Neon kicking my butt!

[michaeljmeuse]

Fist off, happy 4th everyone. Here's the problem i have.
There are four neon tubes. Three of them are six feet long and the last one is two feet long.
Im using a 12.5 KV transformer. The indicator light tells me that everything is hooked up properly.
When I hook all the tubes up, i can only get one to light up, the other tubes are dim.
I've tested each tube individually and they all light up when hooked up by themselves.
I have a good ground, voltage is where it should be, and every tube works on its own. Is my transformer not big enough?

This was a service call so I have no idea about what voltage these tubes take to ignite the gas. This is kicking my butt. I can not figure this out. Last neon service call i'll ever take..hahaha. Any help would be great. I know there is probablly some something i left out. If you need any other info, let me know

 

[mgookin]

Absent any experienced neon people interjecting, I'll suggest those gas bulbs have a finite lifespan like any other gas bulb. Can you have them charged by a neon shop?

 

[michaeljmeuse]

Thanks for the reply. The owner of the business said these tubes are brand new, but you know how customers can be sometimes when it comes to getting info out of them. I dont think they need to be charged, since i can get each one to come on when i hook them up individually, but with lack of neon experience, that may not mean the lamps are charged properly. This is driving me nuts :slaphead:

 

[kwired]

No real neon lamp experience here either, but it makes sense that if they all light when individually supplied but they fail to light when all are applied together that maybe the source doesn't have the capacity to run all of them.

Do you know the load rating of each tube as well as the output rating of the source?

 

[michaeljmeuse]

Kwired, not sure of the required voltage. Its a strange situation. This resturaunt is a small chain and provided these lamps and a 4.5 KV transformer. The owner said the 4.5 KV transformer worked on the other resturaunts. I have a hard time believing that because a basic neon, bud lite sign, for example in a bar uses a 4.5 KV transformer. There is no info on these tubes. I purchased a 12.5 KV transformer thinking it would resolve it, but it did not. Like i said, each tube works by itself, which leads me to believe it the transformer. Im guessing i could bump it to a 40 KV.. if that does not work, i can always make a bad ass jacobs ladder out of it

 

[kwired]

Kwired, not sure of the required voltage. Its a strange situation. This resturaunt is a small chain and provided these lamps and a 4.5 KV transformer. The owner said the 4.5 KV transformer worked on the other resturaunts. I have a hard time believing that because a basic neon, bud lite sign, for example in a bar uses a 4.5 KV transformer. There is no info on these tubes. I purchased a 12.5 KV transformer thinking it would resolve it, but it did not. Like i said, each tube works by itself, which leads me to believe it the transformer. Im guessing i could bump it to a 40 KV.. if that does not work, i can always make a bad ass jacobs ladder out of it

Not only do you need to know what voltage is needed to light the lamps but you also need to know the volt-amps necessary for the source to be able to provide.

Secondary amps is going to be low but VA is still VA, and if your supply can't deliver enough VA you are not going to get the desired result.

I think you need to talk to someone that builds neon signs, if nobody on the forum here with experience in this area doesn't chime in.

I don't know anything about how to size tubes and supplies as my involvement with these has mostly just been running the supply circuit to such items.

 

[ELA]

no direct experience either.
Found this interesting and may be helpful:

http://www.franceformer.com/products-neon/FAQ/NeonFAQ.html

 

[GoldDigger]

Not only do you need to know what voltage is needed to light the lamps but you also need to know the volt-amps necessary for the source to be able to provide.

Secondary amps is going to be low but VA is still VA, and if your supply can't deliver enough VA you are not going to get the desired result.

I think you need to talk to someone that builds neon signs, if nobody on the forum here with experience in this area doesn't chime in.

I don't know anything about how to size tubes and supplies as my involvement with these has mostly just been running the supply circuit to such items.

If the neon tubes are run in series (the normal configuration for a sign), then they will all be pulling the same current even though they have different lengths and voltage drops in use (the working voltage can vary from one lamp to another based on fill pressure and temperature among other things.) The same current value should result in roughly the same brightness per inch of tube, as long as the manufacturer chose the phosphors correctly.

If somebody incorrectly wired the tubes in parallel, then only one of them will ever see full operating voltage unless there is a separate resistive or magnetic ballast for each tube.
Were the internal connections within the sign already made when it came from the sign shop, or did somebody complete the wiring in the field? Or when replacing the tubes in the field?

If you cannot put the tubes in series, then IMHO you will need a separate sign transformer for each one. Each transformer should be current limiting and rated by output current as well as by max voltage.

PS: Getting a higher rated transformer, in terms of KVA not KW, may be causing too much current to be fed to the sign, burning out the tubes prematurely.

PPS: The Neon FAQ information ELA found is very good, but does not address the issue of multi-tube fixtures, except peripherally in its discussion of midpoint wired system and transformers.

PPPS: Happy Fifth! Yesterday was great for me too.

 

[Anthony Cox]

Wiki has some information on Neon Signs That might Help

Wiki has some information on Neon Signs That might Help

http://en.wikipedia.org/wiki/Neon_sign

 

[kwired]

If the neon tubes are run in series (the normal configuration for a sign), then they will all be pulling the same current even though they have different lengths and voltage drops in use (the working voltage can vary from one lamp to another based on fill pressure and temperature among other things.) The same current value should result in roughly the same brightness per inch of tube, as long as the manufacturer chose the phosphors correctly.

If somebody incorrectly wired the tubes in parallel, then only one of them will ever see full operating voltage unless there is a separate resistive or magnetic ballast for each tube.
Were the internal connections within the sign already made when it came from the sign shop, or did somebody complete the wiring in the field? Or when replacing the tubes in the field?

