I got the system up and running with the L6388.
Works like a charm.

I never quite understood
why the Aussies were claiming a minimum of two
sparks at high RPM until I looked at the signal
across the 2.5 ohm resister in series with the 1 uF
cap. This resister is simulating the coil,
for now, in the low voltage (12V) test set up.

With�  12 volts I am getting a peak current
of .4 AMPS!! through that resistor when the lower
FET turns on and ANOTHER .4 AMPS!! when it turns
off. This is due to the totem pole configuration
of the FET switches. Most CD system use only one
switch.

Imagine what the current would be with 300
volts. Of course the inductance of the coil
will make�  a difference.

In this set up these two current pulses are 20 usec
apart. The pulse width and timing are controlled
by the ZBasic computer with a simple BASIC
program. RPM is about 9500. The final version
of course will be stand alone with no
computer needed.

Here is a scope picture. The upper
trace shows what the upper FET switch's
input trigger is doing and the lower trace
is the +/- 10 volts across the 2.5 ohm
resister. E = I x R and I = E/R.

In other words when the lower FET
turns on the current pulse in the coil flows
one way and when the lower FET turns off
the current in the coil flows the other way.
Duh!

This means we will have a total of 8 ignition
sparks for each leading spark plug. Groups
of two 10 degrees apart from 22 deg. BTDC
to 10 deg. ATDC. Up to 11,000 RPM or more.

Next step is get the high voltage power
supply and the stock Mazda 2nd gen coil
working. I'll be very surprised and disappointed
if this system does not significantly improve
the BSFC of the rotary.


Hello Paul;

This looks like a nice design.�  Relatively simple and I
like the pulse pair with each trigger.�  Even closely
spaced pulses should increase your probability of getting
a good burn started vs a single spark.

But be careful when you choose the 300V supply.�  Some
quick calculations based on the energy stored/dissipated
in the 1uf capacitor shows that 90mJoules is consumed for
each pulse pair produced. ( energy, in Joules, stored in
a capacitor is CxVxV/2 )� � � Each of the two pulse pairs
uses the same energy.


 At 10k Rev/minute that translates to:
10k/60 pulses/second x 9E-2 Joules/pulse= 15 Joules/second or 15 Watts.
That's for one pulse pair per shaft revolution for one spark plug.

 Multiple by the total number of pulse pairs (you always get a pair)
you will use per shaft rotation to get the total DC power
you will need at 300V.

Could be a significant amount of power.

Craig Taylor


I have a 400 watt 12 volt to 220 volt AC converter waiting
in the wings :)

Kind of old tech because of the 50 Hertz. Heavy and large
but cheap.

My new 300 volt 30 watt power supplies are
converting at 120 Khz (120,000 cps).

---------------------------------------------

I did away with the computer and used the actual
hardware to control the L6388. The pulse width
is now controlled by the LMC555. One of the neat
things about this chip is it will not allow
both switches to be on at the same time (disaster) so
that eases the timing requirements. The doc is
not great but fooling around with it will teach
you how it works. I already blew the top
off one but they are cheap :)

I connected a 2nd gen RX7 coil just to see what
would happen. It looks like it wants a 1 ms wide
pulse but that may not be necessary or desirable.

That allowed the coil oscillations to damp
down after several oscillations. See the
attached scope picture. Of course it is still
running on 12 Volts but the time constants
should be the same. This will vary of course
and some coils will oscillate faster than others.

I'll dig up some other coils and try them out.
If you have any old coils lying around you
don't need please send them to me.

About the max we can do with this coil is 8 msec
(7500 RPM) /36 or 222 usec if my math is correct.
2.2 to 10 to the -4 or 0.000222222... 222 usec
I think. We will probably get one or two oscillations
going down and the same going back up.

Next step is the 300 volt power. I'll use
the 400 watt inverter as I don't want to risk the
expensive power supplies just yet.

BTW for dyno test I don't need the inverter.
It will be possible to merely plug this
ignition system into the 220 volt wall outlet
found in the shop :)

Paul Lamar


Paul, I recall there being a "low inductance" ignition
coil designed for CD ignition systems.�  With the standard
Kettering system, the energy to produce the spark is stored
in the inductance of the coil, which makes a substantial
amount of coil inductance desirable.�  With the CD system,
the energy is stored elsewhere and too much inductance can
be a problem, as you are discovering.

Craig Taylor

Yes I think you are right. Probably the best bet
is a MSD coil designed for CD systems.

BTW I just noticed that Klaus (or Paul Lipps the designer) is
using three Hall Effect sensors spaced 1/4 inch apart. Could he be
using the same idea? :) In case somebody accuses me of copying
Klaus's system I did not know about this until yesterday when
I noticed it on his web site.

http://www.lightspeedengineering.com/Products/MiniSensor.htm



"Single systems require only one Mini Sensor.�  On dual 4 cylinder
engine installations, there are two Mini Sensors at 180 degree
intervals. On dual 6 cylinder installations, a second Mini Sensor
is mounted 120 degrees from the first."

"The Mini Sensor consists of two billet aluminum machined halves
that capture a small circuit board holding 3 Hall effect sensors
at 0.250�?� spacing."

End quote. I don't know what KLaus is using for coils but
they appear to be off the shelf. Looks can be deceiving:)

I have seen it many times but I never paid any attention.

Klaus's excellent results indicates this idea will
also improve the BSFC of the rotary.


BTW Craig the output of my 220 volt bridge rectifier looks
like this.

220V____�  �  ________�  �  _______
�  �  �  �  |�  |�  �  �  �  |�  |
0V�  �  �  |__|�  �  �  �  |__|

Do you think I have a bad diode in�  that bridge?

Paul Lamar


Load it's output with ONLY a resistor and test it with
10-30VAC from an isolation transformer of any common
type.�  24-28VAC out versions are often called "control
transformers" and are used in industrial equipment
to drive low voltage indicator bulbs and relay coils
because the use of low voltage wiring lowers the system
wiring cost.
� �  Use a 100 Ohm or so resistive load and use an
oscilloscope to view the + output with the negative
output of the bridge connected to the scope common
(ground) terminal.�  If it's busted you will see it
easily.
�  Or just replace the rectifier bridge.�  Mail order
surplus companies like All Electronics or Electronic
Goldmine have a variety of 10+A bridge rectifiers
available at low cost.�  Use at least 600V rated
ones.�  Don't forget the heat generated needs to
go somewhere ;-)

Craig Taylor

That did not come across too good. I think you converted the
text to html, We have standardized on plain text here so
everybody should be able to read the same thing.

I did what you said and this is what I got.

In any event I figured out what the problem is. These
cheap 12 Volt to 220 volt inverters simulate a sine wave
with the first diagram on this jpg. There is actually a cheap
single chip computer in there switching the FET's on
and off. It also monitors temp and load so it can shut
the whole works off if it gets out of bounds.

There are two transformers and two power supplies in there.
One negative 120 volts and one positive 120 volts.
The CPU alternately puts out the negative going
wave and the positive going wave with a common ground.
Very straight forward. At least I think that is the
way it is working.

I can deal with it externally by adding another diode
and filter cap but I am thinking of just buying them
and redesigning  them for 300 Volt DC out. Nice transformers,
case and over all packaging. All that would cost a bunch in
small quantities. I learned a long time ago it was
cheaper to modify something that is mass produced
rather than reinvent the packaging wheel.

Paul Lamar