NEON21 Power

[clarkmcc]

How does this look for a demo fusor transformer. I noticed it has a single electrode, is there something that can be done about this.

http://www.amazing1.com/profneon2.htm

NEON21
Neon Transformers, Neon Power Supplies Input: 12-14vdc, 1000 ma (14DC/1G adapter sold below, if needed)
Output: 7kv open circuit at 10 ma short circuit

Open frame with potted transformer 5 x 1-1/4". Lights over 12 feet of 12 mm tubing from a single electrode. Excellent for small plasma globes and other gas filled figurines, "luminglass" plates and other small gas filled objects.


Quantity
NEON21 - Transformer (without adapter) ........$34.95
10-24 @ $29.95ea. 25-99 @ $26.95ea. 100+ @ $22.95ea.

If you need a power supply, our 12-14 volt 1 amp wall adapter with grounded third pin
eliminates the external ground wire often necessary for larger single ended displays:
14DC/1G - Wall Adapter for NEON21 .....................................................$19.95

NEON21/115 - NEON21 Transformer + 14DC/1G Wall Adapter ......$49.95

[Carl Willis]

These devices aren't what is meant here by a "neon sign transformer" (NST), although they commonly replace the NST in modern gas-tube sign installations. They are not transformers, but actually high-frequency inverters that produce high voltage at high frequency. They are not known to be useful for fusor power supplies, being easily destroyed by load conditions that differ from neon tubing. Some of the larger inverters sold by Information Unlimited could presumably operate a fusor by way of a voltage multiplier or rectifier. However, this implementation would be very different from that pertaining to an NST.

If you want to go the NST route, check on eBay or craigslist for REAL NSTs. These are heavy, typically rectangular metal boxes with porcelain insulators.

-Carl

[Doug Coulter]

These are even being deprecated in the almost defunct custom neon sign business. As Carl said, they are high frequency pulse devices (kind of a flyback inverter) and what happens in neon tubes if you drive them "too fast" is all the ions wind up at one end and the one electrode sputters badly in the tube, shortening its life vs nice old 60hz which gives more even wear on the electrodes. You could get lucky, but likely not.

[clarkmcc]

Would you take a look at this one. This is also a neon sign transformer (they claim). It is bigger and is rated at 1-20kv at 20ma. I would add the rectifier and circuit that Richard Hull mentioned in his NST in his FAQ post.
Although, as you say, it would probably be better to get one of the big guys off of ebay.



PVM12
Powers up to 14" Plasma Globes from 12VDC

Neon Transformers, Neon Power Supplies

INPUT - 12VDC 3A (requires a 12V power supply)
OUTPUT - Variable 1k-20kV
FREQUENCY - Variable 20k-50kHz
CURRENT - Reactance Limited to 20mA

Front panel adjustable output plasma power supply, excellent for driving plasma globes up to 14" in diameter and other similar-sized plasma cells and displays such as our plasma tornado, neon tubing, etc. Single ended driver for gas-filled displays operates from 12 volt input at 3A minimum. Variable open circuit voltage of 1k-20kV with short circuit current of 20mA. Frequency is adjustable from 20k to 50kHz and is controlled from the front panel; voltage automatically adjusts to capacitive load & frequency. Unit is built on a metal chassis with plastic cover. Size is 2 x 3 x 6" rectangular with a 12" output lead and 3" input leads.

Free Instructions

Quantity
PVM12 - Transformer ............$79.95
10-49 @ $69.95ea. 50-99 @ $62.95ea. 100+ @ $59.95ea.

Adapter for PVM12
Allows operation from a standard wall socket in the range of 100 to 240VAC. Provides an output of 12 Volts @ 4 Amps, fully regulated. Has a 3-foot input cable with a standard 3-prong US plug, and a 3-foot output cable with a 5mm output plug. Included IEC power cord. CE recognized.
12DC/4AR ..............$29.95

[clarkmcc]

I was reading an ebay description about a NST and they said that no parts that would make the supply variable should be added. Does this include a variac. Has anybody had some experience with this.

