neon sign transformer current regulation - Page 1
Forum section: electronics / beginners

author: wachanna
author_rank: Newbie
timestamp: August 19, 2024, 01:15:50 am
content: hello. im wondering if there is a simple way to change the output current of a neon sing transformer. i have no idea whats inside it. this is one example of the kind i am referring tohttps://www.amazon.com/gp/product/B07GPV5KSM/ref=ox_sc_saved_image_5?smid=A1JEC2HEDYPE1B&th=1the output on this particular one is 3kV 30mA. would it work to just add some sort of variable resistor on the input side? i dont know much so i dont know if that would also change the output voltage for some reason. i want the voltage to stay the same, i just want to change the current. 3000 volts times 30 milliamps is like 90 watts. id like to make it so i can vary just the current so i can adjust the wattage to hopefully anything in-between zero to max. i need it this way so i can have more control over experiments. ive seen people put electrodes inside a "chamber" that is evacuated of essentially all air and then they turn on the power and what appears is some sort of illuminated current that flows from one electrode through the vacuum to the other electrode. its pretty interesting but i never saw it in real life. there are also educational videos that show what happens when you put a magnet near the illuminated flow of current which makes the current "bend". but i feel most comfortable by having the most control over the experiment and in order to do that i need to figure out a simple, hopefully cheap, way to vary the current, which will also be more interesting to see what happens at one current level compared to another. also, from what i understand, neon sign transformers like the one i put a link to have super high frequencies, compared to regular 60hz mains, i would also like to change the output to DC, which i believe would automatically change the frequency to zero, right? i believe there is only one way to change the output voltage from i believe is AC to DC, i could be wrong, maybe there are other ways, but the one i know of is to make a full bridge rectifier. when it comes to the full wave rectifier, is it as simple as buying 4 diodes that are rated to handle a voltage higher than the neon sign transformer output voltage and frequency? maybe there are already made high frequency high voltage full bride rectifiers? i will look around myself but would appreciate any suggestions to known trustworthy safe ones. when it comes to current regulation, im thinking a variable resistor either on the input or output. is that the simplest cheapest way, thats also safe? any better alternative solutions? also, i dont specifically need a neon sign transformer, what i would like is what i described, a moderately high voltage with the ability to vary the current output and not the voltage output. if there are any already made devices that are around as cheap as the neon sign transformer in the link that would probably be simplest and safest. even one thats a bit more would be ok for an already made version. up to say 150 usd. also, since im guessing there are real electrical/electronics engineers on here, if you are willing to build it for me im willing to pay, so long as the price is reasonable and the product is safe. we can talk about the product details if you are interested, just let me know. thanks

author: coppercone2
author_rank: Super Contributor
timestamp: August 19, 2024, 06:22:40 am
content: a transformer spec is its maximum load circuit current.regulating a transformers maximum current requires a special transformer, as is used for welding, that is adjustable, if you want to do it like 1950.http://vijayelectronicsforu.blogspot.com/2018/07/welding-transformer-current-control.htmlWhat you have is a power supply, not a transformer. don't call that a transformer.

author: Zero999
author_rank: Super Contributor
timestamp: August 19, 2024, 07:36:24 am
content: To be honest, I've not read the wall of text, just skimmed and clicked the link. Some punctuation and paragraphs would make it easier.It appears to be a swithched mode power supply, rather than a transformer. Its small size and 100-240 VAC 50/60Hz gives it away. It might be possible to reduce the current by changing a sense resistor, but not increase it. A rectifier, possibly high speed, as the output frequency could be hundereds of kHz is required to covert the output to DC.

author: gbaddeley
author_rank: Regular Contributor
timestamp: August 19, 2024, 07:54:50 am
content: 30mA is the max output current. A load could draw less than that. The PS would likely only regulate the voltage, not the current. Above 30mA, the PS may hard limit, shutdown, or the voltage will sag significantly.

author: Zero999
author_rank: Super Contributor
timestamp: August 19, 2024, 09:39:43 am
content: Quote from: gbaddeley on August 19, 2024, 07:54:50 amNote this is a neon lamp power supply. It regulates the curent, not voltage, up to an open circuit voltage of 3kV. Quite often the current regulation isn't great and the voltage is completely unregulated.

author: SeanB
author_rank: Super Contributor
timestamp: August 19, 2024, 10:51:04 am
content: As well the entire power supply will be, because of the need to use it outdoors and where it can get damp, entirely potted in a hard epoxy fill, burying the PCB under the rock hard epoxy. Thus they are not adjustable, because removal of the epoxy tends to be destructive.

author: wachanna
author_rank: Newbie
timestamp: August 19, 2024, 01:42:02 pm
content: thanks everyone for your replies. since my goal is to create a current to flow through a vacuum, somehow i didnt think about it until after making that initial post the question: whats the minimum voltage that would work? do i even need voltages in the kilovolt range?

