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Neon's

 * Original msg to: rmr-at-christa.unh.edu

Quoting Ryan M Ruel <rmr-at-christa.unh.edu>

> I'm ready to power up my coil, but I don't have any method of 
> powering it. Anybody know a way to get some neons?

If you are interested in making a high voltage, high current,
power supply, I can tell you how to do it almost for free....

First call the local neon shop(s) and tell them that your working
with Tesla coils. Ask them to hold all of their failed xfrmrs so
you can pick them up. Make sure you talk to the boss or foreman,
and tell them that you want dead units. I have never had a shop
turn me down for free cores. They are happy to get rid of them.

There are two types of failed neon xfrmrs: warranty units, and
old junk. The local shop must return units that fail within the
two year warranty period back to the distributor for credit. Old
junk (older than two years) you can pick up for free right from
the local shop, but I also scavenge from the distributor. Ask
where the failed warranty units go.

If you can locate the distributor who sells wholesale, and
handles failed warranty units, you have found a gold mine of high
voltage xfrmrs. The distributor removes the PLATE from the xfrmr
for return to the manufacturer, and throws the unit away. The
manufacturer credits the distributor for the plate, as the
shipping is too expensive. The cores go to the dumpster.

After locating your source of failed units, be selective. Try to
bring home the high current units. Ratings commonly used are 9
kv, 12 kv, & 15 kv, with common current ratings of 30 & 60 ma.
Once in awhile you will come across a 120 ma unit. I grab all
of the high current units (60 ma+) I can get in these voltages.
If you can't find any 60s, then grab all the 30s.

First test your units. Use wire with a 15 kv rating or better.
This wire can be obtained where you pick up the transformers.
If you ask they will usually cut you off a few feet for free.
I prefer using the solid polyethylene core from RG-213 or poly
core RG-8 coax, as it will withstand the voltage with gobs of
extra safety margin. Draw an arc from the HV bushing to the case,
one at a time.

About 50% of the "failed" units I pick up are just fine and need
nothing other than a clean up. There is nothing wrong with them.
Often shops get these units from signs they have dismantled, and
they just toss them into the junk pile with the rest. The other
50% are bad. Either one, or both, of the HV windings have broken
down. These units can frequently be repaired:

Remove all hardware, and insulators if possible. Take a hammer
and a chisel and remove the cases by splitting them down the
corners. Break off any stubborn insulators, but try to preserve
the lead wire. You are left with a block of asphalt. Set the unit
outside when it is very cold, and let it freeze solid overnite;
or place in a freezer or deep freeze until frozen solid. The next
morning, short the high voltage lead wires with a clip lead, and
connect 110 volts across the primary. Since the cores on these
transformers are shunted, they may be shorted without harm or
blowing fuses. Let the unit cook for 15-30 minutes.

Disconnect your leads, and with the chisel and hammer, chip a
groove around the block. You want to score a groove lengthwise
that will allow the block to cleave in two. Then starting from
one end of the block, chip until you hit the core, then do the
same with the other end. Pry and chip the asphalt away from the
core until the xfrmr is free. The core may then be disassembled,
and the windings removed and examined. Kerosene and a stiff brush
will clean up the windings and core of any remaining asphalt.

The "cold-cook" method is fast, clean, and works very well. Since
the asphalt is frozen and brittle, it chips away cleanly. The
"cooking" softens up the asphalt around the core, allowing it to
release. The other ways to free the cores are long soaks in sol-
vent such as kero, diesel, or gas, (the nasty waste makes a good
driveway crack filler and roofing patch), or melting out the
asphalt with external heat from a hot plate, oven, or fire. 

Solvent soaks are the best done outside in summer. Get a rect-
angular kitchen type trash can. A plywood board may be used for a
lid. Fill the container with about two gallons of solvent (enough
to submerge the xfmr completely). Prepare the transformer as
outlined previously by removing the case and hardware. Submerge
the alphalt block in the solvent for several days. Remove the
unpotted core and clean up with kero and a stiff brush. This
method works best in warm weather; when it gets cold unpotting a
core this way can take a week or more. The solvent can be reused
to unpot three to five cores before it must be replaced.

