grounded metal frame of the sign.



Here is what that looks like.



There are no longer any arcing sounds and no shocks when I touch the reflector.
Now I will have a beer

 

[wyliesdiesels]

awesome!!