author: Stray Electron
author_rank: Super Contributor
timestamp: August 19, 2024, 02:15:59 pm
content: Quote from: wachanna on August 19, 2024, 01:42:02 pmThe voltage required all depends on what kind of gasses are in the bulb and how low the pressure is in it and the distance between the electrodes. A simple NE-2 bulb will fire at about 80 volts. And the NE-2s with a bit of radioactive metal will trigger at an even lower voltage. Even light shining on bulb like an NE-2 will lower the triggering voltage. A real neon sign with a tube that could easily be 15 feet in length will require 15,000 to 20,000 volts.A laser tube such as a Helium Neon laser uses has a cavity about 6 inches long and it will operate at a couple of thousand voltages but you need to superimpose a high voltage pulse on it to trigger it.Generally speaking all gaseous discharge type lamps have a negative resistance so they must be used with some kind of ballast or they will overheat.When I was in my teens we could still get old transformer type neon sign transformers and we tried them out on everything that we could get our hands on! But for many years now the sign transformers are actually switcher type power supplies and they operate much differently than a transformer. If you pick up a real transformer you'll know it immediately since they'll weigh at least 20 to 30 pounds and a switcher will only weigh about 4 pounds.A friend of mine used to make those glass orbs that are about eleven inches in diameter and he would fill them will all sorts of gasses and he used old television flyback transformers to power them. In a large (25") color CRT based television a flyback transformer could easily operate at 25,000 volts. Nineteen inch black and white TVs used about 18,000 as I recall and some of the smaller sets used even less.

author: CaptDon
author_rank: Super Contributor
timestamp: August 19, 2024, 04:49:40 pm
content: Current won't flow through a vacuum, until you reach a corona discharge point and very slightly above that it will simply arc over and act like a short circuit. Your experiment and logic seem flawed.

author: CaptDon
author_rank: Super Contributor
timestamp: August 19, 2024, 04:58:49 pm
content: Also, be aware, if it is one of the old style pure transformers it will be center tapped to ground on the high voltage side and it DOES NOT regulate current in any way except through core saturation / magnetic shunt. It will indeed produce more current into a lower impedance load which could cause the transformer to overheat. Generally in high voltage circuits you don't regulate the current, you adjust the voltage to produce the desired current in your load. The highest voltage sign transformer I have dealt with was 75KV for a mercury gas tube that went entirely around the perimeter of a bar room. The voltage would arc to your hand through the glass if placed near either end of the tubing. Also, it 'may' have been 75KV each side of center tap.

author: IanB
author_rank: Super Contributor
timestamp: August 19, 2024, 05:08:49 pm
content: Quote from: wachanna on August 19, 2024, 01:15:50 amIt's not designed to work that way.QuoteIt's not a good idea to play with high voltages when you are a beginner.QuoteIt's a neon sign transformer (well, power supply really), so it's not likely to output the full 90 W continuously. Normally, once a tube is lit the voltage drops quite a lot, and they probably designed it with that in mind to save on costs.QuoteThere's no real point worrying about that as a beginner.QuoteYes, but the vacuum pump and seals are much more complicated to achieve than he electrical supply.QuoteYou should not feel comfortable. You should feel scared shitless. We are talking about 3000 volts here!I won't quote all the rest. You are trying to talk about advanced concepts long before you have enough knowledge to apply them.What I suggest you do is try to obtain some real gas discharge tubes. They can be found in different shapes and colors. Then try to light them up with the power supply/transformer, being very careful not to get your hands anywhere near energized parts of the circuit.

author: janoc
author_rank: Super Contributor
timestamp: August 19, 2024, 05:23:54 pm
content: Quote from: CaptDon on August 19, 2024, 04:49:40 pmThe entire vacuum tube industry would disagree.All it depends on is the voltage between the electrodes and how much electron emission you can get going.Sufficiently high voltage (well, electric field) will "rip out" electrons from the cathode and cause a current to flow. Without arcing over or any sort of corona discharge - both requires ionized gas (it is plasma) - and there is none to be had in a vacuum. That can happen only if some kind of gas (even air) is present when the emitted electrons are hitting the gas molecules and ionizing them.The current will flow at lower voltages if you use special electrode material with higher emissivity (= releases surface electrons easier)- or heat the cathode up, triggering thermionic emission. Et voila - you have just built yourself a vacuum tube.