[Carl Willis]

The components and configuration Richard discussed in reference to an NST are not applicable to the power supply you are pointing to.

NSTs are center-tapped, 60-Hz, iron-cored transformers. The power supply you're looking at now is a high-frequency inverter. Different approaches are needed to adapt these different kinds of supplies for powering fusors.

It may indeed be possible to use the PVM12 to operate a demo fusor. However, at best it still delivers much less power than a typical NST (input power is only 36W maximum from a 12V supply, and output power cannot exceed what is supplied). To rectify the output, you would need to use some HV, fast-switching diodes rather than the diodes Richard's diagram calls for. The diodes you need to use are more expensive and can be hard to find. Also, since the PVM12 has a single-ended output, you would not be using the same circuit configuration that is used for center-tapped NSTs.

-Carl

[Carl Willis]

The description you were reading refers to an inverter-type gas tube power supply, which will not function properly from reduced supply voltage. EBay sellers often erroneously call these "transformers" because they have the same function as an NST in sign installations.

Again, the NST you are looking for is a real transformer.

Examples of real NSTs:

http://www.franceformer.com/products-ne ... P5G-2E.pdf

-Carl

[Richard Hull]

Carl has handled this really well.

Old neon transformers (iron core) are almost indestructable in demo fusor use and a small variac added to one of these 12 kv, 30ma transformers will make a decent 8kv, auto current limiting, DC supply that is smoothly variable from 0-8,000 volts using the circuit I supplied in the FAQ.

You can tie the two big 7.5kv HV output knobs of a 15kv unit into a dead short and plug in the transformer and not hurt it or blow a fuse. When I was de-potting these for Tesla coil use in the late 80's, I used to short out the HV knobs, plug them in and walk way for 20 minutes. On my return, they would be quite warm and I had little trouble separating the tar/asphaltum from the windings to free the entire core. (This was long before internal GFI's were installed.)

You are looking for a 20 lb transformer. Accept no substitute.

Another route is an oil burner transformer. These are common and often found used and are rated at 10kv at 20ma. They weigh about 10-12 lbs.

Everything, including oil burner furnaces have moved to HF inverters now which is the economical way to go based on modern technology. These are fine for lighting neon and setting fire to oil mists, but terrible for DC supplies in fusor use.

This leaves the old neon sign and oil burner transformers of yesteryear as an odd curio for future museums of technology. They will serve as examples of how man once wasted valuable resources like steel and copper locking them into these large, bulky and heavy appliances to merely light signs in bars and restaurants.

I have stopped offering my numerous neon sign transformers for sale in the trading post here, realizing that they will appreciate in value as time goes by. They can, certainly, still be found cheap. At HEAS 2011, I saw 4, snow white, dual female socketed, 7.5 kv @ 30ma units offered for $5.00 each by John Freau. I did not buy them as I had plenty. However, as John was packing up when the fleamarket was shutting down, I noted he still had them, so I bought them and tucked them away among my stash. I have noted that at hamfests they are getting rare and are going for over $25.00 each when I see them.

Richard Hull

[clarkmcc]

I found this oil burner transformer. Do I NEED it to be variable because it will be used for a demo fusor?

http://www.ebay.com/itm/Sid-Harveys-T17 ... 564c86fe3e

[Rich Feldman]

Right kind of transformer, but I think kind of expensive. Let's see what ebay 110968120343 and 110968308446 and 110968124863 go for today.

Re. variable voltage. It's not a feature found in OBITs and NST's; for that you would put a variac between the wall plug and the HV transformer.

I recommend a search of this forum for the words FAQ, neon, and variac. You have time to skim all seven posts. As Conrad F. says in one, you could skip the variability for a demo fusor. But then you would have only one knob, the vacuum pressure, to control the plasma ball.