Melting out the asphalt is best done outside in summer. You will
need two matching galvinized steel pans, such as those used for
catch pans during oil changes. A turkey roasting pan with a lid
will also work. Place a hot plate on some ceramic tiles. Set the
hot plate on high and center a metal pan in the heating coil. Set
the asphalt block in the pan, then cover. It will be necessary to
turn the asphalt block several times. Depending in the wattage of
the hot plate, the temperature may also need adjusting if the
asphalt begins to boil, smoke, and char. You can use a small
charcoal fire in place of a hot plate, but I feel this method is
excessively dangerous: simply set the pans up on bricks, and
build a small charcoal fire under the pan. 

There is a new type of neon potting that has emerged recently. 
This new potting is a cream colored opaque polymer of some type.
It is not affected by the solvents normally used to unpot neon
cores. It is recommended that this material be removed by the 
"cold-cook" method. Freezing makes the material very brittle and 
it will chip away easily, the warm core will allow the polymer
to release from the windings without too much difficulty.

Most neons fail when the high voltage breaks down the asphalt
potting. The resulting carbon track bypasses and shorts out the
winding. Simply removing the carbon rich asphalt brings them back
to life. Other times the coils break down internally. In this
case I discard the winding after disassembling the core, and
replace it with a good winding from another unit of the same
model with the same type failure. Sometimes all that is wrong 
is a faulty ground connection between the winding and core.

While the core is apart, you can beef up the current output by
removing a few of the shunting plates between windings. Never
take out more than 2 or 3 of these plates per side, as the
additional power output will burn out the secondaries. Generally
I get about 70-75 ma out of 60 ma units after I have finished.

Rebuilt units need a little protection from the high voltage
secondary outputs. The first thing I do is solder on a new lead
wire to the high voltage windings. The HV secondaries are wound
with very fine magnet wire, in the 30 ma units the wire is not
much thicker than a coarse hair. Once a good solder connection
is made, bed the connection and the first 1/2 inch or so of lead
wire to the top of the HV winding with hot glue or clear epoxy.
The lead wire need not be anything special, any thin insulated
stranded wire may be used. Heavy wire increases the chances of a
failed connection due to mechanical stress. When setting the unit
up to fire you simply have to route all high-voltage leads on
insulators.

The windings themselves are wedged against the core to prevent
vibration. I have seen wood, bakelite, and plastic wedges used
commercially. What I like to do is to soften up some 30 mil
polyethylene plastic sheet in boiling water, and heat the core in
a warm oven. I wrap dry softened plastic around the core and
gently force the windings down on it. Once cooled, the windings
have some insulation from the core, and they will not vibrate.

The base wire from the HV windings must be grounded to the core.
Use the original grounding point if possible, if not you may
split the core apart slightly with a thin blade and insert the
base wire into the gap before you clamp the core back up. If
required you may also splice on a small piece of wire for added
length.

Neon sign transformers that have been rebuilt may be fired dry.
The asphalt used to pot the cores for neon use does not really
insulate well against the RF and kickback from the Tesla Tank.
The units last longer when they are freed of the asphalt potting.
The only other choice is to sink rebuilt units in mineral or
xfrmr oil (like Shell Diala-X) which is a very good RF insulator.
I choose to fire them "dry"; it works, and there is no mess.

Neons may be run in parallel to deliver the current required to
fire medium sized coils, and I have run up to 4000 watts with
banked neon power supplies. The general practice is to run these
banks off of 240 volt feeds controlled through a variac. Neons
with matched outputs are run in pairs in these banks. The
primaries are paired up in series, and the secondaries are all
paralleled to the HV buss. Phasing is important here, and each
transformer must be checked as it is added to the bank to ensure
it is in phase with the other units. If an xfrmr draws an arc
from a lead wire brought to the HV buss, the primary or secondary
connections must be reversed.

Neons typically have an efficiency of about 50%, in that they
draw twice as much RMS power as they put out. This problem can be
resolved with the use of power factor correction (pfc) capaci-
tance across the line. The pfc capacitors used are the same as
for alternating current motors. The voltage rating should be at
least twice the line current used, and I like a 4x voltage margin
for long life. The formula used to determine ballpark pfc is as
follows:
                                    9
                                  10^
              C = Corrected kVA  ------ 2
                                 2(pi)fe^

This should read C = Corrected kVA times (10 to the ninth power)
                     over, (2 pi times f times e squared)

C = required capacitance in microfarads
f = frequency of applied voltage
e = applied voltage

CORRECTED kVA is determined by dividing the corrected power
factor output of the neon sign xfrmr (Volt-Amps below) by 1000

               Corrected Power Factor

        Secondary Rating         Volt-Amps
             kV,mA

             15,120                 900
             15,60                  450
             15,30                  250
             12,120                 775
             12,60                  400
             12,30                  200
              9,120                 600
              9,60                  300
              9,30                  150
            7.5,120                 500
            7.5,60                  250
            7.5,30                  125
              6,60                  200
              6,30                  100

Using a pair of rebuilt 12 kv, 60 ma neons, with 2 shunting
plates removed from the core next to each HV winding, and power
factor correction capacitance, you can get a nice 1.5 KVA Tesla
power supply with over 90% efficiency. Total cost: $5.00 for the
pfc capacitors, and a few hours of time.

