High-Power Car Ignition Coils

	I must say I am VERY proud of myself. For once I’ve actually made
something that worked well the first time. In fact, it outperformed
even my wildest expectations!
  I have being experimenting with car ignition coils since I was 11
years old. My first high-voltage device was a single ignition coil
driver I built from scrap. Had a rusty old ignition coil that ran at
20W and put out wimpy little 2cm long sparks at a rate of about one
per second. I had to rebuild it 3 times before it worked and I burned
out some of the circuitry more than 10 times while fiddling around.
 It wasn’t much but it was the first time I really dealed with
high-voltages and it was a REALLY exiting project. It thought me a lot
about high voltage safety, insulators, spraying, corona and may
others. It also gave me some really nasty shocks that helped teaching
me a lot about respecting high voltage.
 Well, now you are asking yourselves: “Yeah, so? What does this have
to do with coiling. This IS a Tesla Coil list after all”.
 And you are probably right. To some extent. After all, car ignition
coils are made to produce a spark inside the engine’s cylinder. The
spark occurs at a spark plug that has only a 1mm gap and it only has
to have enough energy to ignite a highly-combustible air-fuel mixture
(piezo-electric igniters can do that). To make matters worst, it only
needs to run on pulsed mode.
 So, obviously you would expect such a device to be far too small for
any real applications. In fact, the quotes I read were that ignition
coils were designed to run at no more than 50 Watts and 20KV.
 Well as you probably know we can’t really get any HV transformers
here in Europe. Neons are limited to 450W 8kV and any other source is
out of question (at least that is how it works here in Holland,
Germany and whereabouts). Plus, even those wimpy neons cost a lot (I
think it was 200 dollars apiece)
 So, I had to, umm, say, “Improvise” :-).
 After doing some work with MOTs and smoking 2 of them in 30 second
runs (they were running at over 2kW:-) Hehe made such a nice Jacob’s
ladder… It started at 3mm and ended 15cm apart! Was 1meter long…
 Well, than I went on to Flybacks, but that didn’t work. As I was
looking for more TVs and microwave ovens (I have never actually found
one and the ones I had I paid $150 for each one), I came across an
ignition coil:-)
 So, remembering Terry’s experiments with his GM coil, I decided to
give it a shot and see just how much power I could get out of it.
 I rebuilt my driver (the original one, which you will not find
ANYWHERE because I designed it myself:-) and started fiddling around.
The driver itself is amazingly simple. It costs less than 50 bucks to
build using top-quality parts and it takes less just a few minutes to
put together. Basically, you charge a capacitor bank to rectified Peak
to peak (PP) mains voltage (350V in my case) and at the same time you
charge a second capacitor trough a resistance/potentiometer
arrangement. When this second cap is fully charged it will ionise the
gas inside a neon lamp, the gas will conduct and trigger an SCR,
dumping all the charge of C1 on the coil. The result are small,
moderately powerful sparks. The first thing I did was try to increase
the energy of the sparks by increasing the value of C1. I found that
anywhere above 4uF the size of the sparks actually DECREASED!
(possibly because the coils stopped resonating or something) That was
pretty crap, but I didn’t give up. By than another 5 or so had to be
rebuilt because I kept screwing up with the circuit and the SCR or the
caps kept on blowing (I had a few SCRs to catch fire and 2 to explode
in a shower of sparks).
 I saw that I would have to go another way. I remembered reading a
post somewhere on this list about using capacitors to limit the power
going in. So I took this 16uF 450VDC motor capacitor from my lawnmower
(hope no-one finds out:-) and substituted the current-limiting
resistance for it. Didn’t work. So I tried the cap in parallel to the
resistance. EUREKA!!! Ha! Now the circuit would ARK instead of just
pulsing little sparks! YES!!! That got me started… I than started
adding more and more resistances in parallel to R1. I used my
soldering iron, and 3 lightbulbs. When I ran out of spare lightbulbs I
went out and got myself a HALOGEN lamp. By than things were getting
REALLY exiting, with the arc getting larger and more powerful as the
value of the resistance increased.
 Right now I am running two German built High-Power oil cooled car
ignition coils in anti-parallel. The coils are rated for 12V and I am
pulsing 300Watts trough 20uF of capacitance at 350V on them and
getting 10CENTEMETERS LONG ARCS!!! And, best of all, they are only
getting moderately warm. Yesterday I ran a Jacob’s ladder for almost
one hour and the temperature seems to stabilise at 50degrees or
whereabouts. The insulation around the terminals had to be stepped-up
and the SCR, which is rated for 5Amps, needs a medium sized heatsink.
The whole circuit is packed in a box measuring 20 X 15X 10cm (smaller
than a shoebox) and weights 1KG.
 Things are getting really interesting now. I KNOW these coils will
take at least 500WATTS before they start getting warm, and I think a
full kW might be possible in short runs. I imagine 15cm long arcs are
within reach… The energy of the arcs I get now is already something to
consider: It melts solder!
 Now, of course this is no match for a pig, or a distribution
transformer, or even a big NST. But think about it: ANYWHERE IN THE
WORLD you can get ignition coils. They cost $20 each new and you can
get them for free from a car shop (they are replaced every 10000KM or
so by safety regulations). So, for that little money and hassle, it
really IS a good deal… I could parallel them for, say, 40kV at
500Watts and I am sure that would run a pretty good Tesla Coil.
Another two and you have a KILOWATT of power…
 But hey, I am just getting started. There is much room for
improvement and I want to push those suckers until they get so hot
that the oil inside them boils and the voltage burns its way right
trough the insulation. THAN I will be able to saw just how far they
will go. I am planning to play around with the values of R1 some more.
I want to reach the highest power possible before they overheat. Than
I will go on to changing the values of the caps until I get the
maximum voltage possible. I might even change C1 for a voltage Doubler
and pump some 700V on the primary to see if it can take the power.
Than I will get myself a bigger SCR and make a 4coil driver that would
handle 1000Watts.
 Whoa this message is getting long. Well, I better get to the point
than. I need some expert advice from you. I know there are some (many)
people on this list who have forgotten more about this than I have
ever known (hey, I said it before: I am ONLY getting started:-). So,
could you help me out on these problems:

