TESLA COILS: HIGH VOLTAGE RECTIFIERS
Magnet wire for coil-winding, HV cable |
Bill Beaty |
(Skip down for magnet wire,
Wire Gauge,
also high-voltage cable)
HV Diodes
One good source for High Voltage Rectifiers
is... Old
Microwave Ovens! These typically contain a 7.5KV to 15KV diode at fairly
high amperage ( 1/3 amp or higher). Follow the usual safety precautions
during disassembly of course, same as you would when messing with TV sets
and tube-type amplifiers. Hint: some ovens hide their diodes within the
can of the high voltage filter capacitor. Those cans are full of
dielectric oil, so sawing them open can be messy.
Some electronics suppliers now sell replacement oven diodes, so
high-current, hi-volt diodes are no longer that rare. Check out your
local seller of TV repair parts (ECG, NTE, etc. replacement lines).
All Electronics
has incredibly low prices on 200mA, 6KV rectifiers, $0.50 (# R6000)
Also try microwave repair suppliers, such as
Some surplus companies such as Nebraska Surplus
Sales carry high-current HV rectifiers for radio transmitters.
See popular replacements NTE517, NTE541, NTE542, NTE 548
Another source of diodes is computer monitors, however these diodes are
usually only rated for 50mA or less. There is always a HV diode in series
with the HV connection to the "rubber cup" against the side of the CRT
tube. However, often the diode is cast inside the plastic block which
holds the HV transformer secondary coil (flyback transformer.) While
their current is low, these diodes usually have a higher rating for
reverse voltage (sometimes as high as 100KV for large screen CRTs.)
Also note that Surplus Sales has some rare
High Voltage Connectors
THIN "MAGNET WIRE" FOR TESLA COIL SECONDARY COILS, ETC.
Where can you find thin-gauge copper wire cheap?
Odd Wire Sources
A creative scrounger can avoid buying new wire. Think OPEN-FRAME
SOLENOIDS
from surplus junk shops! A typical 12-volt or 24v DC solenoid may
contain up to a
half-pound of #30 wire costing two or three dollars. Note that some
solenoids are nearly impossible to open, while others pop apart after
bending with a screwdriver or some vise-grips. So if you're going to buy
twenty of them for their wire, it's wise to first buy a single one to tear
apart.
Also think power transformers! Power transformers and small AC
shaded-pole
motors. If you
obtain an old power transformer or small AC motor, sometimes you can pry a
couple of laminations free
using pliers and a knife,
and the whole stack will then easily disassemble. You're left with a
spool full of wire for free. Besides power transformers, larger "choke"
coils are also a source of free wire. For thin wire, try finding a
transformer with a high voltage secondary such as those used in old
tube-type equipment.
I've heard that you can take apart OLD CAR ALTERNATORS and obtain coils of
wire. Might not be very thin wire though.
Another possibility: neon sign transformers can be disassembled by
carefully heating them in an oven to melt the tar. Be warned that this is
a fire hazard, and can also fill your kitchen with nasty fumes. (Try
sealing the transformer inside a bag of crimped aluminum foil.) Others
suggest tearing off the steel case, then chipping apart the tar using a
chisel or screwdriver.
I personally haven't taken any "neons" apart, and don't know if their wire
size is appropriate for tesla coils. If you want to make some long hot
sparks, usually #24 gauge or larger wire is best for your big Tesla coil
secondary. I suspect that the secondary of a neon transformer contains
far thinner wire, maybe too thin for a good TC secondary, but perhaps the
transformer's primary coil can be salvaged. NOTE: sometimes you can
repair a "dead" neon sign transformer without disassembly by melting its
tar. Dead ones are had for free from certain neon sign shops, while new
ones are extremely expensive.
One final source of wire: Mail-order surplus companies.
These companies often sell damaged 10 lbs spools of electromagnet wire.
Even a slight ding in the spool will cause an automatic coil-winding
machine to tangle, so "damaged" wire is often not really damaged at all.
Over the last few years the price has been around $40 - $60. But a 10lb
spool will last you a lifetime. (Perhaps offwind it onto other spools and
sell to other TC hobbyists?)
Here's a table for: AWG, American Wire Gauge
Wire Suppliers
For full price, Allied
Electronics carries 1lb and 5lb spools, but it's NOT cheap. A good price
for wire is around $8 per pound, not $30 per pound!
http://www.alliedelec.com
Also try otherpower.com, quite large spools in their products section.
Also Electronix Express for 1/4lb and 1 lb spools
Also
Action Electronics for tiny spools, or 1/4lb or 1/2lb
Also Vetco for 1/2 lb spools
In the UK Brocott has spools 250G through 10KG
Magnet wire and even Litz wire is available from Dave's Xtal Radio Page
Or search google for +"magnet wire" +spools,
or try an eBay search
Electronics Goldmine sometiems carries lots of sizes of
9lb spools and smaller.
They also usually have open-frame DC solenoids for $3-$4
Another big company which has been friendly to individuals in the past is:
MAGNET WIRE CO. (Weico)
161 Rodeo Dr.
Edgewood NY 11717
631-254-2970
http://www.weicowire.com/magnetwirecontents.htm
And for tiny quantities, Radio Shack sells a kit of three tiny spools,
#278-1345, $4.99, 200ft of #30, 75ft of #26, and 40ft of #22
HIGH-VOLTAGE CABLE FOR TESLA COIL POWER SUPPLIES
The high-voltage wire sold for use in test-leads is usually rated at
2,000V or 5,000V and is fairly inexpensive from the usual electronics
suppliers. But most Tesla Coils use Neon Sign Transformers up to 30KV
(with 45KV peaks)
For a quick source of short lengths of high-voltage wire, get yourself
some coaxial cable, carefully strip off the black jacket, then remove the
copper braid and any aluminum foil. If the white plastic inner insulation
is the translucent type, and is fairly difficult to cut, then it's "solid
polyethelene" and good for many tens of kilovolts. Avoid using the coax
with the easily-cut spongy foam insulation, since it has a much lower
breakdown voltage. If your voltage is above 20KV, use the much thicker
core taken from RG-8 cable (it's nearly 1/2" diameter!)
Also call around to local neon sign shops. They might sell you shorter
lengths of wire good for 10KV and above.
Note: the absolute voltage rating of HV cable is determined by the
volts-per-cm breakdown rating of the plastic. Manufacturers assume that
your cable will be up against grounded metal, so the entire voltage will
be impressed across the thin plastic layer. This means that you can
GREATLY increase the
breakdown voltage of any HV cable by suspending it well away from any
metal parts, especially avoiding sharp-edged metal. Tall, inexpensive
cable-supporting insulators can be made using cable ties and scraps of
acrylic or polyethelene. If extremely HV cable must pass near sharp-edged
metal, coat the sharp edges with a thick bead of RTV silicone glue, or
perhaps cover them with split hoses made of black conductive rubber. Also
FYI: when the voltage is extremely high,
the individual copper strands inside the cable can begin producing corona
discharge, and this tends to slowly convert plastic into conductive
carbon, leading to eventual HV arcing through the plastic. Manufacturers
get around this
problem by covering the bumpy copper strands with a smooth layer of black
conductive plastic. The smooth layer is "less sharp" than the bare metal
strands, so it suppresses corona. (Where e-fields are concerned,
sometimes the best "shield" is a conductor!) If you strip the insulation
off a
30KV HV cable and find that the metal is coated with a thin rubbery black
layer, now you know why.
Rolls of HV wire can be had from various suppliers:
Also: HV
Connectors, MHV
and SHV
.