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Sam Barros' 5000Watts Car Ignition coil update: tests, and theory.

 Once again I had to rebuild my coil driver. I am beginning to like it
now:-) I don't have to look at the schematics and construction goes
rather smoothly... I took this opportunity to try out some new stuff.
I added a full-wave bridge rectifier to the input, because previous
tests showed that removing the single diode I had at the input caused
maximum sparklength to drop almost 50%. I used the same technique I
described before to make the board 20A+ compatible, and I used larger
resistances, and MUCH larger diodes this time. I also mounted
everything (potentiometer, neon, SCR) on the board, instead of using
sockets and wire connections which, at this level were beginning to
get quite warm.
  So, I took the opportunity to do some probing :P
 Well check out my results:
 Charge on main pulse capacitor bank: 310Volts (! This is rather
interesting really, I was assuming that the coils were running of
220V, when they were actually taking 310V in... Oh well, just you wait
until next week when I'll add a full-wave voltage Doubler into the
mix:-)
 I measured input amperage at 20A, and, strangely, output amperage at
20 A as well… This means that the circuit is virtually 100% efficient,
which is highly unlikely. I’ll try that one again later, with 2 meters.
 That's about it. I need some more probing around. Apparently my
trigger cap is too small to pulse the SCR reliably. I'm getting much
smaller sparks and erratic firing. I will re-test everything, and
include some output tests too (ouch I shiver at the thought of
bringing my Fluke multimeter near those evil coils... I think I'm
going to buy a cheap-ass meter (well, actually another one:-))
 So, that is what I have for the circuit. The thing to keep in mind is
that the coils are pulsed at 310V, and the input is 20A. Note that
high-performance car coils run at as much as 510V in the input (You’ll
see that on the links I give in the end of this post).
  I'm sorry I don't have anything more conclusive, but I hopefully
will next week.
 Now, for some hot new stuff... I tried wiring a 220VIn, 9V 100mA Out
transformer (really small, the core was about 1" squared) in reverse,
and setting the coildriver to 1kW. I was expecting it to saturate and
go up in smoke, but, instead, it gave off a 1cm long super-hot fire
arc that melted the wires it was arcing too, and it kept on arcing for
another 15 seconds (!) than, it decided to go up in smoke:-). Tried it
with a MOT. Same trick. Works just as well but the MOT doesn't smoke.

 Well, now that I am done with the updates, I have something I could
use some help with:
 I am trying to calculate how much power, in theory, an ignition coil
would be able to handle. I suppose I would have to look into how much
current the wire can take, and than see if it is more, or less than
what it takes to saturate the core... Any ideas there? The wire on the
primary is 0.50mm diameter, about 240meters long, and oil-immersed.
The resistance of the windings is 3Ohms.

 Is this correct for the maximum theoretical output of an ignition
coil? And, if so, is di/dt given in Hz?

 V = L di/dt
Where: 
 V is the output voltage 
 L is the inductance in Henrys 
 di/dt is the rate of change of current flow as the field collapses in
the coil. 

 How about this for power output?

P = (L di/dt)^2 / R 
where P is the power in watts and R is the total resistance of the
coil secondary, the plug wire and the ionized spark gap.

 Well, that's about it. I am trying to get all the theory done for my
coildriver before I release the schematics (a good few weeks from now,
as my latest modifications have resulted in more problems to solve:-(

 Finally, I have killed ANOTHER coil. This one due to insulation
breakdown. I set up a simple Tesla Coil like circuit, with a MOT
charging a 4kV, 2uF GE pulse capacitor and discharging it trough a
sparkgap onto a coil's primary. No output. It made a deafening sound
from the sparkgap but the coil failed internally before I could draw
any sparks:-(
 I am now looking for some *REAL* induction coils, something that will
stand the power levels my next drivers will be delivering (like 600V
on the primary and such). So far, I came up with some MSD and Mallory
ignition coils.
 I am, of course interested in other coils, from other manufacturers
but it seems to me that the MSD coils are the best. My requirements
for a GOOD coil are as low as possible resistance in the windings, and
as high amperage and voltage output as possible. SO far the following
seem to be winners.

http://www.centuryperformance-dot-com/mallory2.htm

MAL 28880, for drag racing, etc… Up to 12000RPM

 And MSD Ignition:

http://www.primenet-dot-com/~msdign/1msdcoil.htm

Pro Power HVC Coil

Primary Resistance: .04 ohms Peak Current: 1100mA 
Secondary Resistance: 86 ohms Spark Duration: 150uS 
Maximum Voltage: 45,000 volts Primary Inductance: 1mH 
Turns Ratio: 85:1 


http://www.primenet-dot-com/~msdign/1msdcldr.htm

Pro Power Coil Specifications:
Output Voltage: 55,000 Volts maximum 
Operating Voltage: 12VDC 
Primary Resistance: 0.03 Ohms 
Secondary Resistance:  1000 Ohms 
Turns Ratio: 100:1 


 Not sure which one is best. It would be great if someone could check
this rather interesting pages out and tell me their verdict. Also, how
important is the inductance of such a coil in coildriver applications?


 Well, experimentation goes on. I sure hope someone can help me out
with this calculations and choosing a good coil.
 Finally, I would like to say that the file Coildriver.zip, with
pictures of my recent work and a diagram of my disassembled coil was
sent to 41 people. 3 replied. Did you all get it and didn't think it
was worth a comment or was there a problem while I tried to send the
file? Just wandering. For the ones that didn't get it, it is still
available. The file is 450kB about and I'll send it trough e-mail.
Mail me privately at sambarros-at-yahoo-dot-com for that.


   Sam Barros.
==
 Sam Barros,
sambarros-at-yahoo-dot-com
ICQ#:15156975

 "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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