Question DC vs AC hi voltage to power neon gas sign

[dlucks]

I have what i think is a basic question but i've searched and not been able to find an answer. i recently acquired a neon sign that was in storage for a long time. It came with 2 7.5kv 20ma AC output Franceformers. These transformers are loose and not mounted in any enclosure as well as fairly heavy. They were also not connected to the sign. The 4 wires coming from the neon tubes has bare ends on them whereas the leads on the Franceformers required some kind of connection. I took pictures to a local neon shop to see if I could pay to pay to get these done riight so I could safely take the sign to a pinball show. The sign is for a pinball game. The shop owner seemed to be confused when I asked about the difference between AC and DC to power the sign. He said he would just buy brand new DC variable output power supplies which are a lot lighter and would be easier to mount.
First three questions: I read that AC power will light the gas inside the tubes from both sides of the tube because of the alternating current, possibly prolonging the life of the tube. Is this true? Is it desirable to stay with AC?
Does AC provide cause a more uniform glow of the neon light being that it is being "lit" from both ends?
Fourth question: If it doesn't really matter with AC vs DC, if I get a couple lighter DC transformers should I stay with 7.5KV and that current? I measured the current when the lights where lit using a clamp on current meter and one measured about 15 mA and the other measured about 23 mA.
Final question: Presuming I stay with the heavy Francformers, I would like to put proper high voltage connectors on the bare ends in order to have a better connection as well as safer connection. All ends are now stripped wire. I was thinking of going to auto parts store and getting sparkplug boots and finding sparkplug connectors, but is there a better connector to use?

 

[netsol]

if i am understanding you correctly, it is a very simple answer
AC or DC is not like the choice between vanilla or chocolate
you can only power a transformer with AC. dc on a transformer will only give you smoke and a burned up transformer
DC requires a "chop" or driver circuit and power transistors to simulate AC

in short, you need to use what the device is designed for...

 

[dlucks]

Yes, the transformers input is AC 120V. I'm not talking about that though. The question is about the output being 7500V AC, or can a replacement DC 7500V 30ma power supply which are much lighter and only about $40 on amazon. Recommendations welcome as well as any info to correct any misunderstandings I may have about this.

 

[Billct2]

I wouldn't use a $40 transformer off Amazon. But since its your own piece give it a shot.
But no matter what the numbers should match

 

[dlucks]

Thanks for the advice on matching numbers and amazon. Maybe someone can answer my original questions.
I have another neon bar sign that I hooked the franceformers up to. It flicks on but is unable to keep going, I suspect that the voltage is high enough to light it up but the current is not high enough to maintain the plasma. I measured the linear feet of the tubes and adding in the electrical jumps between some of the tubes, I come up with about 21 feet with diameter of around .25 to .5 inches. And there are two different diameters connected to each other. That will be another test.

 

[Billct2]

are you sure the tubes are good

 

[Johnny Best]

Be careful, from my experience AC gives quite a jolt, DC not so much.

 

[dlucks]

are you sure the tubes are good

I presume you are asking about the bar sign tubes because I included a picture of the pinball sign all lit up nicely.
When the bar sign lights up, it lights up quick and bright, all the tubes are lit, then they all flicker at the same time, After adding up the linear feet I chose a power supply that would work and wouldn't break the bank with a purchase. The new one is the same voltage, although I believe it is DC instead of AC, and says 30mA instead of the 20mA on the one I was trying.
I was going to use it to try the bar sign as well as the pinball sign. I'll let you know when I try it out. But I'll still need to use the right HV connectors.
I appreciate all your feedback

 

[dlucks]

Update on retrofitting my Neutron Star sign and getting bar sign to work.
The 7.5kv DC power supply came in and powers both parts of the Neutron Star sign just fine. But only starts the bar sign, which has quite a longer length set of tubes as well as part of the tubes are smaller diameter. After it starts up it very quickly shuts down never to come back on. Probably because it is an electronic DC ballast of some sort whereas the dumb AC transformer will just keep sending 7.5KV AC to the tubes.
So I'm figuring it needs a higher voltage 10kv probably so I've ordered a 10kv 30ma and for grins I decided to also get a 5kv 30ma.
The 5kv arrived yesterday and it is nice and small, unfortunately it is a bare wire supply with bare wires for the 120v ac input. Jamming the bare wires into a receptacle I was pleasantly surprised that both parts of the Neutron Star sign sparked up and stayed lit when I tested each one. I'm running a longer test on it now to see if it will stay lit. One thing I noticed is that when powering the outside lettering I was getting some light from the internal ovals. The HV wires for the lettering run close to the ovals and moving them away from the lobes stopped the parasitic startup.
The size of this power supply changes my needs as I can easily attach this, and one more to the sign and hardwire the HV leads to the tube leads and just add an inline switch. No need to worry about being able to unplug heavy franceformers from the tubes any more when moving the sign.
The 10kv dc power supply will arrive sometime today and then I can try that on the bar sign to see if I can get that working.

