so what on earth is an ignition coil? Well if you know
a little about cars, you'll know that a 4 stroke engine
goes: SUCK, SQUEEZE, BANG, BLOW. Literally.
BANG bit utilizes an ignition coil
to produce a spark across the spark plug via what's
known as a distributor, initiating the power stroke
of the engine.
coils are essentially pulse transformers - transformers
that work using pulses of current, instead of standard
alternating current. These pulses that are applied to
the primary coil are magnified and the resultant voltage
appearing from the secondary coil can be very high.
Image courtesy of Magnet
to get my ignition coil for $5 from the local car wreckers.
There is limited demand for these things, so the wreckers
usually sell them for quite a bargain. Alternatively,
you could strip one out of your neighbour's car - easy!
old cars also have other goodies in them, like speedometers
in the dashboard, or money in the glove box (haven't
come across this one yet...).
On the whole,
scavenging through old cars can be quite fun, and makes
for some interesting photo opportunites.
run the ignition coil outside of the car, specialised
circuitry is required that produces pulses of voltage
to the primary coil. I took a very common design (a
555 timer driving a MOSFET) and built it. Well, more
like lashed it up... as seen in photo.
the photo, it shows the initial setup with two ignition
coils. The sparks in the photos below are from one ignition
coil only however. I consider the circuitry used here
quite unsophisticated, and I have since fine tuned certain
components in the design.
a poor circuit board being electrified. Notice the corona
at the top of the wire. This is due to the 'roughness'
of the copper - very small sharp kinks in the wire lead
to the build up of charges, and when this charge builds
up past the dielectric breakdown threshold of air, it
shoots off a minute stream of particles into the air,
also known as corona.
tend towards the nearest grounded objects, in this case
the tops of those electrolytic capacitors.
are only about 4cm long - an estimated 44kV (1.1kV/mm).
is a quick demonstration of what happens in a lightning
cloud. The charges build up on the tip of the wire (cloud)
and discharges back to ground, creating a spark (lightning)
and associated 'snap' noise (thunder).
how the spark isn't anywhere near straight, despite
electricity's constant desire to return to ground via
the shortest possible path. In practice, the spark path
also depends on the temperature, humidity, wind draft
and other properties of certain spots in the air.
to say these properties, much like the 'butterfly effect',
influence the spark in a chaotic manner and the exact
path of the spark is thus rarely deterministic.
spark is estimated at around 50kV.
Image artificially intensified in
order to highlight spark
wire is brought closer to ground, sparks are produced
much more frequently, as the amount of charge build
up required to traverse the air gap is reduced.
quite intense and the camera has been saturated.
be incredibly noisy and this is one example where that
the wire is brought very close (this is about 1.5cm),
the sparks are so frequent that a smooth arc forms.
The charges no longer have to build up very much, and
immediately jump onto the circuit board through the
temperature of the arc probably exceeds a few thousand
degrees Celsius, and in a matter of seconds, the copper
wire has heated enough to start melting off its insulation.
that stray spark catching the other corner of the metal
can. This rogue spark probably formed due to wind drafts.
similar photo, you can see that the air around the arc
is heated super hot. In fact, the metal can is untouchable
after a few seconds of arcing.
This is what
happens during arc welding, except that the arc here
is actually much longer. However it lacks the power
and amperage that is forced through the arc in welding
is a demonstration of the ineffectiveness of normal
plastic insulation at very high voltages. The sparks
simply track along the insulating plastic until it reaches
the grounded terminal at the end. This effect is known
as surface tracking, and can be a real nuisance in many
In this picture, the high
voltage terminal is in the center of an insulated wire
at ground potential, causing most of the sparks to track
right around the insulating plastic. Some sparks however,
go right through the plastic, and this leads to a very
burnt, crispy, and generally... well... unpleasant smell
from the leftovers of what used to be plastic.
Insulators break down at
a certain potential known as the dielectric breakdown
voltage, which is typically specified in MV/m. I guess
the lesson learned here is that plastic can be rather
futile as an insulator!
I think we need more insulation here. Here, the ignition
coil is being driven by an improved design and is
experiencing some overvoltage stress on its output
terminal. Perhaps I should fill it with candle wax
seen in the picture is not actually a normal diode,
but rather a TVS (transient voltage suppressor) which
breaks down into a short circuit very quickly once
its terminals experience a voltage past its clamping
voltage. Thus it serves as good protection for all
the sensitive parts of the circuit.
project is available as a kit!
As a kit, it incorporates
the most effective driver I have tested, and can easily
reproduce many of the sparks/arcs on this page with
one coil. There are instructions included that detail
how to connect two coils to double the output voltage.
The ignition coil kit comes
in two forms - Basic (all components, schematic and
PCB), and Complete (all components, schematic, PCB
and ignition coil). There is also an additional TVS
diode that is included for voltage spike protection.
To order or enquire, click
HERE or on the image on the