1- The halogen light gets EXTREMELY hot, and it is so bright it is
giving me headaches. What would be a better substitute for it? I can’t
really get 500Watts resistances and a string of 5 100Watts resistors
would get pretty hot too. How about inductive ballasting? How could I
use it for this device?
2- The insulation around the HV terminal is not enough to keep it from
arcing to the primary terminal screws, which are just outside it. I am
currently using insulation tape but it won’t be long before it breaks
down too. Has anyone done anything like this before? Any ideas on how
to insulate it better? Maybe some PVC pipes with epoxy?
3- Has anyone tried ignition coil drivers before with good results? I
am REALLY interested in your experiments. Anything. Like, what was the
power level you ran your at and how did it behave. Has anyone got more
than 10cm long arcs from it? I think I hold the record for highest
power out of an ignition coil, but hey, I would be quite happy to be
proven wrong!
4-  How much power and voltage is a typical ignition coil really
designed to work at? I now know it is more than 50 watts. Maybe 200?
Does anyone know? What is the actual limit? Core saturation?
Overheating? Insulation breakdown? I wonder if it would saturate
before the power caused it to overheat… Unfortunately I don’t have my
multimeter anymore:-( died while I was doing some tests on this device…

 I want your comments on this. Anything. Just mail me at

 I haven’t posted the circuit yet because it is under construction. I
have a word file with a full explanation of how it works and a parts
list/circuit diagram. It is the full instructions for building it. If
anyone is really desperate for some action I could mail it to you, but
I would rather finish my testing first…

 P.S. I know Terry has a GM high-power ignition coil to spark MUCH
further than this device will ever be able to. But the idea is to use
this to run a Tesla coil, so, effectively it acts as a transformer and
not a resonator. Using this arrangement it would in theory be possible
to run even higher power levels by paralleling several coils.
 In fact, the only transformer I know off that can output more voltage
than this device are x-ray transformer!!! Of course I will be running
more amperage and less voltage on the Tesla Coil power supply voltage…

 Sam Barros

 Sam Barros,

 "The Less You Know, The Better You Sleep"...
 "Evolution Stops When Stupidity Is No Longer Fatal"
 "If At First You Don't Suceed, Increase The Amperage"
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