Re: Neon Transformer Question

On Sat, 22 Aug 2009 07:55:16 -0400, default <default@xxxxxxxxxxxxx>
wrote:

On Sat, 22 Aug 2009 05:15:57 GMT, Jon Kirwan
<jonk@xxxxxxxxxxxxxxxxxxx> wrote:

On Fri, 21 Aug 2009 21:44:59 -0400, default <default@xxxxxxxxxxxxx>
wrote:

On Fri, 21 Aug 2009 18:16:36 GMT, Jon Kirwan
<jonk@xxxxxxxxxxxxxxxxxxx> wrote:

On Fri, 21 Aug 2009 06:52:17 -0400, default <default@xxxxxxxxxxxxx>
wrote:

On Thu, 20 Aug 2009 20:51:12 -0700 (PDT), Bob1001
<quadrunnerkid@xxxxxxxxxxx> wrote:

Hi All,

I recently came across a very large sum of neon transformers. The
input is 277v for the primary, the secondary is kicking out 30
miliamps at 7500v. I have some pictures of the transformer on my
website: www.doranaerospace.com/Images/neon

does anybody have any idea of what they are worth?

Thank you,
Bob Doran

Their worth is determined by the market. Newer neon signs use high
frequency inverters to power the tubes. They are somewhat safer, cost
less, weigh less, good power factor and more efficient.

Neon is being supplanted by high frequency luminescence "wire/tubes"
and LEDs. What you have may be museum pieces before long.

They'd be worth money to Tesla coil addicts. If they are identical
they can be paralleled for more current. The 277 volt input would not
be desirable for TC use though.

I paid $40 for a new oil furnace ignition transformer (about 75 watts
more than what you have)

He stated 7500V @ >30mA, which I think works out to 225W or better.

Yeah my oil burner transformer is 300 W.

for my first Tesla coil. Then a year later
spent $20 on a new NST that was about twice the power. Later I wound
my own transformer from scratch and spent about $100 on magnet wire.

I probably would have considered reusing some spare microwave oven
transformers for this. (My autistic daughter destroys microwave ovens
all too often.) Hmm... thinking about that, there is a microwave oven
repair facility a few miles away -- I'll have to inquire to see what
they do with those they run across.

Jon

Lots of folks are using MOTs for TC's. Their voltage may be a little
low but the power is good. It is probably OK to operate them NST
style with two each and a ground to double the voltage. They do
require some kind of external current limiting.

I had one of the Lindsay reprints by Holler and Cunningham on building
TC's ala 1900's style. They start with how to build an induction coil
and I adapted their design to the materials we use today (PVC instead
of hard rubber, vinyl insulation instead of gutta percha, enamel
magnet wire instead of double cotton covered, etc.) Took a month
total and about one week in winding the secondary. It runs over 1 KW
5-7.5 KV (with a tapped primary) when used as a mains HV transformer
and produces ~100KV+ as an induction coil (5" sparks)

I just did a search and, yup, found a nice site on the subject of MOTs
(learned a new term, I suppose) and TCs. The page I looked at mostly
used four of them and used transformer oil over the whole batch (said
that they discovered motor oil was probably worse than using water.)

The price and availability can't be beat . . .

I hadn't thought of just floating the cores and packing them in oil.
The limiting factor probably is the core to primary insulation.

Interesting. I've been stocking up MOTs here against my wife's mild
objection to it. When I tell her I've got this great idea for which
I'd like to use them that will send meter-long lightening arcs around
my garage, I'm sure that may get a rise out of her. :)

A great hobby IMO. It's not everyone who can command lightening!

My wife is very indulgent when it comes to my hobbies. From her point
of view it keeps me busy, happy, at home, doesn't cost much, and they
do make good conversation pieces. The downside: noise, chemical
odors, TV interference, clutter, and using kitchen utensils for things
they were never intended for.

While the primary TC circuits are deadly, the secondary side is
relatively safe. (relatively, since I imagine an arc from the primary
coil to the secondary would also impress the mains current on the
output)

My stereo speakers took direct hits from the arcs (wood being
conductive at the voltages involved) yet the bi-amped mosfet power amp
wasn't hurt. A nearby computer - turned off, but still plugged into
the same mains supply lost its CMOS settings and eventually a memory
module died too. Drywall and studs took multiple hits yet never
caught fire.

Once you get in the kilowatt range, the arcs are fat white noisy
things that go for several feet looking for a ground - wood or
concrete etc is close enough.

Power and voltage (and a top loading cap) determine what the arcs look
like. Fat corona streamers, to miniature lightening with lots of
forking, to heavy bright white arcs.

Other dangers besides simple electrocution are ozone - they are ozone
generators, so you want some ventilation (preferably blowing the stuff
out an open window). X-rays - only a concern if you put some vacuum
tube on the output terminal. Something like a small evacuated glass
bulb is all it takes - small #47 pilot lamps will do it - the glass
envelope fluoresces green and it will fog photographic film. Standard
incandescent lamps are nitrogen filled and the gas will glow but no
X-rays.

An interesting phenomena was I inadvertently made an electret. I
coated one coil with epoxy and spun it while it catalyzed to give it a
nice even coat with no runs. I powered it up and it stayed "charged"
for months afterwards. Later learned that's how electret's are made,
a plastic insulator is impressed with voltage while it hardens.

And yes, I'm impressed at all the effort you took and mentioned. A
lot of work with good results. Um... would you do it again knowing
what you know now about the work involved? ;)

Jon

Sure, I'd do it again. I'd make it bigger and better.

I potted mine in paraffin wax, I think oil would be better. I used my
pressure cooker as a vacuum impregnator for the four secondary
bobbins. The winding was more or less mindless work. I'd wind a
layer (1-2 minutes) then paint it with varnish and wait for the
varnish to get tacky and put down a layer of paper then wind another
(while watching TV or listening to music). I'd guide the wire on from
6" away with just my fingers or use a fingernail to press it against
the next turn.

My winding machine was crude, but worked very well. I took a heavy DC
motor with a 3/8" shaft and banged a piece of wood on to it. I turned
the wood down to a cylinder using a chisel and sandpaper to make a
mandrel for the bobbins. The bobbins were PVC conduit cores and sheet
Plexiglas for end plates with solvent cement holding it together and
epoxy to make it leak proof. I used a low voltage DC supply and
variac to set the tension and just guided the wire on. To avoid
cutting paper to separate the layers I found some 4" adding machine
paper rolls and just used that and built the bobbins to match the
width.

Another thing would be to use "pies" instead of bobbins (where the
wires have to be hand-laid without overlaps). I found I could cut
thin rings out of PVC pipe with the "winding machine" used as a
lathe, and cut perfect donuts out of Mylar polyester film using a
glass cutter with a pivot against an aluminum plate - perfect for pie
winding. Running the wire through a hot melt adhesive bath on the way
to the pie would give it some extra insulation. Instead of perfect,
close wound, coil bobbins, you end up with many "jumble wound" pies.
Spiral rather than cylindrical winding. Should be lots faster.

There's some 13 miles of wire in the secondary and according to the
resistance (corrected for temperature) I nailed the length to around
300 feet, from the calculated value. My layers were coming up ~7%
short for close wound (wire tables versus a turns counter) so I
increased the layers to compensate.

These days I'm still playing with resonance, but trying to build a
programmable set of chimes to play music. I'm just starting and
haven't settled on a chime/striker yet.

If you haven't already, it would help if you set up a web site on your
experiences, failures, and successes here.

Jon
.

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