I have unpotted dozens of neon transformers from many different
manufacturers. I have tried to make this as informative as
possible, and have checked it over for mistakes. If I have erred,
or was not clear on something, please let me know. Use common
sense whatever you do, and don't expect the first attempt to work
out. On my first attempt I managed to destroy a HV winding during
the unpotting, as I did not know where the windings were located
on the core. But once you see one core unpotted, with minor
differences, you have seen them all.

*****************************************************************
> I'm unpotting a neon transformer the way you described. I have
> basically all the tar off except for some dirt that I didn't 
> clean off yet. I have a few questions. 1) what are the shunts 
> and what are they made of? 2) Is the core the heavy metal band
> that surrounds the windings? 

I am going to use your ASCII art as a start for the following
series of diagrams. The simplest, bare (no windings) core is
depicted below. It is made of stamped sections of flat iron 
sheet that are coated with a thin layer of enamel. This laminated
core is made to come apart, which is how the pre-wound primary
and secondary windings are fitted on to it. Usually where will be
a couple of long screws w/nuts or a couple of rivets that may be
drilled out to separate the iron core into two open sections. The
diagram below shows an assembled neon core in it's simplest form.

      _____________________________________________
     |                                             |
     |                                             |
     |     -----------------------------------     | 
     |     |                                 |     |
     |     |     OPEN RECTANGLE IN CORE      |     |
     |     |                                 |     |
     |     -----------------------------------     |
     |            STAMPED IRON SHEET               |
     |_____________________________________________|


The diagram below shows the simplest core above, but with 
the addition of the primary and secondary windings. The
primary winding is in the center, the two secondary windings
are towards the outside. There are two wires leading from the
120 volt primary winding, and one wire each from the outer layer
of the high voltage secondary windings. This gives a total of
four lead wires exiting the transformer. The base wires of the
two secondary windings are grounded to the core laminate.


                        120 VOLTS
          high voltage    v   v     high voltage
             __I__        I   I        __I__
            |  S  |     __I___I__     |  S  |
            |  E  |    |    P    |    |  E  |
     _______|  C  |____|    R    |____|  C  |______
     |      |  O  |    |    I    |    |  O  |      |
     |      |  N  |    |    M    |    |  N  |      |
     |     -|  D  |----|    A    |----|  D  |-     | 
     |     ||  A  |    |    R    |    |  A  ||     |
     |     ||  R  |    |    Y    |    |  R  ||     |
     |     ||__Y__|     ---------     |__Y__||     |
     |     -----------------------------------     |
     |                     CORE                    |
     |_____________________________________________|


Now, in order to limit the amount of energy, in the form of
magnetic field flux, that is exchanged between the primary 
winding and the two secondary windings: magnetic leakage shunts
are placed in the core on either side of the primary winding.
These shunts are nothing more than small blocks of the same
core laminate that makes up the rest core. The diagram below
shows the simplest neon core from the first diagram, without
windings, but now showing the correct placement for the mag-
netic leakage shunts:


      _____________________________________________
     |                                             |
     |                                             |
     |     -----------------------------------     | 
     |     |     |  |               |  |     |     |
     |     |     |  |  < SHUNTS >   |  |     |     |
     |     |     |  |               |  |     |     |
     |     -----------------------------------     |
     |                                             |
     |_____________________________________________|


> 3) You say to take softened polethylene sheet and press it  
> against the core and then take the windings and press them down
> on it. How would the windings pressed down on the sheet when 
> the core is around the windings?

The windings are around the core. When the two pinch bolts (or
rivets) holding the core together are removed, the core may be
disassembled into two sections. Once the core is apart, the 
windings may be slipped on and off. To prevent vibration, the
windings are usually wedged into place. Before reassembly of the
core it may be warmed; polyethylene carefully wrapped around the
laminate; and the windings gently but firmly pressed into place.

... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12