author: Stray Electron
author_rank: Super Contributor
timestamp: August 19, 2024, 07:34:15 pm
content: Quote from: CaptDon on August 19, 2024, 04:49:40 pmThat's true in an IDEAL world but in the real world it isextremelydifficult to achieve the vacuum necessary to completely stop ionization (and the conduction) of the gasses that remain in the bulb. At very pressures, even the gasses that is trapped within the glass itself begins to be released into the bulb and it too begins to conduct. That's one reason why vacuum tubes use a getter in them.I doubt that the OP has anything that nearly capable of pulling an absolute vacuum so your case probably would not apply.The OP needs to do a LOT more research on this topic. My suggestion to him to get some catalog and technical data sheets of various vacuum tubes and various gas discharge lamps such as the NE-2s and the related bulbs and to read up on all of the technical details. Then get an assortment of pre-made NE-2s and similar bulbs and a decent variable voltage power supply and then experiment with them.I know that they've fallen out of favor due to safety concerns but I did a lot of experiments with a 110 volt variac and some NE-2s and selection of old used carbon comp resistors back in the day. I don't know how hard they are to find these days but you used to be able to buy NE-2 sized lamps but filled with Argon and other gasses.If he really wants to jump into the deep end of the pool, then he should get a copy of the book 'Gaseous Conductors, Theory And Engineering Application' and read it. The CRC Handbook also has a lot of information about the conduction of various gasses.

author: IanB
author_rank: Super Contributor
timestamp: August 19, 2024, 07:48:15 pm
content: NE-2's are miniature neon lamps. They are still readily available.I remember once having a very large neon lamp about the size of an incandescent bulb. I didn't really know what to do with it at the time, but I wish I still had it. It was cool having a discharge lamp that big.

author: TimFox
author_rank: Super Contributor
timestamp: August 19, 2024, 07:52:58 pm
content: I used large neon bulbs (larger than NE51 or NE2) years ago for circuit protection, but they don't seem to be made anymore.If I remember correctly, I used huge ones in an "Edison" base (normal base for 120 V incandescent bulbs).Some large ones are still available from surplus dealers:https://www.surplussales.com/Bulbs-Incan-Panel/BulbsNeon.html

author: schmitt trigger
author_rank: Super Contributor
timestamp: August 19, 2024, 08:12:04 pm
content: About 50 years ago I worked as an intern at a transformer factory. They offered neon transformers. There was a single engineer who knew how to design them. He was a real prima donna and would never ever share his knowledge with an assistant.But I could gather that the secret was in the magnetic shunt’s airgap, since I was the poor sod cutting and polishing the steel laminations to build samples, and he would grade the accuracy of my work via a short circuit current measurement.

author: themadhippy
author_rank: Super Contributor
timestamp: August 19, 2024, 09:33:25 pm
content: QuoteAnother source is candle flicker lamps for examplehttps://www.lampco.co.uk/products/schiefer-e10-candle-c18x72mm-230v-3w-10000h-clear-neon-flicker-flame-2500k-non-dimmable-660240003?srsltid=AfmBOopaydTWJPUhNKTyHpjrfNKuzEh0tB9nQZViex73zQIZPIkPxuT9

author: Terry Bites
author_rank: Super Contributor
timestamp: August 20, 2024, 04:05:30 pm
content: The thing you've linked to is not a real transformer as such. More of an electronic ballast.Open it up at your peril.You can only limit the current with a series resistor or other external device.In the old days it was a real mains transformer and you could add inductance to the primary to limit the current.

author: Wolfram
author_rank: Frequent Contributor
timestamp: August 20, 2024, 08:17:31 pm
content: The HB-C02TE linked is a switchmode neon supply, based around a self-oscillating half-bridge converter with BJTs, the kind found in switchmode halogen transformers and compact fluorescent lamps. It approximates a constant current output that tracks the applied input voltage. There is very little filtering on the input, so it tracks the mains cycle in normal operation, giving output current ripple at twice the mains frequency. It will start up around 45 V, and shuts down once the input falls below 25 V or so, and runs fine from DC. Input current draw tracks the output voltage across the load. If run with too light of a load, i.e. one that doesn't let adequate current flow, the output voltage will rise beyond safe limits and the input overcurrent protection will kick in. It can be made to give constant output voltage up to some practical limit by feeding the input from a constant current supply. You have to be careful to keep the output voltage below the rated 3 kV, as the input overcurrent protection only kicks in around 6 - 8 kV or so, leaving an operational area in between where it will operate, but burn out after some time.I would look at other solutions for regulated high voltage into a variable or unknown load, like a ferrite transformer run from a Royer or Baxandall oscillator, into a voltage multiplier. These schemes will give a constant output voltage that tracks the input voltage. This makes it easy to wrap a control loop around them by feeding them from a linear or buck regulator with feedback from a high voltage divider.

author: unseenninja
author_rank: Regular Contributor
timestamp: August 21, 2024, 07:51:27 am
content: Quote from: wachanna on August 19, 2024, 01:15:50 amThere are very good reasons why there is a Shift key on your keyboard to generate upper case characters. There are also very good reasons why the word "paragraph" is a thing.Please read:https://www.eevblog.com/forum/beginners/why-writing-style-and-grammar-matters-in-posts/