 

[JBurton]

. Jamming the bare wires into a receptacle I was pleasantly surprised

Dude, don't do that. Go and find an old lamp, pc power supply, any frigging power cord off almost anything that no longer works, wire nut the leads to this cord (now called a pig tail), and plug it in. There's no point in trying to jam wires into a perfectly good socket, you'll burn up the contacts inside the outlet after a few times.
You're planning to put a kill switch on the primary side (120v) right?
Neon boots are what you need to cover the connections at the tubes, the wire to handle this voltage on neon is referred to as GTO wire. Strip an inch, twist it together at the end of the tube, and slip the boot over.

 

[netsol]

Yes, the transformers input is AC 120V. I'm not talking about that though. The question is about the output being 7500V AC, or can a replacement DC 7500V 30ma power supply which are much lighter and only about $40 on amazon. Recommendations welcome as well as any info to correct any misunderstandings I may have about this.

current must be equal or greater than what you are replacing

sorry i misunderstood the quesiton

 

[dlucks]

current must be equal or greater than what you are replacing

sorry i misunderstood the quesiton

I've a question about current. According to what I've read, the current must be limited in order to not burn out the tubes. Will going from 20mA to 30mA cause the tubes to have a much lower lifespan? Also according to my understanding the AC transformers for neon lights have a shunt in them to prevent over current.
Since the 5kv-30mA power supplies light up the 2 parts of the Neutron Star sign just fine, I've mounted the two on the back of the sign and positioned them so that I can run the leads thru newly drilled holes and directly to the end of the neon tubes. Except for one which I need to extend the leads to get to the tube end.
This gets rid of the 2 7.5KV 20mA heavy transformers and makes the sign much easier to mount and more portable if I need to move it.
All the tubes seem to glow a brighter with the higher current rating of the new power supply and the tubes all seem to be uniformly bright.
Here is a new picture. I need to put a gto sleeve on the extension connection yet.
I'm including a link to some pictures of the actual Atari pinball Neutron Star

Internet Pinball Machine Database: Atari 'Neutron Star'

www.ipdb.org

 

[dlucks]

Still unanswered though is whether AC is better than DC. The theory I understand is that electrons are emitted from one end and traverse through the tube causing the gas inside to emit photons. An AC current will alternate flow of electrons from one side to the other whereas DC will cause electrons to only go in one direction. This emitting of electrons gradually degrades the electrode. An AC current would in general double the lifespan of a neon tube since each end is alternately degrading instead of one end doing all the work. Does reversing the flow repair the degradation?

 

[netsol]

I would think these are no different than any other electronic circuit
it must be powered by a source that exceeds it's needs
the design of the circuit will limit the current draw
NOT ENOUGH current for proper operation can cause damage, but, it should only draw as
much power as it requires

 

[Bobby H]

Neon signs like that need proper ballasts. And they need right type or amount of ballast(s) to specifically match the amount of current the neon tubes need to draw. It's important to know the the thickness of the neon tube and the tube length. One ballast can power only so many feet of neon/argon-filled glass. If you're having to buy new ballasts you need to buy what will match up with the glass properly.

BTW, a ballast or transformer (big clue in the term) converts the safe and familiar Alternating Current into Direct Current.

 

[netsol]

Neon signs like that need proper ballasts. And they need right type or amount of ballast(s) to specifically match the amount of current the neon tubes need to draw. It's important to know the the thickness of the neon tube and the tube length. One ballast can power only so many feet of neon/argon-filled glass. If you're having to buy new ballasts you need to buy what will match up with the glass properly.

BTW, a ballast or transformer (big clue in the term) converts the safe and familiar Alternating Current into Direct Current.

yes, so it has internal rectifiers

 

[dlucks]

Neon signs like that need proper ballasts. And they need right type or amount of ballast(s) to specifically match the amount of current the neon tubes need to draw. It's important to know the the thickness of the neon tube and the tube length. One ballast can power only so many feet of neon/argon-filled glass. If you're having to buy new ballasts you need to buy what will match up with the glass properly.

BTW, a ballast or transformer (big clue in the term) converts the safe and familiar Alternating Current into Direct Current.

My understanding is that the larger the diameter of the tube the more current is needed. The longer the tube the higher the voltage needed. The bar light I have has two different diameter tubes in series. I've cut the wire that connects the two different diameter tubes and plan to use two different DC power supplies matched to the needs of the two separate tubes.

The standard definition for transformers does not convert AC to DC. They convert one AC voltage to another AC voltage.

According to arizonacommercialsigns.com:
"At each end of the tube, there is an electrode. A neon lamp can use either AC (alternating current) or DC (direct current), although the glow is only visible around one electrode when utilizing DC current. The majority of neon lights you see are powered by AC current."
How true is this statement?

 

[netsol]

Rectifiers concert ac voltage to DC voltage (capacitors FILTER the rectified voltage)
unless neon is different than EVERYTHING ELSE the should be no damage from having more current available than needed. HIGHER VOLTAGE can be very destructive! {HIGHER voltage being supplied can cause HIGHER CURRENT DRAW}. but, I am off on a tangent that NO ONE cares about...