If you cannot put the tubes in series, then IMHO you will need a separate sign transformer for each one. Each transformer should be current limiting and rated by output current as well as by max voltage.

PS: Getting a higher rated transformer, in terms of KVA not KW, may be causing too much current to be fed to the sign, burning out the tubes prematurely.

PPS: The Neon FAQ information ELA found is very good, but does not address the issue of multi-tube fixtures, except peripherally in its discussion of midpoint wired system and transformers.

PPPS: Happy Fifth! Yesterday was great for me too.

As I have said, I have no background in neon tubing, but I do not understand your comment on why only one will see full operating voltage when installed in parallel. I can understand they may need to be connected in series, but I would think if they are to be in series then you must have a specific range of length of tubing for a specific power transformer for optimal performance. Too little length and the tubing maybe will be overpowered and have less life, too much tubing and you will not get the desired brightness or even at a certain length no illumination at all.

 

[GoldDigger]

but I do not understand your comment on why only one will see full operating voltage when installed in parallel.

They will all see the same voltage, but the correct operating voltage will be different for each separate tube. It would have been clearer if I had said that at most one tube would see its correct operating voltage. And the first tube to fire when power is applied will drop the output voltage immediately to the operating range, possibly before the other, lower voltage, tubes have fired. A neon tube does not have filaments or mercury vaporization like a standard fluorescent tube, so the arc must be started by applying a high enough overvoltage. But like a fluorescent tube, it is a negative resistance device, in which heating from the arc reduces the voltage from end to end as the current increases.
The key point remains that the sign transformer's magnetic circuit is designed for constant current output from the secondary. A multi-tube fluorescent lamp ballast provides individual-tube current limiting, but does not have the added complication of transforming the line voltage to a very high load voltage.

 

[kwired]

And the first tube to fire when power is applied will drop the output voltage immediately to the operating range, possibly before the other, lower voltage, tubes have fired.

Now you have described exactly what the OP says is happening. Connecting each tube individually would make sense that they all work, but all in parallel would only light the first one to illuminate, then applied voltage drops enough the others will not light.

Placing them in series means all or none will light.

Thanks for some of the info you have provided.

 

[gar]

130706-1456 EDT

A neon tube is a gaseous discharge type lamp. This is somewhat of a constant voltage load with the voltage drop being defined by the cathode and anode fall potentials, and the voltage drop across the ionized gas. These must be operated with a current limiting source.

There are two broad classes of gaseous conduction. These are arc discharge with a low voltage drop and high current, and glow discharge with a much higher voltage drop, and lower current.

Arc welding falls in the arc discharge category. Neon bulbs, neon tubes, automotive spark plugs, fluorescent bulbs fall in the glow discharge category. Any of these loads must have a current limiting source. In general you can not parallel any of these loads without individual current limiting.

See "Fundamentals of Engineering Electronics", William G. Dow, 1952, John Wiley, Chapter 15 for theory on gaseous discharge.

Almost certainly the tubes are being paralleled without individual current limiting as others have said.

.

 

[beanland]

Neon Xfmr is almost constant current

Neon Xfmr is almost constant current

If I remember right, a neon transformer is high voltage but also high impedance meaning that it is almost constant current. If the lamps are in parallel, the voltage developed across the shortest will set the voltage on all of the lamps, too low for the long lamps. If wired in series, as long as the transformer has adequate voltage and is rated for the lamp current, all lamps will see the same current and the voltage that will develop across each lamps will be according to length (and gas pressure and temperature).

A high voltage in series with a high impedance is a constant current source over a narrow range of loads.

 

[GoldDigger]

If I remember right, a neon transformer is high voltage but also high impedance meaning that it is almost constant current. If the lamps are in parallel, the voltage developed across the shortest will set the voltage on all of the lamps, too low for the long lamps. If wired in series, as long as the transformer has adequate voltage and is rated for the lamp current, all lamps will see the same current and the voltage that will develop across each lamps will be according to length (and gas pressure and temperature).

A high voltage in series with a high impedance is a constant current source over a narrow range of loads.

But that would dissipate a lot of energy in the transformer if the high impedance were restive. If the high impedance were inductive, it would be behaving much like a fluorescent light ballast. But in the particular case of the neon sign transformer the secondary includes a magnetic shunt (not all of the flux from the primary is coupled to the secondary.) This limits the amount of current available from the secondary winding without creating a large power loss within the transformer.
I believe that at 60Hz it looks like a normal low impedance relatively constant voltage transformer up to the point where the flux limit in the secondary winding causes it to stop coupling effectively to the primary. Closer in behavior to an active current regulator than to a voltage source with effective series impedance.

Anyway, a point which has not been mentioned is that the transformer needs to be sized to the intended sign load in terms of current rather than just selected for voltage output. Installing a higher current transformer, instead of being conservative will be damaging to the sign.

 

[michaeljmeuse]

Thank you guys on the response. You've given me a lot of helpful information. I believe the lamps are wired in series, I will be back to that job this week so I will keep you informed

 

[gar]

130714-2058 EDT

michaeljmeuse:

If the lamps are in series, then the same current flows thru each lamp. If a tube does not glow, then there is essentially no current thru that tube. Since only one tube lights, it is the shortest one, and the other tubes do not glow, then this means the tubes are not in series.

Study the theory of corona, glow, and arc discharges thru a gas.

Don't imagine things that can not happen. Use logical analysis. I do not know what you can expect to find, but they